Post on 17-Jul-2020
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
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
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
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)
5
Experimental Setup
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%)
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)
8
Bird’s Eye Neutrino Beam Line
9
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
10
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
11
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
12
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
13
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
14
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
15
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
16
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
17
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
18
Results
19
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
)
20
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.
21
Typical SK Events
22
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
23
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
24
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.)
25
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)
26
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.
27
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
28
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
29
Vertex dist. of 1kt events
2000/Jan-Mar
Agree with MC well.
30
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
31
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
32
Pion Monitor Results
pπ
θπ
w1w2 w3w4 …..: :
: :
33
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.
34
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!
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.
36
# of observed and expected events @ SK
37
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%
38
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.
39
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.
40
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.
41
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
+−
42
予備
43
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.
44
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.
45
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
46
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
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)
48
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)
49
Event POT (All)
FC+OD events
50
Event POT (FC all)
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
52
Systematic Error of Flux Ratio
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
54
Rate of 1kt eventsE
vent
Rat
e/10
PO
T14
1
0.5
0
55
56
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
57
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
58
sin22θ=1
# of observed and expected events @ SK