Present Status and Future Plans of Hypernuclear experiments -- S = -1 sector --

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1 KEK Nuclear Theory WS Aug. 2, KEK 2006WS Aug. 2, 2006 Present Status and Future Plans of Hypernuclear experiments -- S = -1 sector Dept. of Physics, Tohoku University H. Tamura

2 Contents (e,e K + ) spectroscopy γ spectroscopy (π -,K + ) spectroscopy Weak decays Hyperball

3 1. Introduction

4 World of matter made of u, d, s quarks Nu ~ Nd ~ Ns Strangeness in neutron stars ( ρ > 3-4 ρ 0 ) Strange hadronic matter (A ) higher density ΛΛ, Ξ hypernuclei Λ, Σ hypernuclei Proton-rich nuclei Neutron-rich nuclei ordinary nuclei 3-dimensional nuclear chart

5 Present Status of Λ Hypernuclear Spectroscopy Updated from: O. Hashimoto and H. Tamura, Prog. Part. Nucl. Phys. 57 (2006) 564.

6 (π +,K + ) data and ΛN interaction SKS at KEK-PS s Λ p Λ d Λ f Λ g Λ A -> Nuclear potential of Λ U Λ = - 30 MeV (c.f. U N = -50 MeV) -> spin-averaged central force of ΛN Better resolution is necessary for ΛN spin-dependent forces, ΛN-ΣN force,.. γ, (e,e K + ) spectroscopies Mass of hypernucleus -B Λ (MeV) Hotchi et al., Phys.Rev.C 64 (2001) Unified understanding of B-B interactions in the quark (+meson) picture together with Σ and Ξ hypernuclear data

7 Present status of BB interactions from Hypernuclei S=-1 Established Data To be studied Necessary data ΛN: U Λ = -30 MeV B Λ, 89 Y(π +,K + ) 89 ΛY, etc. LS, spin-spin, tensor γ-ray data ( 4 ΛH, 7 ΛLi, 9 ΛBe, 13 ΛC, 16 ΛO, etc.) ΛN-ΣN ( 3 ΛH / 4 ΛH / 5 ΛHe) odd-state force, r-dependence, charge symmetry breaking More γ-ray data, high resolution (e,e K + ) and (π -,K + ) data ΣN: U Σ strongly repulsive 28 Si (π -,K + ) 28 ΣSi,.. strong isospin-dependence 4 ΣHe (T=1/2, T=3/2) LS ΣN scattering data U Σ, spin-isospin dependence High resolution (π -,K + ) A ΣZ data S=-2 ΛΛ: weakly attractive ( B ΛΛ = 1.0 MeV ) 6 ΛΛHe ΞN: U Ξ (~ -14 MeV? 12 C(K -,K + ) 12 ΞBe ) spin-isospin dependence ΞN-ΛΛ H dibaryon resonance? H-like correlation in nucleus? High resolution (K -,K + ) A ΞZ data More ΛΛ Z events and their decays

8 2. γ-ray Spectroscopy

9 Hyperball2 (2005~) Efficiency 2.5% -> 5% SKS Hyperball2 K6 Q10

10 Status of hypernuclear γ spectroscopy Table of Hyper-Isotopes

11 ΛN Spin-dependent interactions and γ spectroscopy Two-body ΛN effective interaction Dalitz and Gal, Ann. Phys. 116 (1978) 167 Millener et al., Phys. Rev. C31 (1985) 499 Low-lying levels of Λ hypernucleus

12 Determination of the spin-dependent force parameters, S Λ, T: consistent E = S Λ T 7/ kev 5/2 + E = S Λ T 3/2 + 3/ / kev Li -310 kev E = 0.70S N 3/ kev 1/2 + E = S Λ T 7 Λ Li Be 9 Λ Be 1/2 + 1/2-15 O kev E = S Λ T 16 Λ O = 0.4 MeV S Ν = MeV S Λ = MeV T = 0.03 MeV PRL 86 ( 00) 5963 PRL 88 ( 02) PRL 93 (2004) All the spin-dependent force parameters determined.

13 Study of ΛN interaction from γ spectroscopy BNL E930 (AGS D6 line + Hyperball) Discovery of Hypernuclear Fine Structure 9 Be (K -, π - γ) 9 Λ Be 16 O (K -, π - γ) 16 Λ O 43 5 kev kev E γ (kev) E γ (kev) MeV MeV Akikawa et al., PRL 88 (2002) Ukai et al., PRL 93 (2004) ΛN spin-orbit force: S Λ = MeV => agree with quark-model predictions ΛN tensor force: T = 0.03 MeV => agree with meson-exchange model predictions

14 Consistency Test (Millener s framework) = 0.4 MeV, S Λ = MeV, S Ν = MeV, T = 0.03 MeV + size correction, ΣΛ effect (Millener) 0 + T= / /2-3/ /2 + 1/ / /2 + T= Li Be 3/2 + 1/2 + 7 Λ Li 3/2 + 5/ /2 9 Λ Be + 1/2-15 O 3/2-9 B 16 Λ O < Λ B < 0.3? MeV input [kev] test predicted measured or other effects? 3/ N B 15 Λ N 3/2+ 5/ Λ B 1/ /2 + 1/2 + Hints for Λ-Σ coupling S N ~ MeV?

15 Comparison with BB interaction models S Λ S N T (MeV) ND NF NSC NSC97f ( Quark ) Exp G-matrix calc. by Yamamoto Strength equivalent to quark-model LS force by Fujiwara et al. Spin-orbit forces (S Λ, S N ) cannot be explained by meson models. Data seems to favor quark models. Consistent with Hiyama et al. --but 9 ΛBe calculation by Fujiwara et al. (quark+meson) cannot reproduce it. Tensor forces (T) is well explained by meson-exchange models.

16 Extraction of YN interaction properties by cluster model Be 9 Λ Be 3/2 + 5/2 + 1/2 + input 1.1 MeV input 43 kev NSC97f 0 + T= Li + V(ALS)= V(SLS) Hiyama et al., PRC submitted. 1/2 + 7/2 + 5/2 + 3/2 + 7 Λ Li 1/2+ Calc Exp + V(E1), V(E3), V(O1), V(O3) adjusted MeV MeV B Λ input

17 12 C (π +,K + ) 12 Λ C 12 Λ C and 11 ΛB data -B Λ (GeV) Preliminary Slightly lower than prediction of 415 kev from = 0.43 MeV (1-2 -> 1-1 ) consistent with S N = MeV

18 Proposed DAY-1 experiment at J-PARC (K -,π - γ) at p K = 1.5 GeV/c Feasible even with low intensity beam (~2µA) (1) Spin-flip B(M1) measurement and g Λ in a nucleus 7 Λ Li : Least ambiguities exist and most reliable. (500 hrs) (2) Further ΛN interaction study from p-shell hypernuclei 10 Λ B and 11 ΛB: ( hrs) Confirmation of ΛN spin-dependence ΛN ΣN coupling Inconsistency exists. Experimental data not enough. Few-body approach as well as shell model is possible. (3) Radial dependence of ΛN interaction from sd-shell hypernuclei 19 Λ F : Easiest in sd-shell (100 hrs) (4) Charge symmetry breaking in ΛN interaction and spin-flip property in hypernuclear production 4 Λ He : Largest CSB is suggested but previous data is suspicious. Easiest to observe a spin-flip state (100 hrs) (K -,K + γ) at p K = 1.8 GeV/c Ξ-atomic X-ray measurement (Ag, Br, Fe,..) -> ΞN interaction

19 Proposed DAY-1 experiment at J-PARC (K -,π - γ) at p K = 1.5 GeV/c Feasible even with low intensity beam (~2µA) (1) Spin-flip B(M1) measurement and g Λ in a nucleus 7 r (s Λ -d ΛN Li ) > : r Least (s Λ -p N ) ambiguities exist and most reliable. (500 hrs) (2) Further ΛN interaction study from p-shell hypernuclei 10 Λ B and 11 ΛB: ( hrs) Confirmation of ΛN spin-dependence ΛN ΣN coupling Inconsistency exists. Experimental data not enough. Few-body approach as well as shell model is possible. (3) Radial dependence of ΛN interaction from?? sd-shell hypernuclei 19 Λ F : Easiest in sd-shell (100 hrs) sensitive to interaction range and exchanging meson mass (4) Charge symmetry breaking in ΛN interaction and Very large CSB!? B Λ (MeV) spin-flip property in hypernuclear Not theoretically production understood. (K -,π - ) 4 Λ He : Largest CSB is suggested but previous data is suspicious. Easiest to observe a spin-flip state (100 hrs) (K -,K + γ) at p K = 1.8 GeV/c Ξ-atomic X-ray measurement (Ag, Br, Fe,..) -> ΞN interaction

20 B(M1) measurement and g Λ in nucleus µ Λ in nucleus -> medium effect of baryons Direct measurement of µ -- extremely difficult. B(M1) of Λ-spin-flip M1 transition -> g Λ Can be investigated using a Λ in 0s orbit ~100% Doppler Shift Attenuation Method Established for hypernuclear shrinkage in 7 Λ Li from B(E2) : PRL 86 ( 01)1982 J c J c +1/2 core nucleus M1 J c -1/2 Λ g Λ in s-orbit hypernucleus Λ c "hypernuclear fine structure" Λ c Difficulty: DSAM works only when τ < ~ t stop τ is very sensitive to E γ as B(M1) 1/τ E γ3. But E γ is usually unknown.

21 Test data on B(M1) in 7 Λ Li (BNL E930) 10 B (K -, π - ) 10 ΛB*, 10 Λ B*(3 + ) -> 7 ΛLi*(3/2 + ) + 3 He indirect population simulation g Λ = µ N g Λ (free) = µ N preliminary (statistical error only) First data of g Λ in nucleus Indirect population => more background, ambiguities in production

22 Proposed B(M1) measurement at J-PARC To avoid ambiguities, we use the best-known hypernucleus, 7 Λ Li. Energies of all the bound states and B(E2) were measured, γ-ray background level was measured, cross sections are reliably calculated. τ = 0.5ps, t stop = 2-3 ps for 1.5 GeV/c (K -,π - ) and Li 2 O target (K -,π - ) Calc. by Motoba PRL 84 (2000) 5963 PRC 73 (2006)

23 3. (e,e K + ) Spectroscopy

24 First (e,e K + )Data -- Jlab Hall C (E89-009) 12 C(π +,K + ) 12 ΛC SKS 11 B(gs) Λ(0s) 11 B(gs) Λ(0p) 12 C(e,e K + ) 12 ΛB Calc. by Motoba/ Millener Spin-flip states p->λ : mirror/ n-rich hypernuclei Resolution can be improved. 1.5 MeV FWHM by (π +,K + ) 0.9 MeV FWHM by (e,e K + ) 0.3~0.4 MeV FWHM w/ HKS Miyoshi et al., PRL 90 (2003)

25 Hall C --Dedicated (e,e K + ) Spectrometer ENGE ( tilted! ) High-resolution Kaon Spectrometer (HKS) p/p = 5 x > 2 x 10-4 [FWHM] Ω = 4 msr -> 16 msr (w/ splitter) Offset Tilt method Avoid bremss. & Moeller electron bg. singles rate ~ 200 MHz < 1 MHz => much higher beam current heavier targets Tilt angle ENGE Splitter e associated w/ virtual photon Bremsstrahlung

26 4. Neutron-Rich Λ Hypernuclei

27 (π -,K + ) Reaction Data (KEK E521, K6+SKS) Motivation Production mech. 2-step charge exch. (π - p->π 0 n, π 0 p->k + Λ etc.) Σ - admixture (π - p->σ - K +, Σ - p->λn) Λ Σ coherent coupling Behavior of n-halo with a Λ Results Larger cross section for 1.2 GeV/c π - than 1.05 GeV/c -> Σ contrbution is large? Cross section for bound region (π -,K + ) / (π +,K + ) ~1x GeV/c Almost no background B (π -, K + ) 10 ΛLi Saha et al., PRL 94 (2005) First data on n-rich hypernucleus

28 Coherent Λ-Σ coupling and n-rich hypernuclei Correctly describes the binding energies of 3 ΛH, 4 ΛH/ 4 ΛHe, 5 ΛHe (Solves the overbinding problem of 5 Λ He) Important for large-t hypernuclei Large effect on structure and cross sections 4 Λ He L Akaishi et al., PRL 84 (2000) 3539 Exp SC97e(S)

29 Study of n-rich hypernuclei at J-PARC Proposed by Sakaguchi et al. (πl -,K + ) reaction with SKS and K pions/spill -- Not limited by proton beam intensity 6 Li (π -,K + ) 6 ΛH 9 Be (π -,K + ) 9 ΛHe 10 B (π -,K + ) 10 ΛLi (again) 12 C (π -,K + ) 12 ΛBe

30 Future: n-rich hypernuclei by (K -,π 0 γ) reaction --- Disappearence of n-halo in 7 ΛHe He Drastic B(E2) change E2 7 Λ He Calc. by Hiyama

31 5. Weak Decay

32 Weak Decays in Hypernuclei Mesonic q~ 100 MeV/c (1N) (2N) Nonmesonic q~ 400 MeV/c Sensitive to short range part of BB interaction Γ n / Γ p ( np ratio) puzzle: Large statistical and systematic errors (FSI, n-detection, proton energy loss,..) Inconsistent with theories (3-Body)

33 Singles spectra in NMWD Slide from H.C. Bhang N n / N p (60 < E < 110 MeV) ~ n / p = N n / N p (E > 60 MeV) ~ n / p = N =0 was assumed to derive these values. Okada et al., PLB 597 (2004) 249

34 Slide from H.C. Bhang Coincidence Yields (NN correlations) ; 5 He Y NN (E sum ) Y NN (cosθ) N NN (cosθ) (a) Λp np coin E sum (MeV) (c) Λp np coin nn coin 8 6 (b) Λn nn E sum (MeV) (d) Λn nn nn coin Pair Energy Sum Spectum Sharp peak in Y np (He) at Q value( p np). FSI not severe in He. Angular correlation cosθ np cosθ nn Γ n /Γ p ~ N nn / N np = B.Kang et al., PRL 96 ( 06)

35 Slide from H.C. Bhang Γ n / Γ p results and hint for three body process Γ n / Γ p Exp. Coincidence Singles 5 He : (E462) 12 C: (E508) 5 He : (E462) 12 C: (0.05) (E508) The difference can be understood if there were Γ 2N (J-PARC proposal by Bhang et al.)

36 Present questions in weak decay Three body decay (Γ 2N ) exists? -> 3N coincidence data, more accurate Γ n, Γ p (Proposed by Bhang) A y not understood yet Maruta et al. by pn coin.: α p NM = <-> theory: α p NM ~ > Theoretical challenge I = 1/2 not experimentally examined yet -> precise measurement of 4 ΛHe (Λn ->nn) or 4 ΛH (Λp ->np) (Proposed by Ajimura/Sakaguchi)

37 6. Summary New experimental techniques for Λ hypernuclear studies. High-precision γ spectroscopy (e,e K + ) spectroscopy at Jlab (π -,K + ) spectroscopy for n-rich hypernuclei pn, nn coincidence measurement in NMWD γ spectroscopy has done for most of the p-shell Λ hypernuclei. All the ΛN spin-dependent force strengths were determined, and consistency seems almost OK. Planning a precise B(M1) measurement for g Λ. (e,e K + ) spectroscopy at JLab achieved < 1 MeV FWHM resolution. Hall A and C are studying various hypernuclei with improved (~0.4 MeV) resolutions. Future plans for heavier hypernuclei with a new apparatus. First observation of n-rich hypernuclei 10 Λ Li and future plans for others by (π -,K + ) reaction In the weak decays, the n-p ratio puzzle was solved but A y, Γ 2N, I=1/2 rule are to be studied. J-PARC as well as JLab will start data collection from 2008 with improved beam and apparatus.