Recent K2K ResultsTakanobu Ishii (KEK IPNS)

for the K2K collaboration

NOON2004 Feb.11-15Tokyo

K2K Collaboration• JAPAN: High Energy Accelerator Research Organization (KEK)

Institute for Cosmic Ray Research (ICRR), University of TokyoKobe University / Kyoto University

Niigata University / Okayama University Tokyo University of Science / Tohoku University

• KOREA: Chonnam National UniversityDongshin University / Korea University

Seoul National University• U.S.A.: Boston University / University of California, Irvine

University of Hawaii, ManoaMassachusetts Institute of Technology

State University of New York at Stony BrookUniversity of Washington at Seattle

• POLAND: Warsaw University / Solton Institute

Since 2002• JAPAN: Hiroshima University, Osaka University

• CANADA: TRIUMF / University of British Columbia• EUROPE: Rome / Saclay / Barcelona / Valencia / Geneva

• RUSSIA: INR-Moscow

Contents

1. Introduction2. Beam and Detectors3. Data accumulation (K2K-I + K2K-II)4. Oscillation analysis (K2K-I)5. Search for νe appearance (K2K-I)6. New near detector (SCIBAR)7. Summary

1. Introduction• K2K is the first accelerator-based long-baseline neutrino

oscillation experiment to investigate the neutrino oscillation observed in atmospheric neutrinos.

KKEKEK--12GeV PS12GeV PS

SuperSuper--KKamiokandeamiokande

~1%50 %νe /νµ

> 2・10-3 eV210-1 ~10-4eV2∆m2

~ 1.3GeV0.1~100GeVEν

250km(fix.)10~104kmL

K2KAtm.-ν

P(νµ→νX) =

sin22θ・ sin2(1.27∆m2L/EEνν)

L=250 kmL=250 km

•• Do Do ννµ µ events decrease ?events decrease ?•• Is Is EEνν spectrum distorted ?spectrum distorted ?

•• Does Does ννee appear ?appear ?

2. Beam and Detectors

PS: 12GeV proton1.1µsec spill/2.2sec6x1012protons/spill

P ion Monitor

200m

p+Al π+ µ+ + νµe++νe (1.3%) +νµ (0.5%)

Near Detectors

Pion Monitor

MuonMonitor

Neutrino Beam Production

Muon range detector

K2KK2K--II From Mar.1999 ~ Jul.2001Near neutrino detectorsNear neutrino detectors

39m

41.4

mSuperSuper--KamiokandeKamiokande II

Outer detector

Inner detector

1885 8” PMTs

11146 20” PMTs

K2KK2K--IIaIIaAfter the successful resume of the experiment After the successful resume of the experiment Dec.21,2002~Dec.21,2002~

SuperSuper--KamiokandeKamiokande IIIIInner detector

~5200 PMTs with FRP+Acrylic coverRemove Lead Glass detectorto explore lower energy region

ＮＮear neutrino detectorsear neutrino detectors

SciBar detector

K2KK2K--IIbIIbUpgraded near neutrino detectorsUpgraded near neutrino detectors

Oct.3,2003~Oct.3,2003~

Detectors

MRD

1KT

Delivered P.O.T. Delivered P.O.T. (since March 1999)

12/21

5~6x1012 (ppp)

1/16

10/76/23

1999 2000 2001

20032003

K2KK2K--II

20022002

K2KK2K--IIII12/23

8.4x10199.5x1019Total

1.3x10191.5x1019K2K-IIb(-Dec.’03)

2.3x10192.4x1019K2K-IIa

4.8x10195.6x1019K2K-I

AnalysisDelivered

3. Data Accumulation

Neutrino Direction Measured by MRDNeutrino direction isStable within 1 mrad.

99 2000 2001 2003

+- 1 mrad.

-100-80-60-40-20

020406080

100

prof

ile c

ente

r x

(cm

)

-100-80-60-40-20

020406080

prof

ile c

ente

r y

(cm

)

integrated day (1 data point / 5 days)

Neutrino flux MC

Spectrum Stability

Muon energy spectrum stability

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3

99Nov

00Jan

00Feb

00Mar

00May

00June

01Jan

01Feb

01Mar

01Apr

01May

01June

01July

03Jan

03Feb

03Mar

03apr

03May

03June

03Oct

03Nov

Eµ (GeV)

arbi

trar

y un

it

Muon angle distribution stability

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70 80 90

99Nov

00Jan

00Feb

00Mar

00May

00June

01Jan

01Feb

01Mar

01Apr

01May

01June

01July

03Jan

03Feb

03Mar

03apr

03May

03June

03Oct

03Nov

θµ (deg.)

arbi

trar

y un

it

Neutrino spectrum was measured by the Pion monitor at the beginning.Spectrum stability is confirmed by the measurements of energy and angle of muons produced in the CC interactions by MRD.

1

10

10 2

10 3

-500 -250 0 250 500

FC

∆(T) µs

even

ts

∆(T) µs

even

ts

0

5

10

15

20

-5 0 5

SK Event Selection

Tspill TSK

GPS

TSpill: Abs. time of spill startTSK: Abs. time of SK eventTOF: 0.83ms (KEK to Kamioka)

sec3.1TOF2.0 µ≤−−≡∆≤− SpillSK TTT

No Decay-eHE Trig.

FC: fully contained (No activity in Outer Detector) FV: 22.5kt Fiducial Volume

Expected Atm. ν BG ~2x10-3 within 1.5µs.

1.5µs

±500µsec

±5µsec

FCFV

72 events

Jun.’99 – Apr.’036.4 x 1019 proton on target

∆T (µsec)

K2K-I + part of K2K-II

Super-Kamiokande Events(Jun.1999~Apr.2003)

FC 22.5kt

POT vs events

KS probability = 64.3%

CT *1018 POT

even

ts

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60

K2KK2K--IIII+16events+16events

K2KK2K--II56events56events

ct diff

FC 22.5kt

mean slope = 1.14/1018POT

fitted slope = 1.17 ± 0.16/1018POT

log likelyhood

CT diff *1018 POT

10-3

10-2

10-1

1

10

0 0.5 1 1.5 2 2.5 3 3.5 4

Event-gap distribution

Spectrum Measurements @ ND

4. Oscillation Analysis (K2K-I)

• 1KT : Pµ<1.5GeV/c, 4π acceptance– 1-ring µ-like(1Rµ) fully contained

in Fid.25ton(FC) : 22,476ev.• SciFi : Pµ>1GeV/c, θµ<60deg.

– 1-track µ-like : 5963ev.– 2-track QE-like (∆θp<25deg.) : 764ev.– 2-track nonQE-like (∆θp>30deg.) : 1288ev.

• PIMON– π (p,θ) distribution ⇒ Neutrino Spectrum (>1GeV)

Fitting ParametersEν : 8 bins, nonQE/QE ratio

SciFi 2 track cos(∆ΘP) distribution

0

100

200

300

400

500

600

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Data

MC

(CCQE) <25o>30o

cos(∆ΘP)

ν

µ

Pexp.

Pobs.

∆ΘP

Published in PRL 90 (2003) 041801-1

Measured spectrum @ near site

Eν (GeV)

0

1000

2000

3000

0 0.5 1 1.5 2

0

1000

2000

3000

4000

5000

0 50 100 150

Data

MC

MC(QE)

(a)

Pµ [GeV/c]

even

ts / 0

.1 G

eV

/c

(b)

θµ [deg.]

even

ts / 1

0o

0

50

100

150

200

250

0 1 2 3

0

100

200

300

400

0 1 2 3

∆θp < 25o(c)

Pµ [GeV/c]

ev

en

ts /

0.2

5 G

eV

/c

∆θp > 30o(d)

Pµ [GeV/c]

ev

en

ts /

0.2

5 G

eV

/c

Eν spectrum1kt 1Rµ Scifi

2trkQE enriched

2trknQE enriched

Pµ (GeV/c)

Pµ (GeV/c)

Pµ (GeV/c)

Allowed region

Results of the Oscillation Analysis (K2KResults of the Oscillation Analysis (K2K--I)I)Use both Number of events + Spectrum shape

(June ’99 – July ’01) (Nov. ’99 – July ’01)

Null oscillation probability: less than 1%.∆m2=1.5~3.9 x 10-3 eV2 @sin22θ=1(90%CL)

68%90%99%

80.1+6.2-5.4 exp56obs⇔

0

1

2

3

4

5

6

7

8

9

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Eν

rec

Even

ts

Normalized by area

reconstructed Eν

Expectationw/o oscillation

Best FitBest fitpoint2.8x10-3

5. Search for νe Appearance in K2K-I

0

5

10

15

-10 0 10

0

5

10

15

-10 -5 0 5 10

PID (pattern)

(a)

PID (opening angle)

(b)

Fully contained – Single ring – e-like(ring pattern and opening angle)

Visible energy>100MeV – Without decay electrons

Ring pattern

Opening angle

To be submitted for publication

data

νµ MC

NC of νµ MCνe MC

Reduction Summary (νµ νe)DATA SET: June’99 – July’01 (4.8×1019POT)

16 18 18 20 28

signal νe MC (CC)sin22θµe=1 ,

∆m2=2.8x10-3eV2

2.0 2.6 2.9 50 80

νµ MC

0.35 1w/o decay-e

beam νe MCDATA

0.41 1Evis>100MeV

0.42 1PID (e-like)0.48 32Single ring0.82 56FCFV

NC:87% CC1π:7% CCmπ:4% CCQE:2%electron candidate: 1 event observed

2.4 events expected.

10-4

10-3

10-2

10-1

0 0.1 0.2 0.3 0.4 0.5

Results of νµ νe Analysis

sin22θµe

∆m2

(eV

2 )K2K(90%CL)

CHOOZ(90%CL)νe disappearance

SK atm.νallowed (90%CL)

6. New Near Detector (SciBar)

• Extruded scintillator with WLS fiber readout

• Neutrino target is scintillator itself• 2.5 x 1.3 x 300 cm3 cell• ~15000 channels• Light yield

7~20p.e./MIP/cm (2 MeV)• Detect 10 cm track• Distinguish proton from pion by

using dE/dxHigh 2-track CC-QE efficiencyLow non-QE backgrounds

ν

Extrudedscintillator(15t)

Multi-anodePMT (64 ch.)

Wave-lengthshifting fiber

EM calorimeter

1.7m

3m

3m

Just constructed in this summer!

SCIBAR Event DisplayRun 4999, Spill 19016, beam trigger

p

µ

CCQE candidate

3track event

SCIBAR is working well since October 2003

Photo-electrons of SciBar scintillators

Light Yield = 16.52±2.31 p.e./MIP/cm@ 40cm from PMT

(SciBar + MRD) track timing distribution

9-micro-bunch structure is observed

7. Summary•K2K-I data set has been analyzed.

•Reduction of νµ flux together with a distortion of the energy spectrum are observed.

•Probability of non-oscillation is less than 1%.•Oscillation parameters are consistent with those suggested by atmospheric neutrinos.

•Appearance of νe has been searched for.•One candidate event is found, which is consistentwith the background.

•Exclude region is set for the νµ νe oscillation.•K2K-II data taking is going on smoothly.

•Event rate is consistent with K2K-I.•New near detector SCIBAR is working well.•Low energy neutrino data is coming.

Supplement

Pion Monitor

Measure Momentum / Angle Dist.of π’s Just after Horn/Target

+Well known π Decay Kinematics+Well Defined Decay Volume Geometry

⇒PredictνμEnergy Spectrum at Near Site

Far Site

νμ Flux Ratio (Far/Near)as a Function of Neutrino Energy

Ring Image Gas Cherenkov Detector(Index of Refraction is Changeable)

To Avoid Severe Proton Beam Background,νμ Energy Information above 1GeV is Available(β of 12GeV Proton ~ β of 2GeV π)

Muon Monitor

Behind beam dumpsensitive to initially high energy µ (>5.5GeV)

Provide fast (spill-by-spill) monitoring of Intensity targeting/horn stabilityProfile beam direction

Segmented Ionization Chamber

Silicon Pad Detector Array

Muon Range Detector (MRD) as a Neutrino Beam Monitor

100 cm

Run 1244 Spill 20799 TRGID 1 99 6 22 17 48 56 0

Nvtx 0

Large area coverage Vertex DistributionMom. and Angle of Inclusiveμ

High Mass 329ton for r<3mHigh Statistics (~ 5/100pulses)

Good Neutrino Beam Monitor(Stability of Direction, Spectrum and Intensity)

Inclusive Muon

Event Vertex

Neutrino/Fe Charged Current(CC) InteractionFe /Drift tube Sandwich(Fe: 10cm×4＋20cm×8)

8m

ΔEμ=150MeV

Beam

Horn and Target System

×20 νFlux Enhancement(Above 500MeV)

Two-horn system operated with 250kA.

To get maximum π collection efficiency,target is embedded in the 1st horn.

1 2 3 4 E ν（GeV）0

Neu

trin

o In

tens

ity

250kA

0kA

0

Near Site νμ Spectrum

Inferred Neutrino Energy Spectrum at Far/Near by Pion Monitor

10 >2.521 (GeV)2 >2.5

Far to Nearνμ Flux Ratio

(GeV)

Simulation is Validated by Pion Monitor MeasurementEvaluation of Far/Near Uncertainty is Based on this Measurement

Pion MonitorSimulation

×10-5

0.1

0.2

0.3

0

Far Site νμ Spectrum0 >2.521 (GeV)

Beam Direction Measured by Muon MonitorMuon Center wasStable within 1 mrad.

99 2000 2001 2002-2003

+- 1 mrad.

Profile comparsion(2000:2001:2003)

Comparison(2000:2001:2003)

Energy spectrum Angle distribution

Allowed regions

Both indicate consistent ∆m2 region

10-4

10-3

10-2

0 0.2 0.4 0.6 0.8 1sin22θ

∆m2 (eV

2)

68%90%99%

10-1

%%

Total no. of Events only Spectrum Shape only

excl.

Comparison with the SK Result

10-4

10-3

10-2

10-1

0 0.2 0.4 0.6 0.8 1

sin22θ

∆m2 (

eV2 )

90%confidencelevel

K2K

SK

10-4

10-3

10-2

10-1

0 0.2 0.4 0.6 0.8 1

sin22θ

∆m2 (

eV2 )

Main Systematic Errors (νµ νe)

• Particle ID– shift likelihood distributions in MC

• +11%−11% in νµ BG• +7%−12% in νe appearance signal

• Ring Counting– shift likelihood distributions in MC

• +15%−13% in νµ BG– compare likelihood of atm.ν DATA

and MC• ±6% in νe appearance signal

• NC Cross Section– change NC cross section within

30%• +20%−25% in νµ BG

0

0.2

0.4

0.6

-20 0 20

K2K νµ MCFCFV elike+X

Evis>100MeVw/o decay-e

Single Ring

20-20

π0

multi-ring likelihood

-10

-5

0

5

10

-10 -5 0 5 10

νµ MC

angle PID

patte

rn P

ID

π0 in K2K-SK

2.0(1.7)

1νe

2.6(2.4)

2π0

80.1(7.7)

56FCFV

νµ MC(NC w/ π0)

DATA

π0 : FCFV & 2 e-like ring & 90<mass<190MeV & Evis>100MeV w/o decay-eνe : FCFV & 1 e-like(tight) ring & Evis>100MeV w/o decay-e

check for amount of π0 production

0

100

200

300

0 100 200 300

150MeV

Reconst. Mass = 119MeV

Reconst. Mass (MeV)

νµ MC

Expectation by νµ MCis consistent withobserved 2 events

K2K status• All detectors working stable. • Trying to update result till next May.• SK-II

– Calibration (PMT, energy scale, water parameter etc.) is on going. – Reconstruction algorithm is being corrected from SK-I.

• 1KT– NC π0 measurement– Improvement on calibration and PID.

• SciFi– Developing PID algorithm and improving tracking.– Study neutrino interaction such as MA and NC.

• MRD– Stability check using off-spill events.

νe appearance– Preparing paper. (Result already shown at a past PAC.)