1. 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 Contents based on hep-ph/0502143, hep-ph/0503149[PRD] & hep-ph/0505134 RCNP & NuRI Exotic Hadrons Workshop, 27th May 2005, Nara, Japan

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

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

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

5. Introduction RCNP & NuRI Exotic Hadrons Workshop, 27th May 2005, Nara, Japan 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  KN continuum subtracted from J  preferable like Lattice QCD J P =1/2 - preferable like Lattice QCD Y.Kwon et al, hep-ph/0505040

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

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

8. Introduction RCNP & NuRI Exotic Hadrons Workshop, 27th May 2005, Nara, Japan Dead end of  + ?: The newest CLAS experiment @ JLAB  + photoproduction via  p scattering in high statistics  + 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%Ratio N(  *)/N(  + ) ~ 0.2%Questions Why so small ratio? How can we explain positive results from neutron? Is there suppression mechanism for proton?

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

10. Motivation RCNP & NuRI Exotic Hadrons Workshop, 27th May 2005, Nara, Japan 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 in the frame work of effective Lagrangian appraoch at tree level  (1520) and  + are assumed to be hyperons at hadron 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  bar 0  +  n  -  +  p  bar 0  +  n  -  + Non Charge-exchange Charge-exchanged Non Charge-exchange Charge-exchanged Suppressed! Enhanced! Suppressed! Enhanced! Is it possible for interpreting the null results of CLAS??

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

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

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

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

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

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

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

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

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

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

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

22. Summary RCNP & NuRI Exotic Hadrons Workshop, 27th May 2005, Nara, Japan 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 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 performed spin-3/2  + photoproduction We considered spin-3/2  + photoproduction with K and K* in the final state using effective Lagrangian approach state using effective Lagrangian approach Large asymmetries were shown for K due to contact term contribution: strong suppression for proton contribution: strong suppression for proton

23. Summary RCNP & NuRI Exotic Hadrons Workshop, 27th May 2005, Nara, Japan 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 We thank to T.Nakano, T.Hyodo, K.Hicks and V.Koubarovski