Lulin Yuan / Hampton University 2008 APS April Meeting St. Louis Missouri, Apr. 12, 2008

Hypernuclei: Strangeness in Nuclei Hypernucleus: Bound hadronic many body system of nucleons and one or more hyperons ( ,   ) -- nuclei with strangeness Hypernuclei add a new dimension: strangeness into normal nuclei – Hyperon-nucleon interaction – New hadronic many body structure induced by strangeness – Role of strangeness inside neutron star n S Z Hypernuclei Chart Pb: 208 La: 139 S=0 S=1 S=2

Hyperon-nucleon interaction Hypernuclear Spectroscopy: A way to extract hyperon-nucleon(  N) efffective interaction inside medium H = H core * + H  + V  N Nuclear core-  residual interaction  Single particle shell structure KEK E369: YK  Y  Single Particle Potential 89  Y

Spin Dependent Hyperon-nucleon interaction  Spin-orbit splittings due to spin-dependent interaction : – Energy seperation: ~100keV; increasing with higher orbit l – Energy seperation and level order differ between different models Resolution of previous data (>1MeV) not good enough to resolve spin-doublet splittings above p-shell Properties of  inside nuclear medium;  mixing Core NucleusHypernucleus J J+1/2 J-1/2 Peak splittings: Spin-doublet splitting or other core excited states?

New dynamical features induced by  : extreme neutron rich systems. An example: 7  He --  added to a neutron halo state 6 He Role of hyperon in the core neutron star: need precise YN potential to determine onset of hyperon formation and maximum mass of neutron star Need high resolution hypernuclear spectroscopy in a wide mass region New Structure Induced by Strangeness Oberserved Hypernuclei Below p-shell n Z 11  Be

Experimental Road Map HNSS: Completed in 2000 Spectrometer: Splitter + SOS (K) + Enge (e’) First hypernuclear spectrum by (e,e’K) reaction: 12  B (resolution~1 MeV) HKS : Data taking summer 2005, analysis approaching final stage Spectrometer: Splitter + HKS (K) + Enge (e’) Targets: 12 C, 28 Si, 7 Li HES : Approved and preparation under way Spectrometer: New Splitter + HKS + HES Targets: 40 Ca, 52 Cr, etc

HKS Experimental Goals JLab HKS experiment: Hypernuclear spectroscopy from lower p-shell to medium- heavy mass systems with ~400 keV resolution by electroproduction – Electroproduction: A Z + e  A  (Z-1) + e’+ K + – A few hundred keV energy resolution achievable by utilizing high precision electron beam Focus: – High spin, unnatural parity states complementary to hadronic reactions; Neutron rich systems -- Targets: 7 Li, 12 C – High resolution spectroscopy beyond p-shell --Target: 28 Si

HKS Experimental Setup Experimental setup: Increasing yield and reduce accidental background Accept very forward angle e’: using Splitter magnet on target Vertically tilt electron spectrometer e Beam e’:0.3 GeV/c K + :1.2 GeV/c   p 1.8 GeV/c Bremsstralung flux Virtual photon flux factor 

Spectrometer System Optical Calibration Spectrometer system optical calibration: key to reach 400 keV energy resolution On-target splitter field – only one fixed kinematics setting available High accidental background in calibration data Using known masses of ,   from CH2 target and identified hypernuclear bound states for spectrometer calibration HKS spectrometer system Beam Target Splitter HKS Enge Sieve Slit To beam dump Kaon Momentum (MeV/c) Electron Momentum (MeV/c)   12  B (gs)   Al Kinematics coverage

Spectrometer System Calibration Strategy Minimize Chisquare w.r.t reconstruction matrix M by an Nonlinear Least Square method Kinematics calibraion: important to determine correct binding energy, energy resolution Iteration Starting optics Calculate missing mass Optical and kinematics calib. by minimize Chisquare New optics Better signal to background ratio More accurate bound state mass Iteration procedure for spectrometer calibration

Counts (0.3MeV/bin)  00 Accidentals Events from C p(e,e’K + )  &  0 used for kinematics and optics calibration HKS-JLAB CH2 target ~ 70 hours Preliminary  = 660 keV  M  = -9 keV  M  = -18 keV

s  (2-/1-) p       C.E. #1 C.E. #2 12 C(e,e’K + ) 12  B used for kinematics and optics calibration Preliminary Accidentals JLAB – HKS ~ 120 hrs w/ 30  A  ~400 keV FWHM B  g.s. = MeV B  p.s = MeV B  (MeV) Counts (0.15 MeV/bin)

Preliminary SS pp d ?d ? C.E. ? 28 Si(e,e’K + ) 28  Al – First Spectroscopy of 28  Al Counts (0.15 MeV/bin) B  - Binding Energy (MeV) JLAB – HKS ~ 140 hrs w/ 13  A Accidentals Major shell structures seen Indication of core excited states * Motoba 2003 …… 1s 1p 2s 1d 1f 2p 1/2 3/2 1/2 5/2 1/2 3/2 7/2 28Al 51V 89Y p Single particle level scheme  = ~300 keV FWHM B  g.s. = MeV B  p.s = MeV

7 Li(e,e’K + ) 7  He – First Observation of ½ + G.S. of 7  He Counts (0.2 MeV/bin) B  - Binding Energy (MeV) S  (1/2 + ) Accidentals Preliminary 7  He:  added to a neutron halo state 6 He “glue role” of  : 6 He 7  He 0+  +n+n  +  +n+n ½ = =3.55 fm * Hiyama 1997 α N N Λ  = ~360 keV FWHM B  g.s. = MeV

Summary The HKS experiment carried out at Jefferson Lab aims to obtain high precision hypernuclear spectroscopy from lower p-shell to medium-heavy systems by electroproduction The preliminary spectrum has a resolution ~400 keV (FWHM) for 12  B gs ;The gs and major shell structures of 28  Al and 7  He have been observed A special calibration procedure was developed for the optical calibration of the specrometer system; The same procedure is applied on simulated events to estimate systematic error from the calibration process A upgraded experiment HES is under preparation which will increase hypernuclear yield by more than a factor of 8 and extend hypernuclear spectroscopy to heavier mass region

– L. Tang (Spokesperson), O.K. Baker, M. Christy, P. Gueye, C. Keppel, Y. Li, L. Cole, Z. Ye, C. Chen, L. Yuan (Hampton U) – O. Hashimoto (Spokesperson), S.N. Nakamura (Spokesperson), Y. Fujii, M. Kaneta, M. Sumihama, H. Tamura,K. Maeda, H. Kanda, Y. Okayasu, K. Tsukada, A. Matsumura, K.~Nonaka, D. Kawama, N. Maruyama, Y. Miyagi (Tohoku U)  S. Kato (Yamagata U)  T. Takahashi, Y. Sato, H. Noumi (KEK)  T. Motoba (Osaka EC) – J. Reinhold (Spokesperson), B. Baturin, P. Markowitz, B. Beckford, S. Gullon, C. Vega (FlU)  Ed.V. Hungerford, K. Lan, N. Elhayari, N. Klantrains, Y. Li,S. Radeniya, V. Rodrigues (Houston)  R. Carlini, R. Ent, H. Fenker, T. Horn, D. Mack, G. Smith, W. Vulcan, S.A. Wood, C. Yan (JLab)  N. Simicevic, S. Wells (Louisiana Tech)  L. Gan (North Carolina, Wilmington)  A. Ahmidouch, S. Danagoulian, A. Gasparian (North Carolina A&T)  M. Elaasar(New Orleans)  R. Asaturyan, H. Mkrtchyan, A. Margaryan, S. Stepanyan, V. Tadevosyan (Yerevan)  D. Androic, T. Petkovic, M. Planinic, M. Furic, T. Seva (Zagreb)  T. Angelescu (Bucharest)  V.P. Likhachev (Sao Paulo)