Electrophoto-production of strangeness and  Hypernuclei Osamu Hashimoto Department of Physics, Tohoku University October 21-22, 2004 Jeju University

Strangeness production by pions and photons σ total (  b) E γ (GeV) p( ,K + )  Total cross section Phys. Lett. B 445, 20 (1998) M. Q. Tran et al.

Basic characteristics of the (e,e ’ K + ) spectroscopy Proton converted to   Neutron rich  hypernuclei Large angular momentum transfer  Similarly to (  +,K + ) reaction Spin-flip amplitude  Unnatural parity hypernuclear states High quality primary beam  Sub MeV resolution

The (e,e ’ K + ) reactions --- elementary and hypernuclear --- Elementary process Hypernuclear production

 n  K 0  reaction data near the threshold play an important role No contribution from the t-channel Born term Less contribution of resonances terms Isobar model Elementary processes of photo-strangeness production g(K 0  0 n) = -g(K +  0 p) Coupling constants Resonances to be included New high-quality data being available for K + However, Six possible isospin channels: (1) p( ,K+)  (2) p( ,K+)  0 (3) p( ,K0)  + (4) n( ,K+)  - (5) n( ,K0)  (6) n( ,K0)  0

n( ,K)  Model calculation γ + n → K 0 + Λ Energy dependence Angular distribution calculated by Sotona’s code γ + p → K + + Λ E γ = 1.05 GeV Kaon-MAID : T.Mart, C.Bennhold, Phys. Rev. C61 (2000) (R) kaon/kaonmaid.html SLA : T.Mizutani et al., Phys. Rev. C58 (1998) 75.

Laboratory for Nuclear Science, Tohoku University at Sendai Neutral Kaon Spectrometer ( NKS ) 200 MeV LINAC 1.2 GeV Booster/stretcher ring エネルギー標識化光子ビー ム up to 1.1 GeV/c Good duty factor

First observation of neutral kaons in the threshold region K 0 ~ 450 Background Invariant Mass (     ) (GeV/c 2 ) counts/20MeV K 0 s : c  2.68cm 12 C target K s 0   + +  - (64 %)

solid: Kaon-MAID n( ,K 0 )  only dashed: Kaon-MAID include p( ,K 0 )  + + n( ,K 0 )  0 solid: SLA n( ,K 0 )  N eff = 4.2 k F 0 =0.22GeV/c Comparison with recent models  + 12 C  K 0 + X ( Quasi-free K 0 production) preliminary

Neutral kaons from the liquid deuterium target K 0 S : c  ～ 2.68 cm  x ～ 1.6mm

Comparison of D2 target data with theoretical models preliminary

Upgrade plan at LNS, Tohoku STB ring radiator 1.2 GeV e - NKS2  Pole diameter : 160 cm B MAX : 0.5 T High momentum & mass resolution Efficiency more than 2X for K 0 Efficiency more than 10 x for  Ready in 2005

K + detection At very forward angle (~ 0 degrees) Maximum hypernuclear production cross section e’ detection At extremely forward angles Advantage : Large virtual photon flux Disadvantage : Huge backgrounds from Bremsstrahlung Hypernuclear production by the (e,e ’ K + ) reaction p e =0.3GeV/c e’ K+K+ p K =1.2 GeV/c E e =1.8 GeV e - Beam Target nucleus E  =1.5 GeV

Angular distribution of electrons and kaons Ee = GeV Ee’=0.4 GeV Ee = GeV Ee’ = 0.38 GeV angle (deg) d  /d  (nb/sr) electronskaons (degrees) Calculated by Sotona’s code

Jlab Accelerator Hall BHall AHall C Beam characteristics E max 6 GeV Max. Current 200  A Duty factor 100% Emittance 2.0  m·mrad  E beam 2.5  (FWHM) E E E97-107

E experimental setup To beam dump

E calibration p(e,e’K + )  p(e,e’K + )   12 C(e,e’K + ) quasi-free Accidental e e’e+e+ e-e- 815 keV (FWHM) CH x target A(e,e’;(e+,e-))A

138 nb/sr 12  B spectrum of E d  /d  nb/sr/0.3 MeV -B  (MeV) (2+,3+)(1-,2-) (1-,0-) (2-,1-) Ground state doublet B  = 11.52±0.35 MeV Cross section 140±17(stat) ±18(sys) nb/sr Motoba’s calculation J  cross section nb/sr nb/sr Binding energy Emulsion data B  = MeV 750 keV(FWHM) 1 month data

7  He Spectrum of E No peaks observed in the bound region A suggestive bump at around 7-8 MeV Background subtracted d  /d  nb/sr/0.3 MeV Li(e,e’K+) 7  He Sotona -B  ( MeV)  He + n 6 He +  5/2 + 3/2 + 3/2 - 1/2 + 5/2 - 7/2 - 3/2 - 5/2 - -B  ( MeV) Shell model calc. by Sotona

 E~400 keV 12 C (e,e’K) 12 B  Very Preliminary Data with Multiple Uncorrected Beam Energies “Standard” PID Full statistics with fitted peaks. Resolution still not fully optimized Subsets of data appear to have better resolution Limited statistics + cut on Beam x position at 1C12 + ± 50 keV on relative beam energy  E=1.3 MeV (FWHM) Guarantees beam within specs Projected Data Beam energy spread and spectrometer resolutions as planned  E~800 keV From Prof. Garibaldi HALL A

Hypernuclear spectroscopy experiments at Jlab Area Ee (GeV) E  (GeV)  e (deg.) p K (GeV/c)  K (deg.) Spectrometers Run year E89-009Hall C SOS+ENGE, Splitter 2000 E94-107Hall A HRS+HRS, Septum 2004 E01-011Hall C HKS+ ENGE (Tilt), Splitter 2005 ???Hall C ~ HKS+HES, New splitter 2007? MAINZ to join

The tilt method for higher luminosity Side view

Future spectrometer system for the (e,e ’ K + ) reaction High resolution Electron Spectrometer HES (2.2~2.5GeV)

Yield comparison of E and E Item E E 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 Beam current(  A) Estimated yield ( 12  B gr :counts/h) ~ (measured) 60

Expected 28  Al hypernuclear spectra SKS E140a 28 Si(  +,K + ) 28  Si

Summary Photo strangeness production in the 1 GeV region Neutral kaon measurement plays a unique role NKS at LNS, Tohoku measured neutral kaons NKS2 for further experimental study of neutral kaon production is under construction Hypernuclear production by the (e,e ’ K + ) reaction The first 2 experiments were successfully carried out at Jlab Hall C and Hall A 2 nd generation hypernuclear spectroscopy by the (e,e ’ K + ) reaction is to be carried out in 2005 High resolution electron spectrometer is under construction for the 3 rd generation (e,e ’ K + ) spectroscopy

E top 2pass (GeV) Acceptable energy windows of HKS system with ENGE or HES revised 04/10/ E e’ (GeV) E e at Hall (GeV) Acceptable Central Energy (GeV) HES ENGE E top 1 pass (GeV)

Invariant mass spectrum Invariant mass [GeV/c 2 ] K 0 mass region 0.46 – 0.54 GeV/c 2 accidental events miss ID events k0 candidates

Momentum distribution Error : statistical only

Virtual photon energy E   1.5 GeV Beam energy E e = 1.721, GeV Reaction Threshold(MeV)  p  K   K   K   K * (892)  σ total (  b) E γ (GeV) Total cross section Phys. Lett. B 445, 20 (1998) M. Q. Tran et al. Experimental condition Limited by bremsstrahlung electrons at 0 deg. in scattered electron spectrometer p( , K + )  Beam current < 2  A < 0.6  A for 12 C target Target thickness < 100 mg/cm 2 nat C 22 mg/cm 2 CH mg/cm 2

N T : target density N X :  or 12  B g.s yield N  : Number of virtual photon integrated over Ee’ and  e’  total : total correction factor Cross section Cross sections were extracted with experimental yields Triple-differential cross section

12  B spectrum fitting results Fitted by 3 Gaussians and a constant Energy resolution was fixed 0.9 MeV(FWHM) Constant = 5±1 nb/sr/400keV

Energy level of 12  B spectrum Emulsion data B  =11.37±0.06 MeV 3/2 - 1/2 - 3/ S factor 12 C(e,e’p) 11 B 11 B x s   12  B Ex(MeV) d  /d  (nb/sr) Ex(MeV) B  (g.s)=12.20±0.06±0.25 MeV : 30±15±4 59±14±7 122 ±12 ±15

12  B spectrum v.s 12  C spectrum 12  C KEK E369 Structure is similar S  and P  states are observed SS PP SS PP

E  =1.3GeV,   =3deg., 900 keV(FWHM), NSC97f DWIA calculation with phenomenological potential by Motoba Theoretical prediction of 12  B spectrum

Theoretical calculation of 28  Al spectrum 300 keV (FWHM) ls splitting ??? high spin and unnatural parity states Calculated by Sotona et al.

DWIA calculation by a code of M.Sotona Angular distribution Angular distribution of 12  B states (p3/2) -1 (p3/2)  3 + (s1/2) -1 (p1/2)  2 - (p3/2) -1 (s1/2)  2 - (s1/2) -1 (s1/2)  1 + Expected yield ratio between g.s.