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Osamu Hashimoto

Reaction spectroscopy of L hypernuclei. (1) Introduction (2) The L hypernuclear spectroscopy (3) Mass dependence of L binding energy (4) Light L hypernuclear spectra 12 L C, 16 L O, 13 L C , 9 L Be, 7 L Li, 10 L B (5) Future prospect and summary. Osamu Hashimoto.

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Osamu Hashimoto

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  1. Reaction spectroscopy of L hypernuclei (1) Introduction (2) The L hypernuclear spectroscopy (3) Mass dependence of L binding energy (4) Light L hypernuclear spectra 12LC, 16LO,13LC, 9LBe, 7LLi, 10LB (5) Future prospect and summary Osamu Hashimoto Department of Physics Tohoku University APCTP Workshop on Strangeness Nuclear Physics (SNP'99) Seoul National University February 19-22, 1999

  2. Reaction spectroscopy of L hypernuclei (1) Introduction (2) The L hypernuclear spectroscopy (3) Light L hypernuclear spectra 12LC, 16LO,13LC, 9LBe, 7LLi, 10LB (4) Future prospect and summary Osamu Hashimoto Department of Physics Tohoku University APCTP Workshop on Strangeness Nuclear Physics (SNP'99) Seoul National University February 19-22, 1999

  3. Excited states of L hypernuclei n or p L BL p Narrow widths < a few 100 keV p Likar,Rosina,Povh Bando, Motoba, Yamamoto Bp n 207LTl Bn 207LPb g 208LPb Weak decay nonmesonic mesonic

  4. L hypernuclear spectroscopy • Narrow widths of nucleon-hole L-particle states • less than a few 100 keV • LN interaction weaker than NN • LN spin-spin interaction weak • L isospin = 0 • No exchange term • A L hyperon free from the Pauli exclusion principle • Smaller perturbation to the core nuclear system L hypernuclear structure vs. LN interaction Precision spectroscopy required

  5. S=-1 hyperon production reactionsfor L hypernuclear spectroscopy DZ = 0 DZ = -1 comment neutron to L proton to L (p+,K+) (p-,K0) stretched, high spin in-flight (K-,p-) in-flight (K-,p0) substitutional at low momentum stopped (K-,p-)stopped (K-,p0) large yield, via atomic states virtual (g,K) spin flip, unnatural parity (p,p’K0) (p,p’K+) virtual (p,K) (p,K+) (p,K0) very large momentum transfer (e,e’K0) (e,e’K+)

  6. Cross section vs. momentum transferfor some hypernuclear production reactions mb/sr Inflight(K-,p) Stopped (K-,p) Hypernuclear Cross section mb/sr (p+,K) (g,K) nb/sr (p,K) 0 500 1000 Momentum transfer (MeV/c)

  7. The (p+,K+) spectroscopy • Large momentum transfer • angular momentum stretched states are favorably populated • neutron-hole L-particle states are excited • Higher pion beam intensitycompensates lower cross sections • 10 mb/sr for (p+,K+) vs 1 mb/sr for (K-,p-) • Pion beams are cleaner than kaon beams • 1 GeV/c pion beam is required For the spectroscopy a good resolution p beam spectrometer and a good-resolution and large-solid angle spectrometer

  8. The SKS spectrometer Optimized for the (p+,K+) spectroscopy • Large momentum transfer • Higher pion beam intensitycompensates lower cross sections • Pion beams are cleaner than kaon beams • 1 GeV/c pion beam is required • Good energy resolution --- 2 MeV FWHM • Large solid angle --- 100 msr • about 60 % of 12LC ground state yield • Short flight path --- 5 m • 40 % kaon survival rate • Efficient kaon identification Characteristics Large superconducting dipole at KEK 12 GeV PS The performance of the SKS spectrometer was demonstrated by the 12LC excitation spectrum

  9. The (p+,K+) experiments with the SKS spectrometer • E140a (Hashimoto, Tohoku) • Systematic spectroscopy of L hypernuclei • E278 (Kishimoto, Osaka) • Nonmesonic weak decay of polarized 5LHe • E307 (Bhang, Seoul) • Lifetimes and weak decay widths of light and medium-heavy L hypernuclei • E336 (Hashimoto,Tohoku) • Spectroscopic investigation of light L hypernuclei • E369 (Nagae,KEK) • Spectroscopy of 89LY • E419 (Tamura,Tohoku) • Gamma ray spectroscopy of 7LLi Weak decay of 209LBi Outa S hypernuclei by the (p+,K+) reaction Noumi

  10. Absolute energy scale MHY-MA = -BL + Bn - Mn+ML dMHY～dpp/bp - dpK/bK (1) dMHY adjusted so that BL(12LC) = 10.8 MeV (2) Energy loss corrected for p+ and K+ in the target ±0.1 MeV + DBL(12LC) Binding energies of 7LLi, 9LBe ground states are consistent with the emulsion data well within ±0.5 MeV.

  11. Heavy L hypernuclei KEK PS E140a KEK PS E369 • Three heavy targets with neutron closed shells 8939Y50ng9/2 closed 2.2 MeV 1.7 MeV 13957La82 nh11/2 closed 2.3 MeV 20882Pb126ni13/2 closed 2.2 MeV Background as low as 0.01 mb/sr/MeV Hypernuclear mass dependence of L-hyperon binding energies was derived with different assumptions The binding energies are not strongly dependent on the assumption

  12. La & Pb Spectra

  13. Background level in heavy spectra

  14. Fitting by assuming ….

  15. L binding energies

  16. Heavy L hypernuclear spectrasmoother than those of DWIA calculation • Spreading of highest l neutron-hole states of the core nucleus • Contribution of deeper neutron hole states of the core nucleus • Other reaction processes not taken into account in the shell-model + DWIA calculation. • Larger ls splitting ? E369 Nagae

  17. Light L hypernuclei • Playground for investigating L hypernuclear structure and LN interaction • Recent progress in shell-model calculations and cluster-model calculations prompt us to relate the structure information and interaction, particularly spin-dependent part.

  18. E336 Summary High quality spectra 2 MeV resolution and good statistics Absolute cross section and angular distribution Pion beam : 3 x 106/1012ppp at 1.05 GeV/c Spectrometer : SKS improved from E140a Better tracking capability with new drift chambers Targets : 7Li 1.5 g/cm2(99%,Metal) 440 Gp+ 9Be 1.85 g/cm2(metal) 434 Gp+ 13C 1.5 g/cm2(99% enriched,powder) 362 Gp+ 16O 1.5 g/cm2(water) 593 Gp+ 12C 1.8 g/cm2(graphite) 313 Gp+ Absolute energy scale +- 0.1 MeV at BL(12LC ) = 10.8 MeV examined by 7LLi, 9LBe Momentum scale linearity +- 0.06 MeV/c Energy resolution(FWHM) 2.0 MeV for 12LC 1.5 MeV

  19. Summary of L hypernuclear spectra obtained with the SKS spectrometer Pion beam : 3 x 106/1012ppp at 1.05 GeV/c Yield rate : 5 - 8 events/g/cm2/109 pions for 12LCgr ( ～5 - 800 events/day ) E140a10B, 12C, 28Si, 89Y, 139La, 208Pb 2 MeV resolution, heavy L hypernuclei E3367Li, 9Be, 12C, 13C, 16O high statistics, angular distribution absolute cross section E36912C, 89Y best resolution(1.5 MeV), high statistics Absolute energy scale +- 0.1 MeV at BL(12LC ) = 10.8 MeV examined by 7LLi, 9LBe Momentum scale linearity +- 0.06 MeV/c Energy resolution(FWHM) 2.0 MeV for 12LC 1.5 MeV

  20. Peak # E140a E336(Preliminary) Ex(MeV) Ex(MeV) Cross section(20-140)(mb) #1(11-) 0 0 MeV 1.47 ± 0.05 #2(12-) 2.58 ± 0.17 2.71 ± 0.13 0.23 ± 0.03 #3(13-) 6.05± 0.18 0.22 ± 0.03 #3’ 8.10 ± 0.38 0.17 ± 0.03 #4(2+) 10.68 ± 0.12 10.97 ± 0.05 1.76 ± 0.07 12LC E140a spectrum Phys. Rev. Lett. 53(‘94)1245 Example of a good resolution spectroscopy Core-excited states clearly observed • The (13-) state at 6.9 MeV is located higher than the corresponding 12C excited state. • The nature of the state is under discussion • LN spin-spin interaction • Mixing of other negative parity states • The width of the p-orbital is peak broader • consistent with ls splitting E336 spectrum --- 5-10 times better statistics consistent with E140a spectrum Angular distributions and absolute cross sections Statistical errors only 6.89 ± 0.42 Intershell mixing --- positive parity state Motoba, Millener, Gal

  21. 11C vs 12LC MeV 11C x sL 11C x pL 2+ 10.97 (2+)? 8.10 MeV 5/2+ 6.90 6.48 7/2- (1-3) 6.05 1/2+ 6.34 3/2-2 4.80 5/2- 4.32 (1-2) 2.71 1/2- 2.00 3/2-1 1-1 0.00 0.00 11C 12LC

  22. L Hypernuclear spin-orbit splitting “Puzzle” • Very small ----- widely believed VLSO = 2±1MeV • CERN data Comparison of 12LC, 16LO spectra • DE(p3/2-p1/2) < 0.3 MeV • BNL data Angular distribution of 13C (K-,p-) 13LC • DE (p3/2-p1/2) = 0.36 +- 0.3MeV • Larger splitting ? ----- recent analysis • 16LO emulsion data analysis ( Dalitz, Davis, Motoba) • DE(p3/2-p1/2) ～ E(2+) - E(0+) = 1.56 ± 0.09 MeV • SKS(p+,K+) data new 89LY spectrum (Nagae) • > 2 times greater ? Comparison of (K-,p-) and (p+,K+) spectra provides information the splitting High quality spectra required

  23. 16LO 11- : p1/2-1 x Ls1/2 12- : p3/2-1 x Ls1/2 21+ : p1/2-1 x Lp3/2 01+ : p1/2-1 x Lp1/2 ls partner In-flight (K-,p-) CERN 01+ populated Stopped (K-,p-) 21+ and 01+ populated ★SKY at KEK-PS ★ Emulsion new analysis Dalitz et.al. K- + 16O → p- + p + 15LN E(21+)- E(01+) = 1.56 ± 0.09 MeV ? (p+,K+) SKS 4 distinct peaks 21+ populated

  24. 13LC [12C(0+) x Lp3/2]3/2- [12C(0+) x Lp1/2]1/2- ls partner ★p1/2 → s1/2g observed by the (K-,p-) reaction E(Lp1/2) = 10.95 ±0.1±0.2 MeV M. May et.al. Phys. Rev. Lett. 78(1997) ★p3/2,1/2 → s1/2gray measurement Kishimoto 98 at BNL ★The (p+,K+) reaction excites the p3/2 state [12C(1+) x Ls1/2]1/2+ near the 3/2- peak Peak # configuration Ex(MeV) [12C(Jcp,Tc) x Llj]Jpn #1 [12C(0+,0) x Ls1/2]1/21+ 0 #2 [12C(2+,0) x Ls1/2]3/2+ 4.87 ± 0.09 #3 [12C(0+,0) x Lp3/2]3/2-9.63 ± 0.24 ± 0.5* #4 [12C(1+,0) x Ls1/2]1/22+ 11.58 ± 0.20 ± 0.5* [12C(1+,1) x Ls1/2]1/24+ #5 [12C(2+,0) x Lp1/2]5/22- 15.43 ± 0.08 [12C(2+,1) x Ls1/2]3/24+ *A systematical error considering possible contamination from the #4(1/22+) peak is quoted. DE = E(Lp1/2) - E(Lp1/2) = 1.32 ± 0.26 ± 0.7 MeV

  25. 9LBe A typical cluster L hypernucleus ★supersymmetric states Gal et.al. genuine hypernuclear states Bando et.al. (a+a) x p1-,3-,... BNL spectrum ★microscopic three-cluster model Yamada et.al. Cluster excitation taken into account 9LBe = a + x + L x = a, a* a* = 3N + N ★microscopic variational method with all the rearrangement channels Kamimura, Hiyama The present spectrum compared with Yamada’s calculation (1) The genuinely hypernuclear states,1-, 3- identified (2) Higher excitation region shows structure not consistent with the calculated spectrum

  26. 7LLi Cluster model approach Bando et.al. Kamimura,Hiyama a + d + L 3He + t + L 5LHe + p + n Shell model approach Richter et.al. Ground : [6Li(1+) x s1/2] 1/2+ First excited : [6Li(3+) x s1/2] 5/2+ E2 g transition 5/2+ →1/2+ : 2.03 MeV T=1 states around BL = 0 MeV strength observed

  27. What did we learn from MeV hypernuclear reaction spectroscopy ? • Improvement of the resolution, even if it is small, has a great value • 3 MeV → 2 MeV → 1.5 MeV • Hypernuclear yield rate plays a crucial role • feasibility of experiments • expandability to coincidence experiments • hypernuclear weak decay • gamma ray spectroscopy

  28. Future prospect • From MeV to sub-MeV with high efficiency • Wide variety of reactions • angular momentum transfer • spin-flip amplitude • electromagnetic hyperon production • (K,p) at 1.1 GeV/c • proton or neutron to L • hyperon photoproduction • neutral meson detection • New opportunities • (K-,p0) at BNL around 1 MeV • Youn • (e,e’K+) at Jlab 600 keV • Hungerford • New (p+,K+) a few 100 keV • Noumi • Gamma-ray spectroscopy a few keV • Tamura, Tanida 300 keV

  29. Physics outline • 12C spectrum reproduced, the core excited state at Ex=6.6 MeV was puzzling. • 10B spectrum similarly favor strong spin singlet strength for the LN interaction • 7Li and Be are typical L hypernuclei treated by cluster model. • 7Li spectrum is consistent with the gamma ray data. It also show the strength for T=1 states. • 9Be spectrum show the 1--3- band of genuine L hypernuclear states. 8Be* core excited states are also observed with a distinct structure, whose position is not reproduced by the available cluster model. • 13C spectrum shows clear shoulder structure at around Ex=10 MeV, which supposedly consists of 12C(0+)xp3/2 and 12C(1+)xs1/2, from which we may deduce the peak position for the p3/2 state. By combining the recent gamma ray data for p1/2, spin orbit splitting may be derived. • Pik 16O spectrum can be compared with the CERN Kpi spectrum, from which we may conclude that the spin-orbit splitting is quite small.

  30. L spin-orbit splitting from the width of 12LC 2+ peak • pL peak assumed to be “equal strength doublet” & 2 MeV resolution • splitting : 1.2 +- 0.5 MeV • consistent with the emulsion result(Dalitz) • 0.75 +- 0.1 MeV |21+> ～11C(3/2-) x |Lp 3/2> (97.8%) |22+> ～11C(3/2-) x |Lp 1/2> (99.0%)

  31. Summary MeV hypernuclear reaction spectroscopy has matured to a level that allows quantitative investigation of their structure and LN interaction through the structure information. The (p+,K+) reaction has established its value for hypernuclear spectroscopy since it favorably excites L hypernuclear bound states. Much better resolution and high detection efficiency are required for the L hypernuclear spectroscopy in the future. Sub-MeV reaction spectroscopy together with gamma-ray spectroscopy will further explore frontiers of strangeness nuclear physics.

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