J-PARC における 4  He の生成と構造の研究 東北大学 大学院理学研究科 白鳥昂太郎 for the Hyperball-J Collaboration

2007 JPS in Tokyo Metropolitan University 2 Contents  E13 at J-PARC  Physics motivation  Setup : SksMinus  Yield estimate  Summary

2007 JPS in Tokyo Metropolitan University 3 Day-1 experiment E13 at J-PARC  Spin-flip B(M1) measurement and g  in a nucleus ( 7  Li)   N interaction study from p-shell hypernuclei ( 10  B and 11  B)  Radial dependence of  N interaction from sd-shell hypernuclei ( 19  F)  Charge symmetry breaking of  N interaction and Spin- flip property in hypernuclear production ( 4  He) Hypernuclear  -ray spectroscopy experiment

2007 JPS in Tokyo Metropolitan University 4 Motivation (1): Charge symmetry breaking  Mass difference :  +  0  -. Statistics of old  -ray data is poor, in particular 4  He(1 + →0 + ) data. Old data suggest large charge symmetry breaking in  N interaction. 4  H ⇔ 4  He (  n ⇔  p) PL83B(1979)252 Hyperfragment (Stop K - reaction) + NaI detector → In-flight (K -,  - ) reaction + Ge detector Doppler shift correction & Low background

2007 JPS in Tokyo Metropolitan University 5 Motivation (2): Spin-flip property  Confirm spin-flip cross sections  Study of baryon production in nuclei Beam momentum GeV/c    n   Spin-flip property of  hypernuclear production ( 4  He(1 + )) Elementary process Spin-flip by K* exchange G. P. Gopal et al., NPB119(1977)362, T. Harada priv. comm.  -ray spectroscopy is the only way to measure the spin-flip state. Excitation energy ~1MeV ⇔ Magnetic spectrometer resolution ~2 MeV 4  He(0 + ) 4  He(1 + )

2007 JPS in Tokyo Metropolitan University 6 Setup at the K1.8 beam line Beam momentum: 1.5 GeV/c Spin-flip measurement: GeV/c  (K -,  - ) reaction analysis: K1.8 + SksMinus   -ray measurement: Hyperball-J (6 % 1 MeV)  Liquid 4 He target (25 cm, 3.13 g/cm 2 ) 4 He (K -,  -  ) 4  He

2007 JPS in Tokyo Metropolitan University 7 SksMinus setup SksMinus  STOF : Time-of-flight  SAC : K - beam veto (n=1.03)  (SFV : K - beam veto)  SDC1~4 : Particle tracking Background Veto  SMF :  - from K - →  - +  SP0 :  - from K - →  - +  0 _ Requirements for  - of 1.4 GeV/c  Acceptance >100 msr, ~20 o scattering angles  Momentum resolution < 3 MeV/c (FWHM)

2007 JPS in Tokyo Metropolitan University 8 SksMinus basic performance  Acceptance is optimized for (K -,  - ) p K =1.5 GeV/c. Sufficient for 1.0~1.7 GeV/c  - Covering scattering angle up to 20 o  Momentum resolution < 3 MeV/c (FWHM)  PID counters: STOF, SAC (n=1.03)  - momentum [MeV/c] 2.7 T: p  = 1.1~1.7 GeV/c (p K = 1.2~1.8 GeV/c) (2.2 T: p  < 1.1 GeV/c (p K < 1.2 GeV/c))

2007 JPS in Tokyo Metropolitan University 9 Decay veto counters Decay veto counters will be used without changing the setup.  - (passing through)  - (stopped in the iron) Decay veto counters are optimized for 1.5 GeV/c beam condition. SMFSP0

2007 JPS in Tokyo Metropolitan University 10 Decay veto counters: performance Performance of SMF  - rejection 1.5 GeV/c Kinematical region of  - only overlaps less than 3 o.  stopping points follow the same distribution.   W/o veto counters Trigger rate ~ GeV/c (~ GeV/c)  events are greatly reduced in offline 1.5 GeV/c.  - rejection >99% Performance of SP0 1.1 GeV/c1.3 GeV/c 1.5 GeV/c1.8 GeV/c

2007 JPS in Tokyo Metropolitan University 11 Yield estimate Mom. [GeV/c]  eff (0~20 o ) [  b]* Full intensity [×10 8 /h] 3.6 sec spill Yield (1 + state) [/h]  ray yield [/h] Tracking eff = 0.6 Ge live time = 0.7   = 1 MeV  eff : Cross section corrected by acceptance ~200 hours for total beam time

2007 JPS in Tokyo Metropolitan University 12 Summary  4  He study in Day-1  -ray spectroscopy experiment Charge symmetry breaking in  N interaction Spin-flip property of  hypernuclear production  SksMinus is designed for (K -,  - ) reaction at p K =1.1~1.8 GeV/c. One configuration for all beam momentum Sufficient acceptance (> ~1.7 GeV/c)  Total beam time of ~200 hours necessary for ~200 counts per each momentum

Backup

2007 JPS in Tokyo Metropolitan University 14 Experimental advantages  -ray spectroscopy is the only way to measure the spin-flip state. Excitation energy ~1MeV ⇔ Magnetic spectrometer resolution ~2 MeV → It is difficult to resolve the spin-flip state. Early experiment (by NaI detector) Hyperfragment (Stop K - reaction) + Identification via weak decay products  Large momentum transfer + Recoil momentum direction cannot be measured. ×Doppler shift correction = broad peak  Many background events Low sensitivity This experiment (by Ge detector) In-flight (K -,  - ) reaction Doppler shift correction + Low background Advantages for  -ray measurement

2007 JPS in Tokyo Metropolitan University 15 Cross section of 4  He(1 + )&(0 + )

2007 JPS in Tokyo Metropolitan University 16 Particle identification  (K -,  - ) →  - or K - Beam K- can greatly be decreased by SAC (n=1.03) and SFV → less than 30 trigger /spill (500 k/spill beam)  Time resolution of STOF ~150 ps (rms)  For B(M1) measurement, dual SAC is planned because of saving forward events.

2007 JPS in Tokyo Metropolitan University 17 Beam K BACSAC Target 20cm  Decay Background events : Beam decay Fake trigger ~1940 /spill True event trigger ~600 /spill (Contribution of three-body decay ~200 /spill) _  K - →  - (63.4%) (1390 /spill) ⇒ Muon Filter  K - →  -  0 (21.1%) (350 /spill) ⇒ PiZero Veto _  Trigger rate  Missing mass

2007 JPS in Tokyo Metropolitan University 18 Muon Filter -SMF- performance  Rejected  86%  Non-rejected (stopped in the iron) → offline analysis >99%  Over kill for true π ~2.5% Rejected Non-rejected Target SKS magnet Iron SMF Stopping/absorption points STOF

2007 JPS in Tokyo Metropolitan University 19 PiZero veto -SP0- 78% of  -  0 events rejected 6 sets of 5 mm lead plate and 10 mm scintillation counter layer at 1.5 GeV/c beam. Acceptance 85%

2007 JPS in Tokyo Metropolitan University 20 3-body Decay K - →π - π - π + (5.58%) K - →e - π 0 ν (4.87%) K - →μ - π 0 ν (3.27%) K - →π - π 0 π 0 (1.73%)

2007 JPS in Tokyo Metropolitan University 21 Background rejection and trigger rate  (K -,π - ) Reaction rate : 600 ⇒ ~570  K - →  - : 1390 ⇒ ~190  K - →  -  0 : 350 ⇒ ~80  K - Beam : ~30  3-body decay : 200 ⇒ ~70  Total : 2570 (1940) ⇒ 940 (340) /spill Total trigger is reduced by Ge trigger ~1/2. ~470/spill w/ Ge trigger Comparable to the present trigger rate decay 7  Li bound states Offline analysis

2007 JPS in Tokyo Metropolitan University 22 Background rejection and trigger rate ~470/spill w/ Ge trigger Comparable to the present trigger rate decay Total trigger is reduced by Ge trigger ~1/2. 7  Li bound states Offline analysis  (K -,π - ) Reaction rate : 600 ⇒ ~570  K - →  - : 1390 ⇒ ~190  K - →  -  0 : 350 ⇒ ~80  K - Beam : ~30  3-body decay : 200 ⇒ ~70  Total : 2570 (1940) ⇒ 940 (340) /spill

2007 JPS in Tokyo Metropolitan University 23 How about 4  H ?   ray from 4  H by (K -,  0 ) tagging by SP0 ? (To detect no charged particle events ?)