Hypernuclear gammaray spectroscopy at JPARC K 1 8

Hypernuclear gamma-ray spectroscopy at J-PARC K 1. 8 Beam line Tohoku Univ. K. Shirotori 東北大学 大学院理学研究科 白鳥昂太郎 2006 JPS in NARA

Outline Ø Background of experiments Ø Requirement on setup Ø Setup, SKS & Hyperball-J Ø Detectors in detail, SKS & Veto counters Ø Summary 2006 JPS in NARA 2

Previous hypernuclear gamma-ray experiments Investigation of ΛN interaction by Λ hypernuclei. (π+, K+) reaction @ KEK (K-, π-) reaction @ BNL ØGood spectrometer SKS (Momentum resolution ～ 1 Me. V/c) ØLow background ØLow production rate ØHigh production rate ØSpectrometer is worse than KEK ØLarge Background from Beam Kdecay Good spectrometer High production rate +Background rejection Systematic studies of several hypernuclei　→ J-PARC 2006 JPS in NARA 3

Proposed “DAY-1” experiment　E 13 Ø Several light hypernulcear gamma-ray spectroscopy experiments are planed. (4ΛHe, Ø (K-, 7 Li, 10 B, 11 B, 19 F) Λ Λ π- γ) at p. K = 1. 5 Ge. V/c (500 k/spill) (Out going π -～ 1. 4 Ge. V/c) Magnetic spectrometers for (K-, π-) detection Ø Hyperball-J for Gamma-ray measurement Ø 2006 JPS in NARA 4

Hyper. Ball-J or Hyper. Wall-J Wall Type Ball Type ØSingle Ge (r. e. 70%) ～ 30 ØPWO background suppression for higher counting rate ØWaveform readout Target LN 2 cooling ↓ Mechanical cooling by Pulse tube Total photo peak efficiency >5% @ 1 Me. V (Geant 4 simulation) 2006 JPS in NARA 5

Requirement on spectrometer for hypernuclear gamma-ray spectroscopy analyze 1. 4 Ge. V/c-scattered π- by existing spectrometer system. Ø Large acceptance ～ 100[msr], θ～ 20[degree]. Ø To →Enough hypernuclear production yield. Ø Good momentum resolution 2～ 4[Me. V/c]. →To distinguish excited states of hypernuclei. Modify SKS (Superconducting Kaon Spectrometer ) 2006 JPS in NARA 6

The K 1. 8 Beam line and SKS Beam spectrometer ・BH 1, 2 : Time-of-flight ・BAC : π- veto (n=1. 03) SKS ・SAC : K- beam veto (n=1. 03) ・SFV : K- beam veto SKS ・STOF : Time-of-flight MWPC & DC : Beam position measurement Background Veto ・SMF : μ- from K-→μ-+ν ・SP 0 : π- from K-→π-+π0 Target : ～ 20 g/cm 2 Beam spectrometer Hyperball-J : γray 2006 JPS in NARA 7

Present SKS to New SKS 2. 2 T θ～ 20° ØScattered particles are not focused and present drift chambers (SDC 3, 4) are small for large reaction angle (half acceptance). →Large acceptance by large drift chambers ØSmaller bending angle(100°→ 60°) →Momentum resolution gets worse. Momentum resolution 0. 1%FWHM (0. 72 Me. V/c) @ 720 Me. V/c, 2. 2 T Maximum central momentum 1. 0 Ge. V/c @ 2. 7 T Acceptance 2006 JPS in NARA 100 msr @ 0. 72 Ge. V/c 8

Present SKS to New SKS 2. 7 T θ～ 20° ØScattered particles are not focused and present drift chambers (SDC 3, 4) are small for large reaction angle (half acceptance). →Large acceptance by large drift chambers ØSmaller bending angle(100°→ 60°) Parallel scattering →Momentum resolution gets worse. Momentum resolution 0. 1%FWHM (0. 72 Me. V/c) @ 720 Me. V/c, 2. 2 T Maximum central momentum 1. 0 Ge. V/c @ 2. 7 T Acceptance 2006 JPS in NARA 100 msr @ 0. 72 Ge. V/c 9

Present SKS to New SKS ØScattered particles are not focused and present drift chambers (SDC 3, 4) are small for large reaction angle (half acceptance). 2. 7 T θ～ 20° →Large acceptance by large drift chambers ØSmaller bending angle(100°→ 60°) →Momentum resolution gets worse. 2006 JPS in NARA 10

Present SKS to New SKS ØScattered particles are not focused and present drift chambers (SDC 3, 4) are small for large reaction angle (half acceptance). →Large acceptance by large drift chambers SBS ØSmaller bending angle(100°→ 60°) →Momentum resolution gets worse. K- beam directly hit SDC 3, 4. ↓ Scattering beam particles by heavy material (Pb, W) 300 k. Hz→ 60 k. Hz/wire @ 20 mm cell 2006 JPS in NARA 11

SKS : New configuration SKS ・SAC : K- beam veto (n=1. 03) ・SFV : K- beam veto ・STOF : Time-of-flight DC : Beam position measurement Background Veto ・SMF : μ- from K-→μ-+ν ・SP 0 : π- from K-→π-+π0 π Beam K 2006 JPS in NARA 12

SKS Acceptance & Momentum resolution ØAcceptance ～ 120[msr] with large drift chambers (2[m]× 1[m]) 100[msr] for present SKS ØMomentum resolution 2. 1[Me. V/c] (bending angle ～ 60° multiple scattering) 0. 8[Me. V/c] for present SKS Simulation program is checked against previous SKS configuration SKS performance is sufficient for hypernucler gamma-ray 2006 JPS in NARA spectroscopy 13 w/

BAC Background rejection Beam K Target 20 cm SAC μ Decay ν Beam K- decay products make serious background Ø K-→μ-ν (63. 4%) ⇒Muon Filter Ø K-→π-π0 (21. 1%) ⇒Pi. Zero K-→π-π-π+ (5. 58%) K-→e-π0ν (4. 87%) K-→μ-π0ν (3. 27%) K-→π-π0π0 (1. 73%) Veto Fake trigger ～ 1700/spill True event trigger ～ 700/spill Contribution is relatively small ～ 150 trigger 2006 JPS in NARA 14

Muon Filter Thick Material (ex. Iron) μ- Pass through πStopped by hadronic interaction Scintillation counter Only μ-　can be detected. 2006 JPS in NARA 15

Muon Filter Before After Ø 89% of μ can be detected in the trigger ØIn the offline analysis ～ 100% ØOver kill for true π ～ 1. 7% 2006 JPS in NARA 16

Pi. Zero Veto Before Ø 70% of can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of π0 After γ from π0 hit the SP 0) Simulation in progress 2006 JPS in NARA 17

Trigger rate (K-, π- γ) at p. K = 1. 5 Ge. V/c (500 k/spill) Ø Ø Ø (K-, π-) Reaction rate ～ 700/spill K-→μ-ν ～ 1320/spill K-→π-π0 ～ 390/spill K- Beam ～ 10/spill 3 -body decay ～ 150/spill ～ 2570/spill w/o Veto counters Ø (K-, π-) Reaction rate ～ 700/spill K-→μ-ν ～ 140/spill K-→π-π0 ～ 120/spill K- Beam ～ 10/spill 3 -body decay ～ 150/spill 2006 JPS in NARA ～ 1130/spill w/ Veto counters Ø Ø True trigger ～ 350/spill w/ Ge trigger and fake trigger greatly decreased. ～ 500/spill w/ Ge trigger Comparable to the present 18 trigger rate

Summary Ø Several hypernulcear gamma-ray 　 experiments are planed at the J-PARC K 1. 8 beam line. Ø SKS is sufficient for hypernuclear gamma-ray spectroscopy. Ø Simulations in progress show a good veto counter efficiency. Ø Estimation of background from heavy counter materials is necessary. 2006 JPS in NARA 19

Backup 2006 JPS in NARA

Rough Kawazanyou Ø Ø Ø (compared with BNL E 930) Beam 200 k/spill→ 500 k/spill : 2. 5 times Acceptance 60[msr]→ 120[msr] : 2 times Hyperball 2. 5%→ 6% : 2. 4 times S/N : 2 times Cross section 1/3 times (0. 9→ 1. 5 Ge. V/c) → 8 times 2006 JPS in NARA 21

Proposed “DAY-1” experiment　E 13 (K-, π- γ) at p. K = 1. 5 Ge. V/c (500 k/spill) Ø Spin-flip B(M 1) measurement and gΛ in a nucleus 7 Ø ΛLi ΛN interaction study from p-shell hypernuclei 10 Ø ΛB and 11 ΛB : Inconsistency exists. Not enough experimental data Radial dependence of ΛN interaction from sd-shell hypernuclei 19 Ø : Least ambiguities exist and most reliable ΛF : Simplest in sd-shell Spin-flip property in hypernuclear production 4 ΛHe : Easiest to observe a spin-flip state 2006 JPS in NARA 22

Beam Momentum K- + n -> L + p- 2006 JPS in NARA 23

ΛN effective interaction V(r) = V 0(r) + Vs(r) s. N・s. L + VN(r) l. NL・s. N + VL(r) l. NL・s. L + VT(r) S 12 (Core nucleus：p-shell、Λ：s-shell) →Radial Integrals D、SN、SL、T　are determined by previous experiments D= 0. 43　SN= -0. 39　SL= -0. 01　T= 0. 03 [Me. V] Some inconsistencies appear ! Ex. 10ΛB puzzle → Theory fails to predict energy spacing of ground state doublet To solve these problems and for systematic studies of several hypernuclei　→ J-PARC 2006 JPS in NARA 24

SKS Minus ØTime-of-flight : STOF ØPosition measurement : SDC 1 ～ 4 ØBeam veto : SAC ØBeam veto : SFV ØVeto counter, μ- from K→μ-+ν : SMF ØVeto counter, π- from K→π-+π0 : SP 0 2006 JPS in NARA 25

Time resolution ØFlight time ～ 16[ns] ØPath length ～ 4. 6[m] ØMomentum Pk=1. 5 Ge. V/c (ΔP/P=1. 4 x 10 -4) Pπ form (K, π) reaction (ΔP/P=6. 3 x 10 -4) ØPresent TOF → 300[ps] w/o PHC ØPresent BH 1, 2 → 200[ps] w/ PHC 2006 JPS in NARA 26

Beam Veto ØSAC efficiency ～ 99% → 5 k trigger /spill @ 500 k/spill SFV →～ 10 trigger Reduction of acceptance 7. 5% ØBeam size σx=19. 8[mm] σy=3. 2[mm] (u=0. 02, v=0. 002) ØSBS K- beam directly hit SDC 3, 4. ↓ Scattering beam particles by some material (Pb, W) 2006 JPS in NARA 300 k. Hz→ 60 k. Hz　@ 20 mm cell 27

3 -body Decay K-→π-π-π+ (5. 58%) K-→e-π0ν (4. 87%) K-→μ-π0ν (3. 27%) K-→π-π0π0 (1. 73%) 2006 JPS in NARA 28

Muon Filter Before Ø 89% of μ can be detected in the trigger ØIn the offline analysis ～ 100% ØOver kill for true π ～ 1. 7% 2006 JPS in NARA After 29

Muon Filter 2006 JPS in NARA 30

Iron thickness 2006 JPS in NARA 31

Pi. Zero Veto Before Ø 70% of π0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of After γ from π0 hit the SP 0) Simulation in progress 2006 JPS in NARA 32

Pi. Zero Veto Beam K Ø 70% of π0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of Before After γ from π0 hit the SP 0) Simulation in progress 2006 JPS in NARA 33

Percentage of decay in target 25 cm 2006 JPS in NARA 34

2006 JPS in NARA 35

Λ Hypernucleus Ø strangeness S= -1 Λ Ø M=1115. 68 Me. V Ø Jp=1/2+ Ø I=0 Ø Mean life=263. 2 ps Nucleus Λ hypernucleus → Λ is bound in a nucleus N-N interaction → B-B interaction The Baryon which is different from nucleons (p/n) Deeply bound in a nucleus w/o Pauli effect 2006 JPS in NARA The property of baryon changing in the nuclear medium 36

Λ Hypernucleus N-N interaction → B-B interaction The Baryon which is different from nucleons (p/n) Deeply bound in a nucleus w/o Pauli effect The property of baryon changing in the nuclear medium Λ Hypernucleus ⇔ ΛN effective interaction Systematic studies of several hypernuclei　→ J-PARC 2006 JPS in NARA 37

Level scheme of 7 ΛLi 2006 JPS in NARA 38

Calculated cross section for 2006 JPS in NARA 7 ΛLi 39

B(M 1) mesurement 2006 JPS in NARA 40