Spectroscopic Investigation of  hypernuclei in the wide mass region using the (e,e’K + ) reaction (Extension request of the currently running E experiment) Osamu Hashimoto Department of Physics, Tohoku University representing the HKS collaboration JLab PAC28 August 24, 2005 P05-115

Hyper Collaboration 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) L. Tang (Spokesperson), O.K. Baker, M. Christy, L. Cole, P. Gueye, C. Keppel, L. Yuan (Hampton U) J. Reinhold (Spokesperson), P. Markowitz, B. Beckford, S. Gullon, C. Vega (FlU) Ed.V. Hungerford, K. Lan, N. Elhayari, N. Klantrains, Y. Li,S. Radeniya (Houston) R. Carlini, R. Ent, H. Fenker, 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) D. Dehnhard (Minnesota) M. Elaasar(New Orleans) R. Asaturyan, H. Mkrtchyan, A. Margaryan, S. Stepanyan, V. Tadevosyan (Yerevan) D. Androic, T. Petkovic, M. Planinic, M. Furic (Zagreb) T. Angelescu (Bucharest) V.P. Likhachev (Sao Paulo) M. Ahmed (Duke)

Outline of the talk 1.Significance of hypernuclear spectroscopy and goals of the proposed experiment 2.(e,e’K + ) spectroscopy and the current status of E experiment 3. Setup & conditions of the proposed experiment 4. Summary with prospect

Significance of hypernuclear spectroscopy and the goals of the proposed experiment

3D Nuclear Chart with the strangeness degree of freedom

Single-particle nature of  hypernuclei New degree of freedom  free from Pauli blocking Deeply bound nuclear states Baryon structure in nuclear medium Unique structure of hadronic many-body system Nucleus with a new quantum number Core excited states Glue role of a  hyperon  N interaction Unified view of baryon-baryon interaction in SU(3) Central and spin-dependent  N interaction Singly charged atom Core Nucleus +  Core excitation, A  hyperon in the mean field

Nucleon single particle orbits e e’ p

Single-particle nature of  hypernuclei New degree of freedom  free from Pauli blocking Deeply bound nuclear states Baryon structure in nuclear medium Unique structure of hadronic many-body system Nucleus with a new quantum number Core excited states Glue role of a  hyperon  N interaction Unified view of baryon-baryon interaction in SU(3) Central and spin-dependent  N interaction Singly charged atom Core Nucleus +  Core excitation, A  hyperon in the mean field

YN, YY Interactions and Hypernuclear Structure Free YN, YY interaction Constructed from limited hyperon scattering data (Meson exchange model: Nijmegen, Julich) YN, YY effective interaction in finite nuclei (YN G potential) Hypernuclear properties, spectroscopic information from structure calculation (shell model, cluster model…) Energy levels, Energy splitting, cross sections Polarizations, weak decay widths high quality (high resolution & high statistics) spectroscopy plays a significant role G-matrix calculation

Hypernuclear Hamiltonian v  N weak compared to v  H N (Core) : Core nucleus ( Usually hole states) t  :   kinetic energy V  N : effective  N interaction ( Nijmegen, Julich... ) H = H N (Core) + t  +  V  N effective Weaker compared with NN Direct comparison of spectroscopic data with structure calculation Biding energy, energy splitting, cross section, ….

Population of excited  hypernuclear states and  hypernuclear spectroscopy neutron or proton  n p  BB BpBp BnBn 208  Pb 207  Tl 207  Pb Weak decay nonmesonic mesonic  Narrow widths < a few 100 keV  -particle nucleon-hole states ~25 MeV Reaction spectroscopy Gamma-ray spectroscopy

B  =0  Hypernuclear production (  +,K ＋ ) Stopped (K -,  ) (e,e’K+) ( ,K ＋ ) (p,K ＋ ) Inflight(K -,  ) Hypernuclear Cross section Momentum transfer (MeV/c) mb/sr nb/sr  b/sr JLab KEK, BNL BNL, CERN (K -,  - ) (  +,K + )

Light hypernuclei (A<~20) Fine structure Baryon-baryon interaction in SU(3)  coupling in large isospin hypernuclei Cluster structure Heavy hypernuclei (A>~50) Single-particle potential Distinguishability of a  hyperon U 0 (r), m  *(r), V  NN,... Neutron star (A ~ ) Hyperonization  Softening of EOS ? Superfluidity Hypernuclei in the wide mass range -- toward strange matter -- Short range nature of the  N interaction : no pion exchange meson picture or quark picture ?

12 C(  +,K + ) 12  C spectra by the SKS spectrometer at KEK 12 GeV PS KEK336 2 MeV(FWHM) KEK E MeV(FWHM) Hypernuclear spectroscopy established BNL 3 MeV(FWHM) SKS

 Single particle states ->  -nuclear potential  hyperon in heavier nuclei Single-particle orbits in nucleus Hotchi et al., PRC 64 (2001) Hasegawa et. al., PRC 53 (1996)1210KEK E140a Skyrme HF (Yamamoto) DDRH (Lanske) Quark-meson coupling (Saito, Thomas) ……… YLaPb Si

Goals of the proposed experiment 51 V(e,e’K + ) 51  Ti reaction –Next heavier  hypernuclei from 28  Al –  binding energies for s,p,d orbits determined –  hypernuclear structure investigated – ls splitting in l=2,3 orbits to b derived If sizable 89 Y(e,e’K + ) 89  Sr reaction – Exploratory run to examine feasibility of (e,e’K+) spectroscopy in heavier hypernuclei 6,7 Li(e,e’K + ) 6,7  He and 10,11 B(e,e’K + ) 10,11  Be – Precision hypernuclear structure in neutron-rich  hypernuclei – LS coupling effect changing isospins with neutron number

(e,e’K+) spectroscopy and E status

The (e,e’K + ) reaction for hypernuclear spectroscopy Proton to    Neutron rich  hypernuclei Large angular momentum transfer Spin-flip amplitude   Hyperon production reactions for spectroscopy  Z = 0  Z = -1 comment neutron to  proton to  (  +,K + ) (  -,K 0 ) stretched, high-spin large momentum transfer In-flight (K -,  - ) in-flight (K -,  0 ) substitutional stopped (K -,  - ) stopped (K -,  0 ) large momentum transfer (e,e'K 0 ) (e,e'K + ) spin-flip (  K 0 ) ( ,K + ) & large momentum transfer Higher energy resolution & First (e,e ’ K + ) spectroscopy  E (SOS + ENGE) A few 100 keV achievable Only at JLab

What limited the E experiment ? Energy resolution –The kaon arm limited hypernuclear mass resolution Hypernuclear yield rates –High accidental background rate due to Brems electrons –Solid angle of the kaon arm (SOS) limited detection efficiency (1) A high-resolution large-solid-angle kaon spectrometer (HKS) (2) New experimental configuration “Tilt method”

Tilt method and optimization of the tilt angle Side view Singles rate of the e-arm 200 MHz  < a few MHz even with 5  Target thickness and 50  Beam intensity

Maximum momentum 1.2 GeV/c Dispersion 4.7 cm/% Momentum resolution 2 x (FWHM) Solid angle 30 msr w/o splitter 16 msr w splitter Momentum acceptance 12.5 % The HKS spectrometer system for E Tilt method for the electron arm High resolution Kaon Spectrometer (HKS)

E setup in Hall C ENGE HKS Tilted ENGE

Expected singles rates Target HKSENGE e + (kHz)  + (kHz) K + (kHz) p (kHz) e - (kHz)  - (kHz) 12 C , Si , V , E C <1 Hz ,000- SOSENGE I e = 30  A, 100 mg/cm 2 High rejection efficiencies against pions and protons are required Measured values at E I e = 0.66  A, 22 mg/cm 2 Greater hadron rates

Yield comparison of E and E ItemE01-011E Gain factor Virtual photon flux per electron(x10 -4 ) Target thickness(mg/cm 2 ) Scattered electron momentum acceptance(MeV/c) Kaon survival rate Solid angle of K arm (msr) Beam current (  A) Estimated yield ( 12  B gr :counts/h) 41 (expected) 0.9 (measured) 46

Beam currents, singles rates & trigger rates E Target Beam current (  A) COIN Trigger rate (Hz) HKS singles rate (kHz) ENGE singles rate (kHz) CH 2 (5 mm) C (100 mg/cm 2 ) Si (65 mg/cm 2 ) Tilt method proved to work !!

 p K Kaon PID E coincidence time (ns)  tof –  track HKS singles eventsHKS-ENGE coincidence events

p(e,e’K + )  0 reactions 12 C(e,e’K + ) quasi-free Accidental E experimentE experiment Improved! 210 Lambda’s 1390 Lambdas

(2+,3+)(1-,2-) (1-,0-) (2-,1-)  B spectrum ( 12 C target ) 12  B g.s ~ 600 counts (~20 /hr) <1 MeV (FWHM)  400 keV vs. E Hall C ~ 165 counts with ~750 keV (~0.9 /hr) E Hall A ~ 600 counts with ~800 keV (~3 /hr) Preliminary Hypernuclear excitation (300 keV/bin) d  /d  nb/sr/0.3 MeV -B  (MeV) 1 month E E < 1MeV (FWHM)

Proposed experimental setup & conditions Basically similar to those of E except for the new High-resolution electron spectrometer and some improvement based on the E experience

HKS-HES hypernuclear spectrometer system New Splitter

High resolution electron spectrometer (HES) --- widen acceptable beam energy window --- compatible with 6, 12 GeV operation P K (GeV/c) E  * (GeV/c) Ee (GeV/c) Ee’ (GeV/c E & E E HES Option – 1.0 HKSE  dependence 6 GeV 12 GeV Beam energy and spectrometer conditions ( ENGE is used as an electron spectrometer when the beam energy is 1.8 GeV )

E top 1 pass (GeV) E top 2pass (GeV) Acceptable energy windows of HKS system with ENGE or HES E e’ (GeV) E e at Hall (GeV) Acceptable Central Energy (GeV) HES ENGE

Basic specification of HES Configuration DQQD horizontal 50 degree bend Central momentum 0.6 – 1.0 GeV/c Momentum acceptance > 200 MeV/c Momentum resolution 2 x Electron detection angle horizontal : 0 degrees vertical : < 10 degrees Solid angle > 10 msr Maximum D magnetic field 1.6 T

Splitter, HKS, HES geometry HKS HES New Splitter 0.6 GeV/c 1.0 GeV/c Splitter TOSCA calculation

HES mechanical design For 600 MeV/c For 1000 MeV/c

Expected Energy Resolution Item Contribution to the resolution (keV, FWHM) Target 7 Li 12 C 51 V 89 Y HKS momentum 190 ( 500 for SOS) Beam momentum< 180 Enge or HES momentum 93 K + angle Target thickness< 170< 180< 148< 138 Overall< 400< 360< 320< 310 <~400 keV(FWHM) expected

Expected hypernuclear production rates in the (e,e’K + ) reaction Target Beam Intensity (  A) Counts per 100nb/sr /hour Q-free K+ in HKS(Hz) 12 C Si V Target Hypernucle us  orbital Cross section (nb/sr) 12 C 12  B s1/2112 p3/279 p1/ Si 28  Al s1/256 p3/295 p1/257 d5/2131 d3/ V 51  Ti s1/218 p3/241 p1/226 d5/252 d3/248 1s1/216 f7/232 f5/238 Calculated hypernuclear cross sections (Target thickness 100 mg/cm 2 ) Hypernuclear production rates Motoba, Sotona

51  Ti and 51  V spectra KEK SKS data Simulation

50 22 Ti and V

Evolution of (e,e’K + ) spectroscopy E89-009E94-107E01-011P05-115* Configuration SOS+ENGE +Splitter HRS+HRS +Septum HKS+ENGE +Splitter HKS+HES +New splitter Beam intensity (  A) on 12 C thickness (mg/cm 2 )22100 Hypernuclear yield (12  B gr : /hr) ~ (40)(> 40) Resolution (keV) ~ 800(3-400) Beam energy (GeV) * pK (central : GeV) Pe (central: GeV ) – 1.0  K (degree)  e (degree) 064.5< 4.5 ( ) expected * ENGE spectrometer to be used for a 1.8 GeV beam ?

Roadmap of (e,e’K + ) hypernuclear spectroscopy Light  hypernuclear spectroscopy –  N interaction,  coupling p shell hypernuclei 6,7 Li, 9 Be, 10,11 B, 12 C, 13 C, 16 O targets s shell hypernuclei 3,4 He targets Medium to heavy hypernuclear spectroscopy –A  binding in the mean field, quark picture vs. conventional picture 28 Si, 51 V, (Cr)  89 Y  208 Pb ? targets Coincidence experiment – weak decay --- fission – proton, neutron and pion emission HKS as a “strangeness tagger” HES as a “virtual photon tagger” Complimentary to spectroscopy with hadronic beams at J-PARC

Requested beam time TargetHypernucleus# of days# of hours Spectrometer commissioning & calibration 4(8)96(192) Data taking 6,7 Li, 10,11 B 6,7  He, 10,11  Be V 51  Ti Y 89  Sr 5120 Subtotal for data taking Grand total 28(32)672(768)

Summary Precision hypernuclear spectroscopy by the (e,e’K+) reaction plays an essential role in the investigation of hadronic may-body systems that contain “strangeness”. Physics goal of the proposed experiment is two-fold; spectroscopy of heavier  hypernuclei ( 51 V target) and light  hypernuclei( 6,7 Li or 10,11 B targets). A high resolution electron spectrometer (HES) is under construction at TOHOKU as a part of the HKS-HES hypernuclear spectrometer system. It will be shipped to JLab at the end of The HKS-HES spectrometer system allows us to conduct the proposed 3 rd generation (e,e’K+) hypernuclear spectroscopy even with 6 GeV and 12 GeV operation.