Physics Results fromthe first year of the T2K
K. Okumura (ICRR)
for T2K collaboration
Apr. 27th (2011) ICRR SeminarContents
 T2K experiment Experiment performance ne appearance analysis
1

T2K (Tokai to Kamioka)
Super-K

J-PARC
Kamioka

nm50-kt water Cherenkov(22.5 kt fiducial)

Tokai
J-PARC(KEK-JAEA)

Japan

30-GeV 750-kW proton beamLong baseline neutrino oscillation experiment
Intense nm beam at J-PARC
 Measure neutrino oscillation at Super-K (295 km away)
GoalsDiscovery for nm → ne (ne appearance) Precise measurement of n m → n t (nm disappearance)
2

The T2K Collaboration

3

Neutrino Oscillation

atm + accelerator (q23)

q13, dcp

solar + reactor (q12)4Goal of T2K


nm disappearance

3


2 L
Pn m  n m   1 - cos 4 q13 sin 2 2q 23 sin 2 1.27m23

E



2 L
 1 - sin 2 2q 23 sin 2 1.27m23
E

T2K goal w/ 3.75 MW×107s:
MINOS & Super-K preliminary @ Nu10d(m232) ~ 1×10-4 eV2, d(sin22q23) ~ 1% (90% C.L.)ne appearance2 LPm e  sin 2 q 23  sin 2 2q13  sin 2 1.27m13
E

T2K goal w/ 3.75 MW×107s:
sin22q13 down to 0.006 (90% C.L.)(m2 ~ 2.4×10-3 eV2, sin22q23 = 1, dCP=0,
normal hierarchy, 10% syst. error.)~20 times better
than current limit
5Off-Axis Neutrino Beampp

J-PARC 30 GeV
Proton beam

Near detectors

moff-axis

Super-Kamiokande

Decay volume Muon
monitor

0m

120m

nm

280m

295 km

T2K nm beamOscillation maximum: L=295km, m232~2.4×10-3 eV2 → En ~ 0.6 GeV
Signal: Charged Current Quasi Elastic events

En spectrum vs angle
On-axis: large tail at high energy
Off-axis: narrow spectrum

Our choice: off-axis angle = 2.5˚
50 GeV proton beam
(T2K: 30 GeV)

Increase flux at the oscillation maximum
Reduce high energy n background fromnon-CCQE events

Small ne fraction (~1%)

6

T2K Overview
pp

J-PARC 30 GeV
Proton beam
0m

Near detectorsmoff-axis

Super-KamiokandeDecay volume Muonmonitor
120m

nm

280m

295 km Beam monitoring– Primary proton beam monitors (intensity, position, profile)– Muon monitor (MUMON) just after decay pipe: beam direction/intensity Near detector @ 280m

– on-axis (INGRID): n beam direction/intensity– off-axis (ND280): n flavor/flux/spectrum/”cross section” measurement
 Off-axis far detector @ 295km– Super-Kamiokande: n flavor/flux/spectrum measurement
7

The J-PARC facility(KEK/JAEA）

North

181 (400) MeV Linac3 GeV
Synchrotron
Neutrino Beam

Bird’s eye photo in January of 20088Beam Linem++9Near Detector: INGRID and ND280

10Far detector: Super-Kamiokande
50 kT Water Cherenkov detector (22.5 kT fiducial mass)
Inner detector: 11,129 PMTs (20 inch)
Outer detector: 1,885 PMTs (8 inch)
41m

New electronics/DAQ (since 2008)• Stably running• Deadtime-less DAQ→ Improve e-tagging (from m decay) efficiency

39m

Good e-like/m-like separation:
mis-PID probability ~ 1%
Event displays(MC events)

mp0 background rejection

2 ringsep011

EXPERIMENT PERFORMANCE

12Delivered ProtonsResults discussed today

Summer shutdown

T2K run 1 (Jan. to Jun. 2010)

T2K run 2 (from Nov. 2010)• 6 bunches/spill, 3.5 s spill period• 3.23 x 1019 POT for T2K analysis• ~50 kW operation• 8 bunches, 3.2 s spill period• 1.45 x 1020 POT delivered• reaches to ~145 kW

13

Beam Monitor Measurements
Primary proton beam monitoring

Proton beam hits
center of target• Beam orbit: tuned within 2mm from design orbit.
(Critical for controlling beam loss)
SSEM
Horizontal: ±1mm Before tuning
After tuning

OTR x = -0.5mm

OTRMR extraction• Beam position on target:
Succeeded to control < 1mm
during long term operationTarget
SSEM
RMS 0.4mm

SSEM:
Segmented Secondary Emission Monitor

OTR:
Optical Transition Radiation detector

RMS 0.4mm
14MUMON Q / Nproton Profile center (cm)Beam Monitoring (MUMON)
Secondary m beam monitoring by MUMONJan.
+1 mrad-1 mradX profile center
Y profile center

Jun.

Detector intrinsic resolution < 1.5mm

RMS/Mean < 1% (whole period)
Jan.

Jun.

• Beam direction is controlled well within 1 mrad. (1 mrad corresponds to2% change in the SK flux at the peak energy, E n = 0.5 – 0.7 GeV)

• Secondary beam intensity (normalized by proton intensity)
is stable within 1% → reflects stability of targeting, horn focussing, etc

15

Neutrino Beam Monitoring (INGRID)••

Targeting efficiency of proton beam ~99%.
n Beam direction measured by INGRID
from 2010 Jan. ~ Jun.
– Horizontal:+0.01±0.05(stat.)±0.33(syst.) mrad
– Vertical : -0.24±0.05(stat.)±0.37(syst.) mrad
Beam axisn beam width~4.5m @ 280m
Stability: Vertical

Stability: Horizontal

Jan, 2010~~Feb, 2011Jan, 2010~~Feb, 201116

P (MeV/c)

P/range (MeV/c/cm)

Super-K Performancestop-m

RUN1m

RUN2e
Energy scale stability ischecked using cosmic
muon / decay-e

decay-e

RMS/Mean ~ 0.4% forboth samples during SK4

p0 mass
Reconstruction performance:
Energy scale:cosmic m/e, atm n p0
Ring-counting, PID, vertex :cosmic m, atm n data

Data
MCDataMC

decay-e
spectrum17

Observed Events at SK
Identify beam-induced events with GPSRun1• Transfer beam spill information in real time
• Compare GPS time stamps of beam/SK triggerFC:
all particle contained in ID
no activity in OD

LE: Low energy triggered eventsOD: Outer detector events
FC: Fully contained events(T2K Run1: 3.23x1019POT)

No off-bunchFC events

RMS 26 nsCuts

Fully
Contained(FC)Observed Expectedevents
BG

33

~0.01

23~0.001

FC
T0=SK trigger time
- beam trigger time

+ FV cut+ Evis > 30 MeV

1820

RUN1 OSCILLATION ANALYSIS(Mainly ne appearance)
19Analysis Strategy

confidence20Flux Prediction (Beam MC)
nmp+m+p(1) Hadron production byp+C interaction andsecondary interaction intarget is simulated using
FULKA framework.

* Pion production crosssection is corrected using
NA61 data.

NDSK

p+(2) Propagation of produces hadrons(p, K, etc) including Horn focusing issimulated using GEANT3 framework.

(3) n producing decay is simulated.
Geometrical acceptance is calculated.
 n flux obtained at ND & SK, respectively* Secondary interaction cross section
is corrected using existing data byother experiments.

ND MCSK MC* Measured protonparameters is assumed.

21

SHINE / NA61•

SHINE experiment (CERN NA61)– Data was taken in 2007 and 2009.
• p (30GeV) + C (target thin:2cm / thick: 90cm)– p production model in T2K-MC is corrected by NA61
preliminary results which was released in Dec. 2009.
– Systematic uncertainty

NA61
Default in T2K-MC• 10% : Inelastic p + C cross section• 20%: Pion multiplicity

MC(T2K):p+ produce nm @ SK

NA61 2007 data: p+22

ND280 Analysis
Use inclusive events with low level reconstruction
Track start from FGD, and dE/dx cut in TPC
 90% nm purity, 50% CCQETPC1

TPC2FGD1TPC3FGD223

ND280: Normalization DATA/MCPmcosqm# of CC inclusive m events

RData/ MC  1.061  0.028(stat.) +-00..044038( syst.)  0.039( phys.)
Uncertainty on Nexp:NDNSKSKN exp
 Data

NMCND
N MC

±2.7% by data statistics+5.6 % by ND efficiency & phys.
-5.224

ne Analysis: Signal and BGKSignal : nm  ne

BKG : Beam ne CC

BKG : Beam nm CC

BKG : NC p0 production

Dominant fraction in beam
 Powerful rejection by:– Muon PID– Tag delayed electron signal

Main events: ne CCQE Event selection– Single-ring e-like PID– No delayed signal from p, m
– En ~ 600 MeV

Small fraction (~1%) in beam
 But significant after reduction
 No pattern difference with signal
 Higher energy than signal– reduced by energy cut

p0  g + g mis-reconst. of 2nd g could be BKG
 Special p0 fitter to find 2nd gamma
 Reduced by p0 mass peak cut
25

ne Analysis: Selection Criteria
Basic neutrino selection
Fully contained events in inner detectorVisible energy > 30 MeV

Reconstructed vertex >2m from wall
ne selection

nm selection

Single Cherenkov Ring

Single Cherenkov Ring

Electron-like PID

Muon-like PID

Visible energy >100 MeV

Muon momentum > 200 MeV

No delayed electron signal
p0 invariant mass < 105 MeV
Reconst. n energy < 1250 MeV

Cut criteria fixed
before data open26

ne Analysis: Event Selection
Number of Rings

Particle ID

SignalBeam nmBeam neElectronPID

p0 mass cut

NC p0 events

Decay electrons

Rejection:
99% for nm
79% for ne
Reconst. neutrinoenergy

Acceptance:
68% for signal

27ne Analysis: Candidate Event

One electron candidate
remains after selection
Clean electron-like Cherenkov ring28

ne Analysis: MC Expectation and Syst. Error
CCQENC

SignalBackground
ne CC

Expected background
nm0.13anti-nm0.01

ne0.16Total

0.30 ± 0.07 (syst)

NC 95%

Signal + background (sin22q13=0.1)
Total

1.20 ± 0.22 (syst)

Syst. error ~24% (bkg only)~20% (sig+bkg)
29

ne Analysis: Muon PID systematics
Understanding BKG error is important for ne analysis
nm rejection by PID is studied with two method:cosmic-m(0.6-1.2GeV/c)decay-eData
MCe-likem

nm enriched
atm data(w/o PID)

PID likelihood parameter~99% rejection efficiency verified
30

ne Analysis: ne AcceptanceSingle ring selection : ne enhanced atm. n sample

Single-ring

requiring no decay electrons
 Compare selected /Multi-ring

rejected ratio btwn Data-MC

ne enriched
atm data

 Efficiency and syst. error

are confirmed

31

ne Analysis: p0 Rejection Efficiency
p0 is crucial backgroundfor ne searchp 0  g + g  electron-like Develop composite p0sample using:electron data + gamma MC Estimate p0 BKG error: 18%

Now we understand detector
uncertainties for ne analysis !
32

ne Analysis: Upper Limit on sin22q13
Oscillation analysis performed
using # of candidatesContours by statistical method B:

Calc probability to observe 1 ev
considering systematic error
Give q13 upper limit by two
statistical method:

90% C.L.

A. Feldman-Cousins
B. Classical one-sided limit

ABat m232, sin22q23,dcp 2.4x10-3eV2 ,1.0, 0.0)33

nm Analysis: Selection Criteria
Basic neutrino selection
Fully contained events in inner detector
Visible energy > 30 MeV

Reconstructed vertex >2m from wall
ne selection

nm selection

Single Cherenkov Ring

Single Cherenkov Ring

Electron-like PID

Muon-like PID

Visible energy >100 MeV

Muon momentum > 200 MeV

No delayed electron signal
p0 invariant mass < 105 MeV
Reconst. n energy < 1250 MeV

Cut criteria fixed
before data open34

nm Analysis: Result

Consistent with oscillated
Data
expectation
Oscillation analysis is on-going Expected w/ osc.
Expected w/o osc.
including Run2 data

# of Events86.3 ± 0.1 (syst)

22.8 ± 3.2 (syst)

m232, sin22q23 2.4x10-3eV2 ,1.0)35

Prospects in 2011
Collected 1.45 x 1020 POT until
Mar. 2011
CHOOZ limit

Data x 4.5 statistics increased

Possible analysis improvement:
Full proposal

Collected data
until Mar 2011

Syst. error reduction of beam flux using
external hadron data CCQE, spectrum measurements inND280
 ne spectrum analysis in oscillation
analysisWill go into unexplored q13 region36SummaryT2K experiment aims precision measurement for:nm disappearance (m232, q23) ne appearance (q13)Analysis with first half year data (3.23 x 1019POT) :8 nm events observed (consistent with oscillation)
 One ne candidate event observed for expectedbackground 0.30±0.07 (syst) events
 Give upper limit on sin22q13
1.45 x 1020 POT data collected until Mar. 2011


Analysis is ready, and still improving for maximum
sensitivity

37