1

Latest Results of K2K

Contents1. Introduction2. Experimental Setup3. Results

1. Observation at SK2. Measurements @ KEK3. Expected # of Events @ SK

4. Conclusion

Takashi KobayashiIPNS, KEK

2

Neutrino Oscillation

ilil V νννννννν ΣΣΣΣ=Neutrino Mixing

Weakeigenstates

Masseigenstates

Maki-Nakagawa-Sakata Matrix

⋅

−⋅

−⋅

−=

− δδδδiecs

sc

cssccs

scV

00010001

0010

0

00

001

10000

1313

1313

2323

23231212

1212

Oscillation Probability( ) ( )

( ) ( )∑<

→

−−⋅⋅−=

=

ji

ijljmjlimiml

lmml

LEm

iVVVV

tP

2exp1Re2

02

**

2

∆∆∆∆δδδδ

νννννννν

222 energy, neutrino: length,flight : jiij mmmEL −≡∆∆∆∆

Pl m≠δml ⇔ ∆mij ≠0

mass eigenvalues

3

Motivation

Neutrino Oscillation(2flavors))/27.1(sin2sin 222

ννννθθθθ ELmp ∆∆∆∆⋅=

Evidence of osc. in atm. ν observation by SK

K2K: Establish non zero neutrino masswell defined flight length (=250 km)well defined artificial pure ννννµµµµ beam

∆m2 = 2～5 x 10-3 eV2

sin22θ>0.88almost νµ ντ

99/12/1

νµ/νe

4x10-3～1GeV 250kmK2K0.5～5x10-4<5GeV10～104kmAtm ν

E/LEL

4

K2K Overview

•almost pure νµ(99%) beam w/ <Eν> ～　1.3GeV

•Far detector: Super Kamiokande(SK)@250km

•Most sensitive at ∆∆∆∆m2 ～～～～ 7x10-3 eV2

• νµ disappearance and νe appearance

5

Expected Signal

0

10

20

30

0 1 2 3

MC 1ring µ-like

nullsin22θ=1∆m2=0.01

Eν(GeV)0

10

20

30

0 1 2 3

MC 1ring µ-like

nullsin22θ=1∆m2=0.005

Eν(GeV)

0

10

20

30

0 1 2 3

MC 1ring µ-like

nullsin22θ=1∆m2=0.0028

Eν(GeV)0

10

20

30

0 1 2 3

MC 1ring µ-like

nullsin22θ=1∆m2=0.0015

Eν(GeV)

6

Sensitive Region

K2K νµ ντ oscillation sensitivity

10-4

10-3

10-2

10-1

0 0.2 0.4 0.6 0.8 1

22.5ktonFC1 ringµ-likeE

recν G500MeV

90%Y CL99%Y CL99.9%Y CL

sin22θ

∆m2 (e

V2 )

1020 POT (～5year)

7

Experimental Setup

8

Neutrino Beam Production

PS: 13GeV/c proton1.1µsec spill/2.2sec6x1012protons/spill (design)

Beam line: aligned toward SK using GPS(global positioning system)GPS< 0.01mrad, civil const<0.1mrad

Decay pipe: 200m

Pion Monitor

200m

p+Al ππππ++++ µµµµ+ + ννννµµµµe++νe+νµ(1%)

9

Target and Horns

0

2

4

6

8

0 1 2 3 4 E (GeV)ν

Neu

trin

o Fl

ux (a

rb. u

nit)

0kA

250kA

x20

(MC)

10

Bird’s Eye Neutrino Beam Line

11

Neutrino Spectra and Radial Distributions at

300m/250km (MC)

10 2 43 5E (GeV)ν

4

8

12x1010

10 2 43 5E (GeV)ν

2

4

6

8x104

0 4 8 12Radius (m)

0 1 2 3Radius (km)

x105

12

8

4

x1011

16

12

8

4

3mradSK

Almost const flux < 3mr(750m) @ SKNear/Far spectra differ

300m 300m

250km

250km

FD

12

Spectrum Distortion at Off axis (MC)

106

107

108

109

0 1 2 3 4 5Pν (GeV/c)

Neut

rino

flux i

n ar

bitra

ry u

nits

On axis flux

Off axis flux

13

Roles of Detectors in KEK

• Neutrino beam direction– Front neutrino detector (FD) (direct)– Muon monitor (indirect, fast)

• Absolute neutrino flux– FD

• Spectrum extrapolation from near(KEK) to far(250km)– Pion monitor

• Neutrino spectrum– FD– Pion monitor

• Study neutrino interaction– Future

Expected # of SK events

14

Pion Monitor

To decay volume

From 2nd Horn

910

Blind

Beam window

470

230

200

900

1 50

Focal

length

3464

mm

275

332

2100

2750

Sphericalmirror

Photo detector 20 PMTs

600

200

110

910

Top view

Beam view

Pion monitorGas volume

~ Design on May 11,'98 ~

190

2448

Purpose:Measure momentum and angular distribution of pions, N(pπ, θπ)

N(pπ, θπ) Neutrino flux Φ(Eν) at any distanceusing only decay kinematics

R(Eν)≡ΦSK(Eν)/ΦFD(Eν)as a result of pion monitor

Gas Cherenkov detector

to avoid signal from 12GeV protonsinsensitive to pπ <2GeV (Eν<1GeV)

PMT array

15

Muon Monitors

Behind beam dumpOnly sensitive to initially high energy µ

(>5.5GeV)

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

Segmented Ionization ChamberSilicon pad detector array

16

Front NeutrinoDetector(FD)

Purpose1. νµ absolute flux2. νµ directrion(profile)3. νe contamination

Fine Grained Detector

300m from target

1kt water Cherenkov detectorScintillation Fiber Tracker(SFT): SF sheets+water(6cm)Electromagnetic calorimeter : lead glassMuon rande detector (MRD) : drift chamber+iron plates

MRD

17

Neutrino Energy Reconstruction (GeV region)

Assume CC quasi elastic (CCqe) reaction

lllN

llN

pEmmEmE

θν cos22

+−−

=

νl + n → l + p

νννν

l-

p

(El , pl)θθθθl

Water Cherenkov 1ring µ-like sample

qe

inelastic

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5Eν (GeV)

ν µ c

ross

sec

tions

(10

cm)

-38

2

Inelastic

CCqe

Inelastic scattering w/ invisible pion(s) give wrong energy

18

Event categories1kt Event

H2O target (same as SK)Same detection principle as SK

expect least syst. err. for SK exp’edFid. mass 25tonEvent selection: Qtot>1000p.e.～2events/100spill

19

Fe Event

100 cm

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

Nvtx 0

Neutrino int. in MRD iron platesCC inclusive (insensitive to NC)Large area coverage (8m) profile(vtx dist.)Large mass high rate (～5/100spill)

Good for neutrino dir. and int. monitor

8mbeam

20

SFT event

Neutrino int. in SFT H2O target(+Al 20%)

Pos. resolution ~1mmwell defined fid. vol.multi track resolution

Fid. mass = 5.8tonEvent selection: matching SFT&MUC track1event/1000spill

Study neutrino interaction, e.g. σinelastic/σelastic

beam

21

Far Detector

• 1000m underground @ Kamioka• ~40mφ, ~40m high• 50,000t Pure water as target• 11146 PMTs in inner tank• 22.5kt Fiducial Volume• Outer detector (OD) :active VETO

Super-Kamiokande @Kamioka (250km from KEK)

22

StrategyFor now,1. count # of events @ SK

2. calc. expected # of events @ SK

obsSKN

SKFD

FDSK RNN εεεε

εεεε⋅⋅=

obsexp

3. compare expobs and SKSK NN

*eventually,…

use 1kt events as a referencecheck consistency btw. kt/Fe/SFT events

R: Near/far ratio from MC(guaranteed by Pi mon)

εεεε : detection efficiency

obsFDN :observed # of events in one of FDs

( ) ( )νννννννν E and E expobsSKSK NN

23

Results

24

Delivered Beam

Design Proton Int. 6x1012 protons/pulse

almost achieved (5.5x1012)～2.6x1019POT delivered by the end of Jun. ‘00

SK Live = 2.29x1019 POT(Jun99-Jun00)

Horn 200kATarget 2cmφ

Horn250kATarget3cmφ

π-mon

π-mon

0

2

4

6

Apr99 Jul99 Oct99 Jan00 Apr00 Jun00

Pro

tons

/Pul

se (1

0^12

)

Date

0

5

10

15

20

25

Acc

umul

ated

PO

T (1

0^18

)

25

K2K event selection in SK

1. No pre-activity in 30µsec2. p.e. in 300ns win.> 2003. OD Nhit in largetst cluster<104. Deposite Energy > 30MeV5. Fiducial cut (dist. from

wall>2m)

εεεε=79%(93% for CC)

26

SK EventsTspill TSK

GPS

TSpill, TSK: Abs. time of spill start, SK event measured with GPS

TOF: 0.83ms(Time of flight from KEK to Kamioka)

sec3.1TOF2.0 µµµµ≤−−≡≤− SpillSK TTT∆∆∆∆

Exp’ed Atm ν BG<10-3 in 1.5µs win.

110

102103

-500 -250 0 250 500

0

10

-5 0 5

5

∆Τ∆Τ∆Τ∆Τ(µs)

∆Τ∆Τ∆Τ∆Τ(µs)

28 observed.

>200p.e

no pre.act

27

GPS Time Stamping

1PPS-LTC

LTC freq-50MHz

counts

0

200

400

600

800

1000

1200

1400

x 10 3

-1200 -800 -400 0 400

200ns

GPS1pps

LTC(50MHz)

spillSKevent

GPS 1pps interpolated with local time clock(LTC

Stable within ~200ns

28

Typical SK Events

29

Vertex and Direction

fully contained

top view

side view

beam direction

0 2 GeV

x

y

beam direction

0 2 GeV

x

z

30

Measurements @ KEK

• Beam Direction• Rate• Spectrum Stability• Spectrum extrapolation• Neutrino spectrum

– CC µ energy spectrum– CC µ angle

Stability of beam quality is of great impotance.

31

Beam DirectionA

rb. u

nit Horizontal

x (cm)0 200 400-200-400

y (cm)0 200 400-200-400

Vertical

0

2000

4000

6000

8000

Vertex distribution of Fe events (Nov99)

Centered within sys. err. of 20cm (0.7mrad)

Fitted center x: 1±5cmy: －10±4cm from SK dir.

(stat)

32

Stability of Profile Center (Fe event)

-100-80-60-40-20

020406080

100

prof

ile c

ente

r x

integrated day (1 data point / 5 days)

-100-80-60-40-20

020406080

prof

ile c

ente

r y

integrated day (1 data point / 5 days)

1mrad

1mrad

1mrad

1mrad

Stable within ±±±±1mrad.

33

Stability of Muon Profile Center @ Muon Monitor

Fast (spill-by-spill) but indirect monitor

Stable within ±±±±1mrad

1mrad

1mrad

Jun‘99

Jun‘00

Nov‘99

Jan‘00

Feb‘00

Mar‘00

May‘00

34

Measurements of FDs

Event rate

Fe e

vent

s/5x

1012

POT

～5.5events/100spill

Stable.

35

Vertex dist. of 1kt events

2000/Jan-Mar

Agree with MC well.

36

Stability of Spectrum

99-Nov.00-Jan.00-Feb.00-Mar.00-May.00-June

0

0.2

0.4

0.6

0.8

1

Arb

. Uni

t

E (GeV)µ0 1 2 3

Muon Energy of Fe events

Stable within stat. error.

37

Stability of muon angle

00.1

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

99-Nov.00-Jan.00-Feb.00-Mar.00-May.00-June

θµ (deg.)

arbi

tary

uni

t Muon angle of Fe events

Stable within stat. error.

38

Pion Monitor Results

pπ

θπ

w1w2 w3w4 …..: :

: :

39

Pion Monitor Result

-5-4-3-2-1012345

2 3 4 5 6 7Pion momentum (GeV/c)

Pion

ang

le (*

10m

rad)

Relative Pion Distribution in pπ-θπ plane

beam axis

ππππ+θ

40

νµ spectra from Pion Monitor Measurement

Agree with MC very well.

41

Flux Ratio from Pion Monitor

R(Eνννν)=ΦΦΦΦSK(Eνννν)/ΦΦΦΦFD(Eνννν)

SKFD

FDSK RNN εεεε

εεεε⋅⋅=

obsexpFor integrated far/near ratio R in

use MC for central value

syst. error %6%7

+−=R∆∆∆∆ from Pi. mon.

(for 1kt)

Good Agreement!

0

0.1

0.2

0.3x 10-5

0 1 2 3Eν(GeV)

Far/

near

rat

io

Pion monitor

Neutrino Beam Simulation

Integratedabove 2.5GeV

42

Expected # of SK events from 1kt detector

SKkt

ktSK RNN εεεε

εεεε⋅⋅=

obsexp

( ) ( )( ) ( )∫

∫⋅

⋅⋅⋅=

dEEE

dEEE

MM

LLR

kt

SK

kt

SK

kt

SK

νννννννν

νννννννν

σσσσ

σσσσ

OH

OH

2

2

ΦΦΦΦ

ΦΦΦΦ

obsktN : 61585 (in 25t f.v.)

ktεεεε : 0.72 (detection eff. of 1kt)

kt

SKL

L : Live POT ratio (～1.2)

kt

SKM

M: Fiducial mass ratio

SKεεεε : 0.79 (detection eff. of SK)

(syst.) (stat.)2.08.37 5.38.3

exp +−±=SKN

events SFT from (tot.)2.37 :

events Fe from (tot.)0.41:c.f.6.4

5.0-exp

0.66.6-

exp

+

+

=

=

SK

SK

NN

Consistent with each other.

43

Systematic Error for NSK

(syst.) (stat.)2.08.37 5.38.3

exp +−±=SKN

1kt ∆V/V %4±

Multi Event %3±

Near/Far Ratio %67

+−

Spectrum(eff.) %2±

Total %910+−

SK(mainly ∆V/V) %3±

44

# of observed and expected events @ SK

45

Reconstructed Eνννν

MeV/c

0

2

4

6

8

10

0 1000 2000 3000 4000 5000

Fully contained 1-ring µ-like (22.5kt)

Preliminary

Need to estimate syst. err. in MC expect.

DataMC w/o osc.

46

Angle Distribution

cosθKEK 22.5kt 1-ring µ-like

cosθKEK

0

10

-1 -0.5 0 0.5 1

Preliminary

Need to estimate syst. err. in MC expect.

DataMC w/o osc.

47

Toward Spectrum Analysis

0 12 34Pµ0

200400600ets/5ets

/0deg

θµ0 30 60

200400600

800

0

Data agree with MC fairly well.

Need more detailed analysis of FD datato extract spectrum information.

Detailed Study of FD data needed.CCQE neutrino energy spectrum (GeV)

Data

MC CCQE spectrum

Neutrino Energy (GeV)

dN/d

E (1

/GeV

)

Pion Monitor

0

500

1000

1500

2000

2500

3000

0 1 2 3 4 5

48

Conclusions• Accumulated 2.29x1019POT @ SK from

Jun ’99 to Jun ’00.• Neutrino beam is well under control

Direction: always directed to SK within 1mradSpectrum: stable within stat. errorIntensity: stable within stat. errorPi mon proved MC spectra ratio

• # of fully contained events in fiducial volume @ SK

Observed: 28

• Deficit of 90% significance observed.• Todo

reduce systematic errors (∆V/V, σFe,….)spectrum analysis

• need more stat• need more study on FD data

νe appearance search

• Experiment resumed Jan. 2001

osc.) (w/o 8.37:Expected 5.38.3

+−

49

Expected Allowed Region

νµ ντ oscillation allowed region (MC)

10-4

10-3

10-2

10-1

0 0.5 1

sin22θ=1∆m2=0.01

10-4

10-3

10-2

10-1

0 0.5 1

sin22θ=1∆m2=0.005

10-4

10-3

10-2

10-1

0 0.5 1

sin22θ=1∆m2=0.0028

10-4

10-3

10-2

10-1

0 0.5 1

sin22θ=1∆m2=0.0015

sin 22 θsin 22 θ

∆m

(eV

)2

2∆

m (e

V)

22

1020 POT ～～～～ 5 years