Status of the ! " $ % & & search at J-PARC KOTO - PowerPoint PPT Presentation

Kuno and Yamanaka Groups End-of-the Year 1 2019/12/23 Presentation Status of the ! " → $ % & ̅ & search at J-PARC KOTO experiment Satoshi Shinohara 2019/12/23 Kuno and Yamanaka Groups End-of-the Year Presentation KAON2019 @ Perugia Univ. Italy

Kuno and Yamanaka Groups End-of-the Year 2 2019/12/23 Presentation KOTO J-PARC • ! " → $ % & ̅ & - highly suppressed : BR(SM) : 3.0 × 10 -11 - small theoretical uncertainty （ ~2% ） → good probe for new physics search • signal : (π 0 → ２ γ)+ Nothing - 2γ→CsI calorimeter - Nothing → Hermitic veto detectors signal region on the Pt vs. Z plane (blinded analysis)

Kuno and Yamanaka Groups End-of-the Year 3 2019/12/23 Presentation History of data taking Barrel detector 2019 data upgrade (2016 Mar.) 18 10 × 100 100 Accumulated P.O.T. Beam Power (kW) 2016, 90 2017, 2018 80 80 2015 data data 70 2013 data (Phys. Rev. 60 60 Lett. 122, (PTEP 2017 021C01) 021802) 50 Operation 40 40 of Hadron facility was 30 stopped. 20 20 10 0 0 2012 2013 2014 2016 2016 2017 2018 Dec Dec Dec Jan Dec Dec Dec

Kuno and Yamanaka Groups End-of-the Year 4 2019/12/23 Presentation Single event sensitivity (S.E.S) • S.E.S = 1/((K L yield) × (signal acceptance)) reconstructed K L mass distribution from ! " → 2% & analysis ! " → % & ' ̅ ' MC blind region signal region Preliminary Preliminary K L yield (@ beam exit) : signal acceptance : 7.1 × 10 12 ( × ~1.5 from 2015) 2.0 × 10 -4 ( × ~1.3 improved from 2015 ) Signal box : optimized better for S/N ( ↔ S.E.S 2015 : 1.3 × 10 -9 ) S.E.S : 6.9 × 10 -10

Kuno and Yamanaka Groups End-of-the Year 5 2019/12/23 Presentation Hadron cluster BG Physics run Special run n n n n n Al target (10 mm thickness) Control sample Physics data preliminary preliminary

Kuno and Yamanaka Groups End-of-the Year 6 2019/12/23 Presentation Hadron cluster BG in 2015 analysis 2015 run background summary table Hadron cluster BG BG source No. events ! " → $ % $ & $ ' 0.05 ± 0.02 CSI K L BG ! " → 2$ ' 0.02 ± 0.02 neutron Other ! " decays 0.03 ± 0.01 0.24 ± 0.17 Hadron cluster Neutron Upstream $ ' 0.04 ± 0.03 related CV ) 0.04 ± 0.02 BG Total 0.42 ± 0.18 Phys. Rev. Lett. 122, 021802

Kuno and Yamanaka Groups End-of-the Year 7 2019/12/23 Presentation Hadron cluster BG update from 2015 (cut) cluster 1. Cluster shape cut with deep learning - S/N : × ~2 from 2015 2. Pulse shape discrimination with Fourier transformation - S/N : × ~1.8 from 2015

Kuno and Yamanaka Groups End-of-the Year 8 2019/12/23 Presentation Hadron cluster BG estimation (10 mm thickness) (10 mm thickness) • Found contamination in the control sample - Developed more reliable estimation method • based on single cluster reduction - reduction : × 27( ± 19) from w/o concerning scatter K L →2γ

Kuno and Yamanaka Groups End-of-the Year 9 2019/12/23 Presentation Hadron cluster BG Preliminary 0.01 ±0.00 0.00 ±0.00 0.02 ±0.00 0.01 ±0.00 0.00 0.00 ±0.00 ±0.00

Kuno and Yamanaka Groups End-of-the Year 10 2019/12/23 Presentation Overlapped pulse BG • Overlapped pulse shifts measured time for veto detectors - Narrower veto window • recover signal acceptance • increase BG from overlapped pulse example of overlapped waveform (MC) pulse height [a.u.] veto window clock [8ns] (125MHz waveform digitizer)

Kuno and Yamanaka Groups End-of-the Year 11 2019/12/23 Presentation Overlapped pulse BG • Overlapped pulse discriminator - Pulse shape information : Fourier transformation - χ 2 : compared with single hit template χ 2 distribution of upstream detector w/o new method w/ new method Preliminary

Kuno and Yamanaka Groups End-of-the Year 12 2019/12/23 Presentation Overlapped pulse BG • Narrower veto window + overlapped pulse discriminator Overlapped pulse BG from Overlapped pulse BG from ! " → 3% & MC analysis ! " → %'( MC analysis Preliminary Preliminary <0.04 <0.09 Narrower veto window : Recovered 10% signal acceptance No remaining event due to overlapped pulse

Kuno and Yamanaka Groups End-of-the Year 13 2019/12/23 Presentation BG summary Preliminary S.E.S : 6.9 × 10 -10 500 7 #BG Pi0Pt Preliminary 450 ! " → 2% & <0.18 6 ! " → % ' % ( % & <0.02 400 462 0 0 0.07 0.00 ! " → 3% & 350 5 ± 0.05 ± 0.00 (overlapped <0.04 pulse) 300 0.33 ± 0.11 (including signal region) 4 Ke3 250 (overlapped <0.09 pulse) 3 200 0.05 ± 0.02 0 0.18 ! " → 2* 0.001 ± 0.001 150 ± 0.09 2 Upstream π 0 0.001 ± 0.001 100 0.02 473.1 ± 0 0 Hadron cluster 1 ± 0.00 50 4.2 0.08 ± 0.06 0.00 ± 0.00 CV-pi0 <0.10 0 0 2000 3000 4000 5000 6000 CV-eta 0.03 ± 0.01 Total 0.05±0.02 observed Pi0RecZ expectation

Kuno and Yamanaka Groups End-of-the Year 14 2019/12/23 Presentation Unblinded

Kuno and Yamanaka Groups End-of-the Year 15 2019/12/23 Presentation Unblinded 500 7 Pi0Pt Preliminary 450 6 400 350 5 300 4 250 3 200 150 2 100 1 50 0 0 2000 3000 4000 5000 6000 Pi0RecZ unblinded in the end of Aug. 2019

Kuno and Yamanaka Groups End-of-the Year 16 2019/12/23 Presentation 500 7 Preliminary Pi0Pt upstream detector 0.07 0.00 450 6 ± 0.05 ± 0.00 waveform of the event 400 ADC [counts] 350 5 P 0.33 ± 0.11 r e l i m measured i 300 n a r y 4 0.05 ± 0.02 time 250 0.18 3 200 on-time ± 0.09 150 2 100 473.1 ± 1 0.08 ± 0.06 50 4.2 clock [8ns] 0 0 2000 3000 4000 5000 6000 (125MHz waveform digitizer) Pi0RecZ On-timing peak is shifted by large pulse expectation

Kuno and Yamanaka Groups End-of-the Year 17 2019/12/23 Presentation BG estimation related overlapped pulse P r e l i m i n a r y #BG 500 7 Preliminary Pi0Pt 0.07 0.00 KL3pi0 (overlapped pulse) <0.04 450 6 ± 0.05 ± 0.00 Ke3 (overlapped pulse) <0.09 400 350 5 0.33 ± 0.11 • Underestimated the BG 300 4 0.05 ± 0.02 from overlapped pulse? 250 0.18 3 200 ± 0.09 150 2 • Checking the properties 100 473.1 ± 1 0.08 ± 0.06 of the other candidates 50 4.2 0 0 • Did we miss other 2000 3000 4000 5000 6000 Pi0RecZ background sources? expectation • planning to reevaluate other BG sources

Kuno and Yamanaka Groups End-of-the Year 18 2019/12/23 Presentation Summary • ! " → $ % & ̅ & at J-PARC KOTO experiment • S.E.S : 6.9 × 10 -10 • BG estimation : 0.05 ± 0.02 • Opened the box → 4 candidate events in the signal region Event properties: One event : overlapped waveform Checking other candidates carefully

Kuno and Yamanaka Groups End-of-the Year 19 2019/12/23 Presentation END

Kuno and Yamanaka Groups End-of-the Year 20 2019/12/23 Presentation Detector and DAQ upgrade in 2016-2018 Inner barrel (IB) • Barrel detector was upgraded in 2016.4 - 13.5X 0 → 18.5X 0 - ! " → 2% & BG : ×1/3 ! " → 2% & • DAQ upgrade (covered in poster session) Energy deposit online - Online cluster counting (2017~) map of CsI clustering map - Higher DAQ live time ratio • ~80% (2015 @ 42kW beam) → ~99% (2018 @ 51kW beam) cluster

Kuno and Yamanaka Groups End-of-the Year 21 2019/12/23 Presentation Result of 2015 physics run Phys. Rev. Lett. 122, 021802 • Single event sensitivity : 1.30 ± 0.01 -./. ± 0.14 -1-. ×10 34 - No event in the signal region • Upper limit (90% C.L.) : Br( 5 6 → 7 8 9: 9 ) < 3.0 × 10 -9 observed × 10 improvement from expectation contour : ! " → $ % & ̅ & (MC) previous limit (KEK E391a)

Kuno and Yamanaka Groups End-of-the Year 22 2019/12/23 Presentation Toward 2016-2018 data analysis • Higher beam power → larger signal loss due to the accidental hit (76% loss in 2015 analysis) • To achieve better sensitivity → Narrower veto window - Need BG study due to the narrower veto window 2018 June, 51kW study from 2015 data

Kuno and Yamanaka Groups End-of-the Year 23 2019/12/23 Presentation Single event sensitivity (S.E.S) • S.E.S = 1/((K L yield) × (signal acceptance)) signal region ! " → $ % & ̅ blind region & MC 2015 signal box 2016 ~ 2018 signal box signal acceptance : + 6% (from 2015 signal box) signal acceptance : 2.0 × 10 -4 • Signal box : determined by S/N Preliminary • S.E.S : 6.9 × 10 -10 (S.E.S 2015 : 1.3 × 10 -9 )

Kuno and Yamanaka Groups End-of-the Year 24 2019/12/23 Presentation Upstream-π 0 BG CsI n • Halo-neutron hits upstream π 0 ->2γ detector - γ + γ • small visible energy shifted reconstructed Z position Preliminary - n + γ • various reconstructed Z position - Shrink signal box of upstream Z • #BG upstream-π0 : 0.001 ± 0.001

Kuno and Yamanaka Groups End-of-the Year 25 2019/12/23 Presentation CV (front) CSI CV-η BG Z = 5862 Z = 6168 [mm] [mm] CsI • Neutron hits Charged Veto (CV) η->2γ n and generates η - reconstruction : assumed π 0 mass - m η ~ 4m π0 → reconstructed Z position : rec. Pt [MeV/c] Preliminary shifted in the signal region #BG η = 0.03 ± 0.01 rec. Z [mm]