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Kota Nakagiri ( Kyoto Univ. )for the KOTO collaboration
1
Status of KL→π0νν analysisat J-PARC KOTO
OK Tν
νs
d
KL→π0νν Decay
2
⌫⌫̄
s dd̄
W�
t
d̄
Z0V ⇤tdVts
<崩壊ダイアグラムの1つ>
V ⇤ts Vtd
• direct CPV• highly suppressed in the SM : Br = 3×10-11• theoretically clean : ~2%➡ good probe for new physics that violates CP symmetry 0
@d0
s0
b0
1
A =
0
@Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb
1
A
0
@dsb
1
A
λ ~ 0.2λ2λ3
K system ~λ5 << Bd system ~λ3
1
⚫ SM⚫ SM + NP
M.Tanimoto, K.Yamamoto arXiv: 1603.07960
a model w/ O(10TeV) SUSY
indi
rect
limit
1σ from exp.
direct limit : 2.6×10-8 (90% C.L.)indirect limit (Grossman-Nir limit) Br(KL) < 4.4 × Br(K+) = 1.5×10-9 (90% C.L.)
10-8
10-9
10-10
10-11
NP ?
s→d FCNC
a model w/ heavy Z’ (50 TeV)
A.J.Buras, et al. arXiv: 1408.0728
KOTO Experiment @ J-PARC
3
Japan Proton Accelerator Research Complex = J-PARC
KL beam
30GeV Proton Beam
16°
KOTO
Collaboration photo @J-PARC2017 Dec. 16th
K0 at TOkai
Tokai village
Au target
Experimental Method
4
CsI Calorimeter
KL
γ
ν ν
R~1m
(π0) γ
KL ! ⇡0 ⌫⌫̄π0→2γ on CSI calorimeter
5
KL ! ⇡0 ⌫⌫̄missing : hermetic veto
KL
Veto counters
ν ν
(π0)γ
γ
Experimental Methodπ0→2γ on CSI calorimeter
CsI Calorimeter
R~1m
6
KL
Veto counters
(2π0)
γ
γγ
γ
KL ! ⇡0 ⌫⌫̄
Experimental Methodπ0→2γ on CSI calorimeter
missing : hermetic veto
CsI CalorimeterKL→2π0 BG
R~1m
7
Decay Z
π0 P
t Signal boxν ν
KL 2γ
( π0 )
KLZ
θ
γ (E1)
γ (E2)
cos ✓ = 1�M2
⇡0
2E1E2
ν ν
Experimental Methodπ0 reconstruction from 2γs
νν carry away momentum = rec. π0 has large Pt➡ signal box on Pt v.s. Z plane
History of the KOTO data taking
8
Jul2013
Dec2013
Jul2014
Dec2014
Jul2015
Jan2016
Jul2016
Dec2016
Jul2017
Dec2017
Acc
umul
ated
P.O
.T.
0
10
20
30
40
50
601810×
Bea
m P
ower
(kW
)
0
20
40
602015 run2013 run
operation of Hadron facility was stopped
first physics run
First physics run in 2013
9
One event was observed. consistent with BG expectation→ Br(KL→π0νν) < 5.1 ×10-8 (90%C.L.)
Single Event Sensitivity = 1.29 ×10-8
Signal box: 3000 < Zvtx [mm] < 4700 150 < PT [MeV/c] < 250
Lessons from the 2013 run
10π± disappear @vacuum pipe
1st Hit
2nd Hit
neutron
①
②
③
KL ② KL→π+π-π0
π±
2γ
neutron③ π0@NCC 2γ
π± →missing
① hadron cluster BG
dominant BG in the 2013 run
Lessons from the 2013 run
11
π±
new scintillation counterBeam pipe : SUS → Al
Suppress KL→π+π-π0 BG
For ② For ① & ③
thinner vacuum window : 125μm→12.5μm
Beam profile monitor for better beam alignment
Reduce halo neutrons~ 1/20 ~ 1/2
calorimeter
2015 run analysis :
12
Hadron cluster BG
1st Hit
2nd Hit
neutron n
Al plate as a scattering source
Special run to take control sample
Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
5
10
15
20
25
30
5798(4496)
60
2250 576
1932
0277
Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
20
40
60
80
100
0(0)
1707
7856 2170
8315
01233
control samplePhysics data
5798 (4496)
13
Pulse shape discrimination
1/10 BG reduction & 90% signal acceptance
Cluster shape discrimination
neutron pulse hasa longer tail
• cluster shape neural net cut (NEW)
1/1500 BG reduction & 90% signal acceptance
1/300 BG reduction &80% signal acceptance
(NEW)
Hadron cluster BG2015 run analysis :new cuts to discriminate γ-cluster from n-cluster w/ calorimeter
• cluster shape χ2 cut :cluster shape is consistent with that of γ MC → pass
timing information is used
14
Rejection Power
Cluster Shape Cut ( 2.2 ± 1.0 ) ×10-4
Pulse Shape Cut ( 9.1 ± 0.4 ) ×10-2
0.26±0.08
0.11±0.05 0.03±0.01
0.10±0.05
0.02±0.01
Hadron cluster BG2015 run analysis :
※ with ×10 statistics of that of 2013 run
Preliminary
CV-η BG : Mechanism
15Z=6148
Z=6093Z=5842
CV
neutron
η→2γ
rec. π0 Z
Ω
cos⌦ = 1�m2
⇡0
2E1E2Ω is calculated to be smaller because mη > mπ (mη ~ 4mπ).➡ rec. Z goes upstream.
CSI
CV-Eta BG : Estimation
3 Decay Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
0.002
0.004
0.006
0.008
0.01
0.53(0.46)
0.00
0.15 0.02
0.00
0.000.11
CV-Eta BG MC
0.46 events is estimated with Tight cut condition → Need to develop a new cut !
New Cut for the CV-Eta BG
16
MaxEtaThetaChisq cut : • if the cluster shapes are consistent with the assumption that
they are derived from η→2γ decay at CV, the event is rejected• good consistency = small MaxEtaThetaChisq value
BestMaxEtaThetaChisq Distribution
8
BestMaxEtaThetaChisq0 5 10 15 20 25 30 35 40 45 50
a.u.
0
0.05
0.1
0.15
0.2
0.25
0.3
Signal MC CV-Eta MC
※ Tight cut is applied as a pre-cut
MaxEtaThetaChisq
7
0
5
10
15
20
25
MaxEtaThetaChisq
500− 400− 300− 200− 100− 0 100 200 300 400 500500−
400−
300−
200−
100−
0
100
200
300
400500MaxEtaThetaChisq Z = ZFCV
X [mm]
Y [m
m]
True Vertex
BestMaxEtaThetaChisq = min( MaxEtaThetaChisq[i] )
CV-η MC
BestMaxEtaThetaChisq distribution
Preliminary
New Cut for the CV-Eta BG
17
MaxEtaThetaChisq cut : • if the cluster shapes are consistent with the assumption that
they are derived from η→2γ decay at CV, the event is rejected• good consistency = small MaxEtaThetaChisq value
MaxEtaThetaChisq
7
0
5
10
15
20
25
MaxEtaThetaChisq
500− 400− 300− 200− 100− 0 100 200 300 400 500500−
400−
300−
200−
100−
0
100
200
300
400500MaxEtaThetaChisq Z = ZFCV
X [mm]
Y [m
m]
True Vertex
BestMaxEtaThetaChisq = min( MaxEtaThetaChisq[i] )
CV-η MC
BestMaxEtaThetaChisq threshold0 2 4 6 8 10 12 14 16 18 20
Acc
epta
nce
0
0.1
0.2
0.3
0.40.5
0.6
0.7
0.8
0.9
1
N C
V-Et
a B
G
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Signal : 89% CV-Eta : 1/10
Cut acceptance
1/10 BG reduction was obtained
Preliminary
2015 run status : Sensitivity
18
momentum [MeV/c]LRec. K0 2000 4000 6000 8000
# of
eve
nts/1
00.0
0 [M
eV/c
]
1
10
210hmome
Data0π3→LK 0π2→LKγ2→LK
hmome
momentum [MeV/c]LRec. K0 1000 2000 3000 4000 5000 6000 7000 8000
0 1000 2000 3000 4000 5000 6000 7000 8000
Dat
a/M
C
0
1
2
3
ndf = 52 = 34.642χ
p-value = 0.969/ndf = 0.672χ
KL flux from KL→2π0 analysis
KL yield : 4.62×1012
Single Event Sensitivity = 1(KL yield) × (Signal acceptance)
= 1.2 ×10-9
×10 higher sensitivity than that of 2013
Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
10
20
30
40
50
Signal Acceptance from MCKL→π0νν MC
Acceptance : 1.8×10-4
※ including decay probability (3.8%)
Rec. KL momentum—Data —MC
2015 run status
19
Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0(0)
284 0 0
1
01
2015 whole data S.E.S. : 1.2×10-9
0.18±0.04
02.29±0.19
0.70±0.19
0.02±0.02
Observed Estimated
Preliminary
0.88±0.18
mode # of BG KL→2π0 0.07 ± 0.07 KL→π+π-π0 0.18 ± 0.05 KL→3π0 0.17 ± 0.12 KL→2γ 0.02 ± 0.02
Hadron Cluster 0.26 ± 0.08NCC-π0 0.13 ± 0.07
CV-η 0.05 ± 0.02Total 0.88 ± 0.18
2015 run status
20
mode # of BG KL→2π0 0.07 ± 0.07 KL→π+π-π0 0.18 ± 0.05 KL→3π0 0.17 ± 0.12 KL→2γ 0.02 ± 0.02
Hadron Cluster 0.26 ± 0.08NCC-π0 0.13 ± 0.07
CV-η 0.05 ± 0.02Total 0.88 ± 0.18
Possible further reduction :
Higher Pt thresholdOptimize veto cuts
Smaller Z region
10
π0 Rec. Z [mm]
π0 R
ec. P
t [M
eV/c
]
250
130
2000 5000π0 Rec. Z [mm]
π0 R
ec. P
t [M
eV/c
]
250
130
2000 5000
10
π0 Rec. Z [mm]
π0 R
ec. P
t [M
eV/c
]
250
130
2000 5000π0 Rec. Z [mm]
π0 R
ec. P
t [M
eV/c
]
250
130
2000 5000
※ For further reduction in future runs, we plan to upgrade detectors in summer-autumn 2018.
(if necessary)
under discussion
Summary & Prospects
21
• KOTO 2015 run analysis is ongoing• KL→π0νν search with S.E.S. = 1.2 ×10-9• expected to improve the current upper limit by a factor of 10
• Remaining work• finalize sensitivity / BG estimation • final MC production is now ongoing
• evaluate systematic uncertainty
• We will release the result this summer !
22
23
24
KL
Veto counters
(3π0)
γγ γ
γ γγ
KL ! ⇡0 ⌫⌫̄
Experimental Methodπ0→2γ on CSI calorimeter
missing : hermetic veto
CsI CalorimeterKL→3π0 BG
R~1m
25
KL
Veto counters
(π0)
π+
γγ π-
KL ! ⇡0 ⌫⌫̄
Experimental Methodπ0→2γ on CSI calorimeter
missing : hermetic veto
CsI CalorimeterKL→π+π-π0 BG
R~1m
Other detector upgrades
26
new in-beam charged veto was installedfor acceptance recovery
Beam
in-beam charged veto
• wire chamber• insensitive to neutron
additional photon counters are installed for reducing KL→2π0 BG
in-beam photon veto
※ original one was 3-mm-thick plastic scintillator
4 modules of aerogel Cherenkov counterswere added
Acrylic Cherenkov conterwas newly added
Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.77(0.50)
0.14 0.00 0.00
0.05
0.001.09
KL→2π0 BG
Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.09(0.05)
0.00 0.00 0.00
0.00
0.000.23
Loose veto (2013 cut set) 2015 cut set
27
tighter veto
Property of the remaining events in the Signal Box
28
FBAR ineff. (Low-E γ) / CBAR punch-throughID : 43
Rec. Z [mm]0π1000 2000 3000 4000 5000 6000
Pt [
MeV
/c]
0π
0
100
200
300
400
500 veto informationCBARVetoEne : 0.0 MeVBCVVetoEne : 0.2 MeVOEVVetoEne : 0.0 MeVFBARVetoEne : 0.0 MeVNCCVetoEne : 0.0 MeVNCCScintiVetoEne : 0.0 MeVCBARMod39VetoEne : 0.0 MeVBHGCVetoEne : 0.0 MeV
other additional cuts MaxThetaChisq : 0.6 BestMaxEtaThetaChisq : 9999.0
ID : 43
0 2000 4000 6000 8000 10000
1000−
500−
0
500
1000
ID : 43ID : 43
1000− 500− 0 500 1000
1000−
500−
0
500
1000
ID : 43ID : 43
800− 600− 400− 200− 0 200 400 600 800
800−
600−
400−
200−
0
200
400
600
800
50
100
150
200
250
300
800−600−400−200−0200400600800
Gamma 0 Energy : 547.8 MeV (X,Y) = (320.6, 327.3)
: 3.02χ Shape CSD : 1.01
: 0.62χ Theta
Gamma 1 Energy : 139.3 MeV (X,Y) = (485.1, -531.4)
: 4.42χ Shape CSD : 0.911
: 0.12χ Theta
ID : 43FileID : 28936DstEntryID : 16222
RecZ : 4471.4 mm0π Pt : 151.6 MeV/c0π
: -0.2 nsvtxTΔClusDist : 874.3 mmTrueGammaEnerg, EndPos 0 : 143.9 MeV : 495.1 -529.4 6220.4 mm 1 : 538.2 MeV : 326.4 339.4 6192.3 mm 2 : 28.9 MeV : -619.3 -228.3 2743.6 mm 3 : 216.5 MeV : -1262.4 -493.9 5973.2 mm
( KL→2π0 MC )
KL→π+π-π0 BG
※ w/ small data set and loose veto are used1/10 BG reduction for KL→π+π-π0
29
π±
new scintillation counter
Beam pipe : SUS → Al
Observed KL→π+π-π0 MC
➡ 1/2 BG reduction
KL→3π0 BG : masking backgroundBG updates: masking KL→πeν, 3π0
Accidental hits may shift a hit timing to be out of veto timing window. Evaluated by overlaying accidental data (taken with physics data simultaneously) on simulation.
13
Evaluation for 2015 data has been done
Example of an overlaid pulse
Found some contribution (0.17) from KL→3π0 due to a loss in Front Barrel (FB).
複数パルスの重複による背景事象• Accidental Hitの影響で、Veto検出器のHit時間が正しく求められないとイベントのタイミングから外れてVeto出来なくなり、背景事象となる。
• KL崩壊由来背景事象のMCでの見積もりの際にこの影響を考慮する必要がある。
5
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215
sum (0.872MeV, 34.1clock)
MC (0.23MeV, 33.6clock)
acc (0.642MeV, 38.5clock)
CV ModID : 78, AccidentalEntryNo : 111215
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
500
1000
1500
2000
MCMC
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
AccAcc
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215CV ModID : 78, AccidentalEntryNo : 111215
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215
sum (0.872MeV, 34.1clock)
MC (0.23MeV, 33.6clock)
acc (0.642MeV, 38.5clock)
CV ModID : 78, AccidentalEntryNo : 111215
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
500
1000
1500
2000
MCMC
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
AccAcc
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215CV ModID : 78, AccidentalEntryNo : 111215FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215
sum (0.872MeV, 34.1clock)
MC (0.23MeV, 33.6clock)
acc (0.642MeV, 38.5clock)
CV ModID : 78, AccidentalEntryNo : 111215
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
500
1000
1500
2000
MCMC
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
AccAcc
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215CV ModID : 78, AccidentalEntryNo : 111215
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215
sum (0.872MeV, 34.1clock)
MC (0.23MeV, 33.6clock)
acc (0.642MeV, 38.5clock)
CV ModID : 78, AccidentalEntryNo : 111215
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
500
1000
1500
2000
MCMC
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
AccAcc
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215CV ModID : 78, AccidentalEntryNo : 111215
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215
sum (0.872MeV, 34.1clock)
MC (0.23MeV, 33.6clock)
acc (0.642MeV, 38.5clock)
CV ModID : 78, AccidentalEntryNo : 111215
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
500
1000
1500
2000
MCMC
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
AccAcc
FADC sample0 10 20 30 40 50 60
puls
e he
ight
[AD
C c
ount
]
0
1000
2000
3000
4000
5000
6000
7000
CV ModID : 78, AccidentalEntryNo : 111215CV ModID : 78, AccidentalEntryNo : 111215
CsI
CsI
X
XKL→2π0 →4γ
Vetoしたいγのタイミング
Peak Findingで見つかるPeakのタイミング
30ns Shift
AccidentalHit
"Pulse to be Vetoed■Accidental Pulse▲Merged
Pulse
γ γ
γγ
True pulse timing
2015 data analisys
KOTO detector (2012-2015)
Signature of KL→π0νν = 2γ+nothing Calorimeter + Hermetic veto detectors
4
Cutaway view
0�
1�
2�[m]�
0� 2� 4� 6� 8� 10� 12� 14� 16�[m]�
Calorimeter� Concrete/iron shield�
FB� NCC�Hinemos� MB� BCV� CV� OEV�LCV�CC03� CC04� CC05� CC06� BHCV� BHPV�
Decay volume (Vacuum)�
BHTS�
z
y
x
Downstream beam pipe�
Membrane�
KL beam�
introduction
FB is a 2.75-m-long detector with a single-end readout,covering upstream region with less granularity, and could be especially affected.
30
Sensitivity : 2013 run v.s. 2015 run
31
2013 run 2015 run
P.O.T. 1.19×1018 2.21×1019
NKL 2.40×1011 4.62×1012
ASignal 3.25×10−4 1.8×10−4
S.E.S. (= 1/ (A * N)) 1.28×10−8 1.2×10−9
Signal box extension : ×1.35unused neural net cut : ×1.3Tight veto : ×0.7Hadron cluster / CV-η cut : ×0.7Accidental signal loss : ×0.6
×20
×10
×1/2
~ 1/2
Z0 v.s. Physics
32
Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
20
40
60
80
100
0(0)
1707
7856 2170
8315
01233
Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Pt [
MeV
/c]
0 πR
ec.
0
50
100
150
200
250
300
350
400
450
500
0
5
10
15
20
25
30
5798(4496)
60
2250 576
1932
0277
Z0Al Physics
Kinematic VariablesEntries 4769Mean 732.981RMS 269.195Integral 1
Max Gamma Energy [MeV]500 1000 1500 2000
# of
eve
nts/2
0.0
[MeV
]
4−10
3−10
2−10Entries 4769Mean 732.981RMS 269.195Integral 1Entries 18365Mean 734.965RMS 279.595Integral 1
Entries 18365Mean 734.965RMS 279.595Integral 1
h_MaxE2
Z0Phys
Max Gamma Energy [MeV]200 400 600 800 1000 1200 1400 1600 1800 2000 2200
200 400 600 800 1000 1200 1400 1600 1800 2000 2200
Z0/P
hys
0.51
1.52
Entries 4769Mean 316.797RMS 105.8Integral 1
Min Gamma Energy [MeV]200 400 600 800 1000
# of
eve
nts/1
0.0
[MeV
]
4−10
3−10
2−10
1−10
Entries 4769Mean 316.797RMS 105.8Integral 1Entries 18365Mean 310.118RMS 106.847Integral 1
Entries 18365Mean 310.118RMS 106.847Integral 1
h_MinE2
Z0Phys
Min Gamma Energy [MeV]100 200 300 400 500 600 700 800 900 1000 1100
100 200 300 400 500 600 700 800 900 1000 1100
Z0/P
hys
0.51
1.52
MaxGammaE
Entries 4769Mean 466.621RMS 110.274Integral 1
CsI fiducial R [mm]200 400 600 800 1000
# of
eve
nts/1
0.0
[mm
]
4−10
3−10
2−10Entries 4769Mean 466.621RMS 110.274Integral 1Entries 18365Mean 460.866RMS 107.356Integral 1
Entries 18365Mean 460.866RMS 107.356Integral 1
h_MaxFiducialR2
Z0Phys
CsI fiducial R [mm]100 200 300 400 500 600 700 800 900 1000 1100
100 200 300 400 500 600 700 800 900 1000 1100
Z0/P
hys
0.51
1.52
Entries 4769Mean 248.796RMS 66.5324Integral 1
CsI fiducial XY [mm]100 200 300 400 500 600
# of
eve
nts/5
.0 [m
m]
4−10
3−10
2−10 Entries 4769Mean 248.796RMS 66.5324Integral 1Entries 18365Mean 236.154RMS 60.8156Integral 1
Entries 18365Mean 236.154RMS 60.8156Integral 1
h_MinFiducialXY2
Z0Phys
CsI fiducial XY [mm]100 150 200 250 300 350 400 450 500 550 600
100 150 200 250 300 350 400 450 500 550 600
Z0/P
hys
0.51
1.52
33
BlindBox
Pt
Z
MinGammaE
MaxFiducialR MinFiducialXY
Kinematic VariablesEntries 4769Mean 268.453RMS 59.0096Integral 1
Pt [MeV/c]0πRec. 0 100 200 300 400 500
# of
eve
nts/5
.0 [M
eV/c
]
4−10
3−10
2−10
1−10
Entries 4769Mean 268.453RMS 59.0096Integral 1Entries 18365Mean 261.274RMS 57.2687Integral 1
Entries 18365Mean 261.274RMS 57.2687Integral 1
h_Pt2
Z0Phys
Pt [MeV/c]0πRec. 0 50 100 150 200 250 300 350 400 450 500
0 50 100 150 200 250 300 350 400 450 500
Z0/P
hys
0.51
1.52
Entries 4769Mean 4973.2RMS 376.901Integral 1
z pos. [mm]0πRec. 3000 4000 5000 6000
# of
eve
nts/3
5.0
[mm
]
4−10
3−10
2−10
1−10
Entries 4769Mean 4973.2RMS 376.901Integral 1Entries 18365Mean 5002.17RMS 371.666Integral 1
Entries 18365Mean 5002.17RMS 371.666Integral 1
h_RecZ2
Z0Phys
z pos. [mm]0πRec. 2500 3000 3500 4000 4500 5000 5500 6000
2500 3000 3500 4000 4500 5000 5500 6000
Z0/P
hys
0.51
1.52
Pi0Pt
Entries 4769Mean 362.787RMS 52.4854Integral 1
Cluster Distance [mm]300 400 500 600 700
# of
eve
nts/5
.0 [m
m]
4−10
3−10
2−10
1−10
Entries 4769Mean 362.787RMS 52.4854Integral 1Entries 18365Mean 358.64RMS 49.6652Integral 1
Entries 18365Mean 358.64RMS 49.6652Integral 1
h_ClusterDistance2
Z0Phys
Cluster Distance [mm]250 300 350 400 450 500 550 600 650 700 750
250 300 350 400 450 500 550 600 650 700 750
Z0/P
hys
0.51
1.52
Entries 4769Mean 7.52489RMS 2.93675Integral 0.998323
ClusSize []0 5 10 15 20 25
# of
eve
nts/1
.0 []
4−10
3−10
2−10
1−10Entries 4769Mean 7.52489RMS 2.93675Integral 0.998323Entries 18365Mean 7.48664RMS 2.97174Integral 0.99853
Entries 18365Mean 7.48664RMS 2.97174Integral 0.99853
h_ClusSize2
Z0Phys
ClusSize []0 5 10 15 20 25
0 5 10 15 20 25
Z0/P
hys
0.51
1.52
34
BlindBox
Pt
Z
Pi0RecZ
ClusterDistance ClusterSize
Neutron Cut Variables
35
Entries 4769Mean 86.8655RMS 80.6676Integral 1
MaxShapeChisq []0 100 200 300 400 500
# of
eve
nts/5
.0 []
4−10
3−10
2−10Entries 4769Mean 86.8655RMS 80.6676Integral 1Entries 18365Mean 83.5739RMS 79.8065Integral 1
Entries 18365Mean 83.5739RMS 79.8065Integral 1
h_MaxShapeChisq2
Z0Phys
MaxShapeChisq []0 50 100 150 200 250 300 350 400 450 500
0 50 100 150 200 250 300 350 400 450 500
Z0/P
hys
0.51
1.52
Entries 4769
Mean 05−4.02587e−
RMS 0.0394733Integral 0.998952
MinCSDVal []0 0.5 1
# of
eve
nts/0
.0 []
4−10
3−10
2−10
1−10
1
Entries 4769
Mean 05−4.02587e−
RMS 0.0394733Integral 0.998952
Entries 18365Mean 0.00049079
RMS 0.0388277Integral 0.998911
Entries 18365Mean 0.00049079
RMS 0.0388277Integral 0.998911
h_MinCSDVal2
Z0Phys
MinCSDVal []0 0.2 0.4 0.6 0.8 1
0 0.2 0.4 0.6 0.8 1
Z0/P
hys
0.51
1.52
MaxShapeChisq CSD
Entries 4769Mean 0.0576473RMS 0.178028Integral 1
PSLH []0 0.5 1
# of
eve
nts/0
.0 []
4−10
3−10
2−10
1−10
1
Entries 4769Mean 0.0576473RMS 0.178028Integral 1Entries 18365Mean 0.0616346RMS 0.183301Integral 0.999946
Entries 18365Mean 0.0616346RMS 0.183301Integral 0.999946
h_PSLH2
Z0Phys
PSLH []0 0.2 0.4 0.6 0.8 1
0 0.2 0.4 0.6 0.8 1
Z0/P
hys
0.51
1.52
PSLH
Shape χ2
36
size of CsI crystals : 25mm x 25mm (for inner, 50mm x 50mm for outer) < Molier radius (35.7mm) ➡ give us the information of 2D shower shape
compare the observed Edep. in each crystals in a cluster with its expected energy derived from MC
Einc : measured photon energy ei : measured deposit energy in ith crystal in a cluster μ : expected mean e/E σ : expected RMS of e/E
➡ 1/300 BG reduction & 80% signal acceptance (w/ threshold = 4.6)
Cluster Shape Discrimination
37
Neural net cut using cluster shape information compare data with MC input variables: • crystal energy χ2 • crystal energy probability • crystal timing χ2 • cluster energy difference • cluster timing probability • cluster probability • cluster COE, RMS, energy & RMS balance
timing information is used
Neutron samples KL->3π0 & KL->2γ samples
0 10.2 0.4 0.6 0.8 NN output
1
2
0
a.u.
Energy Distribution
0 200 400-200X
Y
0
200
400
-200
Timing Distribution
0 200 400-200
0
200
400
-200
Y
X
0
0.8
-0.8
Δt
[mm][mm]
[mm
]
[mm
]
1/1500 BG reduction & 90% signal acceptance
Pulse Shape Likelihood
38
use waveform information to distinguish photons from neutrons ➡ extract the information by fitting the waveform
difference of dE/dx of EM and hadronic shower may make difference of scintillating mechanism ➡ hadronic cluster has larger tail component ➡ larger “a”
calculate Likelihood ratio and determine which is more likely (nn, γγ)
1/10 BG reduction & 90% signal acceptance
39
KOTO detector since 2016
Inner Barrel detector (IB) installed Additional 5 X0 thickness in barrel region fine sampling (sandwich of 1mm lead and 5mm scintillator)
18
0�
1�
2�[m]�
0� 2� 4� 6� 8� 10� 12� 14� 16�[m]�
Calorimeter� Concrete/iron shield�
FB� NCC�Hinemos� MB� BCV� CV� OEV�LCV�CC03� CC04� CC05� CC06� BHCV� BHPV�
Decay volume (Vacuum)�
BHTS�
z
y
x
Downstream beam pipe�
Membrane�
KL beam�
IB
2016-17 data analisys
IB
40
Calorimeter both-end readout
29
neutron
Signal Background
MPPC PMTundoped CsI : 50cm
Timing difference (TMPPC-TPMT) gamma < neutron background
KL ! ⇡0⌫⌫
2�
2nd cluster by neutron case
photon case
ΔT (γ) < ΔT (neutron) expectedTiming Difference ΔT = T(MPPC)-T(PMT)
Calorimeter upgrade
41
Remaining KL→π+π-π0 in MC
44
Major Background
π0
n π+γ
n γK
π-
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 65000
50
100
150
200
250
300
350
400
450
500
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 65000
50
100
150
200
250
300
350
400
450
500
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 65000
50
100
150
200
250
300
350
400
450
500
Rec. π0 Zvtx (mm)
Rec
. π0 P t
(MeV
/c)
Pion produced at detector upstream.
Neutron direct hit on CsI Particles missing in the downstream gap
Interaction occurs at • membrane between
low and high vacuum • G10 support for membrane • vacuum flanges
motivation• #$ → !&!'!" decay(has(large(contribution(to(BG.-#(of(BG(is(0.04�0.01 at(the(10%(statistics(in(2015(data.
• End(point(of(#$ → !&!'!" MC-Some(events((~30%)(disappeared(around(the(beam(pipe(region.- If(we(can(remove(the(beam(pipe,(we(may(reduce(those(BGs.
2017/1/6 3collaboration(meeting(@Tokai
flange
windowpipe
kamijiUsan(slide@2016(Aug(collaboration(meeting
CC04 CC05 CC06BPCV
vacuum tankbeam pipe
membrane
motivation• #$ → !&!'!" decay(has(large(contribution(to(BG.-#(of(BG(is(0.04�0.01 at(the(10%(statistics(in(2015(data.
• End(point(of(#$ → !&!'!" MC-Some(events((~30%)(disappeared(around(the(beam(pipe(region.- If(we(can(remove(the(beam(pipe,(we(may(reduce(those(BGs.
2017/1/6 3collaboration(meeting(@Tokai
flange
windowpipe
kamijiUsan(slide@2016(Aug(collaboration(meeting
vacuum tankbeam pipe
Liner charged veto inside these structures is effective to reduce this background
➔ New downstream CV (2018 upgrade)
42
Recommended