Hadron physics with GeV photons at SPring-8/LEPS II M. Niiyama (Kyoto Univ.) Introduction to SPring-8/LEPS I Physics motivation for LEPS II Status of LEPS II project Summary Contents

Super Photon Ring 8 GeV (SPring-8)

Schematic View of LEPS I Facility Backward-Compton scattering 8 GeV electron Collision Recoil electron Tagging counter 36m 70m a) SPring-8 SR Laser light b) Laser hutch Compton g-ray c) Experimental hutch

Backward-Compton Scattered Photon 8 GeV electrons in SPring-8 + 351nm Ar laser (3.5eV） 8W ~ 2.4 GeV photon + 266nm Solid+BBO (4.6eV） 1W +3.0 GeV photon Laser Power ~6 W (351nm)  Photon Flux ~1 Mcps (2.4 GeV) E measured by tagging a recoil electron  E>1.5 GeV, E ~10 MeV Laser linear polarization 95-100% ⇒ Highly polarized  beam Linear Polarization of  beam PWO measurement tagged photon energy [GeV] photon energy [MeV]

Setup of LEPS I Acceptance is limited in forward region 1.5

Physics motivation for LEPS II Q+ LEPS vs CLAS LEPS forward angle CLAS large angle PRC 79, 025210 (2009) PRL 96, 212001(2006)

Proton rejection by using dE/dx in Start Counter Pid = (Measured energy loss in SC) – (Expectation of KK) – (Half of expectation of proton) n K- K- K+ K+ SC p SC or SC K- K+ Proton not tagged (Proton rejected) Proton tagged (e ~60%) Peak structure is seen in the M(nK+) for proton rejected events. (Further more data will be taken at LEPS w/ larger acceptance for proton) KKp only KKn and part of KKp Preliminary Signal enhancement is seen in proton rejected events. should be associated with gn reaction. Preliminary p/n ratio: 1.6 before proton rejection 0.6 after proton rejection

Physics motivation for LEPS II Q+ LEPS vs CLAS Strong angular dependence of production rate? LEPS forward angle CLAS large angle TOF Dipole Magnet 　0.7　Tesla Target Start Counter DC2 DC3 DC1 SVTX AC(n=1.03) Angular dependence of production cross section may solve controversial situation. → 4p detector LEPS II. Photons PRC 79, 025210 (2009) PRL 96, 212001(2006)

Physics motivation for LEPS II L(1405) JP=1/2- Mass spectrum of P-wave baryons Meson Baryon molecule picture has been proposed. (ex. Dalitz Phys. Rev.153 1967) 1) 3 quark or meson-baryon molecule? 2) If it is a Kbar N molecule, what is the binding energy? 3/2- 1/2- N(1520) N(1535) h+N　(1485) 3/2- 1/2- Λ(1520) Λ(1405) 30 MeV K+N　(1430) mass (MeV) uud (or udd) uds

Higher mass of Kbar N component of L(1405) D. Jido, et al. NPA725(2003) Confirm by photoproduction. M.Niiyama. PRC78 V.K. Magas, E. Oset and A. Ramos, PRL 95

Hyperon production with K*(892) Parity filter with linearly polarized photon E g K* K p natural parity ex. P=(-1)J K*(890),κ

Hyperon production with K*(892) Parity filter with linearly polarized photon K g K* E p unatural parity ex. P= -(-1)J kaons

K*(890) Λ(1405) photoproduction with linearly polarized photon T.Hyodo et. al, PLB593 g K K* E p High luminosity photon beam with Eg>2.4 GeV. Detect K*+→ K0s p+　→ ppp L(1405) → S0p0 → Lg gg S(1385) → Lp0 Large acceptance charged / photon detector K- p L(1405) S(1385)

Physics motivation for LEPS II h, w, h’ meson in nuclear medium Magic momentum ~2.7 GeV, 0 degree M.Kaskulov, H. Nagahiro, S. Hirenzaki, and E. Oset PRC75,064616 Detection of scattered and decay particles simaltaneously

Schematic view of the LEPS2 facility Recoil electron (Tagging) LEP (GeV g -ray) Laser room Inside SR bldg 30m long line 8 GeV electron Laser Outside SR bldg Experimental bldg Beam dump Backward Compton Scattering SR ring 10 times high intensity： Multi laser injection &Laser beam shaping Best emittance e beam pencil photon beam Two different exp. setup BGO Gamma counter Large 4p spectrometer

High Beam Intensity Need large aperture of the laser injection line LEP intensity  107 cps for E<2.4 GeV beam (355 nm)  106 cps for E<2.9 GeV beam (266 nm) 4-laser injection [x4] Higher power CW lasers. 355 nm (for 2.4 GeV) 8 W16 W, 266 nm (for 2.9 GeV) 1 W2 W [x2] Laser beam shaping with cylindrical expander [x2] prism UV lasers (355/266 nm) expander AR-coated mirror w/ stepping motor 10 um 400 um laser Electron beam is horizontally wide.  BCS efficiency will be increased by elliptical laser beam. Need large aperture of the laser injection line  construct new BL chambers

Laser injection system 4 lasers in the laser hatch

New experimental hatch 2011.12 SP8

(1.5-2.4 GeV~4Mcps w/ a single 24W laser) 2013.1.27 first beam (1.5-2.4 GeV~4Mcps w/ a single 24W laser) Energy spectra of photon beam Beam size in the experimental hatch w/ Laser mm w/o Laser

BGO EGG+TOF g g g RPC-TOF BGO EGG proton target charged particle 1320 BGO crystals polar angle 24°～146° ΔE=1.3% @ 1GeV RPC-TOF wall Δt ~ 50 ps flight length 12m polar angle 0°～5° LH2, LD2 nuclear target Backward meson production from this November. g charged particle tracker

Detector performance BGO EGG RPC prototype 1m RPC prototype Time resolution of RPC-TOF π0 reconstructed with BGO-EGG. Further calibration is underway.

Solenoid spectrometer Magnet (BNL-E949) B=1 T Dp/p 〜 1-5% for q >7 deg g counter RPC detectors for photon, charged particle 3σ K/p/p separation < 2.7 GeV using RPC, TOP, AC Detector construction is underway Physics run from 2015 TOP g TPC DC

Summary Backward Compton g beam line for hadron physics. Hadrons with s-quark. Recoilless production of light mesons in nucleus. Highly polarized photon beam up to 3 GeV. x10 luminosity. ~10Mcps. Two different experimental setups. BGO EGG + TOF Backward meson production from proton and nuclei Solenoid spectrometer Θ+, Λ(1405) First beam in Jan. 2013. BGO EGG experiment from this November!