Rejection Power for the Hadron-cluster Background with the upgraded - PowerPoint PPT Presentation

Rejection Power for the Hadron-cluster Background with the upgraded KOTO CsI calorimeter 2019/12/23 
 Osugi Mayu @ Year End Presentation 1

KOTO Experiment 
 Hadron-cluster background & both-end readout Contents 2 • Introduction 
 • Data samples • Timing Calculation • Performance of both-end readout • Summary

Small theoretical uncertainties (2%) CsI nothing : @ other detectors π 0 → 2γ : @ CsI caloriemeter Signal 3 Sensitive to new physics ) Highly suppressed in SM (BR : 3.0 × CP violating decay Search for KOTO Experiment K L → π 0 ν ¯ ν 10 − 11 ν γ π 0 K L γ ¯ ν

Hadron-cluster background Largest contribution Background estimation (2015 data) 0.42 ± 0.18 Total 0.11 ± 0.04 other source 0.02 ± 0.02 0.05 ± 0.02 0.24 ± 0.17 hadron-cluster background # of events Background source interaction length ~ 40cm 50cm radiation length ~ 2cm 50cm PMT 4 Hadron-cluster Background PMT CsI CsI Upstream beam halo neutron Downstream Should be suppressed K L → π 0 ν ¯ ν γ γ K L → π + π − π 0 K L → 2 π 0

Hadron-cluster background CsI ΔT depth of the interaction Downstream ΔT (MPPC-PMT) = large neutron beam halo ΔT (MPPC-PMT) = small Upstream PMT CsI PMT Hadron-cluster Background 5 deep MPPC K L → π 0 ν ¯ 6 � 6 !! " ν S13360-6050CS (HPK) MPPC γ γ

6 Arbitrary Units 0 2000 Deposit energy Special run data ・ Physics data n Special run setup n Neutron Sample → Enhance the neutron events by placing Al plate decay (BR: 19.52%) Gamma Sample Used data taken in 2019 run Data Samples Deposit energy [MeV] K L → 3 π 0 ‣ Used ‣ Used special run data as a neutron samples CsI n Al plate

Timing Calculation (1) Calculate channel timing Cluster Event Display of the CsI calorimeter Energy → Constant Friction Time Channel Timing 
 0.5*Peak height + pedestal Pedestal Peak height + pedestal Calculate cluster timing (used in analysis) 7 ( t CF ) 2000 ADC counts 1800 1600 1400 1200 1000 800 600 400 200 0 0 10 20 30 40 50 60 t CF Time (clock=8 ns)

Timing Calculation (2) ) ΔT ➡ Energy Weighted Timing (only for E>10 MeV channels) ) 
 ➡ Energy weighted timing ( Cluster Timing (PMT) ➡ Max energy channel timing ( 50MeV Used 2 methods 100MeV 8 30MeV 5MeV Event Display of the CsI calorimeter Cluster Timing (MPPC) 
 T Max Energy MPPC T Energy Weighted MPPC Δ T M.E. = T Max Energy − T PMT MPPC ➡ Δ T E.W. = T Enegy Weighted − T PMT MPPC ➡

Performance of ΔT Cut (downstream one) ) distribution( Max (w/kinematic cut) (w/kinematic cut, w/tight all veto) hadron-cluster control sample (Data) 
 89.9% 9 ΔT range : ΔT : 25 ns < ΔT < 31.05 ns gamma efficiency = 89.9% 
 hadron-cluster background is suppressed to (2.1±0.1)% Δ T E.W. = T Energy Weighted Δ T E.W. − T PMT deltaT MPPC Arbitrary Units K L → 3 π 0 (Data) 0.06 Max Δ T cut at = 31.05 ns 0.05 neutron back ground (2.1 0.1)% ± 0.04 gamma efficiency = 89.9 0.03 v 0.02 0.01 0 26 28 30 32 34 36 38 40 42 44 T (ns) Δ

Energy weighted timing( 10 Efficiency of ΔT cut efficiency (log) than maximum energy channel timing By changing the higher threshold of ΔT, efficiency (γ, hadron-cluster) are calculated Hadron-cluster efficiency gamma efficiency ) has better performance 
 efficiency 1 − 1 10 Δ T M.E. = T Max Energy − T PMT MPPC Δ T M.E. − 2 10 Δ T E.W. = T Enegy Weighted − T PMT MPPC Δ T E.W. 0 0.2 0.4 0.6 0.8 1 Δ T E.W.

Correlation (Pulse Shape Related Cut) Neutron background is suppress to ~4% Neutron Like Gamma Like FPSD Value hadron-cluster control sample (Data) Waveform Template γ and neutron Fourier Transformation (w/ 90% signal efficiency) Pulse Shape Cut : Fourier Pulse Shape Discriminator (FPSD) Correlation btw. ΔT cut and other neutron cut 11 Fourier PSD [peak-10, peak+17] 28 0.35 1000 0.5 0.3 Gamma − 2 π i N − 1 ∑ N kn X k = 0.25 900 x n e 0.4 Neutron 0.2 n = 0 800 0.3 0.15 700 0.2 0.1 600 0.05 0.1 0 Phase : 2 π 0 10 20 30 40 50 60 0 5 10 15 20 25 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 28 Fourier Template 3 Arbitrary Units 1 − 1 10 K L → 3 π 0 (Data) 2 − 10 3 − 10 4 − 10 0 0.2 0.4 0.6 0.8 1 Minimum FPSD Value

Correlation (FPSD vs ΔT) 12 Small correlation but 
 hadron-cluster BG is suppress to 4% 2.1% 4.0% ΔT (w/o FPSD cut) ΔT (w/ FPSD cut) Apply FPSD cut Any correlation btw. FPSD vs ΔT ?

Hadron-cluster background is suppressed to 2.1% 
 (w/90% gamma efficiency) 
 Energy weighted timing has better performance than maximum energy channel timing. Correlation can be seen but enough small. 
 Summary 13 ‣ Performance of ΔT 
 ‣ Correlation btw. pulse shape cut vs ΔT 


N/S Ratio By changing the higher threshold of ΔT, N/S ratio is calculated. (neutron efficiency/gamma efficiency) N/S 
 higher threshold of ΔT (ns) (MPPC channel energy > 10MeV) 
 14 Δ T M . E . Δ T E . W . Δ T M . E . = T MPPC Maximum Energy − T PMT Δ T E . W . = T MPPC Enegy Weighted − T PMT