latest results of k2kjnusrv01.kek.jp/~kobayasi/talks/jps0009.pdf · photo detector 20 pmts 6 0 0 2...
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![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)](https://reader034.vdocuments.site/reader034/viewer/2022042804/5f50490bd6c67b12452d804a/html5/thumbnails/1.jpg)
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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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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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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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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Experimental Setup
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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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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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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
pπ
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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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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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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Event POT (All)
FC+OD events
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Event POT (FC all)
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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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Systematic Error of Flux Ratio
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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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Rate of 1kt eventsE
vent
Rat
e/10
PO
T14
1
0.5
0
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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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sin22θ=1
# of observed and expected events @ SK