New results from K2KNew results from K2K

Makoto Yoshida (IPNS, KEK)for the K2K collaboration

NuFACT02, July 4, 2002London, UK

K2K CollaborationK2K CollaborationHigh Energy Accelerator Research Organization(KEK)

Institute for Cosmic Ray Research(ICRR), University of TokyoKobe UniversityKyoto UniversityNiigata University

Okayama UniversityTokyo University of Science

Tohoku University

Chonnam National UniversityDongshin University

Korea UniversitySeoul National University

Boston UniversityUniversity of California, IrvineUniversity of Hawaii, Manoa

Massachusetts Institute of TechnologyState University of New York at Stony Brook

University of Washington at Seattle

Warsaw University Soltan Institute for 　 Nuclear Study

• Neutrino beam almost pure (98%) <E>~1.3GeV• Near detectors

Measure flux/spectrum• Far detector Super-Kamiokande (SK) 250 km far from KEK• disappearance and e appearance

K2K long baseline neutrino oscillation experiment

KEK beam line Beam monitor Near detectors

Kamioka•Super-K

250km250km

Neutrino oscillations in K2K

)/27.1(sin)2(sin1)( 222 ELmP

Spectrumdistortion

disappearance

K2K aims to observe• deficit in number of events• distortion of spectrum

after 250 km travel

Fixed to 250 km

prob

abili

ty

E=1.3 GeV

232 103,250 eVmkmL

Super-Kamiokande

39 m

41 m

• 50kton Water Cherenkov detector• 1000m underground• 22.5kton fiducial mass• Inner detector 11146 PMTs(20’’)• Outer detector 1885 PMTs(8’’)• Atmospheric B.G. against K2K ~10-5 events/day in beam spill (1.1s/2.2s)

Neutrino Beam Line @KEK

200m

12GeV PS1.1sec / 2.2sec beam spill6x1012 protons/spill

Pion monitor

p, after Horn

p+Al + Near neutrino detectors

Flux/spectrum

Near to Far flux ratio RFN

Double Horn 250kA x20

Muon Range

Detector

Near neutrino detectors

• 1kton water Cherenkov detector (1KT) same type as SK (25ton fiducial)• Fine Grained Detectors (FGD)

• Scintillation fiber tracker (SciFi) w/ water target (6ton fiducial)CCQE identification

• Lead glass calorimeter (LG) detect electrons from SciFi• Muon range detector (MRD) measure muon momentum

beam monitor (Fe, 330ton fiducial)

K2K Results in 2001

Tspill TSK

GPSsecμ3.1TOF0.2 SpillSK TTΔT

w/o pre-activity

p.e. >200

1.5s

500sec

5sec

T (sec)

Fully Contained eventsin Fiducial Volume (FCFV)

56 events observed 7.38.0

80 expected

in null oscillation case

Probability < 3%

Number of FCFV events (NSK)

What’s new

• Same data set as in last year

• spectrum at near site

• Oscillation analysis (NSK+ Shape)only NSK in last year

• Full error treatment

to include correlation

Far site• Total number events• Spectrum shape

Strategy

Near site• Number of neutrino events• muon distributions of neutrino events Fit for neutrino spectrum & interaction model

Near to Far extrapolationRFN(E)

Event categories for spectrum measurement at near site

1KT: single ring -like FCFV events (1RFGD: single track events

proton

p

proton

p

proton

p

p: muon momentum

: muon angle

FGD: QE-like 2-track events

FGD: nQE-like 2-track events

QE and nQE in SciFi 2track events

nQE-like QE-like

Water Target + Al(20%)Fiducial Mass : 6 tonE ~150MeVEvent Rate ~ 1/1000pulses

Fitting Method

Fitted (p) dist. of 1KT and FGD2=227 for 197 d.o.f. (90 from 1KT, 137 from FGD)

••

••

0- 0.5 GeV

0.5- 0.75GeV

0.75- 1.0GeV

E QE (MC) nQE(MC)

MC templates for neutrino spectrum (E) (8bin)and interaction model (QE/nQE)

Fitted (p) = weighted mean of MC templetes

Measured (p)

1KT distributions with fitted results

Reasonable fitted distribution

FGD distributions with fitted results

1-track

2-trackQE-like

2-tracknQE-like

CCQE (MC)

P

Good agreement for ALL sample

μμμN

2μμNrec

ν cosθpEm

2mEmE

proton

: muon angle

p: muon momentum

Reconstruct neutrino energy assuming CCQE

Use single-ring -like FCFV events (1R)

Neutrino spectrum reconstruction in SK

Oscillation analysisData Sets• For number of events (NSK) June ’99-July ’01

FCFV events (56 events)• For spectrum shape

Nov ’99-July ’011R events (29 events)

Method-1 Maximum Likelihood method

Normalization term

Nexp= 80.1+6.2-5.4

Shape term Constraint term for syst. parameter. (error matrices)

Ltot = Lnorm(f) Lshape(f) Lsyst(f)

Method-2 different treatment of syst. term. Generate many MC samples with syst. parm. changed within error.

Ltot = mean value for the MC samples

Allowed m2 by NSK and Shape only analysis

NSK and shape analysis indicate the same m2 region for sin22=1

Number of Events only

Spectrum Shape only

NSK+Shape

Merged analysis (NSK and Shape) to get allowed region.

K2K Allowed region (Shape+Norm)

1.5~3.9x10-3eV2

for sin22=1 @90%CL

Consistent with atm. resultcf. Atmospheric results m2=(1.6~3.9)x10-3 eV2

for sin22=1.0

Best fit oscillation parameter (sin22 , m2)method-1 method-2

Shape only (1.09, 3.0x10-3eV2) (1.05, 3.2x10-3eV2)NSK +Shape (1.03, 2.8x10-3eV2) (1.05, 2.7x10-3eV2)

Shape and NSK @ Best Fit

Best fit

normalized by area

method 1•NSK prediction =54 (obs 56)•KS test prob.(shape)= 79%

method 2•NSK 82%•shape 93%•NSK+shape 50%

Null oscillation

NSK and Shape are reasonable at best fit point

Null Oscillation Probability method-1 method-2

NSKonly 1.3% 0.7%Shape only 15.7% 14.3%NSK+Shape 0.7% 0.4%

Prob. for null oscillation case is less than 1%

Conclusion• Neutrino spectrum in K2K has been measured by usin

g near detectors• Oscillation analysis with number of events and spectr

um shape on June99 ~July01 data

• Analysis for NSK and for shape indicate consistent m2 region for sin22=1

• Analysis for NSK+Shape gives m2=1.5~3.9x10-3eV2

for sin22=1 @ 90%CL• Null oscillation probability is less than 1%

• Resume data taking this winter and make statistics 2 times more