E362 (K2K)
12 GeV PS review
June 7、2004

1. Physics goal
2. Experimental principle
3. Status
4. Run plan for fiscal 2004
5. Activities before T2K

Koichiro Nishikawa
for K2K collaboration
1Japan
KEK, ICRR, Kobe U, Kyoto U, Niigata U, Okayama U,
Tokyo U of Science, Tohoku U

Korea
Chonnam National U, Dongshin U, Korea U, Seoul National U

U.S.A.

Boston U, U of California (Irvine), U of Hawaii (Manoa), M. I.T.
S UNY at Stony Brook, U of Washington

PolandWarsaw U, Solton Institute for Nnuclear Study

New members since 2002
Hiroshima U., Osaka U.

CanadaTRIUMF, U. of British Columbia

EuropeU. of Barcelona, U. of Geneva, U. of Rome, Saclay, U. of Valencia,
Institute of Nuclear Study-Moscow

2

Brief history of K2K
••
•••
•

1995
– Proposed to study neutrino oscillation for atmospheric neutrino
anomaly.
1999– Started taking data.
2000– Detected the less number of neutrinos than the expectation at a distanceof 250 km. Disfavored null oscillation at the 2σ level.
2002– Observed indications of neutrino oscillation. The probability of nulloscillation is less than 1%.
2003– installed new detector (SciBar)
2004– Confirmed neutrino oscillation with both number of events and spectrum
distortion3– Detail will be presented at KEK seminar (June 9) and will be presentedat NEUTRINO04

Principle of K2K
Fixed distance, direction(Eν~1.3 GeV, L=250km)(99% νµ , στ<<σµ )22 1.27 Δmprob. = sin 2θ ⋅ sin (Eν2L)

Observations•Reduction of events•Spectrum distortion

Goal• Does νµ decrease ?
• Does it depend on Eν ?
• What is Δm2 ?
• (Is it consistent to sin2(1/Eν)?)Eν

4

Setup andNeutrino beam monitoring

5µ-monitor
Front (Near) Detector

direction (π → µ) pµ > 5 GeV
direction (ν) low E neutrinos
spectrum , rate

Bird’s Eye Neutrino Beam Line
12 GeV PS>5x1013 ppp
2.2sec/pulse

Target/Double Horn
~ 20 x flux

200m
100 m

6

1 Accelerator
Total Delivered POT
Jun 1999 - Feb. 15, 2004

101.12x1018POT

POT/spill= ~ 5.4x1012
Protons
1999

K2K thanks to the PS division for great accomplishments

20047Requirement from MC and muon monitor results(segmented ionization ch. + Si pads)
109

Center4mrad. off

108

107

106

±1 mrad.
105
01234Eν(GeV)

Neutrino (pion) direction has been controlled within 1 mrad

8

Near Detectors at KEK

kton water CMRD

SciBarAt 300 m from target
1. neutrino beam profile• massive MRD
2. νe contamination
3. rate in KT• same response as SK
for each interaction
4. spectrum• selection of CCQE
5. CCQE nonQE NC• PID (p ̲ π,µ)• Low energy particles
6. neutron backgrounds
9• good timing

MRD (419 ton fid.)
Fe & drift tubes
Run 1244 Spill 20799 TRGID 1
99 6 22 17 48 56 0Nvtx 08m•Profile widthbeam stability
during spill•Center of beam
within 1 mrad
Rateweekly basis•Stability ofEµ, θµmonthly basis

100 cm10Number of events

11

（April 1996 commissioned）

Super-Kamiokande
50,000 ton water Cherenkov detector(22.5 kton fiducial volume)

41.4m

Optically separated INNER and OUTER detector

40m

12

Selection of SK events : TSKGPS – TaccGPS -TOF

No activity
in outer SK

FC 22.5kt

56 events

HE trig.

FC 22.5kt

52 events13

Number of Events vs POT

14

K2K-SK events
K2K-all(K2K-I, K2K-II)
FC 22.5kt
1ringfor Eνrecµ-likee-like
Multi Ring

DATA
(K2K-I, K2K-II)

MC(K2K-I, K2K-II)

108(56, 52)
66(32, 34)
57(30, 27)9(2, 7)42(24, 18)150.9(79.1, 71.8)
93.7(48.6, 45.1 )
84.8(44.3, 40.5)
8.8(4.3, 4.5)
57.2
(30.5, 26.7)
15

Ref; K2K-I(47.91018POT), K2K-II(41.21018POT)Neutrino spectrum and the far/near ratioν beam250km

νµ energy spectrum@ K2K near detector

Far/Near Ratio
beam MC w/PION Monitor

10-6Eν (GeV)

1.0

2.0Eν (GeV)

16

1KT Flux measurement•The same detector technology as Super-K.
(same response for each interaction)• Sensitive to low energy neutrinos.

expobs
NSK = N KT •∫ ΦSK (E ν )σ(E ν )dE ν • MSK • εSK
M
ε
Φ
(E)
σ(E)
dEKT
KTKTν
ν
ν
∫
≡Far/Near Ratio (by MC)~110-6

M: Fiducial mass MSK=22,500ton, MKT=25ton
ε: efficiency εSK-I(II)=77.0(78.2)%, εKT=74.5%

NSK

expect=150.9 +10.3- 9.1

NSKobs=10817

Spectrum measurement

18NEUT: K2K Neutrino interaction MC••

CC quasi elastic (CCQE)– Llewellyn Smith’s with MA=1.1GeV
CC (resonance) single π(CC-1π)•– Rein and Sehgal’s with MA=1.1GeV
DIS– GRV94 + JETSET with Bodek andYang correction.
CC coherent π•– Rein&Sehgal with the cross section
rescale by J. MarteauNC•

σ/E (10-38cm2/GeV)
Total (NC+CC)
CC Total
CC quasi-elasticDIS
CC single π
NC single π0with Nuclear EffectEν (GeV)
19

Eν reconstruction
 1.27 Δm 2 ⋅ L 
P = sin 2θ ⋅ sin
Eν

2

νµ + n → µ + pµθ-p,n no signal in W-C
Ehad measurement!

 CC QE (1Rµ in W-Cherenkov)
can reconstruct Eν ←(θµ,pµ)(Eµ, pµ)µνpνµ + n → µ + p + π

θµ

ν

π’s p

νµ + n → ν + p + π’s
νπ’s pE ν rec =µm N E µ − m µ2 2m N − E µ + p µ cos θ µ-(Eµ, pµ)ν CC nQE
Bkg. for Eν measurement NC

20

Oscillation analysis
1.

Obtain Eν flux and spectrum shape just after production φ KEK(Eν)

Events =∑ σi × F(E ν ) × εi (E ν ) Int. Modeli = QE, nonQE, NC
2.
3.

σ(CCQE), σ(1π), NC ratios known to ~30% 1KT to predict NSK
Extrapolate from near to far without oscillation φSK(Eν)
φ SK(Eν) ⊗ Oscillation (sin22θ,Δm2) ⊗ Int. Model

Prediction
NSK(exp’t) : Expected no. of SK events
SSK(Erec) :1Rµ Erecdistribution(shape)

SK observation
NSK(obs)
1Rµ Erec distribution

Maximum Likelihood Fit in (sin22θ, Δm2)

21

QE and nQE seperation in SciFinQElike

22QElikeeretrimloca

Extrudedscintillator
(15t)

3m

ν
Multi-anode
PMT (64 ch.)3m

• Extruded scintillator with
WLS fiber readout• No dead material• 2.5 x 1.3 x 300 cm3 cell• ~15000 channels• Light yield
7~20p.e./MIP/cm (2 MeV)
• Detect 10 cm track• Proton ID by using dE/dx
High CC-QE efficiency
Low non-QE backgrounds

π0, Ee measurement
EMSciBar Detector
start taking data Oct. 7, 2003

1.7mWave-length
shifting fiber
23

SciBar neutrino interaction study.
• Full Active Fine-Grained detector.
– Sensitive to a low momentum track.
– Identify CCQE events and other interactions (non-QE) separately.

CCQE Candidate

ν

CCQEp

non-QE

DATA
CC QE
CC 1π
CC coherent-π
CC multi-πµΔθp

µ25°

Δθp

24

Used data for φnear(Eν)
KT
Fully Contained Fiducial
Volume (FCFV) events• No. of events(Evis>100MeV)(1)Single µ−like events

SciFi(2) 1-track µ events(3) 2-track QE-like events(4) 2-track nonQE-like events
SciBar(5) 1-track m events(6) 2-track QE-like events(7) 2-track nonQE-like events

norm. (NSK ) from KT & 7 sets of (pµ, θµ) distributions• ν flux φnear(Eν) (8 bins)• ν interaction model (nQE/QE ratio as parameter) 25

Actual Procedure(pµ,θµ) → φ(Eν), nQE/QE

DATA

Eν

QE (MC)nQE(MC)MC templates

0-0.5 GeV

0.5-0.75GeV

0.75-1.0GeV

1.0-1.5GeV

eight 2-dimensional hist’sχ2 =638.1 for 609 d.o.f.

••• 26•

Flux measurements
χ2=638.1 for 609 d.o.f––––––––

Φ1 (Eν < 500) = 0.78 ± 0.36
Φ2 ( 500≤ Eν < 750) = 1.01 ± 0.09
Φ3 ( 750≤ Eν <1000) = 1.12 ± 0.07
Φ4 (1500≤ Eν <2000) = 0.90 ± 0.04
Φ5 (2000≤ Eν <2500) = 1.07 ± 0.06
Φ5 (2500≤ Eν <3000) = 1.33 ± 0.17
Φ6 (3000≤ Eν) = 1.04 ± 0.18
nQE/QE= 1.02 ± 0.10
The nQE/QE error is assigned based on thevariation by the fit condition.
∀ θ>10° cut: nQE/QE=0.95 ±0.04• standard(CC-1π low q2 corr.):
nQE/QE=1.02 ±0.03• No coherent: π=nQE/QE=1.06 ±0.03
27

SciBar (with measured flux)(also for KT,SciFi)
θµ 1trkPµ 1trkflux measurementPµ 2trk QE

θµ 2trk QE

Pµ 2trk nQE

θµ 2trk nQE

28

10

Observed spectrum shape andnull oscillation prediction

Null oscillation normalized byobserved number of events

29

Other Physics in K2K (based on K2K-I data)
νµ +H2O→NC1π0Δm2[eV2]νµ→νe search

Mγγ(MeV)σ (ν µ → NC1π )= 0.065 ± 0.001( stat.) ± 0.007( sys.)σ (ν µ → CCall )=0.064 (MC prediction)
0preliminary

90%CL limit
90%CL sensitivity

sin22θµe

PRL accepted30

Near future
1. Systematic errors– Far Near ratio+5.6 -7.3%• π production measurements should be available soon
–NSK from 1kton detector 5% (fiducial)

Run plan for 2004•••

More data in SciBar (Proton ID, low-E track)~20,000 total events (1,500 CCQE <1 GeV ) ~4 months
Determine neutrino interaction model– Can use 2 ring events in SK( in addtion to 1Rµ like events) almost double
the statistics– SciBar can determine normalization with small fid. error、and spectrum
Low energy neutrino interaction studies– determine background in low Erec
– ………
Anti neutrino (engineering run)
31

Status of proton ID in SciBar
Total dE (MIPs)

Range vs Total deposit energy
DATAdE/dx distribution

Proton-like(2track QE sample)

Mu-like(MRD3D)

P/π identification is performed using dE/dx info. Range in SciBar (cm)32

Spectrum measurement at low energy
w/ exclusive reconstruction
Currently total ~1250 CC-QE candidates
with ~70% purity+ short track( /wo MRD)
+ proton ID

CCQE
w/MRD

*Efficiency for low-energy events will be improved (x 2)33
x2 more data ~200 events <1GeV→ ~1000 events

More data in SciBar

Level of nonQE
background tolow Eνrec ?

34

A hint of K2K forward µ deficit.
K2K observed forward µ deficit.
– A source is non-QE events.
– For CC-1π,• Suppression of ~q2/0.1[GeV2]
at q2<0.1[GeV2] may exist.
– For CC-coherent π,• The coherent π may not exist.
We do not identify which process causes
the effect. The MC CC-1π (coherent π)model is corrected phenomelogically.
Oscillation analysis is insensitive to thechoice.

q2 Preliminary
DATA
CC 1π
CC coherent-π

q2 (GeV/c)2(Data-MC)/MCSciBar
non-QE Events
35

Anti-neutrinos••••

On paper, just flipping the polarity ofhorn.
Need actual testing
Geomagnetic effect to the beam
Scibar– ~400 int / 10days / 10tonMRD– ~15,000 int/ 10days/ 419 ton– Error in– Beam center: 7cm–width : 10cm

36

Activities before T2K
Fiscal yr
K2K data taking

2004

2005

2006

2007

2008

Full paper onoscillation incl. νeAnalysis of neutrinointeractions
SK full rebuild
SK analysis tool
T2K construction
and commissioning?

37

Summary• K2K Oscillation analysis on June 99 ~Feb 04 data
1. Long baseline experimental method is working well
2. We observed νµ deficiency and spectrum distortion over 250
km flight length
3. sin22θ, Δm2 are consistent with atmospheric neutrino results
For detail please attend the KEK seminar day after tomorrow• In 2004, at least 6 months run can improve the quality of K2K• More data in SciBar (at least four more months) can further
improve statistical significance of K2K results• More measurement of low energy neutrino interactions can bedone38