Hypernuclear gamma-ray spectroscopy at KEK & J-PARC

Presentation on theme: "Hypernuclear gamma-ray spectroscopy at KEK & J-PARC"— Presentation transcript:

1 Hypernuclear gamma-ray spectroscopy at KEK & J-PARC
Tohoku Univ. K.Shirotori for the E566 collaboration and the Hyperball-J collaboration

2 18th Indian-Summer School 「Strangeness & Hypernuclei」
Outline Background of experiments Previous KEK E566 experiment Future J-PARC E13 experiment Summary 18th Indian-Summer School 「Strangeness & Hypernuclei」

3 Motivation of hypernuclear gamma-ray spectrpscopy
Spin dependence of ΛN interaction are investigated by measuring energy spacing of hypernuclei (～a few 10 keV). ΛN effective interaction V(r) = V0(r) + Vs(r) sN・sL + VN(r) lNL・sN + VL(r) lNL・sL + VT(r) S12 (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= [MeV] We need more data for checking them. 18th Indian-Summer School 「Strangeness & Hypernuclei」

4 18th Indian-Summer School 「Strangeness & Hypernuclei」
Hyperball2 Germanium detector＋BGO counters x 20 sets Energy resolution 1MeV ⇔ Magnetic spectrometer ～1.5MeV(FWHM) Hyperball2 f7cm Ge BGO Single Ge 　　60% Clover Ge (Add-back) 　　120% Relative efficiency (3”f×3”NaI) Side view Under view 3.5cm 7cm K+ p+ Electronic circuit for high counting rate →Possible to measure gamma-rays from hypernuclei 18th Indian-Summer School 「Strangeness & Hypernuclei」

5 11ΛB/12ΛC experiment at KEK (E566)

6 18th Indian-Summer School 「Strangeness & Hypernuclei」
Purpose of E566 experiment 10B　ground state doublet Deduced value 195keV ⇔Experiment <100keV L 0.53D+1.44SL-1.72T+ΛΣC 0.53D+1.44SL-1.72T 0- 11C 12LC 1- 2- 3/2- 1/2- 0.58D+1.41SL-1.07T+ΛΣB 3/2- 0.58D+1.41SL-1.07T 9B 10LB 1- 2- D= 0.43,　SN= -0.39,　SL= -0.01,　T= [MeV] N L p S ・Model dependence ・ΛN-ΣN coupling Contribution from three- body interaction? Information from 12ΛC Experiment was performed at KEK K6 beam line. (Sep～Oct in 2005 ) 12C(π+, K+)12ΛC reaction 18th Indian-Summer School 「Strangeness & Hypernuclei」

7 18th Indian-Summer School 「Strangeness & Hypernuclei」
Setup Setup for E566 K6 ビームスペクトロメータ SKS Hyperball2 K+ K GeV/c Hyperball2 12C target p+ π GeV/c 18th Indian-Summer School 「Strangeness & Hypernuclei」

8 Preliminary results: states selection
Expected level schemes Preliminary 3/2+ 11C+Λ 2+ 1/2+ 0+ Highly excited states 2+ 7/2+ 2+ 5/2+ 11B+p L 11B L 1- pΛ states 2- 3- 2- sΛ states 1- 2- 1- 12C L 18th Indian-Summer School 「Strangeness & Hypernuclei」

9 Preliminary results: gamma rays from 11ΛB
Both gamma rays were observed in previous experiment (E518 at KEK in 2002). 11B(π+, K+)11ΛB reaction 7/2+→5/2+ transition (261.6 keV) is first assigned. Expected level scheme 3/2+ 11C+Λ 2+ 1/2+ 0+ Highly excited states 2+ 7/2+ 2+ 5/2+ 11B+p L 11B L PΛ states 1- Highly excited states 2- pΛ states 3- 2- SΛ states Preliminary 1- Preliminary 2- 1- 12C L 18th Indian-Summer School 「Strangeness & Hypernuclei」 Statistical error only

10 Preliminary results: states selection
Expected level schemes Preliminary 3/2+ 11C+Λ 2+ 1/2+ 0+ Highly excited states 2+ 7/2+ 2+ 5/2+ 11B+p L 11B L 1- pΛ states 2- 3- 2- sΛ states 1- 2- 1- 12C L 18th Indian-Summer School 「Strangeness & Hypernuclei」

11 Preliminary results: gamma rays from 12ΛC
Expected gamma-ray levels Preliminary Statistical error only 3/2+ 11C+Λ 2+ 1/2+ w/ Doppler shift correction Preliminary 0+ Highly excited states 2+ 7/2+ 2+ 5/2+ 11B+p L 11B L 1- pΛ states 2- In the present analysis, we haven't observed the other gamma-ray. 3- 2- sΛ states 1- 2- 1- 12C L 18th Indian-Summer School 「Strangeness & Hypernuclei」

12 18th Indian-Summer School 「Strangeness & Hypernuclei」
Discussion SN 12ΛC SN Δ 11ΛB Two interaction parameters SN : -0.7～-0.9 MeV Δ : 0.3 MeV SN : ~-0.4 MeV Δ: ~0.43 MeV 18th Indian-Summer School 「Strangeness & Hypernuclei」

13 Future experiment at J-PARC (E13)

14 Hypernuclear gamma-ray spectroscopy at J-PARC
(K-, π-) high intensity K- beam High production rate Good spectrometer, SKS Veto counters for rejecting background events from beam K- decay Several light hypernulcear gamma-ray spectroscopy experiments are approved for “DAY-1” experiment　E13 (started at 2008). (4ΛHe, 7ΛLi, 10ΛB, 11ΛB, 19ΛF) ・これまでの実験状況から良いスペクトロメーターとKビームを使用することでハイパー核γ線分光は飛躍的に研究が可能となる 18th Indian-Summer School 「Strangeness & Hypernuclei」

15 The K1.8 Beam line and SKSMinus
Acceptance ～120msr Momentum resolution ～2.1MeV/c Hyperball-J Background veto counters SMF SKSMinus 2.7T SP0 Target ・ビームと散乱粒子パートに分かれている ・スペクトロメーターでハイパー核生成事象を識別し、γ線測定と合わせる事でバックグラウンドが非常に小さい状態でγ線測定が出来る。 ・詳細な説明を行うのは、SKS側のみで、SKSのアクセプタンスと運動量分解能、バックグラウンドVETOカウンターについて述べる。 Target : ～20 g/cm2 Expected gamma-ray yield ～10 times higher Beam spectrometer 18th Indian-Summer School 「Strangeness & Hypernuclei」

16 18th Indian-Summer School 「Strangeness & Hypernuclei」
Summary Spin dependence of ΛN interaction is investigated by hypernuclear gamma-ray spectroscopy. 2 gamma rays from 11ΛB and 1 gamma ray from 12ΛC are observed in E566 experiment. Not all spacing are reproduced by present frame work. We need more data for understanding ΛN interaction. Several hypernulcear gamma-ray spectroscopy are planned at the J-PARC K1.8 beam line. ・カウンターによるバックグラウンドの見積もりは非常に重要 18th Indian-Summer School 「Strangeness & Hypernuclei」

17 Backup

18 Proposed “DAY-1” experiment E13
(K-, π- γ) at pK = 1.5 GeV/c (500k/spill) Spin-flip B(M1) measurement and gΛ in a nucleus 7ΛLi : Least ambiguities exist and most reliable ΛN interaction study from p-shell hypernuclei 10ΛB and 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 4ΛHe : Easiest to observe a spin-flip state 軽いハイパー核で実験が決められた→内容はバックアップ ・ビームはこれを”想定” １、核内での磁気モーメントの変化など核内でバリオンの変化を測定する実験 ・測定を重視するのでよく分かっているLiを使う ２、これまでのΛN相互作用の相違した結果を確認、または再測定 ３、再外部のsd核の核子とS軌道のΛの相互作用（ｓとｐの相互作用というときは、最外部の核子とΛが相互作用する） ４、通常、メソンはスピンを持たないので、ハイパー核生成のときにΛのスピンを変えないが、ある運動量では変化することもある。S軌道のN→Λの時にスピンが変化し1+になると0+の基底状態に遷移するγ線を出す。この量を測定することで、スピンフリップの運動量依存性を得る。 （また4Hと4Heでγ線の測定を行うことで、荷電対称性の破れを確認できる） 18th Indian-Summer School 「Strangeness & Hypernuclei」

19 18th Indian-Summer School 「Strangeness & Hypernuclei」
Λ Hypernucleus strangeness S= -1 M= MeV Jp=1/2+ I=0 Mean life=263.2 ps Λ Nucleus Λ hypernucleus Λ hypernucleus → Λ is bound in a nucleus N-N interaction → B-B interaction The Baryon which is different from nucleons (p/n) 次のページとつなげる ・核子と異なるバリオンを原子核に入れることで、 １、核子の相互作用をバリオン相互作用に拡張 ２、核構造の変化 など、通常核の実験とは異なったアプローチで核力の描象にせまることが出来る。 Deeply bound in a nucleus w/o Pauli effect The property of baryon changing in the nuclear medium 18th Indian-Summer School 「Strangeness & Hypernuclei」

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Beam Momentum K- + n -> L + p- 18th Indian-Summer School 「Strangeness & Hypernuclei」

21 Hypernuclear gamma-ray spectroscopy
Λ hypernuclei is produced by (π+, K+) or (K-, π-) reaction. Magnetic spectrometers for (π+, K+) or (K-, π-) detection Missing mass analysis To measure the hypernuclear mass spectrum from (π+, K+) or (K-, π-) events Combined ・これまでの実験状況から良いスペクトロメーターとKビームを使用することでハイパー核γ線分光は飛躍的に研究が可能となる Hyperball for gamma-ray measurement Information of energy spacing of hypernuclear exited states 18th Indian-Summer School 「Strangeness & Hypernuclei」

22 HyperBall-J or HyperWall-J
Wall Type Ball Type Single Ge (r.e.70%) ～ 30 PWO background suppression for higher counting rate Waveform readout LN2 cooling ↓ Mechanical cooling by Pulse tube Target ・軽く流す程度。質問されたら答える ・現在、2通りの配置を考えている→まだ決定できていない(ビーム強度が分かれば良いが、もし500k/spillを考えると、Wallタイプが良い) ・PWOは発光減衰時間が短く、dead timeが小さくなる ・１で2.5%、２で4.5％としておくべし Total photo peak efficiency >5% @ 1MeV (Geant4 simulation) 18th Indian-Summer School 「Strangeness & Hypernuclei」

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Target 20cm Background rejection BAC SAC Beam K μ Decay ν Beam K- decay products make serious background K-→μ-ν (63.4%) ⇒Muon Filter K-→π-π0 (21.1%) ⇒PiZero Veto ・図は単純な運動学的な計算で出したものでアクセプタンスを要求していない ・バックグラウンドがかかるのは見たい状態がある領域 →5°前後 ・SKSのアクセプタンスは0～25程度 Fake trigger ～1700/spill True event trigger ～700/spill 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 18th Indian-Summer School 「Strangeness & Hypernuclei」

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Veto counters π- (stopped in the iron) μ- (passing through) Iron block 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) 18th Indian-Summer School 「Strangeness & Hypernuclei」