Latest Results of K2Kjnusrv01.kek.jp/~kobayasi/talks/jps0009.pdf · Photo detector 20 PMTs 6 0 0 2...

58
Latest Results of K2K Contents 1. Introduction 2. Experimental Setup 3. Results 1. Observation at SK 2. Measurements @ KEK 3. Expected # of Events @ SK 4. Conclusion Takashi Kobayashi IPNS, KEK Sep. 23, 2000 JPS Meeting @ Niigata

Transcript of Latest Results of K2Kjnusrv01.kek.jp/~kobayasi/talks/jps0009.pdf · Photo detector 20 PMTs 6 0 0 2...

Page 1: Latest Results of K2Kjnusrv01.kek.jp/~kobayasi/talks/jps0009.pdf · Photo detector 20 PMTs 6 0 0 2 0 0 1 1 0 9 1 0 Top view Beam view Pion monitor Gas volume ... (SFT): SF sheets+water(6cm)

Latest Results of K2K

Contents1. Introduction2. Experimental Setup3. Results

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

4. Conclusion

Takashi KobayashiIPNS, KEK

Sep. 23, 2000JPS Meeting @ Niigata

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2

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

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3

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

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4

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)

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5

Experimental Setup

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6

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%)

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7

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)

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8

Bird’s Eye Neutrino Beam Line

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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 < 1km(4mr) @ SKNear/Far spectra differ

300m 300m

250km

250km

FD

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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

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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 protons

insensitive to pπ <2GeV (Eν<1GeV)

PMT array

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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

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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 chamber (MUC) : drift chamber+iron plates

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Event categories1kt Event

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

expect least syst. err. for SK exp’edFid. mass 50.3tonEvent selection: Qtot>1000p.e.~2events/100spill

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Fe Event

100 cm

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

Nvtx 0

Neutrino int. in MUC iron platesCC inclusive (insensitive to NC)Large area coverage (8m) profile(vtx dist.)Large mass (fid. mass=312 ton)

high rate (~5/100spill)

Good for neutrino dir. and int. monitor

8mbeam

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SFT event

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

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

Fid. mass = 4.9 tonEvent selection: matching SFT&MUC track1event/1000spill

Study neutrino interaction, e.g. σinelastic/σelastic

beam

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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

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Results

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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

)

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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∆∆∆∆

∆t of F.C. candidates

µsec

even

ts

10-1

1

10

10 2

10 3

-400 -200 0 200 400

µsec

even

ts

0

5

10

15

20

-4 -2 0 2 4

27 in fid. vol.

No Decay-e

HE Trig.Qtot cut

No act. in OD(fully contained)

Exp’edAtm ν BG<10-3 in1.5µs win.

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Typical SK Events

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Event POT Distribution

FC 22.5kt

POT vs events CT *1018 POT

even

ts

0

10

20

30

40

50

60

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5

Event rate 1.18/1018POTK-S prob.: 7%

fully contained, vertex in fiducial volume

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Vertex and Directionvertex position

vertex XY X cm

Y c

m

0 2 GeV

-1000

0

1000

-1000 0 1000

vertex position

vertex XZ X cm

Z cm beam direction

0 2 GeV

-2000

-1000

0

1000

2000

-1000 0 1000

fully contained

top view

side view

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Measurements @ KEK

• Beam Direction• Absolute neutrino flux• Spectrum extrapolation• Neutrino spectrum

– CC µ energy spectrum– CC µ angle

Stability of beam quality is of great impotance.(pi mon is not full-time det.)

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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)

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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.

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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

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Absolute neutrino fluxCount # of neutrino events in FDs

18.221.019.1Live POT(1018)2,953223k64kNFD

SFTFe1kt

Event rate stablity

Fe e

vent

s/5x

1012

POT

~5.5events/100spill

very stable

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Vertex dist. of 1kt events

2000/Jan-Mar

Agree with MC well.

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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

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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

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Pion Monitor Results

θπ

w1w2 w3w4 …..: :

: :

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νµ spectra from Pion Monitor Measurement

2

4

6x 1011

0 1 2 3 4 5

Pion monitorMC

1234

x 105

0 1 2 3 4 5

Pion monitorMC

Eν(GeV)

Φν

(/cm

/10

PO

T)2

21

FD

SK

Agree with MC very well.

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Flux Ratio from Pion Monitor

0

0.05

0.1

0.15

0.2

0.25

0.3x 10-5

0 1 2 3 4 5Eν (GeV)

far/

near

Pion monitor

MC

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!

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35

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 : ~64k

ktεεεε : 0.71 (detection eff. of 1kt)

kt

SKL

L : Live POT ratio (~1.2)

kt

SKM

M: Fiducial mass ratio

SKεεεε : 0.81 (detection eff. of SK)

(syst.) (stat.)2.03.40 7.46.4

exp +−±=SKN

events SFT from (tot.)0.40 :

events Fefrom (tot.)4.41:c.f.2.5

5.5-exp

2.66.4-

exp

+

+

=

=

SK

SK

NN

Consistent with each other.

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# of observed and expected events @ SK

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Systematic Error for NSK

1kt Fe SFT (SK expected) 7.4

6.43.40 +−

2.64.64.41 +

− 2.55.50.40 +

− ∆V/V 6% <2% 3% Multi event 3% Background 1% 1% Flux %3.1

%7.1+−

3% 3-4%

Detection Efficiency

3% 5%

NC/CC(±30%) %8.0%9.0

+−

6% 6%

Cross section 10% 3% ∆V/V(SK) 3% 3% 3% ∆R(Flux ratio) %6

%7+−

%6%7

+−

%7%9

+−

Total %10%11

+−

15% 13%

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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.

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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.

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µµµµ distributions in ννννµµµµ CC int.

0 12 34Pµ0

200400600ets/5ets

/0deg

θµ0 30 60

200400600

800

0

Data agree with MC fairly well.

Neutrino spectrum

SFT events

Need more detailed analysis of FD datato extract spectrum information.

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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: 27

• Observation is 2 σ σ σ σ smaller than expected.• Todo

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

• need more stat• need more study on FD data

νe appearance search

• Experiment will resume Jan. 2001

osc.) (w/o 3.40:Expected 7.46.4

+−

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予備

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Visible Energy Distribution

Evis F.C. 22.5kt

MeV

0

10

20

30

0 1000 2000 3000 4000 5000

Preliminary

need to estimate syst. err. in MC expect.

DataMC w/o osc.

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Reconstructed µmomentum

F.C. 1-ring µ-like MeV/c

0

2

4

6

8

10

0 1000 2000 3000 4000 5000

Preliminary

need to estimate syst. err. in MC expect.

DataMC w/o osc.

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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

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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

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47

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)

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Far/Near Spectrum ratio(MC)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 1 2 3 4 5Neutrino Energy (GeV)

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49

Event POT (All)

FC+OD events

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Event POT (FC all)

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51

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

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52

Systematic Error of Flux Ratio

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53

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

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54

Rate of 1kt eventsE

vent

Rat

e/10

PO

T14

1

0.5

0

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55

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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

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Vertex Dist. of SFT events

Horizontal

Vertical

Z(Beam dir.)

-100 100 (cm)0

-100 100 (cm)0

0 100 (cm)

Non neutrino (cosmic, µ from upstream, fake)BG : negligible

Agree well

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58

sin22θ=1

# of observed and expected events @ SK