K2K far detector analysis

NuFact04@Osaka2004/Aug/27

K2K far detector analysis

ICRR, Univ. of TokyoKenji Kaneyukifor the K2K collaboration

• oscillation analysis strategy• SK data• oscillation analysis• conclusion

NuFact04@Osaka2004/Aug/27

)27.1

(sin2sin.2

22

E

Lmprob

neutrino oscillation probability

atmospheric observation

zenith angle distribution : L dependence @ each energy

L =250km : fixed reduction of events spectrum distortion

E

K2K Long baseline experiment

NuFact04@Osaka2004/Aug/27K2K oscillation analysis strategy

number of eventsp, measurement

@ ND

flux, spectrum interaction

@ ND

flux, spectrumexpectation

@ SK

number of events reconstructed E

observation@ SK

ND

SK

Far/Near ratio

oscillation analysis(sin22,m2)

NuFact04@Osaka2004/Aug/27

measured flux @ ND (previous talk)– 1 ( E< 500) = 0.78 0.36– 2 ( 500 E < 750) = 1.01 0.09– 3 ( 750 E <1000) = 1.12 0.07– 4 (1500 E <2000) = 0.90 0.04– 5 (2000 E <2500) = 1.07 0.06– 5 (2500 E <3000) = 1.33 0.17– 6 (3000 E ) = 1.04 0.18– nQE/QE = 1.02 0.10

2=638.1 for 609 d.o.f

10-6

1.0 2.0

Far/Near flux ratio

beam MCconfirmed by PION monitor

E(GeV)

NuFact04@Osaka2004/Aug/27

Super-Kamiokande (Far detector on K2K)

39.3m

41.4m

50kt total volume22.5kt fiducial volume

20’PMT photocathode coverage SK-I 11,146 40%SK-II 5,182 19%

1000m underground

NuFact04@Osaka2004/Aug/27

Summary of SK-2 absolute energy calibration

various sources (decay-e, 0, low-energy , high energy ) are usedto estimate the energy uncertainty.data agree with MC within ±1.9%time variation : ±0.9%

total uncertainty : ±2.1%

NuFact04@Osaka2004/Aug/27event reconstruction on K2K-II

sub-GeVsub-GeV Evis>500MeV/c

likelihood distribution for ring counting likelihood distribution for PID

1-ring ≥2-ring

atmospheric dataMC exp.

w/ osc.

Likelihood distribution of atmospheric neutrino data agree with MC.(dis-agreements are taken into account to the systematic error.)

e-like -like

NuFact04@Osaka2004/Aug/27SK event selection

500sec

5sec

Decay electron cut.

20MeV Deposited Energy

No OD activity, fiducial volume,Evis 30MeV

TOF (0.83ms) cut using GPS

108 FC events in fiducial volume

1.6BG eventswithin 500msec

NuFact04@Osaka2004/Aug/27SK event summary

K2K-I+II

(K2K-I, K2K-II)

Data

(K2K-I, K2K-II)

MC

(K2K-I, K2K-II)

FC 108 (56, 52) 150.9 (79.1,71.8)

1ring 66 (32,34) 93.7 (48.6, 45.1)

-like

(for shape)

57 (30, 27)

(56 (29, 27))

84.8 (44.3, 40.5)

e-like 9 (2, 7) 8.8 (4.3, 4.5)

multi-ring 42 (24, 18) 57.2 (30.5, 26.7)

K2K-I(47.9×1018POT), K2K-II(41.2×1018POT)

NuFact04@Osaka2004/Aug/27K2K oscillation analysis

• Total Number of events

• Erec spectrum shape of FC-1ring- events

• Systematic error term

)(),2sin,(),2sin,(

),2sin,(22

2

xsyst

xshape

xnorm

x

fLfmLfmL

fmL

f x : Systematic error parameters

Poisson prob. for FC events

shape for Erec

for 1ring eventsystematic error

normalization, spectrum, nQE/QE, Far/Near, SK systematic uncertainty

NuFact04@Osaka2004/Aug/27Best fit

All parameter region(sin22, m2)=(1.53, 2.12x10-3)

In physical region(sin22, m2)=(1.00, 2.73x10-3)

logL=0.64

1.00

2.73

• NSKobs=108

• NSKexp (best fit)=104.8

shape : KS prob.=52%

Best fit expectation reproduce data well.

sin22≥1.53 can be occurred by statistical fluctuation with 14.4%.

data

oscillated expectation

w/o osc.

NuFact04@Osaka2004/Aug/27

- oscillation allowed region

best fit(sin22, m2)=(1.53, 2.12x10-3) (all)=(1.00, 2.73x10-3) (phys.)

1.7×10-3 ≤Δm2 ≤3.5×10-3 (90%C.L.) @ sin22=1.0

K2K-I+II 8.9x1019POT

NuFact04@Osaka2004/Aug/27

number of events v.s. E shape distortion

•

sin22sin22

m2[eV

2]

m2[eV

2]

number of events E shape

Oscillation analysis results based on number of events and the E spectrum distortion are consistent.

NuFact04@Osaka2004/Aug/27K2K-I vs K2K-II

K2K-I and K2K-II results are consistent.

K2K-I K2K-II

data

best fitoscillated expectation

w/o osc.

Erec

allowed region

NuFact04@Osaka2004/Aug/27

Oscillation analysis results based on neutrino interaction model (CC 1 re-weighted and no coherent )

oscillation results are robust to interaction assumption.

NuFact04@Osaka2004/Aug/27

- oscillation allowed region

K2K

SK-I 2flavor SK-I L/E

K2K result is consistent with SK-I results.

NuFact04@Osaka2004/Aug/27

Null oscillation probability (lnL)

K2K-I K2K-II K2K-I+II

number of events 2.0% 3.7% 0.33%(2.94)

E spectrum distortion 19.5% 5.4% 1.1% (2.53)

Combined 1.3%(2.48)

0.56%(2.77)

0.011%(3.86)

K2K confirmed neutrino oscillation discovered in Super-Kamiokande atmospheric neutrinos at 3.86.

Both number of events and E spectrum distortionare consistent with neutrino oscillation.

NuFact04@Osaka2004/Aug/27

ConclusionK2K confirmed neutrino oscillation at 3.86.

Both number of events and E spectrum distortionare consistent with neutrino oscillation. number of events 2.94 E spectrum distortion 2.53

Allowed region for dis-appearance is1.7×10-3 ≤Δm2 ≤3.5×10-3 (90%C.L.) @ sin22=1.0