Outline

1. Outline • Laser-Electron Photon from Synchrotron facility. • Uniqueness of SPring-8 LEPS experiment. • Vector Meson Photo-Production near production threshold. • Good polarization of photon beam. • Ability of measuring the single and double polarization observables. • Status of SPring-8 experiment. • Detector configurations and performance. • Run summary and preliminary results. • New Detector Upgrade and Physics proposals. • Time-Projection Chamber: Medium effect of vector mesons production in nuclei. • Gamma detector: Search of  resonance with 2 reconstruction. • Polarized target. • Summary. Wen-Chen Chang

2. What the world is composed of? Wen-Chen Chang

3. How do we study? • Different probes: p, e, A, and , etc… • Interaction at small distance scale: accelerate the particles to high energy and make something happen. (Accelerator and collisions at higher and higher energy: keV (103eV).MeVGeVTeV (1012eV).) • “See” what happens: detectors+event constructions. • Understand what happens: simulation work. Wen-Chen Chang

4. Super Photon Ring 8 GeV (SPring-8)in Osaka, Japan Harima Science Garden City Wen-Chen Chang

5. SPring-8 Beam-Lines Wen-Chen Chang

6. Synchrotron Radiation Wen-Chen Chang

7. Laser Electron Photon Wen-Chen Chang

8. Tagging of Photon Energy Timing Counter Energy Counter Plastic scintillator ×20 (3mm(T),7.4mm(W),10 mm(H)) Silicon Strip Detector ×2 (Analog readout,100mm pitch 640 ch) Accelerator chamber wall Scattered electron 1cm 8GeV electron beam Wen-Chen Chang

9. Laser-Electron-Photon Spectrum • Source:Polarized laser is directed into the storage ring and backward-Compton-scatters with 8 GeV/c electron bunches • Emax: 2.4 GeV(3.5GeV) • Flux:5*106 /sec ( 1*107 /sec) • Polarization:100% at Emax 2.4 GeV Wen-Chen Chang

10. BLP33 Experimental Hutch Wen-Chen Chang

11. BLP33 Experimental Hutch Wen-Chen Chang

12. Total Cross Section of Hadronic Interaction (I) Universal Scaling : = 0.5,  = 0.08 Wen-Chen Chang

13. Total Cross Section of Hadronic Interaction (II) • Pomeron exhange: • Positive power-law scaling of s. • Dominating at large s. • Natural parity (J=0+). • Exchange particles unknown; successful phenomenology for diffractive process. • Reggeon exchange: • Negative power-law scaling of s. • Dominating at small s. • Un-natural parity (J=0–). • Exchange particles like ,; Vector Meson Dominated Model. Wen-Chen Chang

14. Photo-Production of  Mesons Pomeron Exchange Boson Exchange  Emission from Nucleon (OZI Suppressed!) Wen-Chen Chang

15. Unpolarized Differential Cross section of  p   p (t=0) A.I.Titov et. al., PRC 59, R2993 Wen-Chen Chang

16. Polarized Photon Beam: disentangle exchanges of different parity : angle between the photon polarization vector and CMS production plane. Experimentally we measure W’s functions where density matrix  could be decomposed. Parity Asymmetry • P= +1, only natural parity • P= –1, only un-natural parity Wen-Chen Chang

17. Strangeness Inside Nucleon -knock out Process A.I.Titov et. al., PRL 79, 1634. Wen-Chen Chang

18. Polarized Photon + Polarized Target Double polarization variable LBT is sensitive to the strangeness content in nucleons. A.I.Titov et. al., PRL 79, 1634. Wen-Chen Chang

19. LEPS Collaboration RCNP, Osaka University, Japan J.K. Ahn, M. Fujiwara, T. Hotta, N. Matsuoka, T. Matsumura, T. Mibe, T.Nakano, M. Nomachi, Y. Sugaya Academia Sinica, Taiwan W.C. Chang, C.W. Wang, D.Oshuev, S.C. Wang Chiba University, Japan H. Kawai, T. Ooba Nagoya University, Japan T. Iwata, A. Wakai Ohio University, U.S. K. Hicks JAERI/Spring-8, Japan H. Akimune, Y. Asano, S. Date,, N. Kumagai, Y. Ohashi, Ho. Toyokawa Kyoto University, Japan K. Imai, M. Yosoi, A. Ichikawa Osaka University, Japan T. Kishimoto, A. Sakaguchi, M. Sumihama Wakayam Med. University, Japan S. Makino Yamagata University, Japan H. Shimizu Wen-Chen Chang

20. LEPS Experiment • Detector: • Large acceptance at forward small |t| region, mostly diffractive production. • Effective e+e- events suppression at trigger level. • Good K/ separation with TOF detector. • Physics Program: •  photo-production around and beyond threshold: study interplay of Pomeron exchange and quark exchange. • , photo-production in u channel at large |t| region.. • Strangeness content of the nucleon using polarized beam and target. • Nuclear medium effect from vector meson photo-production in nuclei. Wen-Chen Chang

21. LEPS Detector Configuration Wen-Chen Chang

22. Capability of LEPS detectors and DAQ • DAQ • 1 kHz trigger rate. • LEP beam intensity • 5*106 photon/sec. • Yield of f1.72x10-2/sec with 0.1 radiation length target. • Mass resolution (f from CH2) • Tagging Gamma energy resolution:15 MeV. • Drift chamber resolution: 200 mm. • Particle ID • Time-of-Flight(TOF) timing resolution: 100 psec. • 4s separation of K/p/e at 2 GeV/c momentum. Wen-Chen Chang

23. Laser System Wen-Chen Chang

24. Liquid Hydrogen Target Wen-Chen Chang

25. Dipole Magnet and Drift Chambers Wen-Chen Chang

26. Time-of-Flight Wall Wen-Chen Chang

27. Performance of Time-of-Flight Detector • Totally 40 scintillator slats of geometry: 12cm(W)x200cm(L) x4cm(T). • Each slat with top and bottom PMTs readout. • Timing resolution ~100 psec. • Essential to 4 K/ separation up to 2 GeV/c momentum. Wen-Chen Chang

28. Run Summary • Events in AS group • AS group(C.W. Wang and S.C. Wang) built the TOF detector. • W.C. Chang, C.W.Wang and S.C. Wang participated the data-taking and data analysis mainly on • S.C. Wang left the group in the fall of 2000. • D.S. Oshuev joins the group on 02/08/2001. Wen-Chen Chang

29. Particle Identification using TOF and Tracking Wen-Chen Chang

30. Particle Identification in Mass Wen-Chen Chang

31. Signal of K+K Wen-Chen Chang

32. Detector Upgrade Gamma Detector Time Projection Chamber • Backward triggering. • Detection of  resonance • with 2 reconstruction. • Vertex detection around the target. • Nuclear medium effect in vector mesons. • Photo-production of (1405). Wen-Chen Chang

33. Summary • The LEPS experiment at SPring-8 is unique in measuring the photo-production of vector mesons near threshold regions and the capability of high-flux polarized photons. The physics goal is clearly defined. • The detector and DAQ system works and meet the need of physics measurement. Tasks of data-taking and analysis are currently intensively under way. • It is a nice start for AS nuclear group to work on high-energy project with an international collaboration. Even with a lack of man-power, we would work on the TPC upgrade project aiming at detecting nuclear medium effect from the production of vector mesons in nuclei. Wen-Chen Chang