Production of  Mesons on Protons near Threshold by Linearly Polarized Photon at SPring-8/LEPS Wen-Chen Chang for LEPS collaboration Institute of Physics, Academia Sinica Taipei 11529, Taiwan XVI Particles and Nuclei International Conference September 30 - October 4, 2002, Osaka, Japan PaNic02

Outline P hoto-production of  mesons at high energy and near production threshold. –Pomeron exchange. –Pseduo-scaler particle exchange. How linearly polarized photon beam can help us in distinguishing different sources of contribution? –Spin density matrix element. –Decay asymmetry in Helicity Frame. Measurement by LEPS experiment at SPring-8. –Reconstruction of  mesons in KK modes. –Angular distribution of K+ in Helicity Frame at forward direction. Summary.

Total Cross Section of Hadronic Interaction Universal Scaling :  = 0.5,  = 0.08 A. Donnachie and P.V. Landshoff

Photo-Production of  Mesons at Forward Region (small |t|) Pomeron Exchange Pseudo-scaler Exchange (OZI Suppressed!) Exotic knock-out process

Photo-Production of  Mesons at Backward region (large |t|)  Emission from Nucleon Exotic shake-off process

At Forward region: Pomeron: –Positive power-law scaling of s. –Dominating at large energy. –Natural parity (=+1). –Exchange particles unknown; likely to be glueball : P1(J  =2 + ), P2(J  =0 +, negative power-law scaling of s). (Ref. T. Nakano and H.Toki, 1998) –Successful phenomenology for diffractive process. Pseudo-scaler particle: –Negative power-law scaling of s. –Showing up at small energy. –Un-natural parity (= –1). –Exchange particles like , . –OZI suppressed.

Differential Cross section of  p   p with un-polarized photon beams A.I.Titov et. al., PRC 59, R2993 (t=0)

With Linearly-Polarized Photon Beam Experimentally we measure W’s functions and density matrix   could be determined by spherical harmonics decomposition. The contributions of natural and un-natural parity exchange in the t-channel are represented by the matrix element of Re(  0 ), Re(  1 ).  H : polar angle of K+ in Helicity frame  H : azimuthal angle of K+ in Helicity frame   : angle between the photon polarization vector and CMS production plane.

Spin Density Matrix Elements K.Schilling et. al., Nucl. Phys. B15 (1970) 397

The Spin Density Matrix Elements at small |t| regions Two important spin-conserving processes: Pomeron exchange:  = –Im  = +0.5, and all diagonal  ’s = 0 at  =0. ,  exchange:  = –Im  = – 0.5, and all diagonal  ’s = 0 at  =0. A.I.Titov et. al., PRC60,

Angular Distribution of K+ in Helicity Frame  =0,  =+0.5  =1,  = – 0.5

SLAC Measurement J.Ballam, et. al, PRD 7(1973), 3150

LEPS Collaboration RCNP, Osaka University, Japan H. Fujimura, M. Fujiwara, T. Hotta, H. Kohri, T. Matsumura, N. Matsuoka, T. Mibe, M. Morita, T.Nakano, T. Yorita Osaka University, Japan N. Nomachi, A. Sakaguchi, Y. Sugaya, M. Sumihama 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.Niiyamma,M. Yosoi Nagoya University, Japan S. Fukui, T. Iwata, Y. Miyachi, A. Wakai Ohio University, U.S. K. Hicks Pusan National University, S. Korea J.K. Ahn Saskatchewan University, Canada C. Rangacharyulu Tohoku University, Japan H. Shimizu Wakayam Med. University, Japan S. Makino

LEPS detectors 1m1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T) Liquid Hydrogen Target 50mm-long (2000 Dec.-2001June) 150mm-long (2002May-July) Start counter Silicon Vertex Detector Aerogel Cerenkov (n=1.03) 

Charged particle identification Mass(GeV) Momentum (GeV) K/  separation (positive charge) K+K+ ++ Mass/Charge (GeV) Events Reconstructed mass d p K+K+ K-K- ++ --

Signal of   K+K 

Reconstructed  events Large acceptance at forward angles ~5000  ’s (Dec, June, 2001) Runs with 150mm-long LH 2 target (May-July, 2002 ). KK eventKp event

Experimental Acceptance at -0.2< t < |t| min GeV < E  < 2.4 GeV

Simulation at -0.2< t < |t| min GeV < E  < 2.4 GeV  =0  =0.5  =1

Decay angular distribution of K + in  rest frame (Helicity frame) |M(KK)-M  |< 10 MeV, |M((KK)X)-M proton |< 30 MeV -0.2< t < |t| min GeV 2, 2.2 < E  < 2.4 GeV w/o Acceptance Correction Raw Data Vertically polarized beamHorizontally polarized beam

Summary About 5000 events of photo-production of  mesons by linearly polarized photons from E  = 1.6GeV(threshold) to 2.4GeV are measured by LEPS experiment at SPring-8/Japan. In comparison with measurement at high energy, our preliminary results show that the contribution of natural-parity exchange still composes a larger fraction in the total scattering amplitude while that of un-natural parity component becomes more significant at E=2.3 GeV and t>-0.2 region. With the ongoing studies of the acceptance correction and systematic errors, the cross section, differential cross section and spin density matrix elements at the forward regions will be reported in the near future. A presentation of detailed results will be shown in the poster session: “Polarization observables in the \phi(1020) meson photoproduction with linearly polarized photons” by T. Mibe (RCNP, Osaka Univ.).

Decay Angular Distribution in  p   p

Example 

Super Photon Ring 8 GeV (SPring-8)