Updated results from21
T2K experiment with 3.13x10 POT

Kimihiro OKUMURA (ICRR) for T2K collaboration
okumura@icrr.u-tokyo.ac.jp

ICRR seminar, January 10th 2019

T2K (Tokai to Kamioka) (2010~)• Long baseline neutrino oscillation experiment with high intensity muon
neutrino beam from J-PARC MR to Super-Kamiokande (Super-K)• Goals:• Precise measurement of νµ disappearance• Measurement of νe appearance à Discovery
à

Search for leptonic CP violation (δCP)• Search for non-standard oscillation, Cross section measurements!2T2K collaboration
12countries, ~500 members

Neutrino Oscillation
Mass state

Flavor state(Propagation)(Interaction)

UPMNS
Atmospheric, LBL

Still unknown:

Leptonic CP (δCP)

Reactor, LBL

Normal(Δm232>0)

Solar, KamLAND

Inverted(Δm232<0)

Mass Hierarchy(Mass Ordering)θ23 Octant

Sterile neutrino!4

Neutrino Oscillation in T2K• Disappearance of muon neutrino (θ23, Δm232) :↑ Leading term

• Appearance of electron neutrino (θ13) and CP measurement (δCP)← Leading term

↖︎CP violating term!5CP effect on electron appearance• ~25% change at oscillation peak between δ=-1/2π and 1/2π
• Opposite direction for neutrino and anti-neutrinoàPossible to measure CP by independent ν and ν̅ measurements• Marginal effect due to neutrino mass hierarchy!6

T2K experimentJ-PARC Accelerator(KEK/JAEA

North

181 (400) MeV Linac
3 GeVSynchrotron
Neutrino Beam

30 G
750 eVkW

M(des ain
ign v rin
alue g)Bird’s eye photo in January of 2008!8

Off-Axis Beam• Neutrino beam are pointed to 2.5°

off-axis direction from SK direction• Produce intense narrow-band beam
• Optimize peak energy by off-axis angle（~0.6GeV）• Suppress high energy flux （Eν>1GeV)
producing νe backgrounds

Osc. Prob• First experiment to utilize oﬀ-axis beam
Far Detector(Super-K)

ptarget /Hornprotonνμπ

θ: off-axis angle

on-axisDecay volume

Neutrino Energy (GeV)!9T2K overview Near detectors
pπ

J-PARC 30 GeV
Proton beam

µDecay volume0mνµoff-axis

Muonmonitor
120m

2.5oon-axis

Super-Kamiokande

280m

295 kmOff-axis (2.5 ˚) νµ beam

Muon monitor– Intense, low energy narrow-band– Peak Eν tuned for oscillation max. ( ~0.6GeV)– Reduce BG from high energy tail– Small νe fraction (~1%)

On-axis detector (INGRID)– Monitor intensity and profile
spill-by-spill– Monitor ν beam day-by-day– Detector coverage is 10m x 10m

ND280
OA2.5 ˚

INGRID
Muon monitor
10pπJ-PARC 30 GeV
Proton beam0m

Near detectorsµDecay volumeoff-axis

on-axisMuonmonitor120m

νµ2.5oSuper-Kamiokande

280m

295 kmOff-axis detector (ND280)

Far detector (Super-Kamiokande)– Predict interaction rate before oscillation– UA1 magnet– Fine grained detector (FGD)
FGD1: CH target, FGD2: 42% water– Time projection chamber (TPC), ECAL, P0D– Water Cherenkov detector (total mass ~50 kton)– Excellent particle ID for µ / e particle with ~99%
efficiency
Simulation events

Super-K detector

μ-like42 m

νµND280
Top view ofdetector

39.3 me-like11

Beam Power and Accumulated POT• 3.16 x 1021 Proton On Target (POT) accumulated until May 2018
• neutrino: 1.51 x 1021 POT, anti-neutrino: 1.65 x 1021 POT• ~30% increase of anti-neutrino data from previous result!12[mrad][events/1e14 POT]

Neutrino Beam Stability
1.8
1.6
1.4
1.2
10.8 Event rate
0.6
0.4
0.5

Horn250kA
Horn205kA
Horn-250kA

Horizontal beam direction

INGRID
MUMON

Vertical beam direction

INGRID
MUMON

Day

0

[mrad]

−0.5
−10.5
0
−0.5

T2K Run1

T2K Run2

T2K Run3

Jan.2010-Jun.2010 Nov.2010-Mar.2011Mar.2012-Jun.2012

T2K Run5 T2K Run6

T2K Run7

T2K Run8

T2K Run9

T2K Run4May.2014

Feb.2016-May.2016

Oct.2016-Apr.2017

Oct.2017-May.2018

Oct.2012-May.2013-Jun.2014

Oct.2014-June.2015−1Day• Neutrino event rate and direction are stable!13

Super-K Data Quality
Beam timing

Neutrino Rate Stability
Neutrino-mode(FHC)

Anti-Neutrino-mode(RHC)• Data taking is stable and efficient (~1% inefficiency)• Clear bunch structure in beam timing• Stable event rates for both ν and ν̅ mode!14

Oscillation Analysis

Oscillation Analysis Strategy!16

Neutrino Flux Predictions
NA61/SHIN dataFluka simulation+++

NA61 / SHINE!17

Neutrino Flux Predictions
Neutrino-mode

Anti-neutrino-mode(Forward Horn Current: FHC)

(Reverse Horn Current: RHC)

• ~8% absolute error• Still hadron prod.
uncertainty isdominant!18

Near Detector Fit
Pre-Fit• Initial uncertainties on fluxand cross section are further
constrained by ND280 data

• Significant reduction on SK
prediction uncertainties

Post-Fit

Uncertainties on SK event rate w/ and w/o ND fit

SamplePre-fitPost-fit

ν-mode 1Rµ

14.6%

5.1%

ν̅-mode 1Rµ12.5%4.5%

ν -mode 1Re

16.9%

8.8%

ν̅-mode 1Re

14.4%

7.1%
!19

Super-K neutrino data sample
1Ring μ-likeνμNeutrino-mode(FHC)

1Ring e-like

μ-νe

W+

1Ring CC1π+e- νee-W+

W+

Δ++
npnp

ν
̅μμ+

ν̅ee+

Anti-Neutrino-mode(RHC)

W-pp

π+p

W-npn!20ν-mode 1Rµν̅-mode 1Rµν-mode 1Re

Super-K DataSample

δ=-π/2δ=0

δ=π/2

δ=πObs.

ν-mode 1Rµ272.4

272.0

272.4

272.8243ν̅-mode 1Rµ139.5

139.2

139.5

139.9140

ν-mode 1Re

74.4

62.2

50.6

62.7

75

ν̅-mode 1Re

17.1

19.6

21.7

19.3

15

ν CC1π+

7.0

6.1

4.9

5.9

15

ν̅-mode 1Re

ν CC1π+!21

New νe̅ appearance data
Full Run1-9 Data (~May 2018)• Number of ν̅e 1Re events:9 (prev.) à 15 events• Distribution of new data points agrees
better with ν̅e signal• Convincing that T2K is reallyobserving ν̅e appearance

Previous Data (~Dec 2017)!22

Systematic uncertainties in NSK!23

Oscillation fit result: θ13 vs δCPT2K only

Sensitivity• Update reactor constraint:
T2K with reactor

sin2θ13 = 0.0219 ± 0.0012→ 0.0212 ± 0.0008 (PDG2018)( sin22θ13 = 0.0857 → 0.0830)• Preferred δCP ~ -π/2
• Better fit result than sensitivity!24

Constraint on δCPData (2σ CL)

Sensitivity• Best fit: δCP = -1.885 radian• 2σ confidence interval NH: [-2.966, -0.628], IH: [-1.799, -0.979]• CP conservation points (δCP =0, π) are both outside of 2σ CL!25

νe / νe̅ events and δCP/MO/θ23 exp’d!26

νe̅ Appearance Result (New)• Test with two analysis methods:“Rate-only” and “Rate + Shape”

Rate-only• Introduce scaled ν̅µ->ν̅e probability:(β: 0=no ν̅e appearance, 1=PMNS)• Rate+shape result excludes noappearance hypothesis by 2σ level
though still inconclusive

Rate +ShapeRate-only

Rate+Shape

No app. (β=0)

0.0686 (1.82σ)

0.0244 (2.25σ)

PMNS (β=1)

0.246 (1.16σ)

0.261(1.12σ)!27Future Prospects

Beam Plan and Expected Sensitivity• MR PS upgrade in 2020
• Upgrade to 1.3 MW beam by• repetition rate (2.48 → 1.16 sec)
• increase proton / pulse (+28%)• Associated improvement inneutrino beam line

• 20 x 1021 POT by 2028

• Reducing systematic error is necessary• ~9% (current) → 4% (goal)!29

Near Detector Upgrade
New detectors• Upgrade for 4% systematicerror and 3σ exclusion of
CP conservation• Increase acceptance oflarge angle scattering andlow energy particles• Highly granular scintillator:
detector (Super-FDG)• High angle TPC (x2) + TOF• TDR under review!30Super-K refurbishment and SK-Gd• Refurbishment work is on-goingfrom summer 2018 for SK-Gd• Water filling almost completed

and will resume from next month• Gd loading schedule withconsideration of J-PARCschedule• Start from 0.01% Gd→ 0.1% Gd!31

Summary• T2K collaboration has released updated oscillation resultswith increased anti-neutrino data up to May 2018

• CP conservation values (δCP =0, π) are not within 2σ CLintervals• Strong motivation for further beam data taking for 3σ
exclusion• New result of ν̅e appearance with 2σ CL level• Many upgrade plans (Beam, Near detector, SK-Gd) areon-going!32

Atmospheric parameter: Δm232 and θ23• With reactor constraint• Best fit lies in 2nd octant(sin2θ23=0.532)• Consistent with maximal
mixingBest-fit and 1σ conf. interval
NHIH|Δm232|
(eV2)

2.452
[2.382, 2.523]

2.432[2.361, 2.501]

sin2θ230.532[0.495, 0.562]

0.532[0.497, 0.561]!34