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Photoproduction of Pentaquarks Seung-il Nam *1,2 Atsushi Hosaka 1 Hyun-Chul Kim 2

RCNP & NuRI. Photoproduction of Pentaquarks Seung-il Nam *1,2 Atsushi Hosaka 1 Hyun-Chul Kim 2 1.Research Center for Nuclear Physics (RCNP), Osaka University, Japan 2.Department of Physics and Nuclear physics & Radiation Technology Institute (NuRI), Pusan National University, Korea

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Photoproduction of Pentaquarks Seung-il Nam *1,2 Atsushi Hosaka 1 Hyun-Chul Kim 2

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  1. RCNP & NuRI Photoproduction of Pentaquarks Seung-il Nam*1,2 Atsushi Hosaka1 Hyun-Chul Kim2 1.Research Center for Nuclear Physics (RCNP), Osaka University, Japan 2.Department of Physics and Nuclear physics & Radiation Technology Institute (NuRI), Pusan National University, Korea Contents based on hep-ph/0502143, hep-ph/0503149[PRD] & hep-ph/0505134 Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  2. RCNP & NuRI Introduction Observation of evidence of exotic pentaquark + •In 1997, D.Diakonov et al. predicted a baryon resonance: JP=1/2+ , I=0, Mass=1540 MeV and =15 MeV (30MeV) •Motivated by the prediction, LEPS collaboration announced the observation of evidence of + from the photoproduction in 2002 D.Diakonov, ZPA359,305 Exotic Hadrons Workshop, 27th May 2005, Nara, Japan T.Nakano, PRL91,012002

  3. RCNP & NuRI Introduction Experiements on the exotic pentaquark + •Positive and negative results have been appeared Positive result Negative result Exotic Hadrons Workshop, 27th May 2005, Nara, Japan K.Hicks, hep-ex/0504027 •Statistics problem

  4. RCNP & NuRI Introduction Theories on the exotic pentaquark + : CQSM •CQSM: QCD based on the instanton vacuum •Baryon as a SU(3) collective quantized object: JP=1/2+ Antidecuplet •N(1710) as a non-strange antidecuplet Exotic Hadrons Workshop, 27th May 2005, Nara, Japan •1710 MeV-180 MeV = 1530 MeV D.Diakonov, ZPA359,305

  5. RCNP & NuRI Introduction Theories on the exotic pentaquark + : QCD sumrule •OPE of a baryon field based on QCD  Phenomenological property •Borel weighted quantities and Dimension of condensate for convergence •KN continuum subtracted from J Exotic Hadrons Workshop, 27th May 2005, Nara, Japan Y.Kwon et al, hep-ph/0505040 • JP=1/2- preferable like Lattice QCD

  6. RCNP & NuRI Introduction Theories on the exotic pentaquark + : Reaction Dynamics •Effective quantum theory via fundamental symmetries & phenomenology •Providing a guidance to experiments of various reactions Exotic Hadrons Workshop, 27th May 2005, Nara, Japan S.I.N et al, PLB602,180 • JP=1/2+ believed to give larger total cross section • Have we been biased to JP=1/2? Then, what about JP=3/2

  7. RCNP & NuRI Introduction Theories on the exotic pentaquark + : Spin-3/2 problem •If + has JP=3/2- (0s)5 , it will not decay into KN in the quark model A.Hosaka et al, PRD71,074021 • JP=3/2- + has narrower width than JP=1/2+ using phenomenological analysis T.Hyodo et al, PRD71,054017 Exotic Hadrons Workshop, 27th May 2005, Nara, Japan •JP=3/2- assigned to + via QCD SR T.Nishikawa et al, PRD71,076004 •Reaction for JP=3/2X.G.He et al, PRD71,014006 •Resonant structure for JP=3/2+ on Lattice QCD B.G.Lasscock et al, hep-lat/0504015 And more…..

  8. RCNP & NuRI Introduction Dead end of +?: The newest CLAS experiment @ JLAB •+photoproduction via p scattering in high statistics •Missing mass technique for (1520) •Invariant mass technique for + •No significant signal observed •Estimation for + production •Ratio N(*)/N(+ ) ~ 0.2% •Questions Why so small ratio? How can we explain positive results from neutron? Is there suppression mechanism for proton? Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  9. RCNP & NuRI Introduction Strong suppression in (1520) phtoproduction •Suppression for neutron target S.I.N et al, hep-ph/0503149[PRD] Exotic Hadrons Workshop, 27th May 2005, Nara, Japan •Reason why for strong suppression Dominant contact term only for proton Charge exchange process enhanced Non-charge exchange suppressed •Qualitatively well reproduced data and large asymmetry shown actually

  10. RCNP & NuRI Motivation Photoproduction of Spin-3/2 + •We noticed that (1520) photoproduction is quite similar to that of + in the frame work of effective Lagrangian appraoch at tree level •(1520) and + are assumed to be hyperons at hadron level •Effectively, main difference is change of charges (np or pn) •From the experience of (1520) photoproduction, we expect tha pbar0+ n-+ Non Charge-exchange Charge-exchanged Suppressed! Enhanced! Exotic Hadrons Workshop, 27th May 2005, Nara, Japan •Is it possible for interpreting the null results of CLAS??

  11. RCNP & NuRI Formalism Photoproduction of Spin-3/2 + with K in the final state •Born diagram for +(JP=3/2) photoproduction from nucleon target Exotic Hadrons Workshop, 27th May 2005, Nara, Japan gKN=0.53 (4.22) for positive (negative) + : M=1540MeV and =1MeV gK*N=0.533 (2.00) for positive (negative) + Quark model calculation by A.H. F.E.Close et al.,PLB586,75

  12. RCNP & NuRI Formalism Photoproduction of Spin-3/2 + •We introduce four-dimensional gauge invariant form factor •Cutoff  set to 750MeV determined from (1520) photoproduction •Qualitatively well reproduced data Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  13. RCNP & NuRI Numerical results Photoproduction of Spin-3/2 + •Check amplitudes separately •We observe dominant contact term contribution •K*-exchange important for proton target case •Strong suppression for proton! S.I.N et al, hep-ph/0505134 Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  14. RCNP & NuRI Numerical results Photoproduction of Spin-3/2 + Neutron Proton •Total cross sections n~25 p for positive parity n~50 p for negative parity •Differential cross sections Forward enhancement for neutron due to contact term Bump around 60 for proton due to K*-exchange S.I.N et al, hep-ph/0505134 Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  15. RCNP & NuRI Numerical results Photoproduction of Spin-1/2++ •Total cross sections All are in similar order except for the proton without K* •Differential cross sections Bump around 45 due to K and K*-exchange •((1520))=500~800 nb S.I.N et al, hep-ph/0505134 Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  16. RCNP & NuRI Formalism Photoproduction of Spin-3/2 + with K* in the final state •Subprocess  p  Kbar0* + in  p  K- + + •Born diagram for +(JP=3/2) photoproduction from nucleon target Exotic Hadrons Workshop, 27th May 2005, Nara, Japan •We include K*K* vertex in terms of gauge invariance •Parameters used are the same with the previous R.B.Clark, PRD1,2152

  17. RCNP & NuRI Numerical results Photoproduction of Spin-3/2 + with K* in the final state •Physical observables for +(JP=3/2+) Obvious asymmetry not shown :Due to dominant K-exchange Forward scattering for all and enhancing as energy grows Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  18. RCNP & NuRI Numerical results Photoproduction of Spin-3/2 + with K* in the final state •Physical observables for +(JP=3/2-) Overall tendencies for the others are very similar to that of JP=3/2+ Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  19. RCNP & NuRI Numerical results Photoproduction of Spin-1/2++ with K* in the final state •Physical observables for +(JP=1/2+) Nearly same orders for the total cross sections Forward scattering •Very similar to the previous reaction with K in the final state Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  20. RCNP & NuRI Numerical results Photoproduction of Spin-3/2++ with K* in the final state •Inclusion of K*0(800,0+) Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  21. RCNP & NuRI Numerical results Photoproduction of Spin-3/2++ with K* in the final state •Inclusion of K*0(800,0+) making K*-contribution zero Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  22. RCNP & NuRI Summary Exotic pentaquark + real? •For several years, + has been the hottest issue in hadron physics •Its existence is still in question: Null results of CLAS experiment •If QCD does not forbid five quark state and we consider positive results, we should explain what happens in the newest CLAS experiment A possible interpretation for the null results •Hinted by the asymmetry shown (1520) in photoproduction, we performed spin-3/2 + photoproduction •We considered spin-3/2 + photoproduction with K and K* in the final state using effective Lagrangian approach •Large asymmetries were shown for K due to contact term contribution: strong suppression for proton Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

  23. RCNP & NuRI Summary Suppression to proton •By assuming spin-3/2 +possible explanation for suppression •The ratio estimated by CLAS well reproduced theoretically (~0.2%) •When spin-1/2 considered, proton ~ neutron •We wait for new neutron data We thank to T.Nakano, T.Hyodo, K.Hicks and V.Koubarovski Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

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