T2K neutrino oscillation results

Transcription

1 T2K neutrino oscillation results K. Okumura (ICRR Univ. of Tokyo) for T2K collaboration The 19th Particles and Nuclei International Conference (PANIC 11) Contents Introduction n e appearance result n m disappearance result 1

2 T2K Collaboration Canada U. Alberta U. B. Columbia U. Regina U. Toronto TRIUMF U. Victoria York U. France CEA Saclay IPN Lyon LLR E. Poly. LPNHE Paris Germany U. Aachen Italy INFN, U. Bari INFN, U. Napoli INFN, U. Padova INFN, U. Roma Japan ICRR Kamioka ICRR RCCN KEK Kobe U. Kyoto U. Miyagi U. Edu. Osaka City U. U. Tokyo Poland A. Soltan, Warsaw H.Niewodniczanski, Cracow U. Silesia, Katowice T. U. Warsaw U. Warsaw U. Wroclaw Russia INR S Korea Chonnam N. U. U. Dongshin Seoul N. U. Spain IFIC, Valencia U. A. Barcelona Switzerland ETH Zurich U. Bern U. Geneva UK Imperial C. L. Lancaster U. Liverpool U. Queen Mary U. L. Oxford U. Sheffield U. STFC/RAL STFC/Daresbury Warwick U. USA Boston U. B.N.L. Colorado S. U. U. Colorado Duke U. U. C. Irvine Louisiana S. U. U. Pittsburgh U. Rochester Stony Brook U. U. Washington International collaboration (~500 members, 59 institutes, 12 countries) 2

3 T2K physics goals Search for n m n e appearance by non-zero q 13 Last unknown mixing angle important for CP phase and mass hierarchy observation ~20 times better sensitivity than CHOOZ limit (sin 2 (2q 13 )<0.15) expected P( n m n e) sin 2q 13 sin q23 sin 1.27Dm13 E L ~20 times better than CHOOZ Precise measurement of Dm 232 and sin 2 (2q 23 ) via n m disappearance n m n m 1sin 2q sin 1.27D P 23 m23 E L Expected sensitivity w/ full T2K dataset d(dm 232 ) ~ ev 2, d(sin 2 2q 23 ) ~ 1% (90% C.L.) T2K exp d sensitivity w/ 3.75 MW x 10 7 s (90%C.L.) 3

4 T2K overview p J-PARC 30 GeV Proton beam p m Decay volume Muon monitor Near detectors off-axis n m Super-Kamiokande 0m 120m 280m 295 km Off-axis (2.5 ) n m beam Intense, low energy narrow-band Peak E n tuned for oscillation max. ( ~0.6 GeV) Reduce BG from high energy tail Small n e fraction (~1%) Muon monitor Monitor intensity and profile spill-by-spill On-axis detector (INGRID) Monitor n beam day-by-day Detector coverage is 10m x 10m OA2.5 ND280 Muon monitor INGRID 4

5 42 m p p m Near detectors off-axis n m J-PARC 30 GeV Proton beam Decay volume Muon monitor Super-Kamiokande 0m 120m 280m 295 km Off-axis detector (ND280) Predict interaction rate w/o oscillation 0.2 T UA1 magnet Fine grained detector (FGD) full active for n int. w/ FV 1.6 ton Time projection chamber (TPC) Particle ID by de/dx in gas Far detector (Super-Kamiokande) Water Cherenkov detector w/ FV 22.5 kton Excellent particle ID for m / e particle with ~99% efficiency Super-K detector Simulation events μ-like n m de/dx (TPC: data) ND280 Top view of detector 39.3 m e-like 5

6 Beam data for analysis Delivered protons for analysis RUN1 (Jan ~ Jun. 2010) 3.23 x p.o.t. achieved in ~50 kw running RUN2 (Nov ~ Mar. 2011) x p.o.t. achieved in ~145 kw running RUN1+RUN2 total 1.43 x p.o.t. (2% of final goal) Beam timing of SK events Stable operation of n beam during this period Direction stability well within 1mrad. by m mon. and INGRID (de n <2%) INGRID day-by-day interaction rate is stable Clear peak of SK events around beam trigger timing low background (3x10-3 % exp d in FV) 2 atm n events (1.9 ev exp d) Stability of n beam direction (INGRID) Poster by V. Galymov n beam dir. stability < 1mrad Stability of n interaction rate normalized by # of protons (INGRID) Run1 Run2 clear bunch structure Stability of beam direction (Muon monitor) Beam dir. stability < 1mrad 6

7 n e appearance analysis 7

8 Analysis strategy and selection criteria Select single-electron events by oscillated n e CCQE interactions Main background: intrinsic n e, NC p 0 production Compare # of selected events and expectation at sin 2 (2q 13 )=0 Signal (n e CCQE) BG (NC p 0 ) Selection Criteria Beam timing, fully-contained, fiducial volume Single-ring electron like Visible energy > 100 MeV No delayed electron signal p 0 invariant mass (M inv ) < 105 MeV/c 2 Reconstructed n energy (E rec n ) < 1250 MeV/c 2 Selection criteria are fixed before data analysis Invariant mass cut Reconst. n energy 8

9 Expected # of events at Super-K N exp SK R R m, Data ND m, MC ND N MC SK Expected SK events by Monte Carlo simulation Calculated by F, s, e, and osc. probability Summed for beam-n m, n e, anti-n m, and oscillated n m n e Normalization by ND nm event rate Measurement of # of inclusive nμ charged-current events in ND280 R R ( stat.) (det. syst.) 0.038( phys.) m, Data m, MC ND ND ND280 n e /n m measurement consistent with predicted flux ND280 talk by B. Berger 2E-3 16:40 today Expected number of events at sin 2 (2q 13 )=0 N exp SK ( syst.) events Beam n m CC background Beam n e CC background NC background Oscillated n m n e (solar term) Total # of Events (Dm 232 =2.4x10-3 ev 2, sin 2 (2q 23 )=1.0, d CP =0) 9

10 n e candidate events 6 candidate events observed after all cuts Null hypothesis (q 13 =0): 1.5 ±0.3 (syst.) Up fluctuation probability, p-value = 0.7% corresponding to 2.5 s Invariant mass Reconst. n energy All six events by visual examination are consistent with n e CC events visible energy : 1049 MeV # of decay-e : 0 p 0 Inv. mass : 0.04 MeV/c 2 Recon. energy : MeV 10

11 Vertex distribution Y-X and Z-R 2 plots for final events (w/o FV cut) out of FV in bottom fiducial volume outside of FV Vertex of these six events are located near fiducial volume edge K-S test of R 2 event distribution 3% probability Vertex distribution along beam dir. final sample (sin 2 (2q 13 )=0.1) Check distribution of events outside FV Check distribution of OD events No indication of BG contamination Simulation study of beam-induced BG by mis-id m, p 0 photon, neutron, K from outside of ID very small (3x10-3 ) events estimated in FV FC events w/o fiducial cut (sin 2 (2q 13 )=0.1) 11

12 Allowed region of sin 2 2θ13 for δcp Confidence level intervals for sin 2 2θ13 vs δcp Feldman-Cousins method was used for constructing confidence interval (assuming Δm 2 23=2.4 x 10-3 ev 2 ) Normal Inverted 90% C.L. interval and best fit (for Δm 2 23=2.4 x 10-3 ev 2, sin 2 (2q 23 )=1, δcp=0) 0.03 < sin 2 2θ13 < 0.28 sin 2 2θ13 = < sin 2 2θ13 < 0.34 sin 2 2θ13 =0.14 Published in Phys. Rev. Lett. 107, (2011) 12

13 n m disappearance analysis 13

14 Event selection Select for n m CC quasi-elastic events Beam-timing, fully-contained, FV cut Single-ring & PID is muonlike Reconst. m momentum > 200 MeV/c # of delayed electrons 1 31 events selected after applying cuts 104 events expected w/o osc Neutrino energy reconstructed (E rec n ) with P m and q beam Expected composition w/ osc. Event Fraction (%) w/ osc. w/o osc. nm CC QE nm CC non-qe NC anti-nm ne A selected single-ring m-like event Pm and cosq beam dist. for selected events P m m q beam beam dir. 14

15 n m oscillation fits Oscillation fit performed with 2-flavor oscillation assumption L Pn m n m 1sin 2q sin 1.27Dm E 2 = -2logL is defined with # of events (N sk ) and E rec n shape L L L L 2 norm shape sys Two independent fits with same inputs Fit A : w/ systematic error fitting Fit B : w/o systematic error fitting 2log Feldman-Cousins prescription is used for constructing confidence interval L E n rec shape syst. errors w/ oscillation Assigned N sk syst. errors w/ and w/o oscillation Estimate ~15% w/ oscillation 15

16 Ratio Dm 2 (ev 2 ) Number of Events Allowed region in (Dm 2, sin 2 2q) (Fit A) (Fit B) Reconstructed n energy Fit A Fit B Best-fit (Dm 2, sin 2 2q) Fit A (2.6x10-3 ev 2, 0.99) Fit B (2.6x10-3 ev 2, 0.98) 90% C.L. allowed region Dm 2 (ev 2 ) sin 2 (2q) Fit A 2.1 ~ 3.1 x 10-3 > 0.85 Fit B 2.1 ~ 3.2 x 10-3 > 0.84 Consistent with MINOS/SK results sin 2 2q (GeV) Clear oscillation pattern observed 16

17 Summary First off-axis experimental n e and n m results from T2K, based on RUN1+2 data (1.43x10 20 p.o.t.) Indication of n e appearance consistent with non-zero q 13 Observe 6 n e candidate events when 1.5 ± 0.3 (syst.) BG expected at sin 2 (2q 13 )=0 (p-value = 0.7% equivalent to 2.5 s 0.03 (0.04) < sin 2 (2q 13 ) < 0.28 (0.34) at 90% C.L. for normal (inverted) hierarchy (assuming Dm 2 23=2.4 x 10-3 ev 2, dcp=0) New result from n m disappearance analysis Observe 31 events for single-r muon-like ( 104 events expected w/o osc.) 90% C.L. allowed region: 2.1x10-3 < Dm 2 < 3.1x10-3 ev 2, sin 2 2q > 0.85 Consistent with other n m oscillation results Resume J-PARC operation in Dec and restart T2K data taking as soon as possible 17