Spectroscopic Research of Lambda Hypernuclei at JLab Hall C

1. B2-PTh-3 APPC12 @ Makuhari, Chiba, Japan (2013) 1. Introduction 2. Physics motivation 7ΛHe, 9ΛLi, 10ΛBe, 12ΛB, 52ΛV, Λ, Σ0 • Λ, Σ0 • Elementary production of K+Λ,Σ0 • Contribution of longitudinal terms • The (e,e’K+) experiment • FWHM ~ 0.5 MeV • A few MeV by the (π+,K+), (K-,π-) • p  Λ • n Λ by the (π+,K+), (K-,π-) • 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 Figure.1 : HES-HKS group photo in the experimental hall C in JLab (2009). Spectroscopic Research of Lambda Hypernucleiat JLab Hall C ~ 0.1g/cm2 • YN interaction(baryon-baryon interaction) • Structure of Λ hypernuclei 7Li , 9Be , 10B , 12C , 52Cr ( , CH2 , H2O ) ( 7ΛHe, 9ΛLi, 10ΛBe, 12ΛB, 52ΛV ) ( , Λ , Λ ) Figure.2 : The experimental setup of JLab E05-115 (2009) 4. Missing Mass M2HY = (Ee + MT - EK+ - Ee’)2 - ( pe- pK+- pe’ )2 JLab E05-115 CH2, ~ 450 [mg/cm2] ~ 2.0 [μA] ~ 38 [hours] p(e,e’K+)Λ ~1.8MeV (FWHM) Δm = 19 ± 17 keV/c2 Measure with spectrometers Preliminary 3. Kaon identification p(e,e’K+)Σ0 ~1.8MeV (FWHM) Δm = 73 ± 47 keV/c2 Figure.3 : A photographof the HKS detector package 1 [m] Accidental coincidence QF Λ from 12C K+ p, π+ Figure.7 : Coincidence time between K+s and scattered electrons. Figure.6 : A missing Mass spectrum of Polyethylene (CH2) target Online π+ : 0.074 % K+ : 91.3% p : 3.8% The polyethylene target was used as a proton target to optimize energy scale and to study an elementary process of K+Λ production. Mass squared [GeV/c2]2 Graduate School of Science, Tohoku University Toshiyuki Gogami for the HES-HKS collaboration Figure.4 : Mass squared distribution Drift chambers -KDC1,KDC2- • Cherenkov detectors -AC,WC- • Aerogel (n=1.05) • Water (n=1.33) Aerogel (n=1.05) p , x’ , y’ @Target x , x’ , y , y’ @Focal Plane σ ≈ 250 [μm] TOF walls -2X,1Y,1X- (Plastic scintillators) Offline π+ : 6.1 % K+ : 86.7% p : 31.3% π+ NPE TOF σ ≈ 170 [ps] 6th order transfer matrix π+ : K+: p p K+ 80 : 1 : 30 Tunedwith Λ, Σ0and 12ΛB g.s. Water (n=1.33) Online 12C(e,e’K+)12ΛB K+ p NPE 0.47: 1: 4 0.7 MeV (FWHM) pΛ π+ Offline The matrix tuning is on progress not only to get better energy resolution but also to keep linearity. sΛ Mass square [GeV/c2]2 0.0045: 1: 0.0006 Figure.5 : NPE of Cherenkov detector vs. mass squared 5. Electro-/photo- production of K+Λ Preliminary Accidental coincidence events JLab E05-115 (HES-HKS) 192±6±89 [ nb / sr ] Figure.8 : A missing mass spectrum of 12C target. 12C(e,e’K+)12ΛB Preliminary 6. Summary Figure.10 : 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) • Light to medium heavy Λ hypernucler spectroscopy • Λ, Σ0, Λ, 7ΛHe, 9ΛLi, 10ΛBe, 12ΛB, and 52ΛV • Clean kaon identification • High background rejection efficiency with low K+ loss fraction. • Matrix tuning with Λ,Σ0 and 12ΛB • In progress not only to get better resolution but also to keep linearity. • K+Λ elementary production data at very forward kaon angle • cosθγkCM ~ 0.95 , W~1.9 GeV , Q2~0.01 [GeV/c]2 • Q2 dependence Figure.9 : 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 Preliminary Figure.11 : Q2 dependence of differential cross section of K+Λ production