1. T2K neutrino oscillation results Kei Ieki for the T2K collaboration Lake Louise Winter Institute 2014/2/22 1 ν T okai K amioka

2. Neutrino oscillation 2 The flavor of neutrino changes periodically as it propagates νμνμ νeνe ντντ ν2ν2 ν1ν1 ν3ν3 = Flavor eigenstates mass eigenstates time U PMNS × Mixing matrix (PMNS matrix) described by mixing angles θ 12, θ 23, θ 13 and CP phase δ CP (m 1 ) (m 2 ) (m 3 ) Unknown!

3. Neutrino oscillation 3 The flavor of neutrino changes periodically as it propagates νμνμ νeνe ντντ ν2ν2 ν1ν1 ν3ν3 = Flavor eigenstates mass eigenstates time U PMNS × Mixing matrix (PMNS matrix) described by mixing angles θ 12, θ 23, θ 13 and CP phase δ CP (m 1 ) (m 2 ) (m 3 ) Unknown!

4. Oscillation probabilities 4 Combining T2K and Reactor allows to measure δ CP ! (sub-leading term)

5. The T2K experiment 5 Discovery of ν μ  ν e We observed ν μ  ν e with 7.3σ significance in 2013! Precise measurement of ν μ  ν μ Updated result reported on Feb 18 Main goals νμνμ ν e,μ,τ Far Detector (Super-Kamiokande) Far Detector (Super-Kamiokande) Near Detector (ND280) Near Detector (ND280) J-PARC 295km High intensity ν μ beam & giant water Cherenkov detector SK ~40m μ p π+π+

6. Super-Kamiokande (SK) 6 e-e- ~40m Measure ν interactions after oscillation.  J. Hignight’s talk 1-ring e-like/μ-like events are selected for ν μ →ν e /ν μ  ν μ analysis. 50 kton water Cherenkov detector (FV: 22.5 kton) 1000m underground Kamioka mine Identify e/μ from Cherenkov ring shape

7. Data taking summary 7 6.6×10 20 protons on target (~8% of the final goal) collected/analyzed. Beam power has steadily increased and reached 220kW continuous operation with a world record of 1.2×10 14 protons per pulse. <1mrad beam direction stability (<2% beam energy shift) Tohoku Earthquake (Mar. 11, 2011) Recovering facility

8. Neutrino oscillation analysis 8 MC Data ④ Neutrino oscillation analysis ② Constraints from ND280 ① Neutrino flux & cross section prediction Flux: NA61/SHINE hadron production experiment etc. Cross section: Event generator NEUT + constraints from MiniBooNE experiment etc.  T. Duboyski’s talk  J. Hignight’s talk

9. ν μ  ν e measurement 9 Observed 28 ν e candidate events. Reconstructed ν e energy distribution Expected backgrounds: 4.9±0.6 events 0 1000 500 Energy (MeV) T2K ν μ flux

10. ν μ  ν e result (sin 2 2θ 13 ) 10 Electron momentum and angular distribution Significance to exclude θ 13 =0: 7.3σ “Observation” of ν μ  ν e Fit to measure the oscillation parameters: Maximum likelihood fit based on the number of ν e events and electron momentum and angular distribution (6.57×10 20 POT, normal hierarchy) νeνe e-e-

11. ν μ  ν e result (δ CP vs. sin 2 2θ 13 ) 11 68% and 90% allowed region of sin 2 2θ 13 for each value of δ CP 17.2 sin 2 2θ 13 =0.1, δ CP =021.6 25.7 Normal hierarchy Inverted hierarchy Fit performed for different values of δ CP. (sin 2 2θ 13 =0.098±0.013) Observed: 28 NOTE: These are 1D contours for various value of δ CP, not 2D contours

12. ν μ  ν e result, combined with reactor 12 Combined with reactor measurement (sin 2 2θ 13 =0.098±0.013 from PDG2012) 90% CL excluded region This is an important step towards the discovery of CP violation in the lepton sector! Regions above these lines (derived by Feldman-Cousins method) are excluded with 90% C.L. δ CP negative log likelihood curve 90% excluded regions Best fit

13. ν μ  ν μ measurement 13 Expected ν μ events (no osc.): 446±23 events Observed 120 ν μ candidate events. ν μ energy spectrum Ratio to no oscillations Updated result reported on Feb 18! (3.01×10 20  6.57×10 20 POT)

14. ν μ  ν μ result 14 Likelihood fit based on the number of ν μ events and reconstructed neutrino energy 90% CL allowed region World’s best measurement of θ 23 (normal hierarchy)

15. Summary 15

16. BACKUP SLIDES 16

17. ν μ  ν μ result 17 Previous T2K result PRL 111, 211803 (2013) 2D confidence regions T2K new [NH] Great improvement from the previous T2K result! T2K favors maximal mixing 1D intervals  23 [NH]  23 [IH] Normal hierarchy (NH) Inverted hierarchy (IH)

18. ν μ  ν μ result 18 T2K measures  23 with the world-leading precision! Comparison w/ other experiments Normal hierarchy Inverted hierarchy

19. ν μ  ν μ measurement Lively discussion motivated by CCQE cross section inconsistency between MiniBooNE/other experiment Not incorporated directly into analysis – But we have a large systematic uncertainty (100%) on decays of  resonances w/ prompt  absorption (“  -less  -decay”). It has similar impact on neutrino energy reconstruction as a 100% uncertainty in the multi-nucleon interaction model (Nieves model) – Dedicated MC study shows the impact on oscillation analysis is small relative to our current statistical error. 19 Multi-nucleon systematic error

20. ν μ  ν μ measurement Lively discussion motivated by CCQE cross section inconsistency between MiniBooNE/other experiment Not incorporated directly into analysis – But we have a large systematic uncertainty (100%) on decays of  resonances w/ prompt  absorption (“  -less  -decay”). It has similar impact on neutrino energy reconstruction as a 100% uncertainty in the multi-nucleon interaction model (Nieves model) – Dedicated MC study shows the impact on oscillation analysis is small relative to our current statistical error. 20 Multi-nucleon systematic error

21. Prospect Expected improvements: – ν μ →ν e & ν μ →ν μ joint fit analysis will be ready soon – Neutrino interaction model implementations ongoing (spectral function, multi-nucleon etc.) Data taking: – Anti-ν test run is forecast : Switch horn current in 2014 – LINAC upgrade is done (181  400MeV) – Future MR upgrade to operate at 750 kW ν-N cross section measurements: Charged current interaction measurements (ν μ CCQE, ν μ CC inclusive, ν μ CC coherent π, ν e CC inclusive etc. at ND280, INGRID) will be released. 21

22. Accident at J-PARC hadron hall building 22 Hadron hall ν beam Picture of Au target Proton beam -Malfunction of the beam extraction system -Gold target was damaged and radioactive material was discharged. 2013 May 23 Thirty four registered radiation workers in the controlled area of the HD Facility received total (internal plus external) radiation doses between 0.1 and 1.7 mSv

23. J-PARC neutrino beam 23 -High intensity 30GeV proton beam -Pions are focused by magnetic horns -Off-axis beam: direction of the beam is shifted by ~2.5 degrees. Energy spectrum peaked at oscillation maximum. BG ν interaction modes for ν μ  ν e at high energy are reduced. ν energy spectrum Oscillation prob. p beam Magnetic horns Decay volumeBeam dump Muon monitor ND280 INGRID μ+μ+ νμνμ νμνμ To SK π+π+ π+π+ μ+μ+ off-axis on-axis 0m 118m 280m

24. ND280 24 0.2T magnet TPC1 FGD1 FGD2 TPC2 TPC3 μ +SMRD νμνμ FGD - Scintillator bars (~1 ton for FGD1) - ν target & tracking - Time Projection Chambers - 3D tracking, momentum measurement, PID TPC Measures ν interactions to constrain the beam flux & cross section uncertainty.  T. Duboyski’s talk

25. ν μ  ν e appearance probability 25

26. Systematic errors 26 Error sourcesError Neutrino flux & cross section (constrained by ND280)2.9% Neutrino cross section (not constrained by ND280)7.5% SK detector & Final state interaction & γ-N interaction3.5% Total8.8% Error sourcesError Neutrino flux & cross section (constrained by ND280)2.7% Neutrino cross section (not constrained by ND280)5.0% SK detector & Final state interaction & γ-N interaction5.6% Total8.0% Systematic error on predicted number of ν e Systematic error on predicted number of ν μ

27. Neutrino beamline 27

28. Beam direction stability (by muon monitor) 28 Stability of beam direction (Muon monitor) (＊)(＊) 1 mrad change of ν beam direction results in 2-3% change of the neutrino energy scale (~16MeV) X direction Y direction

29. Beam stability (by INGRID) 29 Stability of ν interaction rate normalized by # of protons (INGRID) Stability of beam direction is much better than 1mrad during whole run period Fluctuation of ν interaction rate (/10 19 p.o.t) is less than 0.7% whole run period

30. Beam flux prediction 30 Beam flux is predicted based on NA61/SHINE π, K production measurements and T2K proton beam measurements overlaid plot

31. Systematic error sources for neutrino flux 31 1 proton beam measurement 4. Horn current & field 5. Beam direction 2. Hadron production Super-K p π µ ν 3. Alignment error on target/horn 1. Measurement error on monitoring proton beam 2. Hadron production 3. Alignment error on the target and the horn 4. Horn current & field 5. Neutrino beam direction (Off-axis angle) INGRID ν µ uncertainty at Super-K

32. Constraints on cross section from external data 32 We use effective parameters (M A QE, normalization parameters etc.) with uncertainties that span the base model and data, and allow the ND280 to constrain the model. Past measurements of M A QE CCQE M A QE (axial mass)1.21±0.45 GeV/c 2 CCQE norm1±0.11

33. Constraints on cross section from external data 33 CC1π + NC1π 0 We use MiniBooNE 1π data (CC and NC) and fit to NEUT predictions. Resonant π production M A RES (axial mass)1.41±0.22 GeV/c 2 CC1π norm1.15±0.32 NC1π 0 norm0.96±0.33

34. A New Event Reconstruction Algorithm for Super-K For each Super-K event we have, for every hit PMT – A measured charge – A measured time For a given event topology hypothesis, it is possible to produce a change and time PDF for each PMT – Based on the likelihood model used by MiniBooNE (NIM A608, 206 (2009)) Framework can handle any number of reconstructed tracks – Same fit machinery used for all event topologies (e.g. e - and π 0 ) Event hypotheses are distinguished by comparing best-fit likelihoods – electron vs muon – electron vs π 0 – 1-ring vs 2-ring vs 3-ring...

35. The Likelihood Fit A single track in the detector can be specified by a particle type, and 7 kinematic variables (represented above as the vector x): – A vertex position (X, Y, Z, T) – A track momentum (p) – A track direction (θ, φ) For a given x, a charge and time probability distribution function (PDF) is produced for every PMT All 7 track parameters fit simultaneously For particle ID: compare final likelihoods for different particle hypotheses Time PDF Charge PDF PMT Charge Response: Property of the electronics and PMT properties Predicted Charge (μ): - Number of photons that reach the PMT - Depends on detector properties (scat, abs, etc.) Predicted Charge (μ): - Number of photons that reach the PMT - Depends on detector properties (scat, abs, etc.)

36. ν μ  ν e fit 36 Number of ν e Constraints on systematic parameters Systematic parameters oscillation parameters sin 2 2θ 13 =0.0 (BG only) 04008001200 6060 120 180 0 Extended maximum likelihood fit: 04008001200 Fixed parameters ： sin 2 θ 12 = 0.306 Δm 2 12 = 7.6×10 -5 eV 2 δ CP = 0 Constraints on oscillation parameters

37. sin 2  23 /  m 2 32 1  Precision vs. POT 37 50% POT + 50% POT anti- Solid Lines: no sys. err. Red Dashed: with conservative projected sys. err. (~7%, ~14% anti- ) Statistical limit of 1  precision at full POT sin 2  23 (  23 ): ~0.045 (~2.6°)  m 2 32 : ~4×10 -5 eV 2 Assuming true: sin 2 2  13 =0.1,  CP =0°, sin 2  23 =0.5,  m 2 32 =2.4×10 -3 eV 2, [NH]  13 constrained by  (sin 2 2  13 ) = 0.005 [NH] Normal hierarchy, [IH] Inverted hierarchy now ~2016 now ~2016 Precisions will drastically improve over the next few years.

38. Sensitivity for Resolving sin  CP ≠0 38 7.8×10 21 POT (50% POT + 50% POT anti- ) True [NH] True [NH] True [IH] True [IH] No sys. err.w/ 2012 sys. err. (~10% e, ~13%  ) Assuming true: sin 2 2  13 =0.1,  m 2 32 =2.4×10 -3 eV 2  13 constrained by  (sin 2 2  13 ) = 0.005 [NH] Normal hierarchy, [IH] Inverted hierarchy

39. Appearance 90% C.L. Sensitivity 39 [NH] Normal hierarchy, [IH] Inverted hierarchy 7.8×10 21 POT (50% POT + 50% POT anti- ) Solid Lines: no sys. err., Dashed: with 2012 sys. err. (~10% e, ~13%  ) Case study (1): True  CP = 0° Case study (2): True  CP = -  Assuming true: sin 2 2  13 =0.1, sin 2  23 =0.5,  m 2 32 =2.4×10 -3 eV 2, [NH] T2K w/ Reactor  (sin 2 2  13 ) = 0.005 T2K only

40. 40 T2K + NO A Sensitivity for Resolving sin  CP ≠0 Assuming 5% (10%) normalization uncertainty on signal (background) Assuming true: sin 2 2  13 =0.1,  m 2 32 =2.4×10 -3 eV 2,  13 constrained by  (sin 2 2  13 ) = 0.005 [NH] Normal hierarchy, [IH] Inverted hierarchy Region where sin  =0 can be excluded by 90% C.L. solid(dash): w/o (w/) systematics NO A T2K Both T2K/NO A -> full POT (50% POT + 50% POT anti- ) Shown in [NH] case. Sensitivity to resolve sin  =0

41. 41 T2K + NO A Sensitivity to Mass Hierarchy Both T2K/NO A -> full POT (50% POT + 50% POT anti- ) Shown in [NH] case. Assuming true: sin 2 2  13 =0.1,  m 2 32 =2.4×10 -3 eV 2,  13 constrained by  (sin 2 2  13 ) = 0.005 Red: T2K alone, Blue: NO A alone, Black: T2K + NO A [NH] Normal hierarchy, [IH] Inverted hierarchy Region where MH can be distinguished by 90% C.L. Sensitivity to resolve MH solid(dash): w/o (w/) syst. NO A