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KL→π0νν at KOTO
Koji SHIOMI for the KOTO collaboration(Osaka University)
CKM 2014, Vienna, Austria2014/09/11
1
14年9月11日木曜日
KL→π0νν decay• Brakes CP symmetry directly• Highly suppressed in the SM• Small theoretical uncertainty (2~3%)• Sensitive to New Physics.
2
Standard Model predictionBR(KL→π0νν)=2.4×10-11
Experimental limitBR (KL→π0νν) <2.6×10-8@90% C.L. by KEK E391a
14年9月11日木曜日
KOTO experiment• Study of KL→π0νν@J-PARC 30GeV Main Ring.• Successor to the E391a experiment• Goal is to observe few SM events.J-PARC Laboratory
•Main ring (30 GeV protons)J-PARC Laboratory
KOTO = KL0 at TOkai
3
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Primary proton !30 GeV/c Target (Ni, Pt, Au)
KOTO area
Hadron hall
Linac
3 GeV !Synchrotron
30 GeV !Main Ring Extraction!
in 16 degree
Tokai, Ibaraki, Japan
J-PARC
30 GeVMain Ring
Hadron hall
3 GeVSynchrotron
LinacJ-PARC
3
14年9月11日木曜日
Experimental principle
proton
targetNeutral beam line
4
θγγ
νν
Rec. Z
Rec
. Pt “2γ+Nothing+Pt”
Assuming 2γ from π0,Calculate z vertex.
Calculate π0 transverse momentum
M2(π0)=E1E2(1-cosθ)
E1E2
KL→π0νν decay
Signal Box
π0KL
14年9月11日木曜日
KOTO detector FB NCC MB CV
CsI calorimeter
CC03OEV
CC04 CC05 CC06 BHCV BHPV
LCVBCVHINEMOS
Saturday, April 20, 2013
γγ
KL
ν ν
CsI calorimeter + Herme1c veto system
OK T�
�s
d
KAON13 @ Univ. of Michigan Ann Arbor
CsI calorimeter• The main detector of KOTO experiment• 2m diameter 500mm length full active pure CsI• Fine granularity • 25%25mm : 2240 crystals + 50%50mm : 476 crystals•
10
2014/7/30 5
KOTO detector“Two γ from π0 and nothing else” CsI calorimeter and Hermetic veto
π0 with high PT discriminate K
L→2γ
Other K decays have charged or γ more than two
“Veto almost everything” experiment
We installed all detectors by May 2013.
514年9月11日木曜日
KOTO first physics run• The first physics run: May 17-23, 2013–Beam power:24kW( 10% of design intensity)–Unfortunately, the data taking was terminated after100 hours due to an accident in J-PARC Hadron hall.
• We have been analyzing the KL→π0νν mode withoutlooking inside the signal box.
• Today, “inside the signal box” is presented for the first time.
6
14年9月11日木曜日
]2#
of e
vent
s/2.0
[MeV
/c
1
10
210
310
410
kmass
Data
MC0/3AK
]2 mass [MeV/cLRec. K400 450 500 550 600
400 450 500 550 600
Dat
a/M
C
0.51
1.52
# of
eve
nts/1
00.0
[mm
]
1
10
210
310
410
510
hrecz
Data
MC0/3AK
pos [mm]LRec. K2000 4000 6000
2000 4000 6000
Dat
a/M
C
0.51
1.52
CsI calorimeter performance• 6 cluster samples • BR(KL→3π0)=20%• High statistics
7
ZvtxM6γ
γ
14年9月11日木曜日
]2#
of e
vent
s/10.
0 [M
eV/c
1
10
210
310
410
510
kmass
Data MC0/0/AK
MC0/3AK
]2 mass [MeV/cLRec. K200 300 400 500 600 700
200 300 400 500 600 700
Dat
a/M
C
0.51
1.52
]2#
of e
vent
s/10.
0 [M
eV/c
1
10
210
310
410
510
kmass
Data MC0/0/AK
MC0/3AK
]2 mass [MeV/cLRec. K200 300 400 500 600 700
200 300 400 500 600 700
Dat
a/M
C
0.51
1.52
Veto detector performance• 4 cluster samples
w/o veto cut
8
M4γ M4γ
γγBR(KL→3π0)
=20%
w/ veto cut
BR(KL→2π0)=8.6×10-4
14年9月11日木曜日
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
00.511.522.533.54
FB NCC MB CVCsI calorimeter
CC03OEV
CC04 CC05 CC06 BHCV BHPV
LCVBCVHINEMOS
Saturday, April 20, 2013
Events outside the signal box
9
3
9
0
1
0
2.0±1.1
7.64±0.53
0.72±0.40
1.70±0.42
0.002±0.002
ObservedExpected
2.16±1.06We understand the events outside the signal box well.
108106±12
signal region
Pt vs Z distribution after applying loose selection cuts
14年9月11日木曜日
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
00.511.522.533.54
Upstream eventsFB NCC MB CV
CsI calorimeter
CC03OEV
CC04 CC05 CC06 BHCV BHPV
LCVBCVHINEMOS
Saturday, April 20, 2013
Halo neutron π0 γγ
nA→π0X
10
• The number of upstream events expected in the signal box
• less than 0.1
14年9月11日木曜日
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
00.511.522.533.54
Low Pt eventsFB NCC MB CV
CsI calorimeter
CC03OEV
CC04 CC05 CC06 BHCV BHPV
LCVBCVHINEMOS
Saturday, April 20, 2013
γ
γπ0 π+
π-
KL→π+π-π0
KL
CC05 CC06
π-π+
Vacuumpipe
-π+/π- interacted in the vacuum pipe.-Cannot enter the signal box due to the kinematical limit. (133MeV/c)
1114年9月11日木曜日
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
00.511.522.533.54
High Pt and downstream events
• Hadron interaction events• Events spread into thethe signal box
• A possible mechanism• Single halo neutron make two clusters.
n
12
1.9±1.1
Halo neutron
14年9月11日木曜日
Special data to study hadron interaction events
nAl target
13
-Al target was inserted into the beam
-Core neutrons scattered at the Al target
-Collect many hadron interaction events
nCore neutron
14年9月11日木曜日
Neural net cuts to reduce hadron interaction events
R [mm]0 200 400 600 800 10000
50
100
150
200
250
300h1
[mm]1aRMS0 50 100 1500
500
1000
1500
2000
2500
3000h1
NN Output-0.5 0 0.5 1 1.50
100200300400500600700800
h1
NN Output-0.5 0 0.5 1 1.50
1000
2000
3000
4000
5000
h1
Black:KL→π0νν MCRed: Al target data
Accept
Accept
Hit position
Energy spread in a cluster
14
Kinematical neural net(5 variables)
Shape neural net(12 variables)
#BG reducedto 10%
14年9月11日木曜日
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP0
50100150200250300350400450500
00.511.522.533.54
KL→π0νν plot after imposing allselection cuts
15
0.17±0.12
7.24±0.52
0.033±0.027
0.026±0.025
0.0018±0.0016
1
9
0
0
0
8787
BG source #BGHadron interaction events 0.18±0.15Kaon decay events 0.11±0.04Upstream events 0.06±0.06
Sum 0.36± 0.16
Summary of #BG inside the signal box
S.E.S. of the first physics run1.29×10-8 (preliminary)
KOTO achieved nearly the same sensitivity as KEK E391a experiment with only 100 hours of data
S.E.S. of KEK E391a:1.11×10-8
0.36± 0.16
ObservedExpected
Apply all selection cuts (Loose + Neural net cuts)
Preliminary Prelim
inary
14年9月11日木曜日
Opened the signal box
16 Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
00.511.522.533.54
14年9月11日木曜日
Opened the signal box
17
• One event was observed inside the signal box.
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
00.511.522.533.54
14年9月11日木曜日
Opened the signal box
18 Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
00.511.522.533.54
0.36± 0.161
• One event was observed inside the signal box.• Nobs is consistent with Nexp statistically
Observed Expected
Preliminary
00.14±0.11
14年9月11日木曜日
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP0
50100150200250300350400450500
00.511.522.533.54
Check the validity of the BG estimation
• Applying loose selection cuts• Nobs are consistent with Nexp inside the signal box.
3
2
9
0
1
0
2.0±1.1
7.63±0.54
0.72±0.40
1.70±0.42
0.002±0.002
19
Observed Expected
108106±12
2.11±1.06
12.37±1.24
→The number of BG events inside the signal box is estimated properly.
14年9月11日木曜日
Prospect for the next run
• We expect to start the next run in early 2015.• We want to reach the sensitivity 20 times higher than this first run.
• We are preparing new detectors to reduce BG events• We are improving analysis methods to reject hadron interaction events
• We are planning special run to increase the statistics of hadron interaction events
2014年9月11日木曜日
Summary• The KOTO experiment took the first physics data in May 2013.
• Even the run was only 100h long, we achieved nearly the same sensitivity as KEK E391a.
• After opening the signal box, we observed one event• This is consistent with the BG estimation statistically.
• Preparing to suppress the background and to improve the experimental sensitivity for the next run.
2114年9月11日木曜日
• Back up
2214年9月11日木曜日
The event inside the signal box
ener
gy d
epos
it [M
eV]
20
40
60
80
100
120
140
160
180
x position [mm]-1000 -800 -600 -400 -200 0 200 400 600 800 1000
y po
sitio
n [m
m]
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
event display - CsI energy (run00016887_node014_file6_g2ana.root node14 DstEntryID : 10974)
recconstructed valuesrec vertex : z=4437.6mm, 211.0ns
= 170.9 MeV/cT
p0/
vertex time difference = 0.0 ns°projection angle = 81.2
(534.3, -57.4) mm, 519.4MeV = 3.5, 13, 35.0mm ; 02r217.0ns,
(11.5, -244.3) mm, 357.4MeV = 3.5, 9, 16.3mm ; 02r216.8ns,
CsI veto info. (on timing hits)2.6MeV, 331.5mm, 5.8ns, 4195.8MeV, 139.5mm, 0.5ns, 4582.1MeV, 41.3mm, 0.1ns, 9612.3MeV, 45.0mm, 5.8ns, 1082
gnana outputfile
pos.arec.
not in cluster
event display - CsI energy (run00016887_node014_file6_g2ana.root node14 DstEntryID : 10974)
2314年9月11日木曜日
S.E.S.• # of decay KL’s in the signal region(NKL)obtained from KL→2π0 samples
• 7.61×109
• Geometrical Acceptance(Ageo)
• 0.285
• Cut efficiency(Acut)
• 0.0359
• S.E.S.
• 1/(NKL× Ageo×Acut)=1.29×10-8
24
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
020406080100120140160
KL→π0νν MC
S.E.S. of KEK E391a:1.11×10-8
KOTO achieved nearly the same sensitivity as the KEK E391a experiment.
14年9月11日木曜日
KL flux
• # of decay KL’s in the signal box is calculated from 4 cluster samples
• N(KL)= 7.61×109
• Check consistency by using KL→3π0, 2γ modes.
• the result agree within ±4%.
]2#
of e
vent
s/10.
0 [M
eV/c
1
10
210
310
410
510
kmass
Data0/0/AK
0/3AKOther K decays
]2 mass [MeV/cLRec. K200 300 400 500 600 700
200 300 400 500 600 700
Dat
a/M
C
0.51
1.52
# of
eve
nts/1
00.0
[MeV
/c]
1
10
210
hmome
Data0/0/AK
0/3AKOther K decays
momentum [MeV/c]LRec. K0 1000 2000 3000 4000 5000
0 1000 2000 3000 4000 5000
Dat
a/M
C
0.51
1.52
# of
eve
nts/2
00.0
[mm
]
1
10
210
310
hrecz
Data0/0/AK
0/3AKOther K decays
z pos. [mm]LRec. K2000 4000 6000
2000 4000 6000D
ata/
MC
0.51
1.52
14年9月11日木曜日
To reduce Hadron interaction events
FB NCC MB CVCsI calorimeter
CC03OEV
CC04 CC05 CC06 BHCV BHPV
LCVBCVHINEMOS
Saturday, April 20, 2013
-A part of core neutrons are scattered at the beam window. -> Replace the beam window with a thinner one.
Core neutron
beam windowReduce the number of neutrons hitting the CsI calorimeter
2614年9月11日木曜日
• Angle reconstruction • use cluster shape information as neural net inputs
Rec. z [mm]2000 3000 4000 5000 6000
[MeV
/c]
tP
050
100150200250300350400450500
00.511.522.533.54
Results in One Figure
Black dots are the Z vertex from neural net. For better display, Z set
to zero if the value < 0.
Red Stars show the original Rec. Z vertex.
Event ID
0 1 2 3 4 5 6 7
Z v
ert
ex
(cm
)
0
100
200
300
400
500
600
700
Yu-Chen Tung September 4, 2014 11 / 13
Results of Angle Reconstruction
Rec. angle resolution � = 3.2� with Gaussian fit at peak. I haven’t
calculated the resolution along di↵erent incident angles. Despite of
the non-Gaussian tail, now just set � = 3.5� for later calculation.
And, I haven’t studied the tail events, will try to improve the result of
those events if possible.
NNTheta - GenTheta (deg)
-50 -40 -30 -20 -10 0 10 20 30 40 500
50
100
150
200
250
NNTheta (deg)
0 10 20 30 40 50 60 70 80
GenT
heta
(deg)
0
10
20
30
40
50
60
70
80
Yu-Chen Tung September 4, 2014 3 / 13θnn-θtrue(degree)-50 50Loose cut condition
single γ MC
To reduce Hadron interaction events
0
700Rec. Z (mm)
Event ID0 7
300
500
Black:from θnnRed: from θrec27
14年9月11日木曜日
To reduce KL→π+π-π0 BG
-Replace the vacuum pipe with the thinner one-Install new charged detectors outside the beam pipe
FB NCC MB CVCsI calorimeter
CC03OEV
CC04 CC05 CC06 BHCV BHPV
LCVBCVHINEMOS
Saturday, April 20, 2013
γ
γπ0 π+
π-KL
CC05 CC06
π-
Vacuumpipe
π+
New charged detectors
To increase the detection efficiency for π+/π-
2814年9月11日木曜日
Detector upgrade for the next run
FB NCC MB CVCsI calorimeter
CC03OEV
CC04 CC05 CC06 BHCV BHPV
LCVBCVHINEMOS
Saturday, April 20, 2013
Replace the beam window witha thinner one
-Replace the vacuum pipe with a thinner one -Install charged veto counters outside the vacuum pipe
-increase the number of modules-Install new counters around the beam hole
-Install gas chambers
2914年9月11日木曜日