The chiral quark model gives a reasonably good description of many low-energy observables by incorporating the effective degrees carried by the constituent quarks and Goldstone bosons. We calculate the decuplet to octet transition magnetic moments and the

RadiativeDecaysofDecupletBaryons,Λ(1405)andΛ(1520)Hyperons

LangYu,Xiao-LinChen,Wei-ZhenDeng, andShi-LinZhu

DepartmentofPhysics,PekingUniversity,Beijing100871,China

Thechiralquarkmodelgivesareasonablygooddescriptionofmanylow-energyobservablesbyincorporatingthee ectivedegreescarriedbytheconstituentquarksandGoldstonebosons.Wecalculatethedecuplettooctettransitionmagneticmomentsandthedecaywidthsofseveralexcitedhyperonsusingthismodel.ThevariousradiativedecaywidthsfromthechiralquarkroughlyagreewithexperimentaldataincludingtherecentJLABmeasurement.

PACSnumbers:12.39.Fe,13.30.Ce,13.40.Em,13.40.Hq,14.20.-c

arXiv:hep-ph/0602171v1 19 Feb 2006

I.INTRODUCTION

Theradiativedecaysofbaryonscontributeenormouslytoourunderstandingoftheunderlyingstructureofbaryons.Thenon-relativisticquarkmodel(NRQM)ofIsgurandKarl[1,2]hasbeensuccessfulinpredictingtheelectromag-neticpropertiesofthegroundstatesofbaryonsNandtheirresonancesN .However,itisunabletogiveaverygooddescriptionofradiativedecaysofalldecupletandotherlow-lyingexcited-statehyperons.Therefore,severalothertheoreticalapproacheshavebeenproposedtocalculatethesetransitionsbesides(NRQM)[3,4],includingtherelativizedconstituentquarkmodel(RCQM)[5],theMITbagmodel[3],thechiralbagmodel[6],theSkyrmemodel[7],thesolitonmodel[8],thealgebraicmodel[9],theheavybaryonchiralperturbationtheory(HBχPT)[10],the1/NcexpansionofQCD[11]andthelatticecalculations[12].

Recently,oneJLABexperiment[13]reportedsomenewresultsoftheradiativedecaysoftheΣ0(1385)andΛ(1520),suggestingthatmesonice ectsmayplayanimportantroleinΣ0(1385)radiativetransitions[14].Ontheotherhand,aseriesofinterestingworkaboutthechiralquarkmodel[15,16,17,18]indicatesthattheconstituentquarksandinternalGoldstonebosonscano eranadequatedescriptionof avorandspinstructureofbaryonsinthelowQ2 1GeV2region.Withinthesameframework,theoctetanddecupletmagneticmoments,ΣΛtransitionmagneticmomentsandtheexplanationoftheviolationoftheColeman-Glashowsumruleareinremarkablygoodagreementwithexperimentaldata[19,20].Soitisinterestingtoexplorewhetherwecanmakereliablepredictionsofotherimportantobservablesusingthechiralquarkmodel.

Inthispaperwecalculateradiativedecaysofdecuplettooctetandsomeexcitedhyperonswithinthechiralmodelincorporatingquarkseaperturbativelygeneratedbythevalencequark’semissionofinternalGoldstonebosons.Wecandiscernthecontributionsfromseaquarksandpseudoscalarmesonsthroughtheresultsoftransitionmagneticmomentsanddecaywidths.

InSectionII,wegiveanessentialreviewofthechiralquarkmodelandthemechanismforthequarkseageneration.InSectionIII,wepresenttheformalismofthehelicityamplitudesforthebaryonradiativedecays.InSectionIV,wepresentseveraltypicalcasesofthecalculationofdecuplettooctettransitionmagneticmoments.ThenwecalculatetheradiativedecaywidthsofseveralexcitedhyperonsinV.Thenumericalresultsandconclusionsarepresentedinthe nalsection.

II.

MODELDESCRIPTION

Thechiralquarkmodel[15,16,17,18]isane ectivetheoryofnon-perturbativeQCD,whichisbasedontheinteractionbetweenconstituentquarksandGoldstonebosons.ThebasicprocessistheemissionofaninternalGoldstonebosonbyavalencequark:

′

q+ →GB+q →(q

′

q′)+q+,

(2)