Lambda hypernuclear spectroscopy at JLab Hall-C

1. VIII TOURS SYMPOSIUM ON NUCLEAR PHYSICS AND ASTROPHYSICS in Black Forest, Germany (2012) 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 ~ 500 keV • 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). Lambda hypernuclear spectroscopy at JLab Hall-C • YN interaction(baryon-baryon interaction) • Structure of Λ hypernuclei 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.Particle identification p(e,e’K+)Σ0 ~1.8MeV (FWHM) Δm = 73 ± 47 keV/c2 Before Cherenkov cut Figure.3 : Picture of HKS detector package 1 [m] Accidental coincidence QF Λ from 12C K+ p, π+ K+ After Cherenkov cut Figure.6 : Missing Mass spectrum of Polyethylene (CH2) target Figure.7 : Coincidence time The polyethylene target was used as a proton target to optimize energy scale and to study the elementary process of K+Λ production. Graduate School of Science, Tohoku University Toshiyuki Gogami for the HES-HKS collaboration Mass square [GeV/c2]2 Drift chambers -KDC1,KDC2- pΛ • Cherenkov detectors -AC,WC- • Aerogel (n=1.05) • Water (n=1.33) Figure.4 : Mass square distribution σ ≈ 250 [μm] Figure.8 shows preliminary binding energy histogram of 12C(e,e’K+)12ΛB. The peaks of sΛ and pΛ 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. TOF walls -2X,1Y,1X- (Plastic scintillators) Aerogel (n=1.05) sΛ TOF σ ≈ 170 [ps] NPE π+ Preliminary p 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. K+ Water (n=1.33) Accidental coincidence events K+ π+ NPE p Figure.8 : Missing mass spectrum of 12C target. 12C(e,e’K+)12ΛB JLab E05-115 52Cr, ~154 mg/cm2 ~ 7.6 μA ~ 227 hours Figure.9 shows preliminary binding energy histogram of 52Cr(e,e’K+)52ΛV. 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%. Mass square [GeV/c2]2 Figure.5 : NPE of Cherenkov detector vs. mass square Preliminary 5.Electro-/photo- production of K+Λ Accidental coincidence events Lack of consistency at forward angles  High statistical data have been awaited Figure.9 : Missing mass spectrum of 52Cr target. 52Cr(e,e’K+)52ΛV 6.Summary Figure.10 : The differential cross section of photo-production of K+Λ( P.Bydzovsky and T.Mart, Phys. Rev. C 76, 065202 (2007) ) • The (e,e’K+) experiment at JLab Hall-C in 2009 (JLab E05-115) • 7ΛHe, 9ΛLi, 10ΛBe, 12ΛB and 52ΛV, Λ, Σ0 • 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 • cosθkCM ~ 0.97 , W~1.9 GeV , Q2~0.01 [GeV/c]2 Preliminary • Q2is very small ( ~0.01[GeV/c]2) • Almost real photon • W ~ 1.93 GeV • cosθKCM ~ 0.97 JLab E05-115 (HES-HKS) 192±6±89 [ nb / sr ] 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)