1. Wen-Chen Chang 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.

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

3. Wen-Chen Chang 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 (10 3 eV).  MeV  GeV  TeV (10 12 eV).) “See” what happens: detectors+event constructions. Understand what happens: simulation work.

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

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

6. Wen-Chen Chang Synchrotron Radiation

7. Wen-Chen Chang Laser Electron Photon

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

9. Wen-Chen Chang Laser-Electron-Photon Spectrum Source: Polarized laser is directed into the storage ring and backward-Compton- scatters with 8 GeV/c electron bunches E max : 2.4 GeV(  3.5GeV) Flux:5*10 6 /sec (  1*10 7 /sec) Polarization:100% at E max 2.4 GeV

10. Wen-Chen Chang BLP33 Experimental Hutch

11. Wen-Chen Chang BLP33 Experimental Hutch

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

13. Wen-Chen Chang 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.

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

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

16. Wen-Chen Chang 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

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

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

19. Wen-Chen Chang 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

20. Wen-Chen Chang 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.

21. Wen-Chen Chang LEPS Detector Configuration

22. Wen-Chen Chang Capability of LEPS detectors and DAQ DAQ –1 kHz trigger rate. LEP beam intensity –5*10 6 photon/sec. –Yield of   x10 -2 /sec with 0.1 radiation length target. Mass resolution (  from CH 2 ) –Tagging Gamma energy resolution:15 MeV. –Drift chamber resolution: 200  m. Particle ID –Time-of-Flight(TOF) timing resolution: 100 psec. –4  separation of K/  /e at 2 GeV/c momentum.

23. Wen-Chen Chang Laser System

24. Wen-Chen Chang Liquid Hydrogen Target

25. Wen-Chen Chang Dipole Magnet and Drift Chambers

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

27. Wen-Chen Chang 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.

28. Wen-Chen Chang 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.

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

30. Wen-Chen Chang Particle Identification in Mass

31. Wen-Chen Chang Signal of  K+K 

32. Wen-Chen Chang 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).

33. Wen-Chen Chang 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.