T2K neutrino oscillation results

K. Okumura (ICRR Univ. of Tokyo) for T2K collaboration

The 19th Particles and Nuclei International Conference (PANIC 11)

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Contents Introduction ne appearance result nm disappearance result

T2K Collaboration

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International collaboration

(~500 members, 59 institutes, 12 countries）

CanadaU. AlbertaU. B. ColumbiaU. ReginaU. TorontoTRIUMFU. VictoriaYork U.

FranceCEA SaclayIPN LyonLLR E. Poly.LPNHE Paris

GermanyU. Aachen

ItalyINFN, U. BariINFN, U. NapoliINFN, U. PadovaINFN, U. Roma

JapanICRR KamiokaICRR RCCNKEKKobe U.Kyoto U.Miyagi U. Edu.Osaka City U.U. Tokyo

PolandA. Soltan, WarsawH.Niewodniczanski,CracowU. Silesia,KatowiceT. U. WarsawU. WarsawU. Wroclaw

RussiaINR

S KoreaChonnam N. U.U. DongshinSeoul N. U.

SpainIFIC, ValenciaU. A. Barcelona

SwitzerlandETH ZurichU. BernU. Geneva

UKImperial C. L.Lancaster U.Liverpool U.Queen Mary U. L.Oxford U.Sheffield U.STFC/RALSTFC/DaresburyWarwick U.

USABoston U.B.N.L.Colorado S. U.U. ColoradoDuke U.U. C. IrvineLouisiana S. U.U. PittsburghU. RochesterStony Brook U.U. Washington

T2K physics goals

Search for nmne appearance by non-zero q13

– Last unknown mixing angle important for CP phase and mass hierarchy observation

– ~20 times better sensitivity than CHOOZ limit (sin2(2q13)<0.15) expected

Precise measurement of Dm232 and sin2(2q23 )

via nm disappearance

– Expected sensitivity w/ full T2K datasetd(Dm23

2) ~ 1×10-4 eV2, d(sin22q23) ~ 1% (90% C.L.)

~20 times betterthan CHOOZ

2 2 2 2

13 23 13( ) sin 2 sin sin 1.27e

LP m

Emn n q q

D

2 2 2

23 231 sin 2 sin 1.27L

P mE

m mn n q

D

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T2K exp’d sensitivityw/ 3.75 MW x 107 s(90%C.L.)

p

120m0m 280m 295 km

off-axis

Muon monitor

J-PARC 30 GeV

Proton beamSuper-Kamiokande

Near detectors

Decay volume

p nmm

Off-axis (2.5 ˚) nm beam – Intense, low energy narrow-band

– Peak En tuned for oscillation max. ( ~0.6 GeV)

– Reduce BG from high energy tail

– Small ne fraction (~1%)

Muon monitor

T2K overview

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 ˚

INGRID

ND280

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p

120m0m 280m 295 km

off-axis

Muon monitor

J-PARC 30 GeV

Proton beamSuper-Kamiokande

Near detectors

Decay volume

p nmm

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

μ-like

e-like

Super-K detector

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m39.3 m

ND280

dE/dx (TPC: data)

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Simulation events

Top view of detector

nm

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Delivered protons for analysis RUN1 (Jan. 2010 ~ Jun. 2010) 3.23 x 1019 p.o.t. achieved in ~50 kW runningRUN2 (Nov. 2010 ~ Mar. 2011) 11.09 x 1019 p.o.t. achieved in ~145 kW running

RUN1+RUN2 total 1.43 x 1020 p.o.t. (2% of final goal)

Stable operation of n beam during this periodDirection stability well within 1mrad. by m mon. and INGRID (dEn<2%)INGRID day-by-day interaction rate is stable

Clear peak of SK events around beam trigger timinglow background (3x10-3% exp’d in FV)

Beam data for analysis

Beam timing of SK events

2 atm n events(1.9 ev exp’d)

n beam dir. stability < 1mrad

Stability of beam direction (Muon monitor)

Stability of n interaction rate normalized by # of protons (INGRID)

Stability of n beam direction (INGRID)

Beam dir. stability < 1mrad

clear bunch structure Run1 Run2

Poster by V. Galymov

ne appearance analysis

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Analysis strategy and selection criteria

Selection Criteria

Beam timing, fully-contained, fiducial volume

Single-ring electron like

Visible energy > 100 MeV

No delayed electron signal

p0 invariant mass (Minv) < 105 MeV/c2

Reconstructed n energy (Enrec) < 1250 MeV/c2

Select single-electron events by oscillated ne CCQE interactions

Main background: intrinsic ne , NC p0 production

Compare # of selected events and expectation at sin2(2q13)=0

Signal (ne CCQE) BG (NC p0 )

Invariant mass cut Reconst. n energy

8Selection criteria are fixed before data analysis

Expected # of events at Super-K

(Dm232 =2.4x10-3 eV2, sin2(2q23)=1.0, dCP=0)

Beam nm CC background

Beam ne CC background

NC background

Oscillated nmne

(solar term)

Total

# of Events 0.03 0.76 0.61 0.09 1.49

Expected number of events at sin2(2q13)=0

exp 1.5 0.3 ( .) eventsSKN syst

,

,

expData

ND

MC

ND

S

MC

SK K

R

RN N

m

m

Expected SK events by Monte Carlo simulation

Calculated by F, s, e, and osc. probability

Summed for beam-nm , ne , anti-nm , and oscillated nmne

Normalization by ND nm event rate

Measurement of # of inclusive nμ charged-current events in ND280

ND280 ne/nm measurement consistent with predicted flux

, , 0.047

0.0371.036 0.028( .) (det . .) 0.038( .)Data MC

ND NDR R stat syst physm m

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ND280 talk by B. Berger2E-3 16:40 today

ne candidate events

All six events by visual examination are consistent with ne CC events

visible energy : 1049 MeV

# of decay-e : 0

p0 Inv. mass : 0.04 MeV/c2

Recon. energy : 1120.9 MeV

6 candidate events observed after all cuts

Null hypothesis (q13=0): 1.5 ±0.3 (syst.) Up fluctuation probability, p-value = 0.7%

corresponding to 2.5 s

Invariant mass Reconst. n energy

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Vertex distribution

out of FV in bottom

Vertex distribution along beam dir.

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, p0 photon, neutron, K from outside of ID

very small (3x10-3) events estimated in FV

final sample

FC events

w/o fiducial cut

Vertex of these six events are located near fiducial volume edge

K-S test of R2 event distribution 3% probability

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outsideof FV

Y-X and Z-R2 plots for final events (w/o FV cut)

fiducial volume

(sin2(2q13)=0.1)

(sin2(2q13)=0.1)

Allowed region of sin22θ13 for δCP

(assuming Δm223=2.4 x 10-3 eV2)

0.03 < sin22θ13 < 0.28

sin22θ13 =0.11

0.04 < sin22θ13 < 0.34

sin22θ13 =0.14

90% C.L. interval and best fit (for Δm223=2.4 x 10-3 eV2, sin2(2q23)=1, δCP=0)

Confidence level intervals for sin22θ13 vs δCP

Feldman-Cousins method was used for constructing confidence interval

Normal Inverted

Published in Phys. Rev. Lett. 107, 041801 (2011)12

nm disappearance analysis

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Event selection

Select for nm 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 (Enrec )

with Pm and qbeam

Pmqbeam

m

beam dir.

Pm and cosqbeam dist. for selected events

A selected single-ring m-like event

EventFraction (%)

w/ osc. w/o osc.

nm CC QE 57.2 79.4nm CC non-QE 30.0 15.7NC 6.0 1.6anti-nm 6.3 3.1ne 0.4 0.1

Expected composition w/ osc.

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nm oscillation fitsOscillation fit performed with 2-flavor oscillation assumption

norm shape sys L L L L 2 2log L

2 = -2logL is defined with # of events (Nsk) and Enrec shape

Two independent fits with same inputsFit A : w/ systematic error fittingFit B : w/o systematic error fitting

Feldman-Cousins prescription is used for constructing confidence interval

2 2 21 sin 2 sin 1.27L

P mE

m mn n q

D

Assigned Nsk syst. errors w/ and w/o oscillation Enrec shape syst. errors w/ oscillation

Estimate ~15% w/ oscillation

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Allowed region in (Dm2, sin22q)

(GeV)

Consistent with MINOS/SK results

Reconstructed n energy

Clear oscillation pattern observed

Nu

mb

er o

f Ev

ents

Rat

io

Dm2 (eV2) sin2(2q)

Fit A 2.1 ~ 3.1 x 10-3 > 0.85

Fit B 2.1 ~ 3.2 x 10-3 > 0.84

90% C.L. allowed region sin22q

Dm

2(e

V2 )

Best-fit (Dm2, sin22q) Fit A (2.6x10-3eV2 , 0.99)Fit B (2.6x10-3eV2 , 0.98)

(Fit A)

(Fit B)

Fit A

Fit B

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Summary

First off-axis experimental ne and nm results from T2K, based on RUN1+2 data (1.43x1020 p.o.t.)

Indication of ne appearance consistent with non-zero q13– Observe 6 ne candidate events when 1.5 ± 0.3 (syst.) BG expected at

sin2(2q13)=0 (p-value = 0.7% equivalent to 2.5 s

– 0.03 (0.04) < sin2(2q13) < 0.28 (0.34) at 90% C.L. for normal (inverted) hierarchy (assuming Dm2

23=2.4 x 10-3 eV2, dCP=0)

New result from nm disappearance analysis– Observe 31 events for single-r muon-like ( 104 events expected w/o osc.)

– 90% C.L. allowed region: 2.1x10-3 < Dm2 < 3.1x10-3 eV2, sin22q > 0.85

– Consistent with other nm oscillation results

Resume J-PARC operation in Dec. 2011 and restart T2K data taking as soon as possible

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