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Production of  Mesons on Protons near Threshold by Linearly Polarized Photon at SPring-8/LEPS

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

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Production of  Mesons on Protons near Threshold by Linearly Polarized Photon at SPring-8/LEPS

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  1. PaNic02 XVI Particles and Nuclei International Conference September 30 - October 4, 2002, Osaka, Japan 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

  2. Outline • Photo-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.

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

  4. Photo-Production of  Mesonsat Forward Region (small |t|) • 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). • Pseudo-scaler particle: • Negative power-law scaling of s. • Showing up at small energy. • Un-natural parity (= –1). • Exchange particles like ,. • OZI suppressed.

  5. Differential Cross section of p   p (t=0) gp rp Meson gp fp Pomeron M.A. Pichowsky and T.-S. H. Lee PRD 56, 1644 (1997) A.I.Titov et. al. PRC 59, R2993 (1999)

  6. With Linearly-Polarized Photon Beam • W0,W1,W2 can be parameterized by the 9 spin density matrix elements. • r000 ,Re(r010),r01-1 ,r111 ,r100 , • r110 ,r11-1 , Im(r210 ) andIm(r21-1)  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.

  7. Spin Density Matrix Elements at small |t| regions • Spin-conserving processes: • Pomeron exchange: 11-1= –Im 21-1 = +0.5, and all other ’s = 0 at =0. • , exchange: 11-1= –Im 21-1 = – 0.5, and all other ’s = 0 at =0. • Azimuthal angle distribution: A.I.Titov et. al., PRC60, 035205

  8. Simulated Azimuthal Angle Distribution of K+ in Helicity Frame =0, 11-1=+0.5 =1, 11-1= – 0.5

  9. SLAC MeasurementJ.Ballam, et. al, PRD 7(1973), 3150

  10. 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 Collaboration

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

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

  13. Signal of   K+K

  14. Reconstructed fevents • Reconstruct photo-production of f from both K+K- events and Kp events. • Large acceptance at forward angles • ~5000 f’s (Dec,2000 - June,2001) KK event Kp event

  15. Simulation at-0.2< t < |t|min GeV2 2.2 < Eg < 2.4 GeV =0 =0.5 =1

  16. |M(KK)-Mf |< 10 MeV , |M((KK)X)-Mproton|< 30 MeV -0.2< t < |t|min GeV2 , 2.2 < Eg < 2.4 GeV w/o Acceptance Correction Decay angular distribution of K+in f rest frame (Helicity frame) Horizontally polarized beam Vertically polarized beam Raw Data

  17. Summary • About 5000 events of photo-production of  mesons by linearly polarized photons from Eg= 1.6GeV(threshold) to 2.4GeV are measured by LEPS experiment at SPring-8/Japan. • The preliminary results show that the contribution of natural-parity exchange still composes a larger fraction in the total scattering amplitude of at photo-production of  mesons 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 [ 6B-26]: “Polarization observables in the \phi(1020) meson photoproduction with linearly polarized photons” by T. Mibe (RCNP, Osaka University).

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