The cross section for open-beauty production in photon-photon collisions is measured using the whole high-energy and high-luminosity data sample collected by the L3 detector at LEP. This corresponds to 627/pb of integrated luminosity for electron-positron

where,again,the rstuncertaintyisstatisticalandthesecondsystematic.Thisresultisinagreementwithourpreviousmeasurementperformedwithjustasubsetofthedatainvestigatedhere[8]andhasanimprovedprecision.Asacrosscheck,thevaluesofNc¯cfoundbythe tareusedtoextractthetotalcrosssectionfortheproductionofopencharmattheluminosity-averagedcentre-of-massenergy√

s =194GeV,wheretheuncertaintiesarestatisticalonly.

Anadditionalcrosscheckshowedthatvaluesoftheopen-beautycrosssectiondeterminedwiththe tprocedurediscussedaboveorwithacountingmethod[8]arecompatible.Inthelattercaseexperimentalcriteriawerechosentooptimisethecharmcrosssectionmeasurementyieldingaresultessentiallyuncorrelatedwiththeb-quarkproductionrate.

Thetotalcrosssectionforopen-beautyproductioniscomparedinFigure5toNLOQCDcalculations[7].Thedashedlinecorrespondstothedirectprocesswhilethesolidlineshowsthepredictionforthesumofdirectandresolvedprocesses.Thecrosssectiondependsonmb,whichisvariedbetween4.5GeVand5.0GeV.Thethresholdforopen-beautyproductionissetat10.6GeV.ThetheorypredictionfortheresolvedprocessiscalculatedwiththeGRVpartondensityfunction[26].ThesameresultsareobtainediftheDrees-Grassiepartondensityfunction[27]isused.Forcompleteness,Figure5alsocomparesthecrosssectionsforopen-charmproduction√measuredinReferences8and28withthecorrespondingpredictions.For