Update of the DeeMe spectrometer design and its performance Nguyen Duy Thong, Masaharu Aoki, Doug Bryman C, Satoshi Mihara A, Yohei Nakatsugawa A, Hiroaki Natori A, Nguyen Minh Truong, Hajime Nishiguchi A, Toshi Numao D, Yoshihiro Seiya B, Kousuke Shimizu B, Kazuhiro Yamamoto B and DeeMe Collaboration Osaka University, KEK A, Osaka City University B, UBC C, TRIUMF D Outline: Introduction DeeMe Project Spectrometer Update Summary

Introduction  Nucleus Muon decay-in-orbit Muon capture    + (A,Z)   + (A, Z-1) MC:DIO = 1:1000 (H), 2:1(Si), 13:1(Cu)  (free  - ) = 2.2  s  (  - in Si) = 0.76  s  -e conversion  - +(A,Z)  e - + (A,Z) Charged Lepton Flavor Violation Forbidden in the Standard Model  -e conversion  - +(A,Z)  e - + (A,Z) Charged Lepton Flavor Violation Forbidden in the Standard Model Theoretical estimation for  -e conversion: SUSY-GUT,SUSY-seesaw, Doubly Charged Higgs Boson.. BR: ~ Recent Upper Limit: SINDRUM-II: BR[  - +Au  e - +Au] < 7x SINDRUM-II: BR[  - +Ti  e - +Ti] < 4.3x TRIUMF: BR[  - +Ti  e - +Ti] < 4.6x Muonic atom in nuclear field

DeeMe project Search for  -e conversion BR: Place: MLF, J-PARC Data taking : from 2015 Search for  -e conversion BR: Place: MLF, J-PARC Data taking : from Signature :  - +(A,Z)  e - +(A,Z) Single mono-energetic electron: ~105MeV Delayed :~1  s Main Physics background: DIO Signature :  - +(A,Z)  e - +(A,Z) Single mono-energetic electron: ~105MeV Delayed :~1  s Main Physics background: DIO DIO BG  -e signal Spectrometer: Bending magnet Multi-Wire Proportional Chambers (MWPC) DeeMe status Stage 2 for construction & physics run: approved HV-switch MWPC: ongoing (28pTH-6). Target: start with Graphite & SiC: R&D ongoing (27aSD-2)

Spectrometer Update To reduce construction cost, PACMAN Magnet existing in TRIUMF will be used PACMAN Magnet PACMAN : Type: rectangular dipole magnet Size = 300x930x760(mm 3 ) Max field = 1 T Sector Magnet

Purpose of this study Purpose of this study: PACMAN can be used or not? Why? Defocusing issue of PACMAN is stronger than Sector Magnet Requirement : Momentum resolution: dP<0.5MeV/c Parameters : a. Bending angle b. Spatial resolution c. Material Thickness d. Size of WC3,4: distributed-source Sector Magnet PACMAN Magnet Mono-energetic 105MeV/c

a. Bending angle Result: consistent with theoretical estimation. dP<0.5MeV/c: bending angle greater than 50-degree for  h =0.3 mm Where d : distance between 2 wires In MWPC 0.5 MeV/c

b. Spatial resolution dP<0.5MeV/c: for 70-degree,  h ≤ 0.7mm Current design  h : 0.3mm. Material thickness: 0.12%X 0 Dominated by multiple scattering 0.5MeV/c (X 0 : radiation length)

dP<0.5 MeV/c: for 70-degree, thickness < 0.20 %X 0 Final MWPC: material thickness ~ 0.12 % X 0 c. Material thickness: contribute to multiple scattering (X 0 : radiation length)

d. Optimization of WC3,4 size Adjust the size of WC3,4: - Obtain a high acceptance - Maximize an accepted energy range Distributed source WC 3 Acceptance exit of Hline DIO BG  -e signal AP background

70-degree Momentum-Acceptance curve The range of accepted momentums : 90 ~ 120 MeV/c The highest acceptance can be obtained if width ≥ 600mm

Summary DeeMe experiment: search for  -e S.E.S Stage 2 : Approved by KEK/IMSS PAC It is being constructed at MLF, J-PARC. Data taking : from 2015 PACMAN magnet can be replaced for Sector Magnet: No difficulty to obtain dP<0.5MeV/c Roughly estimated parameters: Bending angle ≥ 50-degree for  h =0.300 mm Spatial resolution ≤ 0.8 mm for 70-degree Material thickness ≤ 0.25% for 70-degree WC3,4 width ≥ 600 mm For a real design, further optimization is ongoing with full MC.

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Backup dP<0.5 MeV/c Bending angle should be greater than 50 deg Spatial resolution : 0.3mm≤RES≤0.8mm Wire chamber thickness: less than 0.5mm High acceptance : WC3,4 width ≥600mm A trial with realistic Momentum Spectrum Spectrometer configuration: 70-deg bending angle RES=0.3mm Wire chamber thickness = 0.244mm WC3,4 width= 800mm Reconstruction: Kalman-filter with GENFIT library

Observation: dP is inversely proportional to bending angle  consistent with theoretical estimation dP<0.5MeV: bending angle should be greater than 50deg dP : tend to become statured if bending angle >=60deg Conclusion: Bending angle could be greater than 60-deg. Theoretical Estimation : momentum resolution is inversely proportional to bending angle

Theoretical estimation: Momentum resolution is linearly proportional to spatial resolution Observation : dP: not clearly linearly proportional to spatial resolution due to affect of Multiple scattering dP<0.5 MeV/c: RES<0.8mm Current prototype of MWPC: RES=0.3mm We want to increase value of RES in order to reduce number of wires. Conclusion: 0.3mm≤RES≤0.8mm.

DeeMe spectrometer Prompt burst : proton beam creates secondary beam tracker Hodoscope DIO BG  -e signal DIO BG: Magnet spectrometer for suppressing high energy tail Requirements: p=105MeV/c  p<0.5MeV/c (RMS) Material thickness <0.1%X 0 Prompt burst 33k particles /pulse 600ns 300ns Signal window Not in scale 16

PACMAN magnet from TRIUMF

60deg Momentum – Acceptance curve The range of accepted momentum : 90 ~ 120 MeV/c Highest acceptance around 105 MeV/c when width is greater than 500mm

80-deg Momentum-Acceptance curve The range of accepted momentum : 90 ~ 120 MeV/c Highest acceptance around 105 MeV/c when width is greater than 600mm

Sector Magnet Beam exit of Hline

Material Thickness Contribute to Multiple scattering Convert to thickness of kapton Anode frame Potential frame Cathode frame Metal frame Space frame Structure of prototype MWPC