four-dimensional calorimeter to discriminate gammas from ...€¦ · koto experiment 3 koto...
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Four-dimensional Calorimeter to Discriminate Gammas from Neutrons for the KOTO Experiment
Mayu Osugi Osaka University @Calorimetry for the High Energy Frontier (CHEF2019)
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OK Tν
νs
d
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Introduction
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KOTO Experiment
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KOTO Detector
ν ν̄
KL
ν
π0 CsI γ
γ
CP violating decay
Highly suppressed in SM (BR : 3.0 × )
Small theoretical uncertainties (2%)
10−11 Sensitive to new physics
Signal π0→ 2γ: @ CsI caloriemeter nothing : @ other detectors
Search for at J-PARCKL → π0νν̄
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‣ CsI Crystalsundoped CsI (50cm)# of crystals = 27162240 small (25×25mm2) inner 476 large (50×50mm2) outer
‣Excellent energy resolution
‣ Readout with a PMT (rear side)
σE /E = 0.99% + 1.74 % / E[GeV]
CsI Calorimeter
4
small
large
2m
27!"
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Hadron-cluster Background
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Hadron-cluster Backgroundbeam halo neutron
KL → π0νν̄
PMT50cm
radiation length ~ 2cm
CsI PMTCsI
interaction length ~ 40cm
To reach the SM sensitivity, we would suppress the background events further by a factor of 10by the CsI calorimeter upgrade
Single event sensitivity
# of Hadron-cluster BG
2015 run 1.3×10-9 0.242016~2018 run 6.9×10-10 0.02SM sensitivity 3×10-11 0.5
improving the existing cut
γγ
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Upstream shallow distribution
Hadron-cluster Background
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Hadron-cluster Backgroundbeam halo neutron
KL → π0νν̄
PMT50cm
radiation length ~ 2cm
CsI PMTCsI
interaction length ~ 40cm
Downstream wide distribution
Distinguishable using the depth of the interaction
γγ
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Both-end Readout
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Hadron-cluster Background KL → π0νν̄
ΔT(MPPC-PMT)=small
MPPC
Upstream
PMT PMT
ΔT(MPPC-PMT)=large
MPPC
Downstream
S13360-6050CS(HPK)
6�6!!"
‣ ΔT → reflect the depth of the interaction
‣ Obtain four-dimensional informationx, y → hit position on the CsI calorimeterz → ΔT(MPPC-PMT)time → timing of the PMT
γ
depth of the interaction
ΔT
n
deep
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Both-end Readout Upgrade
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‣ Attached 4080 MPPCs
‣ To reduce # of the readout channels
Readout
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5cm5cm
Large
2.5cm
10cm
Small
Crystals
4 MPPCs are connected (1020)
4 readout are summed (256ch)(10cm×10cm region~ EM shower size)
4080
10cm10cm
10cm
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MPPC Installation
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‣ Glued MPPCs on two rows in a day. (1 row : 12 ~ 60 crystals)
‣ Finished installation as scheduled. (2018 Oct. 1st ~ Nov. 15th)
gluing jig
MPPC
CsI from upstream
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MPPC Installation
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~2018 2019~
MPPC readout cable
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• During Aug. 2018 ~ Feb. 2019→ Data taking : 2019/02~04 ← Using this data
Data Taking
12Dec2012
Dec2013
Dec2014
Jan2016
Dec2016
Dec2017
Dec2018
Acc
umul
ated
P.O
.T.
0102030405060708090
1001810×
Bea
m P
ower
(kW
)
0
20
40
60
80
100
CsI upgrade
2019 data(Today’s topic)
2016~2018 analysis2015 analysis2013 analysis
Proton on target
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Analysis
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Gamma Sample
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‣ decay
‣ A pair of gammas from a is used for the control sampleKL → 3π0
π0
reconstructed distributionmKL
rec. [MeV]mKL
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Hadron-cluster Control Sample
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‣ Used special run data as a neutron samples→ Enhance the scattered neutron events by placing Al plate
CsIn n
Al plate
Special run setup
n・ Physics data Special run data
20000
Arbitrary Units
Cluster energy [MeV]
Cluster energy
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ΔT Distribution
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‣ For the decay, a pair of gammas from a is filled.
‣ Both gammas interact at upstreamThe secondary neutron tends to interact at downstream
‣ Use the larger ΔT value out of two clusters to suppress the hadron-cluster background.
KL → 3π0 π0
ΔT distribution of two clustersHadron-cluster control sample KL → 3π0
larger ΔT
smaller ΔTlarger ΔTsmaller ΔT
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ΔT Distribution
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Arbitrary Units (weighted) Data
hadron-cluster control sample Data
KL → π0νν̄90% signal
The hadron cluster background is suppressed to 1/45 with 90% signal efficiency
cluster energy distribution
cluster energy [MeV]
The ΔT distribution of the
→ weighed the ΔT distribution of according to the cluster energy
KL → π0νν̄
KL → 3π0
Larger ΔT distribution out of two clusters
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‣ We succeeded in the CsI calorimeter upgrade
‣ We evaluated the neutron rejection performance using the data taken in 2019
‣ The hadron-cluster background is suppressed down to 1/45 with 90% signal efficiency.
Summary
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