Latest Results from the XENONnT Experiment
Abstract
The XENONnT project is located in the Gran Sasso laboratory in Italy.Its main goal is the direct detection of dark matter, particularly Weakly Interacting Massive Particles (WIMPs). It uses a dual-phase liquid xenon time projection chamber (TPC) to identify particle interactions. When a particle interacts with the target mass, light (S1 signal) and charge (S2 signal) are produced. The experiment is protected by natural shielding, situated under 3600 meters of rock, and has an active system to reduce background noise. The dense liquid xenon also provides effective self-shielding, allowing the definition of a central fiducial volume with minimal background noise.Recently, XENONnT achieved a major breakthrough by observing solar neutrinos from 8B via coherent elastic neutrino-nucleus scattering (CEvNS). This is a significant milestone, as it marks the first direct detection of nuclear recoils caused by solar neutrinos using a dark matter detector. The detection was made with a statistical significance of 2.73σ, confirming the observation. This CEvNS measurement presents a new opportunity for neutrino studies and paves the way for future analyses that may lead to further exciting discoveries. XENONnT continues to collect and analyze more data, raising the potential for new advances in rare interaction searches.
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Latest Results from the XENONnT Experiment Ananthakrishnan Ravindran On behalf of the XENON collaboration. IRN Terascale | IP21 Lyon | Nov 13-15
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 1 The XENON Collaboration 200+ Scientists 29 Institutions 12 Countries Main Motivation Discover Weakly Interacting Massive Particles (WIMPs). Other studies Coherent Elastic NeutrinoNucleus Scattering (CEvNS), 0𝑣𝛽𝛽, Solar Axions and ALPs, Supernovae, etc. How we do it: •Very low backgrounds: active and passive shielding, fiducialization, etc. •Robust tools to correct detector effects and look for very small signals. •Perform a “blind analysis”.
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 1 The XENON Collaboration 200+ Scientists 29 Institutions 12 Countries XENON program timeline 2006 58.6 livedays BG: 600 /(t.d.keV) XENON10 25kg LXe XENON100 160kg LXe 2008 477 livedays BG: 5.3 /(t.d.keV) XENON1T 3200kg LXe 2015 279 livedays BG: 0.2 /(t.d.keV) XENONnT 8600kg LXe 2020 300+ livedays (ongoing) BG: 0.04 /(t.d.keV) Lowest ER background level ever achieved in a LXe based experiment!!
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 2 XENONnT Experiment LNGS, Italy 3600 m.w.e shielding 3 Nested Detectors Sharing the same DAQ ➢LXe Dual Phase Time Projection Chamber (TPC) with 5.9t active volume. (Eur. Phys. J. C 84, 784 (2024), JCAP11(2020)031) ➢Gd-doped Water Cherenkov Neutron Veto (NV). ➢Gd-doped Water Cherenkov Muon Veto (MV) (2014 JINST 9 P11006) Hall B
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 3 Dual Phase Time Projection Chamber •Particle interaction in LXe create both prompt scintillation(S1) and delayed ionization signals. •Ionization electrons drifted upwards by drift field (𝐸𝑑𝑟𝑖𝑓𝑡_𝑋𝑛𝑇 =23𝑉/𝑐𝑚) and extracted into gas phase by extraction field (𝐸𝑒𝑥𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛_𝑋𝑛𝑇 = 2.9𝑘𝑉/𝑐𝑚); leads to electroluminescent light(S2). •Signals collected a total of 493 PMTs in the top and bottom arrays. 3D Position Reconstruction x, y : S2 hit pattern z: Drift time of eEnergy Reconstruction Combined S1 and S2 area; calibrated with known sources.
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 4 Recoil Type Discrimination: ER or NR? Nuclear Recoils (NR) Electronic Recoils (ER) | Gamma & Beta | Neutrino elastic scattering. | Solar axions, ALPs. | Neutrinos (CEvNS) | WIMPs | Neutrons NR ER Signal Background | 136Xe 0𝑣𝛽𝛽, 2𝑣𝛽𝛽.
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 4 Recoil Type Discrimination: ER or NR? Discriminated via different S2/S1 ratio. Rn-220: ER band AmBe: NR band Ar-37: ER low energy Kr83m Other Calibrations TPC characterization and signal correction. High energy response. Low energy NR response specially tuned for the CEvNS search. Th232 YBe Phys. Rev. Lett. 131, 041003 Nuclear Recoils (NR) Electronic Recoils (ER) | Gamma & Beta | Neutrino elastic scattering. | Solar axions, ALPs. | Neutrinos (CEvNS) | WIMPs | Neutrons NR ER Signal Background | 136Xe 0𝑣𝛽𝛽, 2𝑣𝛽𝛽.
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 5 XENONnT Science Data SR0 SR1 •Science data divided into various Science Runs (SR). Total exposure ~340 days. •Very stable detector conditions. <1%(<3%) variation in Light (Charge) Yield. •High liquid xenon purity: electron lifetime ~20ms
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 6 SR0 Results: LowER Excluded LowER Excess observed in XENON1T at 4𝜎 World leading laboratory results for ‘Beyond Standard Model’ Signals. Lowest level of ER background in any Lxe experiment: 15.8 𝑒𝑣𝑒𝑛𝑡𝑠/(𝑡. 𝑦. 𝑘𝑒𝑉) Phys. Rev. Lett. 129, 161805 Solar axions Neutrino Magnetic Moment ALPs DM Dark Photons
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 11 Backgrounds: Accidental Coincidences(AC) •ACs are accidental pairings of Isolated S1 and Isolated S2 signals. •AC rate before mitigation: ➢Isolated S1 rate: ~15 Hz ➢Isolated S2 rate: ~150mHz ➢Raw AC rate: ~400 events/day •ACs mitigation: a) Time Shadow Cut: Uses the time correlation of the previous large S2 peak from HE event. b) S1 Boosted Decision Tree: Uses information from the S1 pulse and spatial distribution; discriminate signals from random PMT pileups. c) S2 Boosted Decision Tree: Uses S2 width correlation with diffusion of electron cloud during drift. No correlation expected for Isolated S2s. (b) (c) (a) Used in inference Used in inference Used in inference Expected AC Events: SR0: 7.5 ± 0.7 | SR1: 17.8 ± 1.0
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 12 Backgrounds: NR, ER and Surface Electronic Recoil Background •Dominated by 214Pb decays. •Assumed flat spectrum with a conservative 100% uncertainty on yields. •SR0: 𝟎. 𝟏𝟑 ± 𝟎. 𝟏𝟑 | SR1: 𝟎. 𝟓𝟔 ± 𝟎. 𝟓𝟔 events. RoI Nuclear Recoil Background •Fission reactions and (𝛼, 𝑛) reactions. •Modelled by data and MC. •SR0: 𝟎. 𝟏𝟑 ± 𝟎. 𝟎7 | SR1: 𝟎. 𝟑𝟑 ± 𝟎. 𝟏𝟗 events. Surface Background •Electronic recoils from 210Pb from the walls. •Impact in RoI negligible due to choice of boundaries to Fiducial Volume.
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 13 Prediction before Unblinding Inference Likelihood •Binned likelihood in 4-D space (34 bins). •Likelihood dimensions: (cs2, S1 BDT, S2 BDT, Time Shadow) •Separate terms for SR0 and SR1. Total Exposure: 𝟑. 𝟓𝟏 ton years. Expected Background: 𝟐𝟔.𝟒 ± 𝟏.𝟓 events Expected Signal: 𝟏𝟐 ± 𝟑 events 48% probability for >3𝜎 discovery.
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 14 Unblinded Results SR0 SR1 Expected Background: 𝟐𝟔. 𝟒 ± 𝟏. 𝟓 Expected Signal: 𝟏𝟐 ± 𝟑 Observed Events: 𝟑𝟕 Best-fit no. of 8B events: 𝟏𝟎. 𝟕−𝟒.𝟐 +𝟑.𝟕 Significance: 𝟐. 𝟕𝟑𝝈 arXiv:2408.02877 [nucl-ex]
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 15 Unblinded Results Measured 8B flux: 4.7−2.7 +3.6 ×106𝑐𝑚−2𝑠−1. In agreement with other measurements. Flux weighted CEvNS crosssection in agreement with Standard Model. First measurement of CEvNS cross section in Xe. First DM experiment to enter the neutrino fog. Smallest solar neutrino detector. arXiv:2408.02877 [nucl-ex]
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 16 Low-mass WIMP Search •Same dataset and analysis framework for CEvNS search is used. •Here, 8B CEvNS becomes a background. •No excess over background observed. ➢New parameter space excluded. ➢First search into the neutrino fog. arXiv:2409.17868 [hep-ex]
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 17 Summary and Outlook ➢First measurement of solar neutrinos with a DM detector and first measurement of CEvNS cross section in Xe. Observes 8B CEvNS at 𝟐. 𝟕𝟑𝝈 significance. ➢XENONnT becomes the first experiment to step into the neutrino fog. ➢XENONnT continues to collect blinded data: Precision measurements for CEvNS possible. ➢Classical 3-fold WIMP analysis with more exposure ongoing. More exciting results very soon!
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 18 Thank you for your attention! XENON Website: https://xenonexperiment.org/
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 19 Backup Slides
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 20 XENONnT Infrastructure Rn Column •Continuous online distillation. •222 Rn conc (SR0): 𝟏. 𝟖𝝁𝑩𝒒/𝒌𝒈 •222 Rn conc (SR1): 𝟎. 𝟖𝝁𝑩𝒒/𝒌𝒈 Eur. Phys. J. C (2022) 82: 1104 Kr Column •natKr/Xe concentration < 50 ppt Eur. Phys. J. C 77, 275 (2017) nT DAQ •Triggerless DAQ. Shared between three detectors. 2023 JINST 18 P07054 Lxe Purification •Removes electronegative impurities. •Electron lifetime ~ 15ms. •Turn-around time ~0.9 days for 8.6t. Eur. Phys. J. C (2022) 82: 860
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 27 Time and Position Shadows Time Shadow Selected Removed •High chance of a train of delayed electrons and lone hits after of large S2 (or S1) from a HE event: HE S2 causes a “shadow effect”. •“Signal” uniformly distributed in time. •Time shadow ( Τ 𝑆2𝑝𝑟𝑒 ∆𝑡) of Iso-S1s typically larger than of signal. Position Shadow Function providing the position correlation of a large S2 and Iso-S2s, accounting for resolution. •Using the position information, Iso-S2s can be removed by combination of time and position shadow.
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 28 S1 BDT Features First: Max S1 hit area Second: Min time between S1 hits Third: No. of hits in top PMT array Fourth: Total no. of hits Dedicated publication in preparation. ACs are mostly lone hits; S1 > 2PE on one PMT is unlikely to be AC. Signal S1 pulse timing impacted by physical processes and DAQ response, AC is random Due to LXe-GXe interface, most signal S1s are collected at bottom array. ACs are random. Reproduces the full recoil spectrum.
Ananthakrishnan Ravindran | ravi[email protected]| IRN Terascale @ IP21 Lyon | 13-15 Nov 29 S2 BDT Features Relies on information about the drift and diffusion of the electron cloud. S2 Signal First: 50% area width Second: Risetime Third: 90% area width Fourth: Drift time Dedicated publication in preparation. Signal events will respect the diffusion model for the drift of the electron cloud; very identifiable distributions in some parameter spaces. ACs are random pairings; would not show the same patterns.