Hypernuclear experiments at K1.1 in future. Tohoku University H. Tamura

Transcription

1 Hypernuclear experiments at K1.1 in future Tohoku University H. Tamura

2 Contents 1. Gamma-ray spectroscopy of Λ hypernuclei at K Light Σ hypernuclei by (K -,π ±,0 ) at K γ decay of Σ hypernuclei at K1.1 Coulomb-assisted hybrid states -> HR pion line (Noumi-san)

3 1. Gamma-ray spectroscopy of Λ hypernuclei at K1.1

4 Beam and Setup for γ spectroscopy SMF: Muon filter to suppress K - ->μ - ν Spectrometer: SKS (modified) Δp ~ 4 MeV (FWHM) Ω ~ 110 msr SDC3,4: Large-size (2.0mx0.8m), fine cell (1~2cm) π - To be constructed SP0: Veto counters to reject K - -> π - π 0 Lower half Beamline: K x10 6 K - /spill at 1.5 GeV/c (9μA) K/π >> 1 Hyperball-J ε ~ 7% at 1 MeV K GeV/c K1.8

5 LOI for γ spectroscopy (2003) Reaction / p (GeV/c) ; Beamline ; Features (1) Complete study of light (A<30) hypernuclei, 20 Λ Ne, 23 Λ Na, 27 Λ Al / 28 Λ Si (K -,π - ) p= 1.1 and 0.8 ; K1.1 ; γγ coin, angular corr., B(E2),.. Table of Hyper-Isotopes ΛN interaction (ΛN ΣN, p-wave,..) Partly in E13 Shrinkage, collective motion,... (2) Systematic study of medium and heavy hypernuclei (K -,π - ) p= ; K1.1 and K1.8 ; p-wave ΛN interaction (3) Hyperfragments 8 Λ Li, 8 Λ Be, 9 Λ B, K - -in-beam (stopped K - ) p=0.8 ; K1.1 ; p/n-rich hypernuclei, 7 (4) n-rich and mirror hypernuclei Λ He, 9 Λ Li, 12 Λ B... Shirotori s talk (K -,π 0 ) p= 1.1 and 0.8 ; K1.1 ; charge sym.break., shrinkage of n-halo, 7 (5) B(M1) using Doppler shift Λ Li and heavier Partly in E13 (K -,π - ) p= 1.1 and (π +,K + ) p= 1.05 ; K1.1 ; μ Λ in nucleus 89 Λ Y, 139 Λ La, 208 Λ Pb (6) B(M1) using γ-weak coincidence (K -,π - ) p= 1.1 and 0.8 ; K1.1 ; ρ, T dependence of μ Λ in nucleus

6 S=-2 Reaction / p (GeV/c) ; Beamline ; Features (7) Ξ atom X rays E03, E07 (K -,K + ) p=1.8 GeV/c; K1.8 ; ΞN interaction (8) ΛΛ-hypernuclei (K -,K + ) p=1.8 GeV/c; K1.8 ; ΛΛ, ΞN-ΛΛ interactions

7 (5),(6) B(M1) measurements μ Λ in nucleus -> medium effect of baryons Constituent quark μ q = eh 2m q c μ q changes in nucleus? J c J c +1/2 core nucleus M1 J c -1/2 Λ g Λ in s-orbit hypernucleus ψ Λ ψ c "hypernuclear fine structure" ψ Λ ψ c Partly in E13 Doppler shift attenuation method [same as B(E2), established] for light hypernuclei; Weak K - or π + beam usable γ-weak coincidence method [new, only possible at J-PARC] for 12 Λ C and heavy hypernuclei; Intense K - beam necessary

8 B(M1) measurement by γ-weak coincidence method 12 Λ C case 900 hours, 9x10 6 K - /spill at K1.1 (50 GeV full beam) -> 5% stat. error of B(M1)

9 Best K - beam momentum K - + n -> Λ + π - K1.1: More yield x4 Less Doppler shift Need to move SKS to K1.1 (and construct SKS2 at K1.8) or construct another SKS at K1.1 Ω= 20 msr (SPESII) Ω= 100 msr (SKS) Both spin-flip and nonflip states should be produced. -> p K = 1.1 or 1.5 GeV/c p K = 1.1 GeV/c : K1.1 + SKS (ideal) p K = 1.5 GeV/c : K1.8 + SKS (realistic) High K/π ratio to minimize radiation damage to Ge detectors -> Double-stage separation. K1.8BR is not good. N(1.1) = 2.0x10 6 /spill at K1.1 N(1.5) = 0.5x10 6 /spill at K1.8 (30 GeV 9μA)

10 2. Light Σ hypernuclei by (K -,π ±,0 ) at K1.1

11 Quark DOF really necessary in BB interaction? ΛN spin-orbit force (Λ spin-dependent LS force ~ 0) -- 9 Λ Be, 13 Λ C γ-spectroscopy data Δ S Λ S N T (MeV) ΣN (T=3/2,S=1) strong repulsion (quark Pauli) -- ND 28 Si(π -,K ) suggests strongly repulsive Σ-nuclear pot. NF Strong NSC89 attraction in H dibaryon channel NSC97f ~ Attraction in ΛΛ/ ΞN / ΣΣ (T=0,S=0) state ( Quark ) -- No H, weak attraction in ΛΛ Strength equivalent to quark-model LS force by Fujiwara et al. Exp G-matrix calc. by Yamamoto

12 Σ hypernuclei and ΣN interaction 4 ΣHe bound state -> T=1/2 attractive 4 He(K -,π + ) -> T=3/2 repulsive Lane term (σ Σ σ N )(τ Σ τ N ) consistent with Nijmegen interactions No bound-state peaks in 6 Σ Li, 7 Σ Li, 9 Σ Be, 12 Σ C Σ atomic data attraction at outer nuclear region (not direct information) 28 Si,..(π -,K + ) spectrum -> spin-averaged pot. strongly repulsive (~ +30 MeV) =>Lane term (σ Σ σ N )(τ Σ τ N ) (by π/ρ.. exchange) consistent, but strength of each spin-isospin channel and ΣN->ΛN not determined yet. T=3/2,S=3/2 channel strongly repulsive? (by quark Pauli) => More data for light (spin-isospin unsaturated) hypernuclei

13 G-matrix results for various interactions Rijken et al., PRC59 (1999) 21 Rijken, Yamamoto PRC73 (2006) ESC04d fss2(quark) Fujiwara et al., Prog.Part.Nucl.Phys. 58 (2007) 439 k f =1.35 fm -1 Lane term (σ Σ σ N )(τ Σ τ N ) by π/ρ exchange quark Pauli effect

14 T=1/2, 3/2 S=0 4 Σ He by (K -,π) Substitutional (ΔL=0) state: n(s 1/2 ) -1 Λ(s 1/2 1) T=1/2, 3/2 S=0 T=3/2 only S=0 Nagae et al., PRL 80 (1995) 1605 T=3/2 only S=0 Hayano et al., PLB B231 (1989) 355 Large spin-isospin dependence (Lane term) Consistent with ΣN interaction in Nijmegen D model (I,S) = (3/2,0), (1/2,1) attractive, (3/2,1), (1/2,0) repulsive No peaks in other Σ hypernuclei Width (ΣN->ΛN) > 10 MeV in general-- spectroscopy difficult

15 Other Σ hypernuclei? No Σ bound states in A>4 Bart et al. PRL 83 (1999) Σ He 6 Σ Li 12 Σ Be Iwasaki Ph.D thesis (1987) 9 Σ Be Yamada, Ikeda 7 Σ Li has a bound state for ND but no bound state for NF.

16 Repulsive potential? U Σ ~ +30 MeV Data: Noumi et al., PRL 87 (2002) Calc: Kohno et al., PRC 74 (2006)

17 Previous 3 He(K -,π - ) data at BNL E774

18 Proposed 3 He experiment 3 He (K -,π ±,0 Λ) at threshold, p K ~0.5~0.6 GeV/c (q < 50 MeV/c) 3 ΣHe, 3 ΣH, 3 Σn : different combination of (T ΝΣ,S ΝΣ ) = (3/2,1), (3/2,0), (1/2,1), (3/2,0) from 4 ΣHe, 4 Σn 3-body systems can be accurately calculated -> direct comparison with various interactions (how sensitive? theoretical calculations essential) Apparatus: Low momentum beam line (K1.1BR) + beam spectrometer + SPESII and π 0 spectrometer + Λ tagger (CDS) Koike-Harada (NPA611(1996)461) Unstable bound states E Σ (Γ) SAP-1(ND) SAP-F(NF) 3 Σ He (T=1,S=1/2) (7.58) MeV 3 Σ0 H (T~1,S=1/2) (1.95) (8.2) MeV 3 Σ n (T=1,S=1/2) (9.05) MeV Spectral shapes should be calculated.

19 Experiment Beam spectrometer ( Δp FWHM <1.5 MeV/c at 600 MeV/c ) in place of K1.1BR B3 3He target Λ tagger => CDS π ± spectrometer (Δp FWHM <1.5 MeV/c at 500 MeV/c) => SPESII π 0 spectrometer (Δp FWHM ~ 3 MeV/c at 500 MeV/c) Yield (K -, π ± ): N K- dσ/dω ΔΩ N target ε(λtag) ε = 5x10 5 /spill 50x10-30 cm 2 /sr 0.02sr 0.09g/cm 3 / 3 10cm 6x => 1400 counts/100hours ->Lower beam momentum? Yield (K -, π ±0 ): => ~100 counts/100hours

20 Λ tagging is essential Data: Nagae et al., PRL 80 (1995) 1605 calc: Harada, PRL 81(1998) 5287

21 3. γ decay of Σ hypernuclei at K1.1

22 Spin-flip M1 transitions Γ B(M1) μ 2 is sensitive to w.f. u S = 0 S = 0 d u d Λ Λ s s S = 1/2 S = 1/2 Spin-flip of s quark small medium effect? + γ u S = 1 d u S = 0 d S = 1/2 s Σ S = 1/2 s Λ + γ Spin-flip of u/d quarks large medium effect?

23 How large is the effect? Shift of constituent quark mass in a nucleus Δm u,d ~ -20%, Δm s /m s ~ -4% -> Δμ (Σ) ~ 20%, Δμ (Λ) ~ 4% ΔB(M1) for Σ ~ +40%, ΔB(M1) for Λ ~ +8% Quark Cluster Model Takeuchi et al., N.P. A481(1988) 639 δμ/μ : 4 Λ He(1+ ) -1% ~ -2%, larger by Σ mixing 4 Σ +Li(1 + ) -40% ~ -100% b = 0.6 fm -> 0.8 fm, μ becomes twice large.

24 Measurement of Γ(Σ 0 ->Λγ) in a nucleus Σ in nucleus = Σ hypernuclear bound states -> 4 ΣHe Free Σ 0 -> Λγ 100%, Eγ = 74 MeV Γ free Σ >Λγ = 1 / 7.4x10-20 sec -1 ~ 9x10-3 MeV Γ ΣΝ >ΛΝ ~ 10 MeV for 4 ΣHe => BR(Σ 0 ->Λγ in nucleus) ~ Γ Σ >Λγ / Γ ΣΝ >ΛΝ ~ (K -,π - ) reaction at 600 MeV/c using K1.1BR dσ/dω ( 4 ΣHe) ~ 100 μb/sr (Nagae et al.) Yield: N K- dσ/dω ΔΩ BR N target BR(Λ->nπ 0 ) ε = 5x10 5 /spill 100x g/cm 3 / 4 20cm 6x => 56 counts/1000hour Background: QF Σ 0 escape, Σ 0 -> Λγ (-B Σ >0 only) π 0 -> γ γ from Λ -> n π 0 (Eγ 50~100 MeV) => Tag 3 energetic (> 50 MeV) γ rays => cover the target region with a calorimeter Theoretical calculation necessary how large change is expected?

25 T=1/2, 3/2 S=0 4 Σ He by (K -,π) Substitutional (ΔL=0) state: n(s 1/2 ) -1 Λ(s 1/2 1) T=1/2, 3/2 S=0 T=3/2 only S=0 Nagae et al., PRL 80 (1995) 1605 T=3/2 only S=0 Hayano et al., PLB B231 (1989) 355 Large spin-isospin dependence (Lane term) Consistent with ΣN interaction in Nijmegen D model (I,S) = (3/2,0), (1/2,1) attractive, (3/2,1), (1/2,0) repulsive No peaks in other Σ hypernuclei Width (ΣN->ΛN) > 10 MeV in general-- spectroscopy difficult

26 Harada, PRL 81(1998) 5287

27 Expected 3γ-tagged spectrum ( イメージ ) Σ 0 Λ γ nπ 0 γγ Assuming that 3 HeΛ, pdλ, ppnλ never emit 3 energetic γ s Σ 0 escape 0 +

28 Summary γ-ray spectroscopy of Λ hypernuclei at K1.1 Various experiments using SKS + Hyperball-J Σ hypernuclei at K1.1BR 3 He(K-,π) for ΣN spin-isospin dependence γ decay of Σ hypernuclear bound states New apparatus to be build 2nd SKS (or SKS2 at K1.8) Beam spectrometer for K1.1BR π 0 spectrometer Calorimeter (crystal barrel)