Plan of Hypernuclear gamma-ray spectroscopy at J-PARC

1. K.Shirotorifor the Hyperball-J collaboration. Tohoku Univ.Japan Purpose of hypernucler gamma-ray spectroscopy Approved “DAY-1” experimentE13 Investigation of ΛN effective interaction Beam Momentum Plan of Hypernuclear gamma-ray spectroscopy at J-PARC (K-, π- γ) at pK = 1.5 GeV/c (500k/spill) V(r) = V0(r) + Vs(r) sN・sL + VN(r) lNL・sN + VL(r) lNL・sL + VT(r) S12 K- + n-> L + p- • Spin-flip B(M1) measurement and gΛin a nucleus 7ΛLi: Least ambiguities exist and most reliable • ΛN interaction study from p-shell hypernuclei 10ΛBand 11ΛB: Inconsistency exists. Not enough experimental data • Radial dependence of ΛN interaction from sd-shell hypernuclei 19ΛF: Simplest in sd-shell • Spin-flip property in hypernuclear production and charge symmetry breaking 4ΛHe: Easiest to observe a spin-flip state and largest CSB is suggested but previous data is suspicious (Core nucleus：p-shell、Λ：s-shell → Radial IntegralsD、SN、SL、Tare determined byprevious experiments D= 0.43SN= -0.39SL= -0.01T= 0.03 [MeV] We need more data for checking parameters. Spin dependent force of ΛN interaction are investigated by measuring energy spacing of hypernuclei (～a few 10 keV). (K-, π- γ) at pK = 1.5 GeV/c (500k/spill) (Out going π-～1.4 GeV/c) for exciting both non-spin-flip and spin-flip states Systematic studiesof several hypernuclei→ J-PARC Setup and Hyperball-J Requirement on spectrometer for hypernuclear gamma-ray spectroscopy Improvement of experimental condition (π+, K+) reaction @ KEK • Good spectrometer SKS (Momentum resolution ～1MeV/c) • Low background • Low production rate (K-, π-) reaction @ BNL • High production rate • Spectrometer is worse than KEK • Large Background from Beam K- decay • To analyze 1.4GeV/c-scattered π- by existingspectrometer system • Large acceptance ～100[msr], θ～20[degree] →Enough hypernuclear production yield • Good momentum resolution 2～4[MeV/c] →To distinguish excited states of hypernuclei High production rate +Background rejection Good spectrometer Modify SKS (Superconducting Kaon Spectrometer ) HyperWall-J or HyperBall-J SKSMinus : New configuration The K1.8 Beam line and SKS • Modified SKS for hypernuclear gamma-ray experiment (SKSMinus) • SKS for (K-, π-) detection • Hyperball-J for Gamma-ray measurement Wall Type Ball Type • Ge (r.e.70%) x30 • PWO background suppression for higher counting rate • Waveform readout for pulse shape analysis SKS SKS Beam spectrometer ・SAC : K- beam veto (n=1.03) ・SFV : K- beam veto ・STOF : Time-of-flight ・BH1,2 : Time-of-flight ・BAC : π- veto (n=1.03) MWPC : Beam position measurement LN2 cooling ↓ Mechanical cooling by Pulse tube DC : Beam position measurement Target : ～20 g/cm2 π Background Veto Beam K ・SMF : μ- from K-→μ-+ν ・SP0 : π- from K-→π-+π0 Total photo peak efficiency ~6% @ 1MeV (Geant4 simulation) Beam spectrometer Previous SKS to SKSMinus SKS Acceptance & Momentum resolution Improvement SKSMinus Previous condition 2.7T 2.2T Rough estimation of yield compared with previous E930(’01)experiment at BNL • Acceptance ～120[msr] with large drift chambers (2[m]×1[m]) 100[msr] for present SKS • Momentum resolution 2.1[MeV/c] (bending angle ～60°w/ multiple scattering) 0.8[MeV/c] for present SKS θ～20° θ～20° Checked by simulation Momentum resolution Present spec • Scattered particles are not focused and present drift chambers (SDC3,4)are smaller for large reaction angle (half acceptance). →Large acceptanceby large drift chambers • Smaller bending angle (100°→60°) →Momentum resolutiongets worse. Simulation program is checked against previous SKS configuration 8 times higher Veto counters for K- decay rejection Summary Background rejection Target 20cm Muon Filter PiZero Veto v v BAC SAC μ Beam K • Several hypernulcear gamma-ray spectroscopy are planed at J-PARC K1.8 beam line. • Experiments will be performed by (K-,π-) reaction at 1.5 GeV/c K- beam with modified SKS and new Hyperball. • We will install veto counters for K- decay rejection and they shows good efficiency by simulations. • Experiment will be started at 2008. Decay ν Beam K- decay products make serious background (Same kinematical region to (K-,π-) reaction) • K-→μ-ν (63.4%) ⇒Muon Filter • K-→π-π0 (21.1%) ⇒PiZero Veto π- (stopped in the iron) μ- (passing through) Iron block Fake trigger ～1700/spill (K-,π-) reaction event trigger ～700/spill • 89% of μ can be detected in the trigger • In the offline analysis ～100% • Over kill for true π ～1.7% • 70% of π0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of γ from π0 hit the SP0) K-→π-π-π+ (5.58%) K-→e-π0ν (4.87%) K-→μ-π0ν (3.27%) K-→π-π0π0 (1.73%) Contribution is relatively small ～150 trigger