Recent results and perspectives from the T2K experiment

Recent results and perspectives from the experiment Sophie King on behalf of the T2K Collaboration Neutrino Telescope 2025 Neutrino Oscillations Neutrino Oscillations Flavour eigenstate: Interact Mass eigenstate: Propagate Neutrino oscillation → mass states do not align with flavour states → non-zero masses Oscillations governed by PMNS flavour-mass mixing matrix, U Amplitude of oscillation: mixing angles and phase Distance of oscillation: squared mass differences and Energy Mass states Flavour states 3 cij= cos(θij) sij= sin(θij) Δm2 ij = m2 i - m2 jx 45° 4 θ23 octant: θ23 < π/4, θ23 = π/4, θ23 > π/4 (lower) (maximal) (upper) Mass Ordering δCP = 0, ±π → CP conserved: P(𝜈𝜇→𝜈e) = P(𝜈𝜇→𝜈e) δCP ≠ 0, ±π → CP violated: P(𝜈𝜇→𝜈e) ≠ P(𝜈𝜇→𝜈e) Compare oscillation of 𝜈 and 𝜈 to probe δCP Matter effects: Matter consists of electrons → causes additional difference between 𝜈e and 𝜈e as they travel through the earth ( mimics effect of δCP ) Normal Ordering (NO) Inverted Ordering (IO) CP violation ? Unitarity: Tightly constraining parameters enables tests of unitarity Remaining Questions In Vacuum T2K ● Long-baseline neutrino oscillation experiment ● High intensity neutrino beam, predominantly 𝜈𝜇 (𝜈𝜇) ● On/Off-axis near detectors: INGRID, ND280 → unoscillated beam (280 m) ● Off-axis far detector: Super-Kamiokande → oscillated beam (295 km) 6 The T2K Experiment INGRID - On-axis, scintillator and iron - monitors beam direction, intensity and stability ND280 - Same off-axis angle as SK ● Magnetised ● Active target mass → 2 x scintillators (FGDs) → vertex reconstruction ● 3 Time projection chambers (TPC) → momentum reconstruction → charge identification → Particle identification (PID) ● Electromagnetic calorimeters (Ecal) → PID ●π0 detector (P0D) and side muon range detector 7 Near Detectors Pre-upgrade ND280 41m 39m 50 kton ultra pure water Water Cherenkov Far detector 295km from the beam source 8 Event displays in T2K-PUB-002 Super-Kamiokande (SK) Need to be careful the gamma is not confused with a michel electron → new selection criteria added to dela with this. Gadolinium sulfate octahydrate Inner detector ~ 11000 PMTs (20”) Outer detector ~ 2000 PMTs (8”) Cherenkov rings reconstructed from PMT hit charge and time. Excellent PID discrimination <1% mis-PID at 1GeV Neutron tagging gives 𝜈/𝜈 separation. SK is adding Gd to the water. Phase I reached 0.01%, and Phase II is at 0.03% which gives ~75% neutron tagging efficiency. Next talk by Lucas Machado: Recent results from the Super-Kamioka Experiment T2K Oscillation Analysis 16 Oscillation Parameters SK fit SK event selection + data SK detector model ND280 selection + data Oscillation model External data (solar, reactor) ND280 fit ND280 detector model Interaction model External cross section data Flux model hadron production data INGRID / Beam monitor data Oscillation Analysis 17 * 30GeV protons → graphite target → charged hadrons * charge selection and focusing of hadrons with 3 electromagnetic horns * hadrons decay to 𝜈 or 𝜈 depending on charge * INGRID and the Muon Monitor continuously measure beam intensity, profile and direction * Dominant systematic error due to hadron interaction modelling → Tuned using NA61/SHINE T2K target replica measurements → Reduces error from ~ 20% →5% around the peak * The flux is further constrained by ND280 data in the fit T2K Flux 18 Oscillation Parameters SK fit SK event selection + data SK detector model ND280 selection + data Oscillation model External data (solar, reactor) ND280 fit ND280 detector model Interaction model External cross section data Flux model hadron production data INGRID / Beam monitor data Oscillation Analysis 19 NC interactions also important e.g. NCπ0, NC1γ → background Interaction modes and Nuclear models tuned to external data plot from t2k official plots feynman from t2k official plots nucleon diagrams stolen from callum Neutrino Interaction Modelling Interactions occur with nucleons bound inside a nucleus → Nuclear effects! Mis-modeling of interaction channel contributions can bias neutrino energy reconstruction ● T2K model is tuned to external data where appropriate. ● CCQE is the dominant interaction at T2K energies. T2K uses the Benhar Spectral Function (models fermi motion and removal energy) and includes short range correlations. ● Single pion production is based on the Rein-Sehgal (RS) model with a RFG nuclear mode. ● T2K uses NEUT cascade model for FSI tuned to recent pion-nucleus scattering data. T2K energies are dominated by CCQE. Significant contributions also come from 2p2h and resonant interactions T2K uses external constraints and the near detector to constrain the interaction model and reduce uncertainties. → Important to have advanced models with the required freedom. e.g. FSI 20 Oscillation Parameters SK fit SK event selection + data SK detector model ND280 selection + data Oscillation model External data (solar, reactor) ND280 fit ND280 detector model Interaction model External cross section data Flux model hadron production data INGRID / Beam monitor data Oscillation Analysis 21 CC 0π CC 1π CC Other Future improvements: Full angular acceptance FGD1: ● Carbon FGD2: ● Carbon ● Water (target in far det) ND280 Inputs CC 0π 𝜈-beam: 𝜈𝜇 CC-Inc 𝜈-beam: 𝜈𝜇 CC-Inc 𝜈-beam: 𝜈𝜇 CC-Inc ND280 FGD1 𝜈𝜇CC 0π0p SK event selection errors(%) Pre fit → post fit FHC 1-Ring mu 15% → 5% RHC 1-Ring 13% → 4% FHC 1-Ring e 17% → 9% RHC 1-Ring e 14% → 7% FHC 1-Ring e + 1pi+ 22% → 18% Fit done in bins of momentum and angle 22 The ND280 fit reduces the error on the number of events selected at SK 𝜈𝜇 ~17% → ~3% 𝜈e ~17% → ~5% official plots – recent results – banff 2017 (same banff selections used for 2018 results) ND280 Fit Pre-fit Post-fit SK SK 23 Oscillation Parameters SK fit SK event selection + data SK detector model ND280 selection + data Oscillation model External data (solar, reactor) ND280 fit ND280 detector model Interaction model External cross section data Flux model hadron production data INGRID / Beam monitor data Oscillation Analysis 24 SK Event Samples Updates since previous analysis ● Additional ~10% of SK data ● First data included from Gd phase I (0.01% Gd) ● Improved decay electron tagging. ● UpdatedSK detector systematics. Significant error reduction for 1Re 1d.e. e-like mu-like nu mode 1Re + 0 d.e 1Rmu + 0/1 d.e 1Re + 1 d.e Multi-Rmu + ½ d.e antinu mode 𝜈-mode 𝜈-mode e-like 𝜇-like T2K Preliminary T2K Preliminary 𝜈-beam: 1Re 𝜈-beam: 1R𝜇 𝜈-beam: 1Re1d.e 𝜈-beam: 𝜈𝜇CC 1π 𝜈-beam: 1Re 𝜈-beam: 1R𝜇 Re - Ring electron R𝜇 - Rung muon d.e - Decay electron 25 Oscillation Parameters SK fit SK event selection + data SK detector model ND280 selection + data Oscillation model External data (solar, reactor) ND280 fit ND280 detector model Interaction model External cross section data Flux model hadron production data INGRID / Beam monitor data Oscillation Analysis T2K and NOvA have complimentary properties and capabilities Combining inputs from both experiments to form a combined fit can help to break degeneracies. A joint fit between the two experiments has been performed. All Results are preliminary. 32 T2K + NOvA Joint Analysis 33 T2K + NOvA Results ● Assuming inverted ordering gives 3σ sigma exclusion of CP-conserving values. ● Weak preference for inverted mass ordering (Also a weak preference for inverted ordering without the reactor constraint) ● Weak preference for upper θ23 octant (weak preference for lower octant without the reactor constraint) 34 T2K + NOvA Results ● The joint fit result is consistent with the separate T2K and NOvA results. ● In NO, the individual experiments preferred different phase-spaces, and the joint fit splits across this. ● In IO, where the experiments had good agreement, the joint fit tightents the constraint. → IO is preferred by the joint fit The Future 36 ● Expanded selection of 𝜈eCC1π by adding a multi-ring topology ● Addition of recent data, with increased Gd-loading ● Updates in simulation and treatment of systematics The future: SK The future: T2K Beam New data to analyze! Recent beam upgrades have been completed ● New Main Ring power supplies allowed repetition rate to be reduced from 2.48 s to 1.36s ● Horn current increased 250 kA → 320 kA to increase neutrino flux by ~10% with higher purity. ● Beam power reached above 800 kW in June 2024. → This data will be included in future analyses The future: ND280 for the oscillation analysis 37 Upcoming developments to the existing/pre-upgrade ND280 oscillation analysis inputs. - 4pi angular acceptance - Anti-neutrino photon selection, neutron tagging - New parameterisation for weighted detector systematics - Improved cross-section model Recent cross-section measurements ● n-capture multiplicity in NCQE-like interactions on oxygen: Phys. Rev. D 112, 032003 ●𝜈e CCπ+ on carbon arXiv:2505.00516 ● NC1π+ on carbon arXiv:2503.06849 → See talk by Ellen Sandford: Latest neutrino cross-section results from T2K Wednesday, 10.10am Neutrino Physics session T2K cross-section results 38 Part of the P0D detector replaced with: ● New scintillator target (SuperFGD) ● Two High Angle TPCs (HA-TPC) ● 6 Time of Flight planes (TOF) The goal is for ND280 to reduce systematic errors in oscillation analyses in the search for δCP : ● Improved 4ⲡ acceptance for charged particles ● Reduce proton momentum threshold (~300 MeV/c) ● Neutron kinematics via time of flight ● Increased target mass for greater statistics The Upgrade installation was completed in May 2024 and data is already being analysed! 6 ToF planes superFGD HA-TPC HA-TPC Upgraded ND280 6 TOF planes Talk by Gioele Reina: First results from T2K's upgraded near detector - Wed, 11am, Data Science and Detector R&D session Summary 40 Summary ●T2K Oscillation analysis with additional SK data (10% more stats, and Gd loading) ○ CP conservation excluded at 90% C.L. ○ Weak preference for normal mass ordering and θ23 upper octant ● T2K + SK joint analysis ○CP-conserving values of the Jarlskog invariant are excluded with a significance between 1.9σ and 2.0σ ○ First joint analysis, and and important step towards combined beam and atmospheric data analyses planned by next-generation neutrino oscillation experiments ● T2K + NOvA ○ Weak preference for inverted ordering, which is where the individual experiments had good agreement. ○ Assuming Inverted Ordering, gives 3σ sigma exclusion of CP-conserving values. ● T2K Future ○New data from SK to be analysed, from the era of beam upgrades and increased Gd loading ○ The first physics results from the ND280 upgrade are in the pipeline! 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