1. Lambda hypernuclear spectroscopy at JLab Hall-C Graduate School of Science, Tohoku University Toshiyuki Gogami for the HES-HKS collaboration 1.Introduction 2.Physics motivation M 2 HY = (E e + M T - E K+ - E e’ ) 2 - ( p e - p K+ - p e’ ) 2 The (e,e’K + ) experiment FWHM ~ 500 keV A few MeV by the (π +,K + ), (K -,π - ) P  Λ n  Λ by the (π +,K + ), (K -,π - ) Figure.1 : HES-HKS group photo in the experimental hall C in JLab (2009). Figure.2 : The experimental setup of JLab E05-115 (2009) Measure with spectrometers HESHKS Δp/p~2×10 -4 Momentum [GeV/c] 0.844 ± 0.1441.20± 0.15 Angle (lab) [degree] 3.0 – 9.01.0 – 13.0 Beam energy [GeV] 2.344 Target (Hypernuclei) 7 Li, 9 Be, 10 B, 12 C, 52 Cr (,CH 2,H 2 O) ( 7 Λ He, 9 Λ Li, 10 Λ Be, 12 Λ B, 52 Λ V) (,Λ,Λ) 3.Particle identification 4.Missing Mass Figure.3 : Picture of HKS detector package NPE Mass square [GeV/c 2 ] 2 π+π+ 1 [m] K + p, π + K+K+ p π+π+ p K+K+ Figure.5 : NPE of Cherenkov detector vs. mass square Cherenkov detectors -AC,WC- Aerogel (n=1.05) Water (n=1.33) Drift chambers -KDC1,KDC2- TOF walls -2X,1Y,1X- (Plastic scintillators) σ ≈ 250 [μm] TOF σ ≈ 170 [ps] Aerogel (n=1.05) Water (n=1.33) Figure.4 : Mass square distribution Mass square [GeV/c 2 ] 2 After Cherenkov cut K+K+ Before Cherenkov cut When the Cherenkov and mass square cuts are applied to keep ~90% kaon in the total events, <2% proton and <1% pion are contaminated in the kaon events. 5.Electro-/photo- production of K + Λ 6.Summary Figure.11 : The differential cross section of K + Λ production SAPHIR : K.H.Glander et al., Eur. Phys. J. A 19, 251-273 (2004) CLAS : R.Bradford et al., Phys. Rev. C 73, 035202 (2006) The (e,e’K + ) experiment at JLab Hall-C in 2009 (JLab E05-115) 7 Λ He, 9 Λ Li, 10 Λ Be, 12 Λ B and 52 Λ V, Λ, Σ 0 Kaon identification When the cuts applied to keep ~90% kaon in total events, <2% proton and <1% pion contaminate in the kaon events. Matrix tuning In progress not only to get better resolution but also to keep linearity. K + Λ elementary production data at very forward angle cosθ k CM ~ 0.97, W~1.9 GeV, Q 2 ~0.01 [GeV/c] 2 p(e,e’K + )Λ ~1.8MeV (FWHM) Δm = 19 ± 17 keV/c 2 p(e,e’K + )Σ 0 ~1.8MeV (FWHM) Δm = 73 ± 47 keV/c 2 QF Λ from 12 C JLab E05-115 CH 2, ~ 450 [mg/cm 2 ] ~ 2.0 [μA] ~ 38 [hours] The polyethylene target was used as a proton target to optimize energy scale and to study the elementary process of K + Λ production. Figure.6 : Missing Mass spectrum of Polyethylene (CH 2 ) target Figure.7 : Coincidence time Accidental coincidence events Figure.8 : Missing mass spectrum of 12 C target. 12 C(e,e’K + ) 12 Λ B pΛpΛ sΛsΛ Preliminary JLab E05-115 (HES-HKS) 192±6±89 [ nb / sr ] Figure.10 : The differential cross section of photo-production of K + Λ ( P.Bydzovsky and T.Mart, Phys. Rev. C 76, 065202 (2007) ) Lack of consistency at forward angles  High statistical data have been awaited Q 2 is very small ( ~0.01[GeV/c] 2 )  Almost real photon W ~ 1.93 GeV cosθ K CM ~ 0.97 Figure.8 shows preliminary binding energy histogram of 12 C(e,e’K + ) 12 Λ B. The peaks of s Λ and p Λ are clearly can be seen, although the widths are a few MeV in the current status. The matrix tuning is on progress not only to get better energy resolution but also to keep linearity. VIII TOURS SYMPOSIUM ON NUCLEAR PHYSICS AND ASTROPHYSICS in Black Forest, Germany (2012) Figure.9 : Missing mass spectrum of 52 Cr target. 52 Cr(e,e’K + ) 52 Λ V Accidental coincidence events JLab E05-115 52 Cr, ~154 mg/cm 2 ~ 7.6 μA ~ 227 hours Figure.9 shows preliminary binding energy histogram of 52 Cr(e,e’K + ) 52 Λ V. 450±80 events are in the binding region (-20 MeV ~ 0 MeV). The number of events will be increased by the parameter optimization of the drift chambers at least by ~10%. 7 Λ He, 9 Λ Li, 10 Λ Be, 12 Λ B, 52 Λ V, Λ, Σ 0 Light Λ hypernuclei (A < ~10) ΛN-ΣN interaction Charge symmetry breaking Light Λ hypernuclei (A < ~10) ΛN-ΣN interaction Charge symmetry breaking Medium heavy Λ hypernuclei (A=52) Mass dependence of Λ single particle energy s-,p-,d-,f-orbit binding energy & cross section ls splitting Medium heavy Λ hypernuclei (A=52) Mass dependence of Λ single particle energy s-,p-,d-,f-orbit binding energy & cross section ls splitting Λ, Σ 0 Elementary production of K + Λ,Σ 0 Contribution of longitudinal terms Λ, Σ 0 Elementary production of K + Λ,Σ 0 Contribution of longitudinal terms YN interaction(baryon-baryon interaction) Structure of Λ hypernuclei Accidental coincidence