Non-perturbative chiral approach to Kp --gamma Y reactions(13)

A recently developed nonperturbative chiral approach to describe the S=-1 meson-baryon reactions has been extended to investigate the near threshold $K^- p \to \gamma \Lambda, \gamma \Sigma^0$ reactions. With the parameters governed by chiral SU(3) symmetr

parameters,indicatesthatthereisprobablystillroominthemodelusedhereformoderatebreakingsofSU(3)beyondthoseimplementedbythedi erentmassesoftheparticles.

Inconclusion,wehaveextendedtheapproachof[19]tomakepredictionsforthebranch-ingratiosfortheK p→γΛ,γΣ0reactionsnearthethreshold.AllcouplingconstantsareconsistentwiththechiralSU(3)symmetry.Withonlytwoparameters,whichwere xedinthestudyofS= 1meson-baryonreactions,ourpredictionsareclosetothedata,inpar-ticulartheratiobetweentwobranchingratios.Inourapproach,neitherthemeson-baryonnorthephotoproductionmechanismsinvolvetheexplicitconsiderationofexcitedhyperonstatessincetheΛ(1405)resonance,whichplaysakeyroleinthesereactions,isgenerateddynamically.OurresultsthereforestrengthentheinterpretationoftheΛ(1405)asaquasi-boundmeson-baryonsystemwithS= 1,asalreadysupportedbythestudyofthestronginteractionsin[15,19].Thisdoesnotexcludeaseedofamorecomplicatedintrinsicquarksubstructure,butthestrongcouplingtothemesonbaryonchannelsimposedbytheunita-rizationreinforcesthemesonbaryoncomponentandallowsthisresonancetoapproximatelyqualifyasamesonbaryonquasiboundstatemuchasithappensfortheresonancesinthescalarmeson-mesonsector[26,27]

Acknowledgements

OneoftheauthorsT.-S.H.Leewishestoacknowledgethe nancialsupportfromtheProgramaC´atedraofBBVandthewarmhospitalityofProfessorE.OsetofUniversityofValencia.J.A.O.wishestoacknowledge nancialhelpfromtheGeneralitatValenciana.WewouldliketoacknowledgeusefulcommentsfromW.Weise.ThisworkispartiallysupportedbyDGICYTcontractnumbersPB95-1249andPB96-0753,andalsobyUSDepartmentofEnergy,NuclearPhysicsDivision,undercontractNo.W-31-109-ENG-38.TheauthorsacknowledgepartialsupportfromtheEEC-TMRProgramundercontractNo.CT98-0169.