Measurement of Photoproduction of  (1020) Mesons on Protons by Linearly Polarized Photons EMI2001, December 5th, 2001 T.Mibe for the LEPS collaboration Research Center for Nuclear Physics, Osaka University, Japan

Outline  photoproduction near production threshold Experiment at SPring-8/LEPS facility Summary

Vector Meson Photoproduction Vector Meson Dominance Meson Exchange Pomeron Exchange  N   N  q _q_q _ qq =  Dominant at low energies Small energy dependence

Cross section of Vector Meson Photoproduction  p  p  p  p M.A. Pichowsky and T.-S. H. Lee PRD 56, 1644 (1997) Data from: LAMP2('83), DESY('76), SLAC('73), CERN('82), FNAL('79,'82), ZEUS('95,'96) Prediction from Pomeron exchange Prediction from meson exchange

 photoproduction near production threshold Titov, Lee, Toki Phys.Rev C59(1999) 2993 P2 : 2 nd pomeron ~ 0 + glueball (Nakano, Toki (1998))

Photoproducion by linearly polarized photon Decay Plane //  if natural parity exchange (-1) J (Pomeron, Scaler mesons) Polarization vector of  K+K+ K-K- K+K+ K-K- Decay Plane  if unnatural parity exchange -(-1) J (Pseudoscaler mesons) In  rest frame (Helicity frame) Decay Angular distribution of  Decomposition of natural parity exchange unnatural parity exchange

Angles In  rest frame (Helicity frame) In center-of-mass frame

At high energies...  p  p E  = 9.3 GeV Linear Pol. Ballam et.al. PLD 7(1973) 3150  tends to decay into direction of the photon polarizaion. Natural parity exchange dominate s-channel helicity is conserved. What is the situation in  p  p near threshold ??? LEPS,Spring-8 CLAS,J.lab.   -  pol (degree)

LEPS collaboration Academia Sinica, Taiwan W.C.Chang, D.S.Oshuev, C.W.Wang, S.C.Wang Chiba University, Japan H.Kawai, T.Ooba, Y.Shiino IHEP, Russia P.Shagin JAERI, Japan Y.Asano, N.Muramatsu, R.G.T.Zegers JASRI, Japan S.Date, N.Kumagai, Y.Ohashi, H.Ookuma Konan University, Japan H.Akimune Kyoto University, Japan K.Imai, T.Ishikawa, M.Miyabe, M.Niiyama, M.Yosoi Nagoya University, Japan S.Fukui, T.Iwata, Y.Miyachi, A.Wakai Ohio University, U.S. K.Hicks Osaka University, Japan M.Nomachi, A.Sakaguchi, Y.Sugaya, M.Sumihama Pusan National University, S.Korea J.K.Ahn RCNP, Osaka University, Japan H.Fujimura, M.Fujiwara, T.Hotta, H.Kohri, T.Matsumura, N.Matsuoka, T.Mibe, M.Morita, T.Nakano, T.Yorita Saskatchewan University, Canada C.Rangacharyulu Tohoku University, Japan H.Shimizu Wakayama Med. University, Japan S.Makino

Linearly polarized Photon Tagging Region : 1.5 GeV< E  < 2.4 GeV Intensity (Typ.) : 5 * 10 5 cps Linear Polarization : 95 % at 2.4 GeV E  (Tagger) (GeV) E  (GeV) Counts Degree of Polarization QED calculation

LEPS detectors 1m1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T) Liquid Hydrogen Target (50mm thick) Start counter Silicon Vertex Detector Aerogel Cerenkov (n=1.03) 

LH 2 target Runs Physics Run : Dec June.2001 Number of  mesons  More than ~5200  ’ s = ( ) *2 Plots in this talk : K + K - mode only, ~30 % of total data K + K - detected K + p detected K - p detected Polarization(Vert./Hori.)

 K + K - events invariant mass (GeV) missing mass (GeV) Number of event /2MeV Number of event /5MeV  p(938) Preliminary Reconstructed mass distributions from K + K - tracks

 p  p 554 events (Vert + Hori) 1.004< M  <1.034 GeV 0.88<Missing mass<1.00 GeV -0.2< t <0.0 GeV 2 w/o Acceptance Correction Decay angular distribution of K + in Helicity frame Preliminary  K -  pol (degree) cos  h Number of event

Summary Photoproduction of  mesons near threshold opens a window to access new mechanisms in addition to the pomeron exchange.  photoproduction is measured with linearly polarized photon beam from E  = 1.6GeV(threshold) to 2.4GeV at SPring-8. The azimuthal angle distribution of K+ from  decay shows non flat distribution with respect to the photon polarization. The s-channel helicity conservation is favoured.