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Recent Results from LEPS/SPring-8

International Conference on Quark Nuclear Physics 2009, Beijing, China. Recent Results from LEPS/SPring-8. Ken Hicks Ohio University, USA Sept. 21, 2009 on behalf of LEPS collaboration. Outline. Short description of LEPS Photoproduction of KY Photoproduction of KY*

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Recent Results from LEPS/SPring-8

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  1. International Conference on Quark Nuclear Physics 2009, Beijing, China Recent Results from LEPS/SPring-8 Ken Hicks Ohio University, USA Sept. 21, 2009 on behalf of LEPS collaboration

  2. Outline • Short description of LEPS • Photoproduction of KY • Photoproduction of KY* • Photoproduction of K*Y • Search for the Q+ using K+K- from deuterium QNP2009

  3. 8 GeV electron Recoil electron Tagging counter 36m 70m a) SPring-8 SR ring Laser light Compton g-ray b) Laser hutch c) Experimental hutch Schematic view of the LEPS facility QNP2009

  4. Backward-Compton Scattered Photon • 8 GeV electrons in SPring-8 + 351nm Ar laser (3.5eV） • E measured by tagging a recoil electron  E ~10 MeV • Laser Power ~6 W  Photon Flux ~1 Mcps • Laser linear polarization 95-100% ⇒ Highly polarized  beam Linear Polarization of  beam PWO measurement tagged photon energy [GeV] photon energy [MeV] QNP2009

  5. LEPS detector atSPring-8/LEPS 1.5 QNP2009

  6. TOF SVTX DC1 AC(n=1.03) Photons Target Dipole Magnet 0.7 Tesla Start Counter DC2 DC3 Particle ID at LEPS K/p separation K+ p+ Momentum [GeV/c] Mass/Charge [GeV/c2] QNP2009

  7. Strangeness Production • Goals: data for • (1020) • , hyperons • Features: • Forward angle measurement, including 0o • Polarization observables • Strangeness production QNP2009

  8. (1116) & (1193) QNP2009

  9. (1385), (1405), (1520) QNP2009

  10. Born Diagrams s-channel u-channel t-channel contact term QNP2009

  11. Angular Distributions of pK+ s-channel t-channel u-channel R. Bradford et al. (CLAS Collaboration), PRC 73, 035202 (2006) QNP2009

  12. Angular Distributions of pK+ s-channel t-channel u-channel R. Bradford et al. (CLAS Collaboration), PRC 73, 035202 (2006) QNP2009

  13. Energy Distribution R. Bradford et al. (CLAS Collaboration), PRC 73, 035202 (2006) LEPS LEPS QNP2009

  14. 0,- L LD2 data LH2 data (1405) 0(1385) - (1385) L 0 (1405) (1385) (1520) (1520) N(, K+) GeV/c2 p(, K+) GeV/c2 Missing Mass of K+ Y  spectrometer K+ p/d QNP2009

  15. Invariant Mass and Its Missing Mass K+ p  spectrometer p K- L* K+ QNP2009

  16. LEPSSAPHIR CLAS Energy Dependence of Cross Sections • K+K*-exchange by M. Guidal (Regge model). • Isobar + Regge by T. Mart and C. Bennhold. • Gent isobar model by T. Corthals L(1116) S0(1193) M. Sumihama et al. (LEPS Collaboration), PRC 73, 035214 (2006) QNP2009

  17. LEPS CLAS Differential Cross Sections S0(1193) L(1116) Forward peaking. Need Regge poles. No forward peaking. QNP2009

  18. Photon-Beam Asymmetry • If the dominant contributions are from t-channel K and K* exchange, they can be further distinguished by photon-beam asymmetry using linearly polarized photon beam. • A=(perp-para)/ (perp+para) • If A is negative (positive), the interaction is dominated by the electric (magnetic) component induced by K (K*) exchange. QNP2009

  19. Photon Beam Asymmetry L(1116) S0(1193) Larger contribution from t-channel K* exchange. QNP2009

  20. Uncertainties in theTheoretical Models Photon asymmetry Used data for fitting in models. SAPHIR/LEPS CLAS/LEPS SAPHIR/CLAS/LEPS T. Mart and A. Sulaksono PRC74 (2006) 055203 QNP2009

  21. L(1116) g p  LX K+ g p  p p- p+ K+S0, K*L, KY* Backward K+L photoproduction K. Hicks et al. (LEPS Collaboration), PRC 76, 042201(R) (2007) Detect L(pp-) at forward angles QNP2009

  22. Theoretical Models Photon asymmetry Used data to fit models. SAPHIR/LEPS CLAS/LEPS SAPHIR/CLAS/LEPS T. Mart and A. Sulaksono PRC74 (2006) 055203 QNP2009

  23. L(1520) Experiments • LAMP2 (real photon) • CLAS(virtual photon) D. P. Barber et al. (LAMP2 Collaboration), Z. Phys. C 7, 17 (1980). S. P. Barrow et al. (CLAS Collaboration), PRC 64, 044601 (2001). QNP2009

  24. Toki, Garcia-Recio and Nieves, PRD, 77, 034001 (2008) • The chiral unitary model predicts a small coupling between Λ(1520) and NK*. Main contribution comes from the K exchange process QNP2009

  25. Nam, Hosaka, and Kim, PRD71, 114012 (2005) Large np isospin asymmetry. Production from Proton Production from Neutron QNP2009

  26. Photoproduction of Λ* N. Muramatsu et al. (LEPS Collaboration), PRL 103, 012001 (2009) QNP2009

  27. Cross sections on H and D • The ratio between deuterons and protons was 1.02±0.11. Production from neutrons is strongly suppressed at LEPS kinematics. • Large isospin asymmetry. QNP2009

  28. Importance of Contact Term A. Hosaka, Workshop of “Challenge to New Exotic Hadrons with Heavy Quarks”. QNP2009

  29. Isospin Asymmetry in + Production QNP2009

  30. Cross Sections: gn K+S*- K. Hicks et al. (LEPS Collaboration), PRL 102, 012501 (2009) • Calculations are from Oh, Ko & Nakayama, averaged over the bin size shown. • Cross sections are only measured at forward angles: complementary to the CLAS data. QNP2009

  31. Beam Polarization Dependence gn K+S*- gn K+S- Due to statistics, only three bins in beam energy (1.5-1.8, 1.8-2.1, 2.1-2.4 GeV) were used for the beam asymmetry fits. The K+S- final state (left), shows the opposite sign for the beam asymmetry when compared with the K+S*- final state (right). QNP2009

  32. Beam Asymmetries Present results (solid points) compared with previously published data (open points) from Kohri et al. (PRL, 2006) Curve (Oh, Ko, Nakanyama) assumes 3-quark structure to the S*. A 5-quark component would have asymmetry of -1 (model of B. Zou). QNP2009

  33. K*0 photoproduction at LEPS K* K* QNP2009

  34. Y. Oh and H. Kim, hep-ph/0605105. Theory: a) K*+L , b) K*0S+ SOLID BLUE: no kappa form factor;DASHED RED: with kappa form factor Hyp-X Conf.

  35. K*+ and K*0 Beam Asymmetry Large sensitivity to the kappa meson for linear polarization. QNP2009

  36. Experimental status of Q+ Searches • Not seen in the most of the high energy experiments: The production rate of Q+/L(1520) is less than 1%. • No signal seen in CLAS gp, KEK-PS (K+,p+) experiments. • The width must be less than 1 MeV. (DIANA and KEK-B). • LEPS could be inconsistent with CLAS gd experiment. • Production rate depends on reaction mechanism. • K* coupling should be VERY small. • K coupling should be small. • Strong angle or energy dependence. QNP2009

  37. Differences: LEPS and CLAS for gn  K-Q+ LEPS Good forward angle coverage Poor wide angle coverage 1.5 – 2.4 GeV photons Symmetric acceptance for K+ and K- MKK>1.04 GeV/c2 Select quasi-free process CLAS Poor forward angle coverage Good wide angle coverage 1.0 – 3.5 GeV photons Asymmetric acceptance MKK > 1.07 GeV/c2 Require re-scattering or large Fermi momentum of a spectator ~ K- coverage: LEPS: qLAB < 20 degree CLAS: qLAB > 20 degree QNP2009

  38. Minimum Momentum Spectator Approximation (MMSA) detected K- tagged Spectator nucleon K+ pCM γ vpn d at rest - pCM p n Nucleon from decay or scattering We know 4 momentum of pn system Mpn and ptot |pCM|and vpn Direction of pCM is assumed so that the spectator can have the minimum momentum for given |pCM| and vCM. QNP2009

  39. Double-role of MMSA Clean-up Estimation of pF quasi-free coherent inelastic pmin pmin QNP2009

  40. Results of L(1520) analysis pK- invariant mass with MMSA: Fermi motion effect corrected. Simple (g,K+) missing mass: No correction on Fermi motion effect. D(-2lnL) =55.1 for Dndf=2  7.1 s QNP2009

  41. Results of Q+ analysis Simple (g,K-) missing mass: No correction on Fermi motion effect. nK+ invariant mass with MMSA: Fermi motion effect corrected. D(-2lnL) =31.1 for Dndf=2  5.2 s QNP2009

  42. Next step Probability of 2 x 10-7 is not good enough. “Extraordinary claim requires extraordinary evidence.” Higher statistics data was collected in 2006-2007 with the same experimental setup. Blind analysis is under way to check the Θ+ peak QNP2009

  43. Summary • LEPS data has had a significant effect on our understanding of strangeness production. • Recent results on L* reveals the importance of the contact term in photoproduction. • Large isospin difference of production cross section. • Recent results on S* shows that SU(3) flavor symmetry works well for the baryon decuplet. • Beam asymmetry is more negative than expected. • Search for Q+ is still in progress. • There are many constraints from other data. QNP2009

  44. LEPS new beam line (LEPS2) • Beam upgrade: • Intensity ---High power laser,Multi laser(x4) • ---Laser elliptic focus • 2x106 107 /sec for 2.4 GeV • 2x105 106 /sec for 3 GeV • Energy ---Laser with short l ,re-injectedSoft X-ray+BCS (2nd stage), •  up to ~7.5 GeV • Detector upgrade: (reaction process & decay process) • Scale & ---General-purpose large 4p detector • Flexibility Coincidence measurement ofcharged particles and • neutral particles (photons)  BNL/E949 detector • DAQ ---High speed for the minimum bias trigger • Physics: Multi-quark (>3) • Workshop on LEPS2(2005/7, 2007/1) QNP2009

  45. w/o N* with N* Missing mass of p ( , K+) X • Possible bump structure at W~2.1 GeV? • Better description of energy dependence with the inclusion of a nucleon resonance H. Kohri et al. (LEPS Collaboration), arXiv:0906.0197 QNP2009

  46. Beam Asymmetry of (1520) Contribution from t-channel K* exchange is dominant at W>2.2 GeV. QNP2009

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