Non-perturbative chiral approach to Kp --gamma Y reactions(10)

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

IV.RESULTSANDDISCUSSIONS

Thecalculationsinvolvetwoparameters:thecuto parameterqmax=630MeVforregularizingtheintegrationsinEqs.(20)and(21)andtheoverallSU(3)couplingstrengthf=1.15Fπ(Fπ=93MeV),approximateaveragebetweenfπandfK.ThesetwoparametersweredeterminedinRef.[19]

andhencethecalculationsbasedonEqs.(19)-(22)donothaveanyadjustableparameters.

Wehavecalculatedthebranchingratiosde nedby

√σK p→γY(√BK p→γY=σK p→all(

sth→µK +Mp.

Ourresultscalculatedwithandwithoutincludingthecoupled-channele ectsarelistedinTableIIandcomparedwiththedata[25].Weseethatwithnoinitialmeson-baryoninteractions( rstrowinTableII),theγΣ0productionisveryweakandthepredictedratiobetweentwoproductionratesisanorderofmagnitudelargerthanthedata.Thisisinagreementwiththe ndingsofSiegelandSaghai[9].Whenthestrongcoupled-channele ectsareincludedourpredictedratio(secondrowofTableII)isclosetotheexperimentalvalue.ThepredictedbranchingratiofortheγΛproductionisabout50%largerthantheexperimentalvalue,butitiswithintheexperimentaluncertaintyfortheγΣ0production.

TounderstandthedynamicaloriginsofourresultslistedinTableII,weexaminethecoupled-channele ectsinsomedetail.Forthispurposeitissu cienttojustconsiderthe rsttwotermsofEq.(19).TheycanbecastintoaformemployedbySiegelandSaghai

[9],ifwefactoroutthephotoproductionamplitudeQγY,MBandevaluateitattheon-shellmomenta.Withthisapproximation,wehave(obviousvariablesareomittedhere)

TγY,K p～ FγY,MB[1+GT]MB,K p.

(25)MB