Neutrino experiments at the LHC

Neutrino experiments at the LHC Tomoko Ariga (Kyushu University) [email protected] Neutrinos at the LHC •LHC produces the most energetic neutrinos created by humankind (~TeV region) •Interest in detecting LHC neutrinos had been expressed earlier, e.g., –A. De Rujula and R. Ruckl, “Neutrino and muon physics in the collider mode of future accelerators”, 1984 •However, neutrinos had never been directly observed at a collider before the 2020s. 2/10/2025 2 𝑝𝑝-𝑝𝑝collisions Conventional detectors Tomoko Ariga, Neutrino Telescopes 2025 Site investigation in 2018 •FASER was proposed in 2018. •Small emulsion prototype was installed on the LHC collision axis, measured backgrounds and provided first neutrino candidates. Dedicated neutrino detector FASER𝝂𝝂was added to FASER. •Another group investigated possible neutrino detector sites in the LHC tunnel, which led to the XSEN proposal. •Later merged with SHiP’s SND proponents to form SND@LHC. 2/10/2025 3 TI12 TI18 Another group (later leading to XSEN and SND@LHC) investigated the background around CMS •VN: Q1 at 25 m •N: UJ53, UJ57 at 90, 120 m •F: RR53 at 240 m FASER measured backgrounds in the tunnels TI18 and TI12, located 480 m from the ATLAS IP. Tomoko Ariga, Neutrino Telescopes 2025 Neutrino experiments at the LHC •Installation and data taking –FASER and SND@LHC installed during LS2 (2019–2022) –Taking data since start of LHC Run 3 (2022) –Operations continue until end of Run 3 (2026) •Future prospects –Upgrades and extended running in Run 4 (from 2030) –Expansion with larger detectors at the HL-LHC: Forward Physics Facility (FPF) 2/10/2025 4 Parallel talks on Oct 1 •Yuxiao Wang, “Neutrino studies with FASER” •Fabio Alicante, “The Scattering and Neutrino Detector at the LHC” FASER𝜈𝜈: 𝜂𝜂> 8.8 SND@LHC: 7.2 <𝜂𝜂< 8.4 Tomoko Ariga, Neutrino Telescopes 2025 5Tomoko Ariga, Neutrino Telescopes 2025 2/10/2025 Neutrino energy and spatial distributions Annu. Rev. Nucl. Part. Sci. 2025. 75:57–81 “Neutrino Experiments at the Large Hadron Collider” Energy and spatial distributions of interacting neutrinos for 350 fb-1 •This prediction uses Epos-lhc to simulate the production of forward light hadrons and the envelope formed by Epos-lhc, Sibyll 2.3d, and Qgsjet 2.04 as well as the forward physics tune of Pythia to define an uncertainty band. •Charm hadron production is modeled using Powheg matched with Pythia 8.3 for parton shower and hadronization, with the uncertainties described by scale variations. •The expected event rates were estimated using the neutrino interaction cross section implemented in Genie, based on the Bodek–Yang model. Experiments 𝜼𝜼 coverage Tungsten target mass [kg] 𝝂𝝂𝒆𝒆𝝂𝝂𝝁𝝁𝝂𝝂𝝉𝝉 FASER 𝜂𝜂 >8.8 1100 N int E average 2331−544 +1227 785 GeV 12014−1636 +1145 716 GeV 46−21 +77 849 GeV SND@LHC 7.2< 𝜂𝜂 <8.4 800 N int E average 307−116 +307 442 GeV 1694−549 +297 357 GeV 15−7 +26 596 GeV 𝝂𝝂𝒆𝒆+ � 𝝂𝝂𝒆𝒆 FASER𝝂𝝂SND@LHC 𝝂𝝂𝝁𝝁+ � 𝝂𝝂𝝁𝝁 𝝂𝝂𝝉𝝉+ � 𝝂𝝂𝝉𝝉 2/10/2025 6Tomoko Ariga, Neutrino Telescopes 2025 Uncertainties in the flux predictions LHC Run 3 with 250 fb-1 LHC Run 4 with 680 fb-1 Phys. Rev. D 110, 012009 (2024) “Neutrino rate predictions for FASER” 𝝂𝝂𝒆𝒆+ � 𝝂𝝂𝒆𝒆𝝂𝝂𝝁𝝁+ � 𝝂𝝂𝝁𝝁 What can be done from neutrino interaction rate measurements 2/10/2025 7 Neutrino flux Neutrino cross section Interaction rate Cross section uncertainty Knowledge of flux Neutrino cross section measurements SM predictions for neutrino cross sections Neutrino flux measurements •Hadron production models •External validation data •Assuming LFU is valid •Test lepton flavor universality •Search for new interactions •Study hadron/neutrino production at very high-energy •Prompt neutrinos •QCD at small 𝑥𝑥 Interaction rate measurements Tomoko Ariga, Neutrino Telescopes 2025 Physics motivation of neutrino interaction measurements •Direct observation of TeV-energy neutrino interactions: 𝜈𝜈𝑒𝑒, 𝜈𝜈𝜇𝜇, and 𝜈𝜈𝜏𝜏 •Measurement of charged-current cross sections at TeV energies for three flavors of neutrinos, and tests of lepton universality in neutrino interactions •Neutral-current interaction measurements and searches for non-standard interactions •Proton and nuclear parton distribution studies to reduce PDF uncertainties 2/10/2025 8 𝝂𝝂𝒆𝒆𝝂𝝂𝝁𝝁𝝂𝝂𝝉𝝉 Eur. Phys. J. C 84 (2024) 369 “The LHC as a Neutrino-Ion Collider” Tomoko Ariga, Neutrino Telescopes 2025 Physics motivation of neutrino flux measurements •Neutrino measurements as a probe of very forward hadron production •Measurements of LHC neutrinos provide novel input to astroparticle physics (prompt atmospheric neutrinos, cosmic-ray muon puzzle), and to QCD studies (low-x PDFs, intrinsic charm, saturation) 2/10/2025 9 conventional prompt (charm) https://indico.cern.ch/event/1296658/contributions/5541999/ mainly 𝐾𝐾 Charm (large uncertainty) Tomoko Ariga, Neutrino Telescopes 2025 𝝂𝝂𝒆𝒆+ � 𝝂𝝂𝒆𝒆at FASER𝝂𝝂 First cross section measurements at TeV energies 2/10/2025 16 Phys. Rev. Lett. 133 (2024) 021802 “First Measurement of 𝜈𝜈𝑒𝑒and 𝜈𝜈𝜇𝜇Interaction Cross Sections at the LHC with FASER’s Emulsion Detector” Physical Review Letters collection of the year 2024 (selected among the top 2% of papers published in Physical Review Letters) Tomoko Ariga, Neutrino Telescopes 2025 Measurement of energy-dependent cross section and neutrino flux 2/10/2025 17 Phys. Rev. Lett. 134, 211801 (2025) “First Measurement of the Muon Neutrino Interaction Cross Section and Flux as a Function of Energy at the LHC with FASER” Integrated luminosity of (65.6±1.4) fb-1 338.1±21.0 𝜈𝜈𝜇𝜇 CC events are identified, with backgrounds from other processes subtracted Tomoko Ariga, Neutrino Telescopes 2025 Comparison with predictions from recent hadronic interaction model 2/10/2025 18 •The predictions are generally consistent with the measured fluxes from FASER, although some discrepancies appear in certain energy bins. •More precise flux measurements with additional data will follow soon, enabling validation of pion, kaon, and charm meson production with finer energy binning, reduced uncertainties, and multi-differential analyses. arXiv:2507.23552 CERN-FASER-CONF-2025-004 Tomoko Ariga, Neutrino Telescopes 2025 Tomoko Ariga, Neutrino Telescopes 2025 Observation of events without final-state muons (0𝜇𝜇) •Expected background: 0.32±0.06 events •Expected signal: 7.2 events (4.9 𝜈𝜈𝑒𝑒 CC, 2.2 NC, 0.1 𝜈𝜈𝜏𝜏 CC) •Expected significance: 5.5 𝜎𝜎 •Number of observed events: 9 •Observation significance: 6.4 𝜎𝜎 •𝜈𝜈𝑒𝑒CC observation significance 3.7 𝜎𝜎 2/10/2025 19 Slide adapted from Fabio Alicante Phys. Rev. Lett. 134, 231802 (2025) “Observation of Collider Neutrinos without Final State Muons with the SND@LHC Experiment” Future prospects •Both FASER and SND@LHC will continue to take data for the remaining period of LHC Run 3. •Upgrades and extended running in LHC Run 4 are planned. •The space at FASER and SND@LHC is limited, Forward Physics Facility (FPF) has been proposed to expand the measurements with larger detectors at the HL-LHC. 2/10/2025 20Tomoko Ariga, Neutrino Telescopes 2025 Forward Physics Facility (FPF) 2/10/2025 21 Eur. Phys. J. C 85:430 (2025) “Scientific program for the Forward Physics Facility” •627-702 m from the ATLAS IP •75 m long and 12 m wide Tomoko Ariga, Neutrino Telescopes 2025 FPF experiments 2/10/2025 22Tomoko Ariga, Neutrino Telescopes 2025 New particle searches and neutrino measurements at the FPF 2/10/2025 23Tomoko Ariga, Neutrino Telescopes 2025 Physics case 2/10/2025 24 Sensitivity to probe NSI operators Expected data set ~106 𝜈𝜈𝜇𝜇, ~105 𝜈𝜈𝑒𝑒, ~104 𝜈𝜈𝜏𝜏 interactions from HL-LHC Tomoko Ariga, Neutrino Telescopes 2025 25Tomoko Ariga, Neutrino Telescopes 2025 Physics case 2/10/2025 PDF uncertainties for the down valence quark and strangeness PDFs Eur. Phys. J. C 84 (2024) 369 “The LHC as a Neutrino-Ion Collider” Eur. Phys. J. C 85:430 (2025) “Scientific program for the Forward Physics Facility”