Transcript スライド 1

June 10th, 2004
@Kyoto U.
M. Yokoyama (Kyoto University)
for K2K collaboration
1
1. Introduction
K2K experiment
since 1999
First accelerator-based long baseline (250km) neutrino experiment.
Search for nm disappearance and ne appearance
250km
Pure nm beam (99%)
w/ <En>~1.3GeV
50 kton Water
Cherenkov detector
12GeV PS
nm beamline
Beam monitor
Near detector



2
Flavor mixing in lepton sector

Flavor eigenstates ≠ mass eigenstates
ne
nm
nt
m1
m2
m3
Sij:sinqij, Cij;cosqij
Parameters: 3 mixing angle (q12,q23,q13)
1 complex phase (d)
3
Neutrino Oscillation

Time evolution of neutrino

Consider mixing b/w two flavors
Consider neutrino generated as pure nm(cosq|n2>sinq|n3>)
22
im
im t /4 p
im
3 t /4 p
3
n ,t
,0  cos q e
n 2  sinq ee
n3
2
2
m
If m2≠m3 , n is in mixed state after time evolution!

2
P  n n ,t
m m
2

Dm
L(km) 
2
2
1 sin 2qsin 1.27 2

eV E(GeV) 


If there is neutrino oscillation →Dm2≠0
→m≠0!
4
Super-Kamiokande atmospheric n
1.3x10-3<Dm2<3.0x10-3eV2
(@ sin22q=1, 90% CL)
nm→nt oscillation?
5
Brief history of K2K





1995
 Proposed to study neutrino oscillation for atmospheric
neutrinos anomaly.
1999
 Started taking data.
2000
 Detected the less number of neutrinos than the expectation
at a distance of 250 km. Disfavored null oscillation at the 2s
level.
2002
 Observed indications of neutrino oscillation. The probability
of null oscillation is less than 1%.
2004

This result!
6
K2K Collaboration
JAPAN: High Energy Accelerator Research Organization (KEK) / Institute for Cosmic Ray
Research (ICRR), Univ. of Tokyo / Kobe University / Kyoto University / Niigata University
/ Okayama University / Tokyo University of Science / Tohoku University
KOREA: Chonnam National University / Dongshin University / Korea University / Seoul National
University
U.S.A.: Boston University / University of California, Irvine / University of Hawaii, Manoa /
Massachusetts Institute of Technology / State University of New York at Stony Brook / University
of Washington at Seattle
POLAND: Warsaw University / Solton Institute
Since 2002
JAPAN: Hiroshima University / Osaka University
CANADA: TRIUMF / University of British Columbia
Italy: Rome France: Saclay Spain: Barcelona / Valencia Switzerland: Geneva
RUSSIA: INR-Moscow
7
2. K2K experiment overview
~1011 nm/2.2sec
(/10m10m)
12GeV protons
p+
p monitor
10
200m
decay pipe
SK nt
100m
mmonitor
~250km
Near n detectors
2
1
.
27
D
m
L
prob.  sin2 2q  sin2 (
)
En
x10
n Energy
4
（ＭＣ）
12
~106 nm/2.2sec
nm (/40m40m)
m
Target+Horn
x10
~1 event/2days
250km
（ＭＣ）
no oscillation
8
6
8
4
Extrapolation
p monitor + simulation
4
0
1
2
3
4
E n (Ge V)
5
Near detectors at KEK
oscillation
2
0
1
2
3
4
E n (Ge V)
Super-K
5
8
Neutrino beamline @ KEK
Bird’s Eye Neutrino Beam Line
200m
100 m
9
Neutrino beam and the directional control
X center
~1GeV neutrino beam by a dual horn system
with 250kA.
Y center

99 Jun
The beam direction
monitored by muons
≤1 mrad
<1mrad
~5 years
04 10
Feb
protons/pulse Accumulated POT
(×1018)
(×1012)
Accumulated POT (Protons On Target)
8.9×1019 POT for Analysis
(previous results: 4.8 ×1019 POT)
Jan 99
K2K-II
K2K-I
Jan 00
Jan 01
Jan 02
Jan 03
Jan 04
11
Near detector system at KEK





1KT Water Cherenkov Detector (1KT)
Scintillating-fiber/Water sandwich Detector (SciFi)
Lead Glass calorimeter (LG) before 2002
Scintillator Bar Detector (SciBar) from 2003
Muon Range Detector (MRD)
Muon range detector
12
SciBar Detector
Full-active, fine-segment Extruded
scintillator
detector made of
Scintillator Bars
(15t)







n
2.5x1.3x300cm3 cell
~15000 channels
Multi-anode
WLS fiber+MAPMT readout
PMT (64 ch.)
3m

Detect short (~10cm) track
p/p separation using dE/dx
Precise n spectrum
measurement
n interaction study
1.7m
Wave-length
shifting fiber
13
Detector Photos
Scintillators (64layers)
EM calorimeter
Fibers and front-end elec.14
Just Completed!
Aug. 22, 2003
Far detector : Super-Kamiokande
 1996.4
Start data taking (SK- I)
C Scientific American
 1999
SK- I
K2K
start
Water Cherenkov
detector
 1000 m underground
 50,000 ton
(22,500 ton fid.)
 11,146 20 inch PMTs
 1,885 anti-counter PMTs
n
42m
~5years
39m
SK- II
K2K-II
 2001.7 Stop data taking for detector upgrade
 2001.11 Accident (~7000 inner PMTs, 1100 outer PMTs were destroyed)
partial reconstruction of the detector
 2002.10 resume data taking (SK- II)
 2002.12 resume K2K beam (K2K-II)
16
SK is back !
Full water on 10-Dec.-2002
Jan.-2003, fully contained event
Acrylic + FRP
vessel
Sep.-2002, before water filling
17
GPS
SK Events
Tspill
SK
TOF=0.83msec
TSK
Decay electron cut.
500msec
20MeV Deposited Energy
No Activity in Outer Detector
Event Vertex in Fiducial Volume
More than 30MeV Deposited Energy
5msec Analysis Time Window
108 events
(K2K-1:56)
-0.2<TSK-Tspill-TOF<1.3msec
(BG: 1.6 events within 500ms
2.4×10-3 events in 1.5ms)
TDIFF. (ms)
18
3. Analysis Overview
KEK
Observation
#n, pm and qm
Measurement
F(En), n int.
n interaction MC
Far/Near Ratio
(beam MC with p mon.)
SK
Observation
#n and Enrec.
(sin22q, Dm2)
Expectation
#n and Enrec.
19
4. Near Detector measurements

Event rate measurement (#of nint.)



Measurement w/ 1KT
Cross-checked by other detectors
Spectrum shape measurement


1KT, SciFi, SciBar (pm, qm)
Measure spectrum and nQE/QE (n interaction
model)
Predict number of event and spectrum
shape at SK
20
Neutrino Interaction @~1 GeV
&
En reconstruction
-
nm + n → m + p
n
m
(Em, pm)
qm
p
-
nm + n → m + p + p
qm
n
m
(Em, pm)
nm + n → n + p + p’s
n
p’s p
m N  E m  p m cosq m

CC QE
 ~100% efficiency for NSK
 can reconstruct En(qm,pm)

CC nQE (1pi, multi-pi, coherent,DIS)
 ~100% efficiency for NSK
 Bkg. for En measurement
NC
 ~40% efficiency for NSK

p’s p
E n rec 
m N E m  m m2 2
s/E (10-38cm2/GeV)
n
1
Total (NC+CC)
CC Total
CC quasi-elastic
DIS
CC single p
NC single p0
5
21
4.1 Event rate measurement @1KT


The same detector technology as Super-K.
Sensitive to low energy neutrinos.
N
exp
SK
N
obs
KT
F


F
( En )s ( En )dEn
M SK  SK


M KT  KT
SK ( En )s ( En ) dEn
SK
Far/Near Ratio (by MC)~1×10-6
M: Fiducial mass MSK=22,500ton, MKT=25ton
: efficiency SK-I(II)=77.0(78.2)%, KT=74.5%
+11.6
exp
NSK =150.9 -10.0
NSKobs=108
22
4.2 Measurement with SciBar

Full Active Fine-Grained detector (target: CH).


Sensitive to a low momentum track.
Identify CCQE events and other interactions (non-QE)
separately.
CCQE Candidate
n
CCQE
p
non-QE
DATA
CC QE
CC 1p
CC coherent-p
CC multi-p
m
Dqp
2 track events
p
m
25
Dqp (degree)
23
4.3 Near Detector Spectrum Measurements

1KT


SciBar


Fully Contained 1 ring m (FC1Rm) sample.
1 track, 2 track QE (Dqp≤25), 2 track nQE
(Dqp>25) where one track is m.
SciFi

1 track, 2 track QE (Dqp≤25), 2 track nQE
(Dqp>30) where one track is m.
24
A hint of K2K forward m deficit.
K2K observed forward m deficit.



A source is non-QE events.
For CC-1p,
 Suppression of ~q2/0.1[GeV2] at
q2<0.1[GeV2] may exist.
For CC-coherent p,
 The coherent pmay not exist.
We do not identify which process
causes the effect. The MC CC-1p
(coherent p) model is corrected
phenomenologically.
Oscillation analysis is insensitive to the
choice.
q2rec
Preliminary
DATA
CC 1p
CC coherent-p
q2rec (GeV/c)2
(Data-MC)/MC
SciBar
non-QE Events
25
q2rec (GeV/c)2
4.4 Near Detectors combined measurements
(pm,qm) for 1track, 2trackQE and 2track nQE samples
 F(En), nQE/QE


Fitting parameters
 F(En), nQE/QE ratio

Detector uncertainties on the energy scale and the track
counting efficiency.

The change of track counting efficiency by nuclear effect
uncertainties; proton re-scattering and p interactions in a
nucleus …
Strategy
① Measure F(En) in the more relevant region of qm20 for 1KT
and qm10 for SciFi and SciBar.
② Apply a low q2 correction factor to the CC-1p model (or
coherent p).
③ Measure nQE/QE ratio for the entire qm range.
26
qm (MeV/c)
En
KT data
QE (MC)
nQE(MC)
MC templates
0-0.5 GeV
0.5-0.75GeV
0.75-1.0GeV
Pm (MeV/c)
• n flux FKEK(En) (8 bins)
• n interaction (nQE/QE)
1.0-1.5GeV
•
•
•
•
27
Flux measurements
c2=638.1 for 609 d.o.f








F(En) at KEK
preliminary
F1 (
En< 500) = 0.78  0.36
F2 ( 500 En < 750) = 1.01  0.09
F3 ( 750 En <1000) = 1.12  0.07
F4 (1500 En <2000) = 0.90  0.04
F5 (2000 En <2500) = 1.07  0.06
F5 (2500 En <3000) = 1.33  0.17
F6 (3000 En
) = 1.04  0.18
nQE/QE
= 1.02  0.10
The nQE/QE error of 10% is assigned
based on the variation by the fit
condition.
 q>10(20 ) cut:
nQE/QE=0.95 0.04
 standard(CC-1p low q2 corr.):
nQE/QE=1.02 0.03
 No coherent: p=nQE/QE=1.06 0.03
En
28
1KT: m momentum and angular distributions.
with measured spectrum
0
800
pm (MeV/c)
1600
0
qm (deg.)
90
29
SciFi (K2K-IIa with measured spectrum)
qm 1trk
Pm 1trk
Pm 2trk
QE
qm 2trk
QE
Pm 2trk
non-QE
qm 2trk
non-QE
30
0
2
(GeV/c)
0
40
(degree)
SciBar (with measured spectrum)
Pm 1trk
Pm 2trk QE
Pm 2trk nQE
qm 1trk
qm 2trk QE
qm 2trk nQE
31
5. Super-K oscillation analysis



Total Number of events
Enrec spectrum shape of FC-1ring-m events
Systematic error term
L(Dm 2 , sin 2q , f x )
 Lnorm (Dm 2 , sin 2q , f x )  Lshape (Dm 2 , sin 2q , f x )  Lsyst ( f x )
f x : Systematic error parameters
Normalization, Flux, and nQE/QE ratio are in fx
Near Detector measurements, Pion Monitor
constraint, beam MC estimation, and SuperK systematic uncertainties.
32
K2K-SK events
K2K-alll
(K2K-I, K2K-II)
FC 22.5kt
1ring
m-like
for Enrec
e-like
Multi Ring
DATA
(K2K-I, K2K-II)
108
(56, 52)
66
(32, 34)
57 (56)
(30, 27)
9
(2, 7)
42
(24, 18)
preliminary
MC
(K2K-I, K2K-II)
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)
Ref; K2K-I(47.9×1018POT), K2K-II(41.2×1018POT)
33
Lnorm (Dm , sin 2q , f )
2
x
Lshape(Dm , sin 2q , f )
2
x
KS probability=0.11%
#SK Events
Toy MC
Expected shape
(No Oscillation)
CC-QE assumption
108
150.9
En
rec

Enrec[GeV]
(mN  V ) Em  mm2 2  mNV  V 2 2
(mN  V )  Em  pm cosq m
34
V: Nuclear potential
6. Results

Best fit values.
 sin22q1.53
 Dm2 [eV2] = 2.1210-3
Best fit values in the physical region.
 sin22q1.00
A toy MC
 Dm2 [eV2] = 2.7310-3
Dm2

preliminary
14.4%
DlogL=0.64
2.73
sin22q=1.53 can occur by statistical
fluctuation with 14.4% probability.
1.00 1.53
sin3522q
Dm2[eV2]
Data are consistent with the oscillation.

preliminary

NSKobs=108
NSKexp (best fit)=104.8
Best Fit
KS prob.=52%
Based on DlnL
sin22q
Enrec[GeV]
36
nm disappearance versus En shape distortion
En shape
NSK (#nm)
Dm2[eV2]
Dm2[eV2]

sin22q
Both disappearance of nm and the distortion of
En spectrum have the consistent result.
sin22q
37
Null oscillation probability
preliminary
The null oscillation probabilities are calculated based on DlnL.
K2K-I
nm disappearance
En spectrum
distortion
Combined
K2K-II
K2K-all
2.0%
3.7%
0.33%(2.9s)
19.5%
5.4%
1.1% (2.5s)
1.3%
0.56%
0.011%
(2.5s)
(2.8s)
(3.9s)
Disappearance of nmand distortion of the energy
spectrum as expected in neutrino oscillation.
K2K confirmed neutrino oscillation
discovered in Super-K atmospheric neutrinos.
38
8. Summary

K2K has confirmed
neutrino oscillations at 3.9s.
With 8.9×1019 POT,


Disappearance of nm
Distortion of En spectrum
Dm2[eV2]
2.9s
2.5s
preliminary
1.7x10-3<Dm2<3.5x10-3eV2
@sin22q=1 (90%C.L.)
0.006
0.004
0.002
0.0 0.2 0.4 0.6 0.8 1.0
sin22q
39
Backup
40
7. Other Physics in K2K (based on K2K-I data)
nm +H2ONC1p0
nmne search
not NC1p0
Mgg(MeV)
s (n m  NC1p 0 )
=0.0650.0010.007
s (n m  CCall )
=0.064 (prediction)
Dm2[eV2]
90%CL limit
90%CL sensitivity
PRL accepted
sin22qme
preliminary
41
1KT: m momentum and angular distributions.
with measured spectrum
flux measurement
low q2 corr.
0
800
1600
pm (MeV/c)
0
20
qm (deg.)
42
90
SciFi (K2K-IIa with measured spectrum)
qm 1trk
Pm 1trk
flux measurement
Pm 2trk
QE
qm 2trk
QE
Pm 2trk
non-QE
qm 2trk
non-QE
43
0
2
(GeV/c)
0 10
40
(degree)
SciBar (with measured flux)
qm 1trk
Pm 1trk
flux measurement
Pm 2trk QE
qm 2trk QE
qm 2trk nQE
Pm 2trk nQE
44
10
Log Likelihood difference from the minimum.
DlnL
DlnL
- 68%
- 90%
- 99%
Dm2[eV2]

- 68%
- 90%
- 99%
sin22q
Dm2<(1.7~3.5)×10-3 eV2 at sin22q=1.0 (90% C.L.)
45
The change of NSKexp in K2K-I (Bugs)

The detector position

295m  294m
-1%
294m 295m

MC difference between KT and SK


KT; MA(QE)=1.1
SK; MA(QE)=1.0
s(NCel)KT=1.1×s(NCel)SK
 Efficiency change! -1%
NSKexp Change ~2%
46
47
CC-1p suppression versus coherent p
48
Systematic Bias without the MC correction.
ND (SciBar) measurement
DATA; MC w/ CC-1p suppression
MC template; Default MC
Oscillation Results
Default MC for ND and SK
sin22q=1.00
Dm2=2.73 ×10-3 eV2
Prob.(null oscillation)=0.0049%
Toy MC
Corrected MC
sin22q=1.00
Dm2=2.65×10-3eV2
Prob.(null oscillation)=0.011%
systematic bias
There is a small bias in nQE/QE
and the low energy flux.
flux
nQE/QE
49
Oscillation result with a default MC
Without low q2 MC correction
The result w/o low q2 MC correction gives the better (biased)
50
measurement due to the more low energy flux and the smaller nQE/QE.
K2K-I vs K2K-II
51
K2K-I vs K2K-II
52
nµ Disappearance Result (K2K-I)
PRL 90(2003)041801
Null oscillation probability: less than 1%.
Dm2=1.5~3.9 x 10-3 eV2 @sin22q1(90%CL)
Normalized by area
Expectation
w/o oscillation
Best Fit
Best fit:
Dm2=2.8
x10–3eV2
Reconstructed En
Allowed region
53
Extrapolation from Near to Far sites
x10
10
x10
16
12
12
8
250km
n beam
x10
10
x10
Energy
12
4
11
Radius
x10 4
8
3
E n (GeV)
4
5
0
x10
4
8
12
Radius (m)
SK
(insensitive to primary
3mradprotons)
Measure, N(pp, qp)
4
just after the horns.
2
0
1
2
3
4
5
4
5
0
x10
Energy
4
8
12
Radius (m)
5
12
Radius
8 SK
3mrad
4
2
0
1
2
3
E n (GeV)
4
5
0
1
2
3
Radius (km)
5
12
PION moniter
6
Gas Cherenkov8 detector:
4
3
6
FD (<2m)
4
2
2
4
8
1
1
x10 4
8
12
4
4
×104 E n (GeV)
16
8
0
8
0
×1010
11
0
1
2
3
1.0×10-6
54
55