Latest neutrino cross-section results from T2K

Latest neutrino cross-section results from T2K Ellen Sandford, University of Liverpool XXI Workshop on Neutrino Telescopes, October 1st 2025 T2K overview •Long-baseline neutrino oscillation experiment in Japan •Running since 2010 •295 km baseline, 0.6 GeV peak neutrino energy •Far detector 2.5° off-axis •Sensitive to CP-violation, mixing angle θ23 and mass splitting Δm223 •Largest systematic uncertainty for oscillation measurements is currently neutrino interaction modelling •Important to make precise crosssection measurements to improve our understanding of neutrino-nucleus interactions •These measurements can be done at our near detectors Cross-section results from T2K, Ellen Sandford, NeuTel 21/10/2025 Oscillated beam is observed at Super-K, allowing measurement of oscillation parameters Beam of (anti-)neutrinos produced at J-PARC Near detector suite Cross-section results from T2K, Ellen Sandford, NeuTel 31/10/2025 ND280 INGRID WagasciBabyMIND (Anti-)neutrino beam from J-PARC 2.5° off-axis on-axis 1.5° off-axis ND280: •Active scintillator and passive water targets (FGD1 and FGD2) •Three TPCs for tracking •Magnetised (0.2 T) •Measurements on carbon and oxygen •Same off-axis angle as Super-K INGRID: •On-axis, unmagnetized detector •Iron-scintillator alternating layers •Monitors direction and intensity of beam WAGASCI/BabyMIND: •Water/CH lattice target (WAGASCI) •Magnetised (1.5 T) iron muon range tracking detector (BabyMIND) Neutrino energy distribution at each off-axis angle T2K flux model 1/10/2025 Cross-section results from T2K, Ellen Sandford, NeuTel 4 It is important for both oscillation and cross-section measurements to understand the neutrino flux 𝑁𝑖 𝑒𝑥𝑝(𝐸ν) = 𝑃(ν𝛼→ ν𝛽) × 𝜎𝑖(𝐸ν) × Φν(𝐸ν) × 𝜀𝑖(𝐸ν) •Systematics dominated by uncertainties on hadron production cross-section •External data from NA61 and other experiments are used for flux tuning, using both thin 2 cm target and replica 90 cm target data to constrain models •This allows reduction of the flux uncertainties to around 6% at peak (reduced from ~20%) Cross-section Neutrino interactions at T2K Cross-section results from T2K, Ellen Sandford, NeuTel 51/10/2025 At the T2K beam energy there is a mixture of interaction channels - CCQE is the dominant interaction, with sub-dominant contributions from CC-RES and DIS In order to model neutrino interactions we need to consider: •Nucleon is not free but part of a nucleus e.g. in oxygen or carbon target •Additional nuclear effects such as 2p2h •Final state interactions (FSI) e.g. pion absorption, scattering •All these effects can lead to smearing and bias in the reconstructed neutrino energy Interaction topologies 1/10/2025 Cross-section results from T2K, Ellen Sandford, NeuTel 6 •Measurements are made on topologies (eg CC0π1p, CC1π) rather than interaction modes (eg CCQE) •Split here by the different leptonic and hadronic sides than can lead to a specific topology Diagram from K. Lachner talk at NuFact 2025 T2K cross-section measurements T2K has published many cross-section measurements in many different channels in the last 15 years – here I highlight some recent results 1/10/2025 Cross-section results from T2K, Ellen Sandford, NeuTel 7 νe CCπ+ on Carbon 1/10/2025 Cross-section results from T2K, Ellen Sandford, NeuTel 8 •First measurement of electron neutrinoinduced charged current pion production on C •Sub-dominant contribution to νe appearance in oscillation measurements •Target is FGD1 of ND280 •Two selection samples: •Pion escapes FGD1 and enters TPCs •Pion decays to Michel electron in FGD1 Comparison of data with NEUT prediction for electron momentum angle and pion momentum Pre-print: arXiv:2505.00516 Signal region: •0.35 < pe < 30 GeV/c •cosθe > 0.7 •pπ < 1.5 GeV/c νe CCπ+ on Carbon 1/10/2025 Cross-section results from T2K, Ellen Sandford, NeuTel 9 Differential measurement in electron momentum, angle and pion momentum phase space Results: Measured total flux integrated cross-section: (2.52±0.60) ×10-39 cm2/nucl. Overall data favours a lower than predicted crosssection, especially for high pion momentum: •2.4σ discrepancy w/ GENIE •2.5σ discrepancy w/ NEUT Pre-print: arXiv:2505.00516 Neutron Capture on Oxygen 1/10/2025 Cross-section results from T2K, Ellen Sandford, NeuTel 16 Results: •Flux-averaged mean neutron capture multiplicity 1.37 ± 0.33 𝑠𝑡𝑎𝑡 −0.27 +0.17(𝑠𝑦𝑠) •Consistent with nominal predictions to within 2.2σ Published in Phys. Rev. D 112, 032003 •Neutrons are identified by delayed gamma emission •Expected capture time is 115±1μs •Rate measured using subtraction between data with beam on and beam off •Measurement using data from Gadolinium loaded Super-K •First measurement of neutron capture multiplicity for NCQE on O •Significant background for diffuse supernova neutrino background (DSNB) searches Measurement at Super-K Status of analyses •νe CCπ+ on C •Accepted to PRL, pre-print: arXiv:2505.00516 •NC1π+ interactions on CH •Accepted to PRD & PRL, pre-prints: arXiv: 2503.06849, arXiv: 2503.06843 •νμCC0πNp TKI measurement •Paper in preparation. •νμCC0π in WAGASCI-BabyMIND • Awaiting publication, pre-print: arXiv:2509.07814 •Neutron capture •Published in Phys. Rev. D 112, 032003 Cross-section results from T2K, Ellen Sandford, NeuTel 171/10/2025 Other analyses to look out for: •K+ production in νμCC on carbon •ഥνμCC1π−on carbon •νμCC1π+ with low-momentum pions on CH and H2O •New analyses from ND280 upgrade! See Gioele Reina’s talk on “First results from T2K’s upgraded near detector” on Thursday for more + more upgrade talks: Asit Srivastava, Matteo Feltre, Wataru Okinaga-san Conclusions •Cross-section measurements are essential for improving neutrino-nucleus interaction models and decreasing systematics for the oscillation analysis •Latest cross-section measurements presented from three different T2K detectors: •ND280: νe CCπ+ on C, NC1π+ on CH, νμCC0πNp on C and O •WAGASCI/BabyMIND: νμCC0πon CH and H2O •Gd loaded SK: neutron capture multiplicity on O •Some tensions seen between measurements and generator predictions •More measurements in preparation! •ND280 has been upgraded and improvements such as lower threshold, high angle acceptance and sensitivity to neutrons will produce even higher precision cross-section measurements Cross-section results from T2K, Ellen Sandford, NeuTel 181/10/2025 Back up 1/10/2025 Cross-section results from T2K, Ellen Sandford, NeuTel 19 1/10/2025 Cross-section results from T2K, Ellen Sandford, NeuTel 20