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The SKS Spectrometer and Spectroscopy of Light L Hypernuclei (E336 and E369)

The SKS Spectrometer and Spectroscopy of Light L Hypernuclei (E336 and E369). Osamu Hashimoto Tohoku University. KEK PS Review December 4-5, 2000. Outline. Motivation Some history The SKS spectrometer E336 experiment Light L hypernuclear spectroscopy

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The SKS Spectrometer and Spectroscopy of Light L Hypernuclei (E336 and E369)

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  1. The SKS Spectrometer and Spectroscopy of Light L Hypernuclei (E336 and E369) Osamu Hashimoto Tohoku University KEK PS Review December 4-5, 2000

  2. Outline • Motivation • Some history • The SKS spectrometer • E336 experiment • Light L hypernuclear spectroscopy for 7LLi, 9LBe,( 10LB,) 12LC, 13LC, 16LO • E369 experiment • 12LC 1.5 MeV resolution spectrum • 89LY high quality spectrum

  3. Significance ofhypernuclear investigation • A new degree of freedom • Deeply bound states • Baryon structure in nuclear medium • New forms of matter H dibaryon... • New structure of hadronic many-body system with strangeness • Nucleus with a new quantum number • Characteristic structure • Electromagnetic properties • Hyperon-nucleon interaction(B-B interaction) • A valuable tool • hyperon scattering experiments limited • Potential depth, shell spacing, spin-dependent interaction • Weak interaction in nuclear medium • Weak decay processes • Nonmesonic decay • Decay widths, polarization

  4. Hypernuclear bound states

  5. YN, YY Interactions and Hypernuclear Structure Free YN, YY interaction From limited hyperon scattering data (Meson exchange model: Nijmegen, Julich) YN, YY effective interaction in finite nuclei (YN G potential) Hypernuclear properties Energy levels, splittings Cross sections Polarizations Weak decay widths

  6. 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 Excited states of L hypernuclei

  7. 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

  8. Issues of L hypernuclear physics • Single particle nature of a L hyperon in nuclear medium • New forms of hadronic many-body systems with strangeness • core excited states, genuine(supersymmetric) states, clustering structure,…. • YN and YY interactions • central, spin-spin, spin-orbit, tesor • Hyperon weak decay in nuclear medium • Lifetimes as a function of hypernuclear mass • Nonmesonic weak decay • Gn/Gp ratios, DI=1/2 rule

  9. 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+)

  10. 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)

  11. Elementary cross section of the (p+,K+) reaction

  12. Comparison of the (p+,K+) and (K-, p-) reaction

  13. The (p+,K+) spectroscopy • Large momentum transfer • angular momentum stretched states are favorably populated • neutron-hole L-particle states are excited • Higher pion beam intensity compensates 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

  14. Required Resolution Good resolution 1-2 MeV High resolution a few 100 keV (1) L hypernuclei (K-,p-),(p,K+),(e.e’K+),… Major shell spacing( Heavy hypernuclei) ~ 1 MeV Spin dependent int.(Light hypernuclei) < 0.1-1 MeV (2) S hypernuclei (K-,p-),(p,K+) G wide SN ---> LN a few MeV for 4SHe, Coulomb assisted states (3) X hypernuclei (K-,K+) G 5-10 MeV or narrower( 1 MeV ?) XN ---> LL

  15. The SKS spectrometer Optimized for the (p+,K+) spectroscopy • Good energy resolution --- 2 MeV FWHM • Large solid angle --- 100 msr • Short flight path --- 5 m • Efficient kaon identification Large superconducting dipole at KEK 12 GeV PS The performance of the SKS spectrometer was demonstrated by the 12LC excitation spectrum

  16. Brief history of hypernuclear physics experiments with the SKS spectrometer • 1985 2,4 Workshop on nuclear physics using GeV/c pions • 1985. 6 Proposal #140 submitted • 1985.10 Workshop on physics with a medium-resolution spectrometer in GeV region • 1985.10 E150 approved • Study of L hypernuclei via ( p+,K+) reaction with a conventional magnet ---> PIK SPECTROMETER • 1987. 4 Construction budget of the SKS approved ( INS ) • 1989. 3 Proposal #140 conditionally approved as “E140a” • Study of L hypernuclei via ( p+,K+) reaction with a large-acceptance superconducting kaon spectrometer • 1991. 9 The SKS magnet successfully excited to 3 Tesla in the North Experimental Hall • 1992. 3 Proposal #269 approved • 1992.11 E269 data taking • 1993. 2 - E140a data taking • 1993 10 E278 data taking • 1995. 1-11 E307 data taking • 1995.11-2 E352 data taking • 1996. 4-10 E336 data taking • 1997.11-2 E369 data taking • 1998.5-7 E419 data taking • 1999. 10-12 E438 data taking • 2000. 11-12 E462 data taking

  17. KEK PS Experiments with the SKS spectrometer • E140a (Hashimoto, Tohoku) • Systematic spectroscopy of L hypernuclei • E269(Sakaguti, Kyoto) • Pion elastic scattering in 1 GeV/c region • 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 • E352(Peterson, Colorado) • Pion-nucleus scattering above the D resonance • E369 (Nagae,KEK) • Spectroscopy of 89LY • E419 (Tamura,Tohoku) • Gamma ray spectroscopy of 7LLi • E438(Noumi,KEK) • Study of SN potential in the (pi-,K+) reactions • E462(Outa, KEK) • Weak widths in the decay of 5LHe

  18. 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

  19. Heavy L hypernuclei KEK PS E140a • Three heavy targets with neutron closed shells 8939Y50ng9/2 closed 2.2 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 were derived taking into account major and sub-major hole states

  20. 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.

  21. La & Pb Spectra

  22. Fitting by assuming ….

  23. Background level in heavy spectra

  24. Heavy L hypernuclear spectrasmoother than those of DWIA calculation (1) Spreading of highest l neutron-hole states of the core nucleus (2) Contribution of deeper neutron hole states of the core nucleus (3) Other reaction processes not taken into account in the shell-model + DWIA calculation. (4) Larger ls splitting ? L binding energies are derived taking into account #1 and #2.

  25. L binding energies

  26. 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 L binding energies are derived taking into account #1 and #2.

  27. Comparison of excitation energies of 16LO states observed by 3 different reactions 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 22+(p3/2-1 x Lp1/2,3/2) 02+(p3/2-1 x Lp1/2,3/2)

  28. 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.

  29. Hypernuclear Hamiltonian H = HN(Core) + tL + SvLN HN(Core): Core nucleus tL : L kinetic energy vLN : effective LN interaction ( Nijmegen, Julich ... )

  30. E336 Summary 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 Momentum scale linearity +- 0.06 MeV/c Energy resolution(FWHM) 2.0 MeV for 12LC

  31. Peak # E140a E336(Preliminary) Ex(MeV) Ex(MeV) Cross section(20-140)(mb) #1(11-) 0 0 MeV 1.46 ± 0.05 #2(12-) 2.58 ± 0.17 2.70 ± 0.13 0.25 ± 0.03 #3(13-) 6.22± 0.18 0.24 ± 0.03 #3’ 8.31 ± 0.38 0.16 ± 0.03 #4(2+) 10.68 ± 0.12 10.97 ± 0.05 1.80 ± 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 positive parity states • Intershell mixing • 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 E369 spectrum best resolution 1.45 MeV

  32. 12LC spectra by SKS 2 MeV(FWHM) E336 1.45 MeV(FWHM)

  33. 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

  34. Angular distributionof the 12C(p+,K+)12LC reaction E336

  35. 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 (E369) • > 2 times greater ? Comparison of (K-,p-) and (p+,K+) spectra provides information the splitting High quality spectra required Recent hypernuclear g ray spectroscopy Small ls splitting in 13LC, 9LBe observed

  36. 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

  37. Angular distributionof the 13C(p+,K+)13LC reaction E336

  38. Angular distributionof the 16O(p+,K+)16LO reaction E336

  39. 13LC Ex(1/2-) = 10.98 ± 0.03 MeV Ex(3/2-) = 10.83 ± 0.03 MeV DE = 0.152 ± 0.054 ± 0.036 MeV E929 at BNL [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 E929 at BNL (Kishimoto) ★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+ 4.81 ± 0.09 #3 [12C(0+,0) x Lp3/2]3/2- 9.59 ± 0.24 ± 0.5* #4 [12C(1+,0) x Ls1/2]1/22+ 11.52 ± 0.20 ± 0.5* [12C(1+,1) x Ls1/2]1/24+ #5 [12C(2+,0) x Lp1/2]5/22- 15.24 ± 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) = 1.36 ± 0.26 ± 0.7 MeV Kishimoto et. al.

  40. E336 Excitation spectrumof the 16O(p+,K+)16LO reaction

  41. 9LBe A typical cluster L hypernucleus ★supersymmetric states Gal et.al.(’76) genuine hypernuclear states Bando et.al.(’86) (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

  42. Excitation spectrumof the 13C(p+,K+)13LC reaction E336

  43. Cluster states of 9LBe Supersymmetric Genuine hypernuclear states T.Motoba, Il Nuovo Cim. 102A (1989) 345.

  44. 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

  45. 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 also plays a crucial role • feasibility of experiments • expandability to coincidence experiments • hypernuclear weak decay • gamma ray spectroscopy

  46. 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%)

  47. Summary • The value of good-resolution (p+,K+) spectroscopy has been demonstrated with the use of a large acceptance superconducting kaon spectrometer.(SKS) • Taking the advantage of the (p+,K+) reactionthat selectively excites bound L hypernuclear states, L single-particle binding energies are derived up to 208LPb.(E140a) • Light L hypernuclear spectroscopy has been extensively performed for p-shell L hypernuclei and compared with theoretical calculations based on shell and cluster models..(E336) • High quality hypernuclear structure information plays an important role in the investigation of the LN interaction, particularly spin dependent part. • High quality hypernuclear spectroscopy was carry out for 89LY.Splittings of L major shell orbitals were observedand is under discussion in terms of spin-orbit splitting and/or structural effect.(E369) • SKS serves also as an efficient tagger of L hypernuclear production and has been intensively used for coincidence measurements of weak and gamma decay processes.

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