Study of γd --> K + Λn through 3-track detected events with the NKS2 HONDA Kazuhisa Tohoku University

Contents 1.Introduction – K + Λ photoproduction on the deuteron – Final State Interaction (FSI) – Aim 2.Experiment – Photon Tagging System – Neutral Kaon Spectrometer 2 (NKS2) 3.Data Analysis – γp --> K + Λ – p π - invariant mass 4.Summary

K + Λ photoproduction on the deuteron By comparing γd → K + Λn to γp → K + Λ, we figure out effects from neutron, such as – Fermi Motion. – Final State Interaction (FSI) γ K+K+ Λ p π- p n deuteron FSI

Final State Interaction (FSI) The FSI affect on the cross section and polarization observables. Differential cross section at K+ emitted in 0 degree, dependent on incident photon energy. Calculations with various ΛN potentials: Dashed curve: the ΛN potential by Bhaduri et al. (Phys. Rev. 55,1671(1960).) Solid curve: the potential by Verma and Sural.(Phys. Rev. C 22, 229 (1980).) Dotted curve: the plane-wave approximation R.A. Adelseck and L.E. Wright, Phys. Rev C39 (1989) 580

Aim By studying the FSI, we investigate the ΛN interaction. We analyze γd → K + Λn to study the FSI between Λ and n. Observed 3 charged track events which include K + Λ – About 150k events with hydrogen target ← consistency check – About 14M events with deuterium target

Photon Tagging System γ ray is produced by Bremsstrahlung of 1.2GeV electron beam. Energy of recoil electron is measured by bending magnet and scintillation counters Tagger radiator: Carbon fiber 11  m Electron beam E 0 = 1.2 GeV (Max) E γ = = GeV

Neutral Kaon Spectrometer 2 (NKS2) We detect charged particle – Tracking by CDC and VDC. – TOF by OH and IH. We identify particles (p, π +, π - ) by mass and charge. Photon Beam VDC CDC IH OH EV Liq. H 2,D 2 Target 1.6 m Dipole magnet : B = 0.42 T, R = 0.8 m

γp --> K + Λ Energy of γ ray is Tagged by Tagging System. Momenta and velocities of 3 particles are measured. →We can reconstruct the K + Λ center-of-mass system. Energy of γ Tagged proton momenta of K + 、 p 、 π - measured Λ γ p Λ K+K+ p π-

p π - invariant mass We reconstruct Λ mass by p and π - momentum A peak around M Λ mass p π - invariant mass (GeV/c 2 ) γ π-π- MΛMΛ Event p Λ K+K+ p

Summary For studying FSI, we are analyzing γd --> K + Λn. Studying FSI, we can investgate the interaction between Λ and n. By measuring 3 charged particles(K +, p, π - ), we can reconstruct the K + Λ center-of-mass system. Reconstruct p π - invariant mass