Hadron physics with GeV photons at SPring-8/LEPS II

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

2. Super Photon Ring 8 GeV (SPring-8)

3. 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

4. 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]

5. Setup of LEPS I Acceptance is limited in forward region 1.5

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

7. Proton rejection by using dE/dx in Start Counter p Pid = (Measured energy loss in SC) – (Expectation of KK) – (Half of expectation of proton) n K- K- K+ K+ SC p SC SC or 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

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

9. 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? 1/2- N(1535) 3/2- Λ(1520) N(1520) 3/2- h+N(1485) mass (MeV) 30 MeV 1/2- Λ(1405) K+N(1430) uds uud (or udd)

10. 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

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

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

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

14. 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

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

16. 400 um laser 10 um High Beam Intensity UV lasers (355/266 nm) prism expander • Electron beam is horizontally wide. • BCS efficiency will be increased • by elliptical laser beam. AR-coated mirror w/ stepping motor Need large aperture of the laser injection line  construct new BL chambers 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]

17. Laser injection system 4 lasers in the laser hatch

18. New experimental hatch 2011.12 SP8

19. 2013.1.27 first beam • (1.5-2.4 GeV~4Mcpsw/ a single 24W laser) Energy spectra of photon beam Beam size in the experimental hatch mm w/ Laser w/o Laser mm

20. BGO EGG+TOF RPC-TOF BGO EGG proton • 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. target g g g charged particle tracker

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

22. Solenoid spectrometer 2.22 m Magnet (BNL-E949) B=1 T Dp/p 〜 1-5% for q >7 deg RPC gcounter 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

23. 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!