Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at √ s = 13 TeV

JHEP06(2018)166 Published for SISSA by Springer Received:February 12, 2018 Revised:May 7, 2018 Accepted:June 11, 2018 Published:June 29, 2018 Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at √s= 13 TeV The ATLAS collaboration E-mail: [email protected] Abstract: A search is conducted for a beyond-the-Standard-Model boson using events where a Higgs boson with mass 125 GeV decays to four leptons (`=eor µ). This decay is presumed to occur via an intermediate state which contains one or two on-shell, promptly decaying bosons: H→ZX/XX →4`, where Xis a new vector boson Zdor pseudoscalar awith mass between 1 and 60 GeV. The search uses pp collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 36.1 fb−1at a centre-of-mass energy √s= 13 TeV. No significant excess of events above Standard Model background predictions is observed; therefore, upper limits at 95% confidence level are set on modelindependent fiducial cross-sections, and on the Higgs boson decay branching ratios to vector and pseudoscalar bosons in two benchmark models. Keywords: Beyond Standard Model, Hadron-Hadron scattering (experiments) ArXiv ePrint: 1802.03388 Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP3. https://doi.org/10.1007/JHEP06(2018)166 JHEP06(2018)166 Contents 1 Introduction 2 2 Benchmark models 3 2.1 Vector-boson model 3 2.2 Pseudoscalar-boson model 4 3 ATLAS detector 6 4 Event reconstruction 6 4.1 Trigger and event preselection 7 4.2 Lepton reconstruction 7 4.3 Definition of invariant-mass kinematic variables 8 4.4 Summary of analysis event selections 8 5H→ZX →4`analysis 8 5.1 Monte Carlo simulation 8 5.2 Event selection 10 5.3 Background estimation 11 5.4 Systematic uncertainties 11 5.5 Results 12 6H→XX →4`(15 GeV < mX<60 GeV) analysis 12 6.1 Monte Carlo simulation 12 6.2 Event selection 14 6.3 Background estimation 15 6.4 Systematic uncertainties 15 6.5 Results 16 7H→XX →4µ(1 GeV < mX<15 GeV) analysis 18 7.1 Monte Carlo simulation 18 7.2 Event selection 18 7.3 Background estimation 18 7.4 Systematic uncertainties 20 7.5 Results 20 8 Interpretation and discussion 21 8.1 Limits on fiducial cross-sections 22 8.2 Limits on branching ratios 22 9 Conclusion 25 – 1 – JHEP06(2018)166 The ATLAS collaboration 34 1 Introduction Following the discovery of the Higgs boson by the ATLAS and CMS collaborations [1,2] at the Large Hadron Collider (LHC), a comprehensive programme of measurements of the properties of this particle is underway. These measurements could uncover deviations from the expected branching ratios for the decays of a Standard Model (SM) Higgs boson or allow for the possibility of decays into non-SM particles. Existing measurements constrain the non-SM or “exotic” branching ratio of the Higgs boson to less than approximately 30% at 95% confidence level (CL) [3–5]. Exotic Higgs boson decays have been proposed as a way to search for evidence of new physics. Due to the extremely narrow decay width of the Higgs boson predicted by the SM, the addition of even a small coupling to a new light state could open up sizeable new decay modes. In addition, new particles may couple preferentially to the Higgs boson since it provides a possible “portal” for hidden-sector particles to interact with SM particles [6– 9]. Such decays are predicted by many theories of physics beyond the SM. For example, they are predicted in theories with a hidden (“dark”) sector [10–19] and in those with an extended Higgs sector such as the Next-to-Minimal Supersymmetric Standard Model (NMSSM) [20–24]. They are also predicted in several models of dark matter [25–30], models that explain astrophysical observations of positron excesses [31–33], models with a firstorder electroweak phase transition [34,35], and theories with neutral naturalness [36–38]. The processes under study here are referred to as pp →H→ZX/XX →4`, with Z being the SM Zboson and with Xrepresenting a possible new vector boson Zdor a new pseudoscalar boson a. Section 2provides an introduction to the theoretical background and specific models examined in this paper. The search uses pp collision data at a centre-of-mass energy √s= 13 TeV collected by the ATLAS detector (described in section 3) at the LHC in 2015 and 2016 corresponding to an integrated luminosity of 36.1 fb−1. Same-flavour decays of the new particle to pairs of electrons and muons are considered, giving rise to the 4e, 2e2µ, and 4µfinal states for particles in the mass range from 15 GeV to mH/2, where mH= 125 GeV. For lower masses, targeting the range from 1 GeV to 15 GeV, only the 4µfinal state is explored. Final states including τleptons are not considered in either mass range. The event reconstruction is discussed in section 4. The search for H→ZX →4`in an Xmass range between 15 GeV and 55 GeV is covered in section 5, while the H→XX →4`searches are included in sections 6and 7 for 15 GeV < mX<60 GeV and 1 GeV < mX<15 GeV, respectively.1Model interpreta1The reason for the two ranges being different is that in the H→ZX →4`search the mass distributions of the Xand the Zbosons begin to overlap significantly for values larger than 55 GeV, thus inhibiting unambiguous identification of the Zand the new bosons. This is not the case in the H→XX →4`search where a Zveto is applied. – 2 – JHEP06(2018)166 tions and discussions are presented in section 8. Finally, the conclusions of the search are presented in section 9. This paper builds on the previous work of ref. [39], in which a similar analysis is reported with data collected at √s= 8 TeV. 2 Benchmark models Two well-motivated benchmark models that predict exotic decays to light beyond-theStandard-Model (BSM) bosons are summarised below, and are used later in this paper when interpreting the results. In the first BSM benchmark model, the SM is extended with a dark-sector U(1) group, denoted U(1)d, leading to the appearance of a BSM vector boson, Zd. In the second BSM benchmark model, there are two Higgs doublets and an additional singlet scalar field (2HDM+S). This leads to the appearance of a BSM pseudoscalar boson, a. The Zdboson and the apseudoscalar could each comprise the intermediate state in the decays H→ZX →4`and H→XX →4`, where the first benchmark model is considered for a higher mass range and the second for a lower mass range. 2.1 Vector-boson model Hiddenor dark-sector states appear in many extensions to the SM [10–19,40]. The darksector states allow a theoretically plausible route for generation of the particle content necessary to account for the astrophysical evidence of dark matter. For example, fermionic dark-matter candidates [30] or dark-sector couplings to normal matter might explain astrophysical observations of positron excesses [31–33]. A dark sector is introduced with an additional U(1)ddark gauge symmetry [14–19], coupled to the SM through kinetic mixing with the hypercharge gauge field [41–43]. The gauge boson of the symmetry is the Zdvector boson. In this hypercharge portal scenario, the kinetic mixing parameter controls the coupling strength of the dark vector boson to SM particles, which in turn determines the lifetime of the Zdboson. The branching ratios of the Zdare independent of the kinetic mixing strength and are instead determined by the gauge coupling. This coupling leads to a significant fraction of decays (≈15%) to pairs of electrons or muons. For Zdmasses between 1 GeV and 60 GeV, the decay would be prompt (relative to the vertex resolution of the ATLAS detector) for &10−5[14]. For smaller values of , the displaced decays provide a unique signature, which has been previously searched for with the ATLAS detector in 8 TeV collisions [44]. For Zdmasses below a few GeV and small values of , the decay products would be highly collimated and require a special analysis [45]. Another possibility involves a mass mixing between the Z boson and Zd, facilitating the decay of the Zdto SM particles. In this mechanism, the strength of the mixing is determined by mass mixing parameter δ[16,17]. If the U(1)dsymmetry is broken by the introduction of a dark Higgs boson, there could also be mixing between the SM Higgs boson and the dark Higgs boson [14–19]. In this scenario, the Higgs portal coupling κcontrols the strength of the Higgs coupling to dark vector bosons. The observed Higgs boson would be the lighter one of an extended Higgs sector and could also decay into dark-sector particles. – 3 – JHEP06(2018)166 H Zd Z Z ϵ H Zd Zd S Figure 1. Exotic Higgs boson decays to four leptons induced by intermediate dark vector bosons via (left) the hypercharge portal and (right) the Higgs portal, where Sis a dark Higgs boson [14]. The Zdgauge boson decays to SM particles through kinetic mixing with the hypercharge field or through mass mixing with the Zboson. The HZZdvertex factor is proportional to whereas the HZdZdvertex factor is proportional to κ. For the processes studied in this paper, the decay H→ZZdprobes the parameter space of and mZd, and does not depend on the presence of mixing between the SM Higgs boson and the dark-sector Higgs boson, κ. However, this BSM signal is indistinguishable from SM H→ZZ∗on an event-by-event basis, and therefore must emerge as a resonance in the dilepton mass above this background process. The SM background to the H→ZdZd process, however, is more easily separated from the signal. This feature makes the latter channel potentially sensitive to much smaller values of kinetic mixing, where the only requirement is that the kinetic mixing must be large enough for the Zdto decay promptly. However, this process depends on the presence of mixing between the SM Higgs boson and dark-sector Higgs boson, and therefore probes the parameter space of κand mZd. Feynman diagrams of both processes are shown in figure 1. These processes are included in the Hidden Abelian Higgs Model (HAHM) that is used in this paper as the benchmark vector-boson model [14]. The presence of the dark sector could be inferred either from deviations from the SM-predicted rates of Drell-Yan (DY) events or from Higgs boson decays through exotic intermediate states. Model-independent upper bounds from electroweak constraints on the kinetic mixing parameter, , below 0.03 are reported in refs. [14,46,47] for dark vector bosons with masses between 1 GeV and 200 GeV. Upper bounds on the kinetic mixing parameter based on searches for dilepton resonances, pp →Zd→``, below the Zboson mass, are found to be in range of 0.005–0.020 for dark vector bosons with masses between 20 GeV and 80 GeV [48]. In the mass range of 10 MeV–10 GeV, values of above ∼10−3are ruled out [49–54].The experiments at the LHC are the only ones sensitive to the production of Higgs bosons, and this makes possible the search for the presence of a Higgs portal presented here. Constraints on the Higgs mixing parameter κare probed through the H→ZdZd→4`search while constraints on the kinetic mixing parameter and the mass-mixing parameter δcan be obtained through the H→ZZd→4`search. 2.2 Pseudoscalar-boson model Another possibility to extend the SM with a hidden sector is to consider two-Higgs-doublet models extended by one complex scalar singlet field (2HDM+S) [15]. – 4 – JHEP06(2018)166 Two-Higgs-doublet models predict two charged scalars (H±), two neutral scalars (H, H) and one neutral pseudoscalar (A). The real mass eigenstate His considered to be the observed Higgs boson, while other states are taken to be heavy in the decoupling limit to ensure that highly non-standard Higgs decays (e.g. involving CP-violation) which are significantly constrained by existing data, are avoided [55,56]. The scalar singlet added to 2HDM only couples to the two Higgs complex fields in the potential and has no Yukawa couplings. Therefore, all of its couplings to SM fermions are acquired through mixing of the scalar field with the Higgs complex fields, which needs to be small to preserve the SM nature of the Higgs sector. With these assumptions, the decay H→aa is allowed, where ais a light pseudoscalar mass eigenstate mostly composed of the imaginary part of the singlet field.2The aforementioned constraints on two-Higgs-doublet models can be incorporated in the 2HDM+S by choosing a region of the 2HDM phase space not yet excluded, and giving the real and imaginary components of the singlet separate masses and small mixings to the Higgs doublets. The branching ratios of ainto fermions are determined by the Yukawa couplings of ato fermions, and lead to a rich decay phenomenology [15], albeit with typically negligible branching ratio to pairs of electrons, and smaller branching ratios to pairs of muons than the dark vector bosons described in the previous section. Among all the models predicting different decay possibilities, type II are theoretically well motivated,3since light pseudoscalars can correspond to the R-symmetry limit of the NMSSM [57,58], which elegantly solves the µ-problem of the MSSM [59] and greatly reduces the fine-tuning and little-hierarchy problems. Furthermore, in the NMSSM the branching ratio for H→aa can be significant. Type-II models can also predict a significant branching ratio for a→µµ, especially in the range 2mµ< ma<2mτ, with values ranging from 10−2to 10−1for some regions of the parameter space [15]. Several searches for a Higgs boson decaying to electrons, muons, τleptons or b-jets via two pseudoscalars have been performed at both the LHC and the Tevatron. The DØ and ATLAS collaborations have searched for a signal of H→aa →2µ2τin the aboson mass ranges 3.7≤ma≤19 GeV and 3.7≤ma≤50 GeV, respectively [60,61]. The DØ and CMS collaborations have searched for the signature H→aa →4µin the range 2mµ≤ma≤2mτ[60,62]. The CMS collaboration has additionally searched for H→aa →4τ, 2µ2τ, 2µ2bin the range 5 GeV ≤ma≤62.5 GeV [63] and the ATLAS collaboration for H→aa →4bin the range 20 GeV ≤ma≤60 GeV [64]. These searches have led to limits on the branching ratio of the Higgs boson decaying to aa, scaled by the ratio of the production cross-section of the Higgs boson that is searched for to that predicted by the SM, σ(H)/σSM ×B(H→aa), between 1% and 3% for pseudoscalar-boson masses between 1 GeV and 3 GeV and between 10% and 100% for masses larger than 5 GeV, assuming a 2HDM+S Type-II model with tan β= 5.0. 2The pseudoscalar state is a= cos θaSI+ sin θaA, where θa1 is a small mixing angle and SIis the imaginary part of the complex singlet field. 3The right-handed states dRand eRcouple to H1,uRto H2, where H1and H2are the two Higgs doublets. See ref. [15] for more information. – 5 – JHEP06(2018)166 3 ATLAS detector The ATLAS experiment [65] is a multi-purpose particle physics detector with forwardbackward symmetric cylindrical geometry and a near 4πcoverage in solid angle.4The interaction point is surrounded by an inner detector (ID) tracking system, a calorimeter system, and a muon spectrometer (MS). The ID covers |η|<2.5 and consists of a silicon pixel detector, a silicon microstrip detector, and a transition radiation tracker. The ID is surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field. One significant upgrade for Run 2 is the presence of the insertable B-layer (IBL) [66], an additional pixel layer close to the interaction point, which provides high-resolution measurements at small radius to improve the tracking performance. The calorimeter system features a high-granularity lead/liquid-argon (LAr) sampling calorimeter that measures the energy and the position of electromagnetic showers within |η|<4.9. LAr sampling calorimeters are also used to measure hadronic showers in the endcap (1.5<|η|<3.2) and forward (3.1<|η|<4.9) regions, while an steel/scintillator tile calorimeter measures hadronic showers in the central region (|η|<1.7). The MS surrounds the calorimeters and consists of three large superconducting air-core toroid magnets, each with eight coils, a system of precision tracking chambers (|η|<2.7), and fast trigger chambers (|η|<2.4). For Run 2 the ATLAS detector has a two-level trigger system. The first-level trigger (Level-1 trigger) is implemented in hardware and uses a subset of the detector information to reduce the accepted rate to 100 kHz. This is followed by a software-based trigger (called high-level trigger) that reduces the rate of events recorded to 1 kHz. 4 Event reconstruction The three analyses presented in this paper all follow a similar event reconstruction and selection procedure. This section describes the basic event selection and lepton reconstruction requirements that are common to all three analyses. Table 1summarises the event selection used in the three analyses that are described in further detail in sections 5–7. Events are preselected in accord with trigger requirements and basic event requirements such as the existence of a reconstructed primary vertex [67], which has the largest sum of p2 Tof the associated tracks. For each event, a selection is applied to the reconstructed final-state leptons. The event is required to have at least four leptons. These leptons are combined into dileptons, and the dileptons are paired into quadruplets. Quadruplets are then filtered by selection criteria specific to each analysis, and a single quadruplet (with a specific dilepton pairing) is selected according to a ranking metric that favours pairings 4ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the centre of the detector and the z-axis along the beam pipe. The x-axis points from the IP to the centre of the LHC ring, and the y-axis points upward. Cylindrical coordinates (r, φ) are used in the transverse plane, φbeing the azimuthal angle around the z-axis. The pseudorapidity is defined in terms of the polar angle θas η=−ln tan(θ/2). The transverse momentum pTand other transverse variables, are defined as the variables’ component in the x−yplane, the transverse energy ETis defined as pm2+p2 T, where m represents the mass of a considered object. The distance in the pseudorapidity-azimuthal-angle space is defined as dR or ∆R=p(∆η)2+ (∆φ)2. – 6 – JHEP06(2018)166 compatible with either a ZX or XX intermediate state, depending on the analysis. If there are no quadruplets in the event that meet the selection criteria then the event is discarded. Final event selections are based on properties of this selected quadruplet and the corresponding dilepton pair. 4.1 Trigger and event preselection Events are preselected by single-lepton, dilepton, or trilepton triggers [68], with a combined efficiency very close to 100% (relative to the signal region events surviving all other event selections). Trigger thresholds were increased slightly throughout the run to compensate for increasing peak instantaneous luminosity delivered by the LHC. The lowest pTthresholds for the single-lepton triggers ranged from 24 GeV to 26 GeV. Dielectron (dimuon) trigger thresholds ranged from 2 ×12 GeV (2 ×10 GeV) to 2 ×17 GeV (22,8 GeV). Trielectron (trimuon) triggers had thresholds of 17,9,9 GeV (3×6 GeV). In the low-mass selection, only the muon-based triggers are used. The events must have at least one primary vertex [67] with two or more associated tracks with pT>400 MeV and satisfy cleaning criteria [69] designed to reject events with excessive noise in the calorimeters. 4.2 Lepton reconstruction An electron is reconstructed from a cluster of energy deposits in the electromagnetic calorimeter matched to a high-quality track in the ID. Its momentum is computed from the cluster energy and the direction of the track. Electrons are required to have |η|<2.47 and pT>7 GeV. Electrons can be distinguished from other particles using several identification criteria that rely on the shapes of electromagnetic showers as well as tracking and track-to-cluster matching quantities. Following the description in ref. [70], the output of a likelihood function taking these quantities as input is used to identify electrons, choosing the loose working point, but with the additional requirement of a hit presence in the innermost layer of the ID.5 A muon is reconstructed by matching a track or track segment reconstructed in the MS to a track reconstructed in the ID [71]. Its momentum is calculated by combining the information from the two systems and correcting for energy deposited in the calorimeters. In regions of limited coverage by the MS (|η|<0.1), muons can be reconstructed by matching ID tracks to calorimeter signals consistent with a minimum-ionising particle (calorimetertagged muons). In regions outside the ID acceptance (2.5<|η|<2.7), muon reconstruction can also be extended by using tracks in the MS (stand-alone muons). Reconstructed muons are required to pass the requirements of the loose working point to maximise the reconstruction efficiency while providing good-quality muon tracks [71]. Muons are required to have |η|<2.7 and pT>5 GeV. Calorimeter-tagged muons must have pT>15 GeV. Leptons are required to originate from the hard-scattering vertex, defined as the primary vertex in the pre-selection. The longitudinal impact parameter of each lepton track, calculated relative to the hard-scattering vertex and multiplied by sin θof the track, is 5When no measurement is expected in the innermost layer of the pixel detector, the requirement is transferred to the next-to-innermost pixel layer. – 7 – JHEP06(2018)166 required to be smaller than 0.5 mm. Furthermore, muons must have a transverse impact parameter calculated relative to the beam line smaller than 1 mm in order to reject muons originating from cosmic rays. The significance of the transverse impact parameter calculated relative to the beam line is required to be less than three (five) for muons (electrons). Stand-alone muons are exempt from all three requirements, as they do not have an ID track. The leptons are required to be isolated from other particles using ID track information and calorimeter information. The sum of the transverse energy ΣETof other topological clusters [72] in the cone of ∆R= 0.2 around the electron (muon) is required to be less than 20% (30%) of the pTof the electron (muon). The ΣpTof tracks within a variable-width cone of ∆R= min(0.2,10 GeV/pT) (∆R < min(0.3,10 GeV/pT)) of the electron (muon) must be less than 15% of the pTof the electron (muon). Contributions to the isolation cones from other leptons in the quadruplet are subtracted before applying the requirements. Overlap removal is applied to avoid identifying the same detector signature as multiple electrons, muons or jets. Electrons sharing an ID track with a selected muon are ignored, except if the muon is only calorimeter-tagged, in which case the muon is ignored instead. Electrons sharing their track or cluster in the calorimeter with a selected higher-pTelectron are ignored. 4.3 Definition of invariant-mass kinematic variables For all three analyses, the convention is adopted that m12 and m34 are the invariant masses of the two dileptons that make up a quadruplet, with the defining constraint that |m12 −mZ|<|m34 −mZ|, where mZis the mass of the Zboson6[73]. Thus m12 identifies the primary pair and m34 is the secondary pair. In the case of quadruplets formed from four electrons or four muons, alternate pairings of same-flavour opposite-sign leptons can be formed. The invariant masses of these alternate pairings are denoted by m14 and m32, where the positively charged lepton from the primary pair is paired with the negatively charged lepton from the secondary pair to compute m14, and the positively charged lepton from the secondary pair is paired with the negatively charged lepton from the primary pair to compute m32. 4.4 Summary of analysis event selections Table 1summarises the event selection used in the three analyses that are described in further detail in sections 5–7, and signal efficiencies of these selections with respect to a minimal fiducial volume are shown in figures 7a and 8a of section 8.1. 5H→ZX →4`analysis 5.1 Monte Carlo simulation Samples of events with H→ZZd→4`, where the Higgs boson with mass mH= 125 GeV was produced in the gluon-gluon fusion mode (ggF), were generated using the Hidden 6Put another way, m12 is the invariant mass of the dilepton that is closer to the Z boson mass, and m34 is the invariant mass of the other dilepton in the quadruplet. – 8 – JHEP06(2018)166 quadruplet. The event is discarded if no quadruplets remain. From any quadruplets remaining, a single quadruplet is selected as the one with the smallest dilepton invariant mass difference δm =|m12 −m34|. This procedure for selecting a single quadruplet can result in the incorrectly paired quadruplet being selected in 4eor 4µsignal events. The fraction of signal events where this occurs was estimated using the ZdZdMC samples to be approximately 2% (1%) in the 4e(4µ) channel for mX= 15 GeV, rising to 8% (5%) at mX= 60 GeV. Events are classified into three channels according to the flavours of the leptons in the selected quadruplet: 4e, 2e2µ, and 4µ(no distinction is made between 2e2µand 2µ2epermutations). The remaining selections are applied to the selected quadruplet of the event, with the event discarded if any selection fails: the four-lepton invariant mass must be in the range 115 < m4`<130 GeV, to select events consistent with a 125 GeV Higgs boson. The ratio of the secondary dilepton’s mass to the primary dilepton’s mass (m34/m12) must be greater than 0.85, which selects events where the dilepton masses are similar. Neither of the dilepton invariant masses is allowed to be in a mass range around the J/Ψ or Υ resonance masses (see table 1), with this requirement also applied to the alternative-pairing dilepton invariant masses (m14 and m32) for events with a 4eor 4µselected quadruplet. Finally, the dilepton invariant masses are required to be in the range 10 < m12,34 <64 GeV and in the case of 4eand 4µquadruplets the alternative-pairing dilepton masses must be in the range 5 < m14,32 <75 GeV. These last two selections suppress backgrounds that contain a Zboson, and are referred to as the Z Veto in the following. 6.3 Background estimation All background estimates for this analysis rely on using MC simulations, and are validated in regions that are orthogonal to the signal event selection described in the previous section. The two main background processes (H→ZZ∗→4`and ZZ∗→4`) are validated by comparison of the background prediction to data in three validation regions that are orthogonal to the signal region. The first validation region (VR1) is defined by reversing part of the Z Veto requirement: VR1 requires m14 or m32 to be greater than 75 GeV. The second validation region (VR2) instead requires that m12 is greater than 64 GeV. These two regions primarily validate the H→ZZ∗→4`prediction. The third validation region (VR3) reverses the requirement on the four-lepton invariant mass window, i.e. requires m4`<115 GeV or m4`>130 GeV. In all three validation regions the m34/m12 >0.85 requirement is removed in order to increase the number of data events. Distributions of the average dilepton mass are shown for the three validation regions in figure 3. The background estimates for the signal region are given in table 3, and include all systematic uncertainties described in section 6.4. 6.4 Systematic uncertainties The systematic uncertainties in the signal and background modelling are the same as those described in section 5.4 (excluding the data-driven background uncertainties, which are not applicable to this search). It should be noted that fewer than four background events are predicted in the signal region for the H→XX →4`analysis, and therefore the dominant uncertainty in the background prediction is the statistical uncertainty. – 15 – JHEP06(2018)166 [GeV]〉 ll m〈 10 15 20 25 30 35 40 45 50 55 60 65 Events / 2.5 GeV 0 2 4 6 8 10 12 14 Data Total Background Reducible bkg )Υ/Ψ/J/tZ+(t VVV/VBS 4l→ZZ*→H 4l→ZZ* =15 GeV Zd m =35 GeV Zd m =55 GeV Zd m ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H cut 12 /m 34 No m Fails Z Veto > 75 GeV) 32 or m 14 (m (a) VR1. [GeV]〉 ll m〈 10 15 20 25 30 35 40 45 50 55 60 65 Events / 2.5 GeV 0 5 10 15 20 25 Data Total Background Reducible bkg )Υ/Ψ/J/tZ+(t VVV/VBS 4l→ZZ*→H 4l→ZZ* =15 GeV Zd m =35 GeV Zd m =55 GeV Zd m ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H cut 12 /m 34 No m > 64 GeV 12 m (b) VR2. [GeV]〉 ll m〈 10 15 20 25 30 35 40 45 50 55 60 65 Events / 2.5 GeV 0 5 10 15 20 25 30 35 40 45 50 Data Total Background Reducible bkg )Υ/Ψ/J/tZ+(t VVV/VBS 4l→ZZ*→H 4l→ZZ* =15 GeV Zd m =35 GeV Zd m =55 GeV Zd m ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H cut 12 /m 34 No m Window 4l Outside m (c) VR3. Figure 3. Distributions of hm``i=1 2(m12 +m34) in three background validation regions of the H→XX →4`(15 < mX<60 GeV) analysis: (a) events failing the Z Veto (4eor 4µ events where m14 or m32 >75 GeV), (b) events where m12 >64 GeV, (c) events outside of the 115 < m4`<130 GeV window. In all cases the m34/m12 requirement is removed to increase the number of events. The (negligible) contamination by the signal in these validation regions is shown for three mass hypotheses of the vector-boson benchmark model: the signal strength corresponds to a branching ratio B(H→ZdZd→4`) = 1 10 B(H→ZZ∗→4`) (with B(H→ZZ∗→4`) corresponding to the SM prediction [93]). 6.5 Results The distributions of hm``i=1 2(m12 +m34) for the events selected in this analysis are shown in figure 4, and the total yields presented in table 3: six events are observed for a prediction of 3.9±0.3 events in the high-mass selection. The biggest deviation from the Standard Model expectation is from a single event at hm``i ≈ 20 GeV, with a local significance of 3.2σ. The corresponding global significance is approximately 1.9σ, estimated using an approximation [114] for the tail probability of the profile-likelihood-ratio test statistic. The significances are calculated using a Gaussian signal model with normalisation, yield, and standard deviation determined by interpolation between the corresponding fits to simulated signal samples (5 GeV intervals in Zdmass). This statistical model, where the signal spans several bins of the hm``idistribution, means – 16 – JHEP06(2018)166 Process Yield ZZ∗→4`0.8±0.1 H→ZZ∗→4`2.6±0.3 VVV/VBS 0.51 ±0.18 Z+ (t¯ t/J/Ψ) →4`0.004 ±0.004 Other Reducible Background Negligible Total 3.9±0.3 Data 6 Table 3. Expected event yields of the SM background processes and observed data in the H→ XX →4`(15 GeV < mX<60 GeV) selection. The uncertainties include MC-statistical and systematic components. [GeV]〉 ll m〈 0 10 20 30 40 50 60 Events / GeV 3− 10 2− 10 1− 10 1 10 2 10 Data Total Background Reducible bkg )Υ/Ψ/J/tZ+(t VVV/VBS 4l→ZZ*→H 4l→ZZ* =15 GeV Zd m =35 GeV Zd m =55 GeV Zd m ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H (a) Signal region hm``idistribution. [GeV] 12 m 20 30 40 50 60 [GeV] 34 m 20 30 40 50 60 70 4e channel [2 evts] channel [7 evts]µ2e2 channel [8 evts]µ4 Failed Z veto [25 evts] Signal region ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H (b) m34 vs m12 distribution. Figure 4. Distribution of (a) hm``i=1 2(m12 +m34) and (b) m34 vs m12, for events selected in the H→XX →4`(15 < mX<60 GeV) analysis. The example signal distributions in (a) correspond to the expected yield normalized with σ(pp →H→ZdZd→4`) = 1 10 σSM(pp →H→ZZ∗→4`). The crossed-through points in (b) fail the Z Veto. The events outside the (shaded green) signal region in figure (b) are events that fail the m34/m12 >0.85 requirement. The diagonal dashed line marks where m12 =m34, and in this range of dilepton masses all events will have m34 < m12. that statistical fluctuations in the background estimate do not significantly impact the calculation of significance. The m34 versus m12 distribution of the selected events is shown in figure 4b. In this figure, the crossed-through markers correspond to the events that fail the Z Veto, which required the alternative-pairing masses m32 and m14 (relevant only to the 4eand 4µ channels) to be less than 75 GeV. This requirement has a significant impact on the signal efficiency (up to ≈40% loss) for mXjust above 15 GeV, but is applied in this analysis to mitigate any small contributions from SM processes involving Zboson production with large cross-sections. The 25 events that fail this veto are shown in validation region VR1 in figure 3, where there is a total background prediction of 38 ±3 events. – 17 – JHEP06(2018)166 7H→XX →4µ(1 GeV < mX<15 GeV) analysis 7.1 Monte Carlo simulation The generation of the signal processes H→ZdZd→4`and H→aa →4µfollows the prescription described in section 6.1. Four samples were generated with Zdmasses of 1 GeV, 2 GeV, 5 GeV and 10 GeV, while the mass of the a-boson was varied for 10 different signal hypotheses in the range 0.5 GeV ≤ma≤15 GeV. The background processes considered in this analysis are described in the following: H→ZZ∗→4`:the modelling of this process is the same as for the H→ZZd→4` analysis, described in section 5.1. ZZ∗→4`:this process was simulated with Sherpa 2.1.1 due to an implicit particlelevel requirement on the mass of the Z∗in the Powheg-Box MC sample used for the high-mass selection described in section 6.1. The gg-initiated production mechanism was modelled in the same way as for the H→ZZd→4`analysis, see section 5.1. Both production mechanisms are estimated using the CT10 PDFs. VVV/VBS: the modelling of this process is described in section 6.1. 7.2 Event selection In this search, only events with at least four muons are considered. Similarly to the searches described above, the selected muons are combined into 4µquadruplets in all possible permutations of pairs of opposite-sign dimuons. In the case of having more than four muons, the different quadruplets that can be formed are all considered. Of the muons in each quadruplet, at least three must have pT>10 GeV, at least two must have pT>15 GeV, and at least one must have pT>20 GeV, and there cannot be more than one stand-alone or calorimeter-tagged muon. The quadruplet selection closely follows the selection described in section 6.2. Nonetheless, low-mass bosons are more boosted and muons less separated. For this reason, to keep signal efficiencies high, no ∆Rrequirement is applied to the muons of the quadruplets. If more than one quadruplet survives this selection, the one with the smallest ∆m`` is selected. Similarly to the H→XX →4`(15 < mX<60 GeV) analysis, a set of requirements are applied to the quadruplet invariant masses as well as to the masses of the different muon pairings in the quadruplet. The quadruplet invariant mass must satisfy 120 GeV < m4`<130 GeV. This window is tighter than the selections described in sections 5.2 and 6.2 because muons have smaller radiative losses than electrons. The dilepton masses must be in the range 0.88 GeV < m12,34 <20 GeV. No restriction is applied to the alternativepairing dilepton masses because more than one third of signal events in this corner of the phase space contains an alternative-pairing dilepton mass that satisfies 75 GeV < m14,32 < 125 GeV, and would therefore be lost if this selection was applied. 7.3 Background estimation The main background contributions for this search come from the ZZ∗→4`and H→ ZZ∗→4`processes, as for the H→XX →4`(15 < mX<60 GeV) case described in – 18 – JHEP06(2018)166 section 6.3. These backgrounds, suppressed by the requirements on the lepton invariant mass, account for 30% each of the total background. Smaller background contributions come from higher-order electroweak processes (with cross-sections proportional to α6at leading order) and account for approximately 19% or the total background. Finally, events with multiple heavy flavour (bottom or charm) quark decays can also contribute to the total background yield. A leading part of this contribution comes from double semileptonic decays, where the b-quark decays to a muon and a c-quark which further decays into another muon and light hadrons. Resonances produced in the heavy flavour quark decay chain (i.e. ω,ρ,φ,J/ψ) that result in pairs of muons also become an important contribution of this background. Events with four heavy flavour quarks may pass the signal region requirements if each bottom or charm quark decays semileptonically. The estimation method for the heavy flavour background was developed using fully data-driven inputs and inspired by a previous analysis from CMS [115]. Using data control samples, the background is modelled as a two-dimensional template in the plane of the invariant masses of the two dimuons. This template is constructed from the Cartesian product of two one-dimensional dimuon invariant mass spectra assuming that each muon pair is independent of the other. The one-dimensional templates are derived in control regions with three muons passing the same quality and isolation requirements used elsewhere in the analysis. The high-pTselection requires three muons, with a muon pair with pT>20 GeV and pT>10 GeV matched to the dimuon trigger, and an additional muon with pT>5 GeV. The low-pTselection also requires three muons, with a pair of muons, each with pT>5 GeV, and an additional muon with pT>25 GeV matched to the single-muon trigger. The choice of pTthresholds for the templates was carefully studied and it is required that the first (second) dimuon pair always passes the high-pT(low-pT) selection. Estimations with alternative pTthreshold selections were found to be compatible with the current prescription. The Higgs boson mass requirement described in section 4introduces a correlation between the dimuon pairs and therefore a correction to the two-dimensional template is necessary. This correction is extracted from data using a sample enriched in events with heavy flavour quarks, with inverted isolation and vertex requirements. The final template covers the full m34 vs m12 plane, including the signal region (defined by the condition m34/m12 >0.85). The normalisation of the template is computed in the region with m34/m12 <0.85, and its effect propagated to the signal region. The heavy flavour processes are negligible in the high-mass region, while they account for 22% of the total prediction in the low-mass region. The modelling of the most important background processes (ZZ∗→4`and H→ ZZ∗→4`) was validated in VR1, VR2 and VR3, defined in section 6.3 for the H→ XX →4`(15 < mX<60 GeV) selection. The ZZ∗→4`process can also be validated by comparing the background prediction to the data in a validation region (VR4) that is orthogonal to this signal region. This validation region is defined by reversing the fourlepton invariant mass window requirement, i.e. m4`<120 GeV or m4`>130 GeV. The average dilepton mass distribution for this region is shown in figure 5. – 19 – JHEP06(2018)166 [GeV]〉 ll m〈 0 5 10 15 20 Events / 2.5 GeV 0 1 2 3 4 5 6 7 8 9 10 Data Total Background Reducible bkg )Υ/Ψ/J/tZ+(t VVV/VBS 4l→ZZ*→H 4l→ZZ* =1 GeV Zd m =2 GeV Zd m =5 GeV Zd m ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H cut 12 /m 34 No m Window 4l Outside m Low-mass Selection Figure 5. Distribution of hm``i=1 2(m12 +m34) in the validation region. The (negligible) contamination by the signal in these validation regions is shown for three mass hypotheses of the vector-boson benchmark model: the signal strength corresponds to a branching ratio B(H→ZdZd→4`) = 1 10 B(H→ZZ∗→4`) (with B(H→ZZ∗→4`) corresponding to the SM prediction [93]). 7.4 Systematic uncertainties In addition to the systematic uncertainties described in section 6.4, this analysis includes additional uncertainties for its data-driven background estimate. Several sources of uncertainty are considered for the heavy flavour background datadriven estimation. Uncertainties in the shape of the one-dimensional templates are propagated to the two-dimensional template to account for shape variations in the dimuon invariant mass spectra. Different parameterisations of the Higgs boson mass requirement are also considered for modelling the effect of this condition on the shape of the distribution in the (m12, m34) plane. The previous two systematic uncertainties affect the shape of the two-dimensional plane, which propagates to a 63% effect on the yield of the heavy flavour background in the low-mass search signal region. Finally, the statistical uncertainty in the normalisation of the template in the signal region (m34/m12 <0.85 region of the twodimensional plane) is also propagated to the signal region to account for fluctuations in the final heavy flavour background yields and has an effect of 13%. Uncertainties from the different sources are added in quadrature, and the total amounts to 65% for this background source. 7.5 Results The hm``idistribution for the selected events is shown in figure 6a. Table 4shows the resulting yields and uncertainties for this analysis: no events are observed to pass the selection, for a total background prediction of 0.4±0.1. The m34 versus m12 distribution in figure 6b shows that there is no evidence of a signal-like resonance even outside of the 120 GeV < m4`<130 GeV window applied in this selection: 16 events are observed outside of this mass window, compared to a MC-based prediction of 15±2 events from non-resonant SM ZZ processes. These 16 events are shown in the validation region in figure 5. – 20 – JHEP06(2018)166 [GeV]〉 ll m〈 2 4 6 8 10 12 14 16 18 Events / 0.2 GeV 0.002 0.004 0.006 0.008 0.01 0.012 0.014 Data Total Background Heavy Flavour VVV/VBS 4l→ * ZZ 4l→ ZZ* →H ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H (a) Signal region hm``idistribution. [GeV] 12 m 2 4 6 8 10 12 14 16 18 20 [GeV] 34 m 5 10 15 20 25 low mass channel [0 evts]µ4 < 130 window [16 evts] 4l Outside 120 < m Signal region Quarkonia veto ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H (b) m34 vs m12 distribution. Figure 6. Distribution of (a) hm``i=1 2(m12 +m34) and (b) m34 vs m12, for events selected in the H→XX →4µ(1 < mX<15 GeV) analysis. The crossed-through points in figure (b) correspond to events that are outside the m4`mass window of 120 GeV < m4`<130 GeV. The events outside the (shaded green) signal region are events that fail the m34/m12 >0.85 requirement. Process Yield ZZ∗→4`0.10 ±0.01 H→ZZ∗→4`0.1±0.1 VVV/VBS 0.06 ±0.03 Heavy flavour 0.07 ±0.04 Total 0.4±0.1 Data 0 Table 4. Expected event yields of the SM background processes and observed data in the H→XX →4µ(1 GeV < mX<15 GeV) selection. The uncertainties include MC-statistical and systematic components (systematic uncertainties are discussed in section 7.5). 8 Interpretation and discussion The results do not show evidence for the signal processes of H→ZX →4`or H→ XX →4`. The results are therefore interpreted in terms of limits on the benchmark models presented in section 2. For the H→ZX →4`analysis, the signal shape is obtained directly from simulation using the Z(d)Zdbenchmark model [14,15]. For the H→XX →4`analysis, a simple Gaussian model is used for a generic signal in the hm``iobservable, with the mean and standard deviation depending on the mass scale and resolution, respectively, in each decay channel. These scales and resolutions are estimated directly from simulation. The mass scale is found to have a −2% bias in X→ee decays, and −0.5% bias in X→µµ decays (i.e. a −1% bias is used in the eeµµ channel). The mass resolutions are estimated to be 3.5% in X→ee decays and 1.9% in X→µµ decays (meaning, for example, that the standard deviation in the 4µchannel is about 1/√2×1.9% ≈1.34% of mX). These scales and resolutions are valid across the full mass range considered (1–60 GeV). – 21 – JHEP06(2018)166 8.1 Limits on fiducial cross-sections The results were interpreted as limits on fiducial cross-sections by estimating the reconstruction efficiencies of each channel cin the fiducial phase spaces defined in table 5. The fiducial selections were chosen to mimic the analysis selections described in sections 5.2 and 6.2. The leptons are “dressed”, i.e. in order to emulate the effects of quasi-collinear electromagnetic radiation from the charged leptons on their experimental reconstruction in the detector [116], the four-momenta of all prompt photons within ∆R= 0.1 of a lepton are added to the four-momentum of the closest lepton. For the H→XX search the efficiencies (shown in figure 8a) are estimated with the ZdZdbenchmark model and were verified to be compatible with the aa benchmark model to within 3% across the whole mass range. For the ZX search the efficiencies (shown in figure 7a) are estimated with the ZZdbenchmark model, but no verification was explicitly made to confirm if these efficiencies are valid for aZa process. Assuming that the verified compatibility between efficiencies of ZdZdand aa processes applies equally to ZZdand Za processes, upper limits on the cross-sections corresponding to these fiducial phase spaces should be applicable to any models of 125 GeV Higgs boson decays to four leptons via one (with an associated Z boson) or two intermediate, on-shell, narrow, promptly decaying bosons. The fiducial requirements are applied to the four leptons in this decay. These efficiencies are used to compute 95% CL upper limits on the cross-sections in the fiducial phase spaces defined for the H→ZX →4`and H→XX →4`searches. These model-independent limits are computed using the CLs frequentist formalism [117] with the profile-likelihood-ratio test statistic [118] (systematics are represented with nuisance parameters which are then profiled in the calculation of the test statistic). The results are shown in figures 7b and 8b, respectively. Impact of the systematic uncertainties on the limits is small. For the H→ZX →4`search, a local excess of 3σat mZd= 23 GeV is observed in the 2`2echannel. However, the total observed and predicted event counts in this channel agree within 0.5σ. No local excess is observed in the 2`2µchannel. The width of the 2σexpected limit bands of figure 8b increases towards large values of mXbecause more events are expected from background-only processes at this end of the mass spectrum; the larger expected background leads to a greater spread in the limits obtained with pseudoexperiments generated with the background-only hypothesis. 8.2 Limits on branching ratios Model-dependent acceptances for the fiducial phase spaces are computed per channel for the H→ZZd→4`and H→XX →4`searches. The acceptance for the benchmark vectorboson model is estimated for both searches, whereas the acceptance for the benchmark pseudoscalar-boson model (type-II 2HDM+S model with tan β= 5) is estimated only for the H→XX →4`search. The acceptances are used in a combined statistical model to compute upper limits on σH× B(H→ZZd→4`) and σH× B(H→XX →4`) for each model. The Zdmodel assumes partial fractions of 0.25:0.25:0.25:0.25 for the 4e:2e2µ:4µ:2µ2echannels, whereas the amodel assumes 100% decay to 4µ. These crosssection limits are converted into limits on the branching ratios of H→ZZd,H→ZdZd – 22 – JHEP06(2018)166 H→ZX →4` (15 GeV < mX<55 GeV) H→XX →4` (15 GeV < mX<60 GeV) H→XX →4µ (1 GeV < mX<15 GeV) Electrons Dressed with prompt photons within ∆R= 0.1 pT>7 GeV |η|<2.5 Muons Dressed with prompt photons within ∆R= 0.1 pT>5 GeV |η|<2.7 Quadruplet Three leading-pTleptons satisfy pT>20 GeV, 15 GeV, 10 GeV ∆R > 0.1 (0.2) between SF (OF) leptons — 50 GeV < m12 <106 GeV m34/m12 >0.85 12 GeV < m34 <115 GeV 10 GeV < m12,34 <64 GeV 0.88 GeV < m12,34 <20 GeV 115 GeV < m4`<130 GeV m12,34,14,32 >5 GeV 5 GeV < m14,32 <75 GeV if 4eor 4µ Reject event if either of: (mJ/ψ −0.25 GeV) < m12,34,14,32 <(mψ(2S)+ 0.30 GeV) (mΥ(1S)−0.70 GeV) < m12,34,14,32 <(mΥ(3S)+0.75 GeV) Table 5. Summary of the fiducial phase-space definitions used in this analysis, appropriate for processes of the form H→ZZd→4`aand H→XX →4`, where Xis a promptly decaying, on-shell, narrow resonance. [GeV] d Z m 15 20 25 30 35 40 45 50 55 c ∈ 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 channelµ2l2 2l2e channel ATLAS Simulation 4l→ d ZZ→H 13 TeV (a) Efficiencies. 15 20 25 30 35 40 45 50 55 [GeV] X m 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 [fb] fid σ95% CL upper limit on µ2l2e 2l2 Observed Expected σ 2± ATLAS 4l→ ZX→H -1 13 TeV, 36.1 fb (b) Fiducial cross-sections. Figure 7. (a) Per-channel efficiencies ccalculated in the fiducial volume described in the H→ ZX →4`column of table 5. The dark band is the statistical uncertainty and the lighter band is the systematic uncertainty. These efficiencies were computed using the H→ZZd→4`model. (b) Upper limits at the 95% CL on fiducial cross-sections for the H→ZX →4`process. The limits from the H→Za →4`search are valid only for the 2`2µchannel as the H→Za model assumes B(a→µµ) = 100%. – 23 – JHEP06(2018)166 [GeV] X m 0 10 20 30 40 50 60 c ∈ 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 4e channel channelµ2e2 channelµ4 SimulationATLAS 13 TeV 4l→ XX →H (a) Efficiencies. [GeV] X m 10 20 30 40 50 60 [fb] fid σ95% CL upper limit on 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Expected σ 2± Observed µ 4µ4e 2e2 ATLAS -1 13 TeV, 36.1 fb 4l→ XX →H (b) Fiducial cross-sections. Figure 8. (a) Model-independent per-channel efficiencies ccalculated in the fiducial volumes described in the 1 GeV < mX<15 GeV and 15 GeV < mX<60 GeV columns of table 5(i.e. separate phase spaces are defined for mXabove and below 15 GeV). The dark band is the statistical uncertainty and the lighter band is the systematic uncertainty. (b) Upper limits at the 95% CL on fiducial cross-sections for the for the H→XX →4`process. The step change in the fiducial cross-section limit in the 4µchannel is due to the change in efficiency caused by the change in fiducial phase-space definition. The shaded areas are the quarkonia veto regions. 15 20 25 30 35 40 45 50 55 [GeV] d Z m 4− 10 3− 10 2− 10 1− 10 ) d ZZ→B(H SM H σ H σ 95% CL upper limit on Observed Expected σ 1± σ 2± ATLAS 4l→ d ZZ→H -1 13 TeV, 36.1 fb Figure 9. Upper limit at 95% CL on the branching ratio for the H→ZZdprocess. and H→aa by using the theoretical branching ratios for Zd→`` and a→µµ from each benchmark model [14,15], and assuming for σHthe SM cross-section8for Higgs boson production at √s= 13 TeV [93]. The limits on these branching ratios are shown in figures 9and 10 for the H→ZZd→4`and H→XX →4`searches, respectively. The observed limit for B(H→aa) (figure 10b) for ma>15 GeV is greater than 1 (i.e. this search has no sensitivity to this model in that mass range). The limit on the branching ratio for H→ZdZd→4`improves on the Run 1 result of ref. 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Feng32, M.J. Fenton56, A.B. Fenyuk132, L. Feremenga8, P. Fernandez Martinez170, J. Ferrando45, A. Ferrari168, P. Ferrari109, R. Ferrari123a, D.E. Ferreira de Lima60b, A. Ferrer170, D. Ferrere52, C. Ferretti92, F. Fiedler86, A. Filipˇciˇc78, M. Filipuzzi45, F. Filthaut108, M. Fincke-Keeler172, K.D. Finelli24, M.C.N. Fiolhais128a,128c,s, L. Fiorini170, A. Fischer2, C. Fischer13, J. Fischer178, W.C. Fisher93, N. Flaschel45, I. Fleck143, P. Fleischmann92, R.R.M. Fletcher124, T. Flick178, B.M. Flierl102, L.R. Flores Castillo62a, M.J. Flowerdew103, G.T. Forcolin87, A. Formica138, – 36 – JHEP06(2018)166 F.A. F¨orster13, A. Forti87, A.G. Foster19, D. Fournier119, H. Fox75, S. Fracchia141, P. Francavilla126a,126b, M. Franchini22a,22b, S. Franchino60a, D. Francis32, L. Franconi121, M. Franklin59, M. Frate166, M. Fraternali123a,123b, D. Freeborn81, S.M. Fressard-Batraneanu32, B. Freund97, D. Froidevaux32, J.A. Frost122, C. Fukunaga158, T. Fusayasu104, J. Fuster170, O. Gabizon154, A. Gabrielli22a,22b, A. Gabrielli16, G.P. Gach41a, S. Gadatsch32, S. Gadomski80, G. Gagliardi53a,53b, L.G. Gagnon97, C. Galea108, B. Galhardo128a,128c, E.J. Gallas122, B.J. Gallop133, P. Gallus130, G. Galster39, K.K. Gan113, S. Ganguly37, Y. Gao77, Y.S. Gao145,g, F.M. Garay Walls34a, C. Garc´ıa170, J.E. Garc´ıa Navarro170, J.A. Garc´ıa Pascual35a, M. Garcia-Sciveres16, R.W. Gardner33, N. Garelli145, V. Garonne121, A. Gascon Bravo45, K. Gasnikova45, C. Gatti50, A. Gaudiello53a,53b, G. Gaudio123a, I.L. Gavrilenko98, C. Gay171, G. Gaycken23, E.N. Gazis10, C.N.P. Gee133, J. Geisen57, M. Geisen86, M.P. Geisler60a, K. Gellerstedt148a,148b, C. Gemme53a, M.H. Genest58, C. Geng92, S. Gentile134a,134b, C. Gentsos156, S. George80, D. Gerbaudo13, G. Geßner46, S. Ghasemi143, M. Ghneimat23, B. Giacobbe22a, S. Giagu134a,134b, N. Giangiacomi22a,22b, P. Giannetti126a, S.M. Gibson80, M. Gignac171, M. Gilchriese16, D. Gillberg31, G. Gilles178, D.M. Gingrich3,d, M.P. Giordani167a,167c, F.M. Giorgi22a, P.F. Giraud138, P. Giromini59, G. Giugliarelli167a,167c, D. Giugni94a, F. Giuli122, C. Giuliani103, M. Giulini60b, B.K. Gjelsten121, S. Gkaitatzis156, I. Gkialas9,t, E.L. Gkougkousis13, P. Gkountoumis10, L.K. Gladilin101, C. Glasman85, J. Glatzer13, P.C.F. Glaysher45, A. Glazov45, M. Goblirsch-Kolb25, J. Godlewski42, S. Goldfarb91, T. Golling52, D. Golubkov132, A. Gomes128a,128b,128d, R. Gon¸calo128a, R. Goncalves Gama26a, J. Goncalves Pinto Firmino Da Costa138, G. Gonella51, L. Gonella19, A. Gongadze68, J.L. Gonski59, S. Gonz´alez de la Hoz170, S. Gonzalez-Sevilla52, L. Goossens32, P.A. Gorbounov99, H.A. Gordon27, I. Gorelov107, B. Gorini32, E. Gorini76a,76b, A. Goriˇsek78, A.T. Goshaw48, C. G¨ossling46, M.I. Gostkin68, C.A. Gottardo23, C.R. Goudet119, D. Goujdami137c, A.G. Goussiou140, N. Govender147b,u, E. Gozani154, I. Grabowska-Bold41a, P.O.J. Gradin168, J. Gramling166, E. Gramstad121, S. Grancagnolo17, V. Gratchev125, P.M. Gravila28f , C. Gray56, H.M. Gray16, Z.D. Greenwood82,v, C. Grefe23, K. Gregersen81, I.M. Gregor45, P. Grenier145, K. Grevtsov5, J. Griffiths8, A.A. Grillo139, K. Grimm75, S. Grinstein13,w, Ph. Gris37, J.-F. Grivaz119, S. Groh86, E. Gross175, J. Grosse-Knetter57, G.C. Grossi82, Z.J. Grout81, A. Grummer107, L. Guan92, W. Guan176, J. Guenther32, F. Guescini163a, D. Guest166, O. Gueta155, B. Gui113, E. Guido53a,53b, T. Guillemin5, S. Guindon32, U. Gul56, C. Gumpert32, J. Guo36b, W. Guo92, Y. Guo36c,x, R. Gupta43, S. Gurbuz20a, G. Gustavino115, B.J. Gutelman154, P. Gutierrez115, N.G. Gutierrez Ortiz81, C. Gutschow81, C. Guyot138, M.P. Guzik41a, C. Gwenlan122, C.B. Gwilliam77, A. Haas112, C. Haber16, H.K. Hadavand8, N. Haddad137e, A. Hadef88, S. Hageb¨ock23, M. Hagihara164, H. Hakobyan180,∗, M. Haleem45, J. Haley116, G. Halladjian93, G.D. Hallewell88, K. Hamacher178, P. Hamal117, K. Hamano172, A. Hamilton147a, G.N. Hamity141, P.G. Hamnett45, L. Han36c, S. Han35a,35d, K. Hanagaki69,y, K. Hanawa157, M. Hance139, D.M. Handl102, B. Haney124, P. Hanke60a, J.B. Hansen39, J.D. Hansen39, M.C. Hansen23, P.H. Hansen39, K. Hara164, A.S. Hard176, T. Harenberg178, F. Hariri119, S. Harkusha95, P.F. Harrison173, N.M. Hartmann102, Y. Hasegawa142, A. Hasib49, S. Hassani138, S. Haug18, R. Hauser93, L. Hauswald47, L.B. Havener38, M. Havranek130, C.M. Hawkes19, R.J. Hawkings32, D. Hayakawa159, D. Hayden93, C.P. Hays122, J.M. Hays79, H.S. Hayward77, S.J. Haywood133, S.J. Head19, T. Heck86, V. Hedberg84, L. Heelan8, S. Heer23, K.K. Heidegger51, S. Heim45, T. Heim16, B. Heinemann45,z, J.J. Heinrich102, L. Heinrich112, C. Heinz55, J. Hejbal129, L. Helary32, A. Held171, S. Hellman148a,148b, C. Helsens32, R.C.W. Henderson75, Y. Heng176, S. Henkelmann171, A.M. Henriques Correia32, S. Henrot-Versille119, G.H. Herbert17, H. Herde25, V. Herget177, Y. Hern´andez Jim´enez147c, H. Herr86, G. Herten51, R. Hertenberger102, L. Hervas32, T.C. Herwig124, G.G. Hesketh81, N.P. Hessey163a, J.W. Hetherly43, S. Higashino69, – 37 – JHEP06(2018)166 E. Hig´on-Rodriguez170, K. Hildebrand33, E. Hill172, J.C. Hill30, K.H. Hiller45, S.J. Hillier19, M. Hils47, I. Hinchliffe16, M. Hirose51, D. Hirschbuehl178, B. Hiti78, O. Hladik129, D.R. Hlaluku147c, X. Hoad49, J. Hobbs150, N. Hod163a, M.C. Hodgkinson141, P. Hodgson141, A. Hoecker32, M.R. Hoeferkamp107, F. Hoenig102, D. Hohn23, T.R. Holmes33, M. Holzbock102, M. Homann46, S. Honda164, T. Honda69, T.M. Hong127, B.H. Hooberman169, W.H. Hopkins118, Y. Horii105, A.J. Horton144, J-Y. Hostachy58, A. Hostiuc140, S. Hou153, A. Hoummada137a, J. Howarth87, J. Hoya74, M. Hrabovsky117, J. Hrdinka32, I. Hristova17, J. Hrivnac119, T. Hryn’ova5, A. Hrynevich96, P.J. Hsu63, S.-C. Hsu140, Q. Hu27, S. Hu36b, Y. Huang35a, Z. Hubacek130, F. Hubaut88, F. Huegging23, T.B. Huffman122, E.W. Hughes38, M. Huhtinen32, R.F.H. Hunter31, P. Huo150, N. Huseynov68,b, J. Huston93, J. Huth59, R. Hyneman92, G. Iacobucci52, G. Iakovidis27, I. Ibragimov143, L. Iconomidou-Fayard119, Z. Idrissi137e, P. Iengo32, O. Igonkina109,aa, T. Iizawa174, Y. Ikegami69, M. Ikeno69, Y. Ilchenko11,ab, D. Iliadis156, N. Ilic145, F. Iltzsche47, G. Introzzi123a,123b, P. Ioannou9,∗, M. Iodice136a, K. Iordanidou38, V. Ippolito59, M.F. Isacson168, N. Ishijima120, M. Ishino157, M. Ishitsuka159, C. Issever122, S. Istin20a, F. Ito164, J.M. Iturbe Ponce62a, R. Iuppa162a,162b, H. Iwasaki69, J.M. Izen44, V. Izzo106a, S. Jabbar3, P. Jackson1, R.M. Jacobs23, V. Jain2, K.B. Jakobi86, K. Jakobs51, S. Jakobsen65, T. Jakoubek129, D.O. Jamin116, D.K. Jana82, R. Jansky52, J. Janssen23, M. Janus57, P.A. Janus41a, G. Jarlskog84, N. Javadov68,b, T. Jav˚urek51, M. Javurkova51, F. Jeanneau138, L. Jeanty16, J. Jejelava54a,ac, A. Jelinskas173, P. Jenni51,ad, C. Jeske173, S. J´ez´equel5, H. Ji176, J. Jia150, H. Jiang67, Y. Jiang36c, Z. Jiang145, S. Jiggins81, J. Jimenez Pena170, S. Jin35b, A. Jinaru28b, O. Jinnouchi159, H. Jivan147c, P. Johansson141, K.A. Johns7, C.A. Johnson64, W.J. Johnson140, K. Jon-And148a,148b, R.W.L. Jones75, S.D. Jones151, S. Jones7, T.J. Jones77, J. Jongmanns60a, P.M. Jorge128a,128b, J. Jovicevic163a, X. Ju176, A. Juste Rozas13,w, M.K. K¨ohler175, A. Kaczmarska42, M. Kado119, H. Kagan113, M. Kagan145, S.J. Kahn88, T. Kaji174, E. Kajomovitz154, C.W. Kalderon84, A. Kaluza86, S. Kama43, A. Kamenshchikov132, N. Kanaya157, L. Kanjir78, V.A. Kantserov100, J. Kanzaki69, B. Kaplan112, L.S. Kaplan176, D. Kar147c, K. Karakostas10, N. Karastathis10, M.J. Kareem163b, E. Karentzos10, S.N. Karpov68, Z.M. Karpova68, K. Karthik112, V. Kartvelishvili75, A.N. Karyukhin132, K. Kasahara164, L. Kashif176, R.D. Kass113, A. Kastanas149, Y. Kataoka157, C. Kato157, A. Katre52, J. Katzy45, K. Kawade70, K. Kawagoe73, T. Kawamoto157, G. Kawamura57, E.F. Kay77, V.F. Kazanin111,c, R. Keeler172, R. Kehoe43, J.S. Keller31, E. Kellermann84, J.J. Kempster80, J Kendrick19, H. Keoshkerian161, O. Kepka129, B.P. Kerˇsevan78, S. Kersten178, R.A. Keyes90, M. Khader169, F. Khalil-zada12, A. Khanov116, A.G. Kharlamov111,c, T. Kharlamova111,c, A. Khodinov160, T.J. Khoo52, V. Khovanskiy99,∗, E. Khramov68, J. Khubua54b,ae, S. Kido70, C.R. Kilby80, H.Y. Kim8, S.H. Kim164, Y.K. Kim33, N. Kimura156, O.M. Kind17, B.T. King77, D. Kirchmeier47, J. Kirk133, A.E. Kiryunin103, T. Kishimoto157, D. Kisielewska41a, V. Kitali45, O. Kivernyk5, E. Kladiva146b, T. Klapdor-Kleingrothaus51, M.H. Klein92, M. Klein77, U. Klein77, K. Kleinknecht86, P. Klimek110, A. Klimentov27, R. Klingenberg46,∗, T. Klingl23, T. Klioutchnikova32, E.-E. Kluge60a, P. Kluit109, S. Kluth103, E. Kneringer65, E.B.F.G. Knoops88, A. Knue103, A. Kobayashi157, D. Kobayashi73, T. Kobayashi157, M. Kobel47, M. Kocian145, P. Kodys131, T. Koffas31, E. Koffeman109, N.M. K¨ohler103, T. Koi145, M. Kolb60b, I. Koletsou5, A.A. Komar98,∗, T. Kondo69, N. Kondrashova36b, K. K¨oneke51, A.C. K¨onig108, T. Kono69,af , R. Konoplich112,ag, N. Konstantinidis81, R. Kopeliansky64, S. Koperny41a, A.K. Kopp51, K. Korcyl42, K. Kordas156, A. Korn81, A.A. Korol111,c, I. Korolkov13, E.V. Korolkova141, O. Kortner103, S. Kortner103, T. Kosek131, V.V. Kostyukhin23, A. Kotwal48, A. Koulouris10, A. Kourkoumeli-Charalampidi123a,123b, C. Kourkoumelis9, E. Kourlitis141, V. Kouskoura27, A.B. Kowalewska42, R. Kowalewski172, T.Z. Kowalski41a, C. Kozakai157, W. Kozanecki138, A.S. Kozhin132, V.A. Kramarenko101, G. Kramberger78, D. Krasnopevtsev100, M.W. Krasny83, – 38 – JHEP06(2018)166 A. Krasznahorkay32, D. Krauss103, J.A. Kremer41a, J. Kretzschmar77, K. Kreutzfeldt55, P. Krieger161, K. Krizka16, K. Kroeninger46, H. Kroha103, J. Kroll129, J. Kroll124, J. Kroseberg23, J. Krstic14, U. Kruchonak68, H. Kr¨uger23, N. Krumnack67, M.C. Kruse48, T. Kubota91, H. Kucuk81, S. Kuday4b, J.T. Kuechler178, S. Kuehn32, A. Kugel60a, F. Kuger177, T. Kuhl45, V. Kukhtin68, R. Kukla88, Y. Kulchitsky95, S. Kuleshov34b, Y.P. Kulinich169, M. Kuna134a,134b, T. Kunigo71, A. Kupco129, T. Kupfer46, O. Kuprash155, H. Kurashige70, L.L. Kurchaninov163a, Y.A. Kurochkin95, M.G. Kurth35a,35d, E.S. Kuwertz172, M. Kuze159, J. Kvita117, T. Kwan172, D. Kyriazopoulos141, A. La Rosa103, J.L. La Rosa Navarro26d, L. La Rotonda40a,40b, F. La Ruffa40a,40b, C. Lacasta170, F. Lacava134a,134b, J. Lacey45, D.P.J. Lack87, H. Lacker17, D. Lacour83, E. Ladygin68, R. Lafaye5, B. Laforge83, S. Lai57, S. Lammers64, W. Lampl7, E. Lan¸con27, U. Landgraf51, M.P.J. Landon79, M.C. Lanfermann52, V.S. Lang45, J.C. Lange13, R.J. Langenberg32, A.J. Lankford166, F. Lanni27, K. Lantzsch23, A. Lanza123a, A. Lapertosa53a,53b, S. Laplace83, J.F. Laporte138, T. Lari94a, F. Lasagni Manghi22a,22b, M. Lassnig32, T.S. Lau62a, P. Laurelli50, W. Lavrijsen16, A.T. Law139, P. Laycock77, T. Lazovich59, M. Lazzaroni94a,94b, B. Le91, O. Le Dortz83, E. Le Guirriec88, E.P. Le Quilleuc138, M. LeBlanc172, T. LeCompte6, F. Ledroit-Guillon58, C.A. Lee27, G.R. Lee34a, S.C. Lee153, L. Lee59, B. Lefebvre90, G. Lefebvre83, M. Lefebvre172, F. Legger102, C. Leggett16, G. Lehmann Miotto32, X. Lei7, W.A. Leight45, M.A.L. Leite26d, R. Leitner131, D. Lellouch175, B. Lemmer57, K.J.C. Leney81, T. Lenz23, B. Lenzi32, R. Leone7, S. Leone126a, C. Leonidopoulos49, G. Lerner151, C. Leroy97, R. Les161, A.A.J. Lesage138, C.G. Lester30, M. Levchenko125, J. Levˆeque5, D. Levin92, L.J. Levinson175, M. Levy19, D. Lewis79, B. Li36c,x, H. Li150, L. Li36b, Q. Li35a,35d, Q. Li36c, S. Li48, X. Li36b, Y. Li143, Z. Liang35a, B. Liberti135a, A. Liblong161, K. Lie62c, J. Liebal23, W. Liebig15, A. Limosani152, C.Y. Lin30, K. Lin93, S.C. Lin182, T.H. Lin86, R.A. Linck64, B.E. Lindquist150, A.E. Lionti52, E. Lipeles124, A. Lipniacka15, M. Lisovyi60b, T.M. Liss169,ah, A. Lister171, A.M. Litke139, B. Liu67, H. Liu92, H. Liu27, J.K.K. Liu122, J. Liu36a, J.B. Liu36c, K. Liu88, L. Liu169, M. Liu36c, Y.L. Liu36c, Y. Liu36c, M. Livan123a,123b, A. Lleres58, J. Llorente Merino35a, S.L. Lloyd79, C.Y. Lo62b, F. Lo Sterzo43, E.M. Lobodzinska45, P. Loch7, F.K. Loebinger87, A. Loesle51, K.M. Loew25, T. Lohse17, K. Lohwasser141, M. Lokajicek129, B.A. Long24, J.D. Long169, R.E. Long75, L. Longo76a,76b, K.A. Looper113, J.A. Lopez34b, I. Lopez Paz13, A. Lopez Solis83, J. Lorenz102, N. Lorenzo Martinez5, M. Losada21, P.J. L¨osel102, X. Lou35a, A. Lounis119, J. Love6, P.A. Love75, H. Lu62a, N. Lu92, Y.J. Lu63, H.J. Lubatti140, C. Luci134a,134b, A. Lucotte58, C. Luedtke51, F. Luehring64, W. Lukas65, L. Luminari134a, O. Lundberg148a,148b, B. Lund-Jensen149, M.S. Lutz89, P.M. Luzi83, D. Lynn27, R. Lysak129, E. Lytken84, F. Lyu35a, V. Lyubushkin68, H. Ma27, L.L. Ma36a, Y. Ma36a, G. Maccarrone50, A. Macchiolo103, C.M. Macdonald141, B. Maˇcek78, J. Machado Miguens124,128b, D. Madaffari170, R. Madar37, W.F. Mader47, A. Madsen45, N. Madysa47, J. Maeda70, S. Maeland15, T. Maeno27, A.S. Maevskiy101, V. Magerl51, C. Maiani119, C. Maidantchik26a, T. Maier102, A. Maio128a,128b,128d, O. Majersky146a, S. Majewski118, Y. Makida69, N. Makovec119, B. Malaescu83, Pa. Malecki42, V.P. Maleev125, F. Malek58, U. Mallik66, D. Malon6, C. Malone30, S. Maltezos10, S. Malyukov32, J. Mamuzic170, G. Mancini50, I. Mandi´c78, J. Maneira128a,128b, L. Manhaes de Andrade Filho26b, J. Manjarres Ramos47, K.H. Mankinen84, A. Mann102, A. Manousos32, B. Mansoulie138, J.D. Mansour35a, R. Mantifel90, M. Mantoani57, S. Manzoni94a,94b, L. Mapelli32, G. Marceca29, L. March52, L. Marchese122, G. Marchiori83, M. Marcisovsky129, C.A. Marin Tobon32, M. Marjanovic37, D.E. Marley92, F. Marroquim26a, S.P. Marsden87, Z. Marshall16, M.U.F Martensson168, S. Marti-Garcia170, C.B. Martin113, T.A. Martin173, V.J. Martin49, B. Martin dit Latour15, M. Martinez13,w, V.I. Martinez Outschoorn169, S. Martin-Haugh133, V.S. Martoiu28b, A.C. Martyniuk81, A. Marzin32, L. Masetti86, T. Mashimo157, R. Mashinistov98, J. Masik87, A.L. Maslennikov111,c, – 39 – JHEP06(2018)166 L.H. Mason91, L. Massa135a,135b, P. Mastrandrea5, A. Mastroberardino40a,40b, T. Masubuchi157, P. M¨attig178, J. Maurer28b, S.J. Maxfield77, D.A. Maximov111,c, R. Mazini153, I. Maznas156, S.M. Mazza94a,94b, N.C. Mc Fadden107, G. Mc Goldrick161, S.P. Mc Kee92, A. McCarn92, R.L. McCarthy150, T.G. McCarthy103, L.I. McClymont81, E.F. McDonald91, J.A. Mcfayden32, G. Mchedlidze57, S.J. McMahon133, P.C. McNamara91, C.J. McNicol173, R.A. McPherson172,o, S. Meehan140, T.J. Megy51, S. Mehlhase102, A. Mehta77, T. Meideck58, K. Meier60a, B. Meirose44, D. Melini170,ai, B.R. Mellado Garcia147c, J.D. Mellenthin57, M. Melo146a, F. Meloni18, A. Melzer23, S.B. Menary87, L. Meng77, X.T. Meng92, A. Mengarelli22a,22b, S. Menke103, E. Meoni40a,40b, S. Mergelmeyer17, C. Merlassino18, P. Mermod52, L. Merola106a,106b, C. Meroni94a, F.S. Merritt33, A. Messina134a,134b, J. Metcalfe6, A.S. Mete166, C. Meyer124, J-P. Meyer138, J. Meyer109, H. Meyer Zu Theenhausen60a, F. Miano151, R.P. Middleton133, S. Miglioranzi53a,53b, L. Mijovi´c49, G. Mikenberg175, M. Mikestikova129, M. Mikuˇz78, M. Milesi91, A. Milic161, D.A. Millar79, D.W. Miller33, C. Mills49, A. Milov175, D.A. Milstead148a,148b, A.A. Minaenko132, Y. Minami157, I.A. Minashvili54b, A.I. Mincer112, B. Mindur41a, M. Mineev68, Y. Minegishi157, Y. Ming176, L.M. Mir13, A. Mirto76a,76b, K.P. Mistry124, T. Mitani174, J. Mitrevski102, V.A. Mitsou170, A. Miucci18, P.S. Miyagawa141, A. Mizukami69, J.U. Mj¨ornmark84, T. Mkrtchyan180, M. Mlynarikova131, T. Moa148a,148b, K. Mochizuki97, P. Mogg51, S. Mohapatra38, S. Molander148a,148b, R. Moles-Valls23, M.C. Mondragon93, K. M¨onig45, J. Monk39, E. Monnier88, A. Montalbano150, J. Montejo Berlingen32, F. Monticelli74, S. Monzani94a, R.W. Moore3, N. Morange119, D. Moreno21, M. Moreno Ll´acer32, P. Morettini53a, S. Morgenstern32, D. Mori144, T. Mori157, M. Morii59, M. Morinaga174, V. Morisbak121, A.K. Morley32, G. Mornacchi32, J.D. Morris79, L. Morvaj150, P. Moschovakos10, M. Mosidze54b, H.J. Moss141, J. Moss145,aj, K. Motohashi159, R. Mount145, E. Mountricha27, E.J.W. Moyse89, S. Muanza88, F. Mueller103, J. Mueller127, R.S.P. Mueller102, D. Muenstermann75, P. Mullen56, G.A. Mullier18, F.J. Munoz Sanchez87, W.J. Murray173,133, H. Musheghyan32, M. Muˇskinja78, A.G. Myagkov132,ak, M. Myska130, B.P. Nachman16, O. Nackenhorst52, K. Nagai122, R. Nagai69,af , K. Nagano69, Y. Nagasaka61, K. Nagata164, M. Nagel51, E. Nagy88, A.M. Nairz32, Y. Nakahama105, K. Nakamura69, T. Nakamura157, I. Nakano114, R.F. Naranjo Garcia45, R. Narayan11, D.I. Narrias Villar60a, I. Naryshkin125, T. Naumann45, G. Navarro21, R. Nayyar7, H.A. Neal92, P.Yu. Nechaeva98, T.J. Neep138, A. Negri123a,123b, M. Negrini22a, S. Nektarijevic108, C. Nellist57, A. Nelson166, M.E. Nelson122, S. Nemecek129, P. Nemethy112, M. Nessi32,al, M.S. Neubauer169, M. Neumann178, P.R. Newman19, T.Y. Ng62c, Y.S. Ng17, T. Nguyen Manh97, R.B. Nickerson122, R. Nicolaidou138, J. Nielsen139, N. Nikiforou11, V. Nikolaenko132,ak, I. Nikolic-Audit83, K. Nikolopoulos19, J.K. Nilsen121, P. Nilsson27, Y. Ninomiya69, A. Nisati134a, N. Nishu36b, R. Nisius103, I. Nitsche46, T. Nitta174, T. Nobe157, Y. Noguchi71, M. Nomachi120, I. Nomidis31, M.A. Nomura27, T. Nooney79, M. Nordberg32, N. Norjoharuddeen122, O. Novgorodova47, M. Nozaki69, L. Nozka117, K. Ntekas166, E. Nurse81, F. Nuti91, K. O’connor25, D.C. O’Neil144, A.A. O’Rourke45, V. O’Shea56, F.G. Oakham31,d, H. Oberlack103, T. Obermann23, J. Ocariz83, A. Ochi70, I. Ochoa38, J.P. Ochoa-Ricoux34a, S. Oda73, S. Odaka69, A. Oh87, S.H. Oh48, C.C. Ohm149, H. Ohman168, H. Oide53a,53b, H. Okawa164, Y. Okumura157, T. Okuyama69, A. Olariu28b, L.F. Oleiro Seabra128a, S.A. Olivares Pino34a, D. Oliveira Damazio27, A. Olszewski42, J. Olszowska42, A. Onofre128a,128e, K. Onogi105, P.U.E. Onyisi11,ab, H. Oppen121, M.J. Oreglia33, Y. Oren155, D. Orestano136a,136b, N. Orlando62b, R.S. Orr161, B. Osculati53a,53b,∗, R. Ospanov36c, G. Otero y Garzon29, H. Otono73, M. Ouchrif137d, F. Ould-Saada121, A. Ouraou138, K.P. Oussoren109, Q. Ouyang35a, M. Owen56, R.E. Owen19, V.E. Ozcan20a, N. Ozturk8, K. Pachal144, A. Pacheco Pages13, L. Pacheco Rodriguez138, C. Padilla Aranda13, S. Pagan Griso16, M. Paganini179, F. Paige27, G. Palacino64, S. Palazzo40a,40b, S. Palestini32, M. Palka41b, D. Pallin37, E.St. Panagiotopoulou10, I. Panagoulias10, C.E. Pandini52, – 40 – JHEP06(2018)166 92 Department of Physics, The University of Michigan, Ann Arbor MI, United States of America 93 Department of Physics and Astronomy, Michigan State University, East Lansing MI, United States of America 94 (a)INFN Sezione di Milano; (b)Dipartimento di Fisica, Universit`a di Milano, Milano, Italy 95 B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk, Republic of Belarus 96 Research Institute for Nuclear Problems of Byelorussian State University, Minsk, Republic of Belarus 97 Group of Particle Physics, University of Montreal, Montreal QC, Canada 98 P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia 99 Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia 100 National Research Nuclear University MEPhI, Moscow, Russia 101 D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow, Russia 102 Fakult¨at f¨ur Physik, Ludwig-Maximilians-Universit¨at M¨unchen, M¨unchen, Germany 103 Max-Planck-Institut f¨ur Physik (Werner-Heisenberg-Institut), M¨unchen, Germany 104 Nagasaki Institute of Applied Science, Nagasaki, Japan 105 Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya, Japan 106 (a)INFN Sezione di Napoli; (b)Dipartimento di Fisica, Universit`a di Napoli, Napoli, Italy 107 Department of Physics and Astronomy, University of New Mexico, Albuquerque NM, United States of America 108 Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands 109 Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam, Netherlands 110 Department of Physics, Northern Illinois University, DeKalb IL, United States of America 111 Budker Institute of Nuclear Physics, SB RAS, Novosibirsk, Russia 112 Department of Physics, New York University, New York NY, United States of America 113 Ohio State University, Columbus OH, United States of America 114 Faculty of Science, Okayama University, Okayama, Japan 115 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman OK, United States of America 116 Department of Physics, Oklahoma State University, Stillwater OK, United States of America 117 Palack´y University, RCPTM, Olomouc, Czech Republic 118 Center for High Energy Physics, University of Oregon, Eugene OR, United States of America 119 LAL, Univ. Paris-Sud, CNRS/IN2P3, Universit´e Paris-Saclay, Orsay, France 120 Graduate School of Science, Osaka University, Osaka, Japan 121 Department of Physics, University of Oslo, Oslo, Norway 122 Department of Physics, Oxford University, Oxford, United Kingdom 123 (a)INFN Sezione di Pavia; (b)Dipartimento di Fisica, Universit`a di Pavia, Pavia, Italy 124 Department of Physics, University of Pennsylvania, Philadelphia PA, United States of America 125 National Research Centre “Kurchatov Institute” B.P.Konstantinov Petersburg Nuclear Physics Institute, St. Petersburg, Russia 126 (a)INFN Sezione di Pisa; (b)Dipartimento di Fisica E. Fermi, Universit`a di Pisa, Pisa, Italy 127 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh PA, United States of America 128 (a)Laborat´orio de Instrumenta¸c˜ao e F´ısica Experimental de Part´ıculas - LIP, Lisboa; (b)Faculdade de Ciˆencias, Universidade de Lisboa, Lisboa; (c)Department of Physics, University of Coimbra, Coimbra; (d)Centro de F´ısica Nuclear da Universidade de Lisboa, Lisboa; (e)Departamento de Fisica, Universidade do Minho, Braga; (f)Departamento de Fisica Teorica y del Cosmos, Universidad de Granada, Granada; (g)Dep Fisica and CEFITEC of Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal – 47 – JHEP06(2018)166 129 Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic 130 Czech Technical University in Prague, Praha, Czech Republic 131 Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic 132 State Research Center Institute for High Energy Physics (Protvino), NRC KI, Russia 133 Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom 134 (a)INFN Sezione di Roma; (b)Dipartimento di Fisica, Sapienza Universit`a di Roma, Roma, Italy 135 (a)INFN Sezione di Roma Tor Vergata; (b)Dipartimento di Fisica, Universit`a di Roma Tor Vergata, Roma, Italy 136 (a)INFN Sezione di Roma Tre; (b)Dipartimento di Matematica e Fisica, Universit`a Roma Tre, Roma, Italy 137 (a)Facult´e des Sciences Ain Chock, R´eseau Universitaire de Physique des Hautes Energies - Universit´e Hassan II, Casablanca; (b)Centre National de l’Energie des Sciences Techniques Nucleaires, Rabat; (c)Facult´e des Sciences Semlalia, Universit´e Cadi Ayyad, LPHEA-Marrakech; (d)Facult´e des Sciences, Universit´e Mohamed Premier and LPTPM, Oujda; (e)Facult´e des sciences, Universit´e Mohammed V, Rabat, Morocco 138 DSM/IRFU (Institut de Recherches sur les Lois Fondamentales de l’Univers), CEA Saclay (Commissariat `a l’Energie Atomique et aux Energies Alternatives), Gif-sur-Yvette, France 139 Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz CA, United States of America 140 Department of Physics, University of Washington, Seattle WA, United States of America 141 Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom 142 Department of Physics, Shinshu University, Nagano, Japan 143 Department Physik, Universit¨at Siegen, Siegen, Germany 144 Department of Physics, Simon Fraser University, Burnaby BC, Canada 145 SLAC National Accelerator Laboratory, Stanford CA, United States of America 146 (a)Faculty of Mathematics, Physics & Informatics, Comenius University, Bratislava; (b) Department of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, Slovak Republic 147 (a)Department of Physics, University of Cape Town, Cape Town; (b)Department of Physics, University of Johannesburg, Johannesburg; (c)School of Physics, University of the Witwatersrand, Johannesburg, South Africa 148 (a)Department of Physics, Stockholm University; (b)The Oskar Klein Centre, Stockholm, Sweden 149 Physics Department, Royal Institute of Technology, Stockholm, Sweden 150 Departments of Physics & Astronomy and Chemistry, Stony Brook University, Stony Brook NY, United States of America 151 Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom 152 School of Physics, University of Sydney, Sydney, Australia 153 Institute of Physics, Academia Sinica, Taipei, Taiwan 154 Department of Physics, Technion: Israel Institute of Technology, Haifa, Israel 155 Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel 156 Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece 157 International Center for Elementary Particle Physics and Department of Physics, The University of Tokyo, Tokyo, Japan 158 Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo, Japan 159 Department of Physics, Tokyo Institute of Technology, Tokyo, Japan 160 Tomsk State University, Tomsk, Russia 161 Department of Physics, University of Toronto, Toronto ON, Canada 162 (a)INFN-TIFPA; (b)University of Trento, Trento, Italy 163 (a)TRIUMF, Vancouver BC; (b)Department of Physics and Astronomy, York University, Toronto ON, Canada 164 Faculty of Pure and Applied Sciences, and Center for Integrated Research in Fundamental Science – 48 – JHEP06(2018)166 and Engineering, University of Tsukuba, Tsukuba, Japan 165 Department of Physics and Astronomy, Tufts University, Medford MA, United States of America 166 Department of Physics and Astronomy, University of California Irvine, Irvine CA, United States of America 167 (a)INFN Gruppo Collegato di Udine, Sezione di Trieste, Udine; (b)ICTP, Trieste; (c) Dipartimento di Chimica, Fisica e Ambiente, Universit`a di Udine, Udine, Italy 168 Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden 169 Department of Physics, University of Illinois, Urbana IL, United States of America 170 Instituto de Fisica Corpuscular (IFIC), Centro Mixto Universidad de Valencia - CSIC, Spain 171 Department of Physics, University of British Columbia, Vancouver BC, Canada 172 Department of Physics and Astronomy, University of Victoria, Victoria BC, Canada 173 Department of Physics, University of Warwick, Coventry, United Kingdom 174 Waseda University, Tokyo, Japan 175 Department of Particle Physics, The Weizmann Institute of Science, Rehovot, Israel 176 Department of Physics, University of Wisconsin, Madison WI, United States of America 177 Fakult¨at f¨ur Physik und Astronomie, Julius-Maximilians-Universit¨at, W¨urzburg, Germany 178 Fakult¨at f¨ur Mathematik und Naturwissenschaften, Fachgruppe Physik, Bergische Universit¨at Wuppertal, Wuppertal, Germany 179 Department of Physics, Yale University, New Haven CT, United States of America 180 Yerevan Physics Institute, Yerevan, Armenia 181 Centre de Calcul de l’Institut National de Physique Nucl´eaire et de Physique des Particules (IN2P3), Villeurbanne, France 182 Academia Sinica Grid Computing, Institute of Physics, Academia Sinica, Taipei, Taiwan aAlso at Department of Physics, King’s College London, London, United Kingdom bAlso at Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan cAlso at Novosibirsk State University, Novosibirsk, Russia dAlso at TRIUMF, Vancouver BC, Canada eAlso at Department of Physics & Astronomy, University of Louisville, Louisville, KY, United States of America fAlso at Physics Department, An-Najah National University, Nablus, Palestine gAlso at Department of Physics, California State University, Fresno CA, United States of America hAlso at Department of Physics, University of Fribourg, Fribourg, Switzerland iAlso at II Physikalisches Institut, Georg-August-Universit¨at, G¨ottingen, Germany jAlso at Departament de Fisica de la Universitat Autonoma de Barcelona, Barcelona, Spain kAlso at Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Portugal lAlso at Tomsk State University, Tomsk, and Moscow Institute of Physics and Technology State University, Dolgoprudny, Russia mAlso at The Collaborative Innovation Center of Quantum Matter (CICQM), Beijing, China nAlso at Universita di Napoli Parthenope, Napoli, Italy oAlso at Institute of Particle Physics (IPP), Canada pAlso at Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania qAlso at CPPM, Aix-Marseille Universit´e and CNRS/IN2P3, Marseille, France rAlso at Department of Physics, St. Petersburg State Polytechnical University, St. Petersburg, Russia sAlso at Borough of Manhattan Community College, City University of New York, New York City, United States of America tAlso at Department of Financial and Management Engineering, University of the Aegean, Chios, Greece uAlso at Centre for High Performance Computing, CSIR Campus, Rosebank, Cape Town, South Africa – 49 – JHEP06(2018)166 vAlso at Louisiana Tech University, Ruston LA, United States of America wAlso at Institucio Catalana de Recerca i Estudis Avancats, ICREA, Barcelona, Spain xAlso at Department of Physics, The University of Michigan, Ann Arbor MI, United States of America yAlso at Graduate School of Science, Osaka University, Osaka, Japan zAlso at Fakult¨at f¨ur Mathematik und Physik, Albert-Ludwigs-Universit¨at, Freiburg, Germany aa Also at Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands ab Also at Department of Physics, The University of Texas at Austin, Austin TX, United States of America ac Also at Institute of Theoretical Physics, Ilia State University, Tbilisi, Georgia ad Also at CERN, Geneva, Switzerland ae Also at Georgian Technical University (GTU),Tbilisi, Georgia af Also at Ochadai Academic Production, Ochanomizu University, Tokyo, Japan ag Also at Manhattan College, New York NY, United States of America ah Also at The City College of New York, New York NY, United States of America ai Also at Departamento de Fisica Teorica y del Cosmos, Universidad de Granada, Granada, Spain aj Also at Department of Physics, California State University, Sacramento CA, United States of America ak Also at Moscow Institute of Physics and Technology State University, Dolgoprudny, Russia al Also at Departement de Physique Nucleaire et Corpusculaire, Universit´e de Gen`eve, Geneva, Switzerland am Also at Institut de F´ısica d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Barcelona, Spain an Also at School of Physics, Sun Yat-sen University, Guangzhou, China ao Also at Institute for Nuclear Research and Nuclear Energy (INRNE) of the Bulgarian Academy of Sciences, Sofia, Bulgaria ap Also at Faculty of Physics, M.V.Lomonosov Moscow State University, Moscow, Russia aq Also at National Research Nuclear University MEPhI, Moscow, Russia ar Also at Department of Physics, Stanford University, Stanford CA, United States of America as Also at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest, Hungary at Also at Giresun University, Faculty of Engineering, Turkey au Also at Department of Physics, Nanjing University, Jiangsu, China av Also at Institute of Physics, Academia Sinica, Taipei, Taiwan aw Also at University of Malaya, Department of Physics, Kuala Lumpur, Malaysia ax Also at LAL, Univ. Paris-Sud, CNRS/IN2P3, Universit´e Paris-Saclay, Orsay, France ∗Deceased – 50 –