New results on inclusive heavy quark production in gamma gamma collisions are presented. Charm and bottom production are investigated at LEP II energies by the experiments ALEPH, DELPHI, L3, and OPAL. The total and differential cross sections for charm qua

SI-2000-8August2000

HEAVYQUARKPRODUCTIONINγγCOLLISIONSA.BOHRER

¨FachbereichPhysik,Universit¨atSiegen,D-57068Siegen,Germany

E-mail:[email protected]

002Newresultsoninclusiveheavyquarkproductioninγγcollisionsarepresented.Charmandbottom productionareinvestigatedatLEPIIenergiesbytheexperimentsALEPH,DELPHI,L3,andOPAL.Thetotalanddi erentialcrosssectionsforcharmquarksaremeasured.Thecontributionsfromtheepdirectandsingle-resolvedprocessesareseparatedandtheirfractionsquanti ed.Moredetailedstudies,Ssuchasthedependenceofthecrosssectiononthetwo-photoncentre-of-massenergyandthecharm

structurefunctionF1γ,2c

,arereported.Theinclusivebottomcrosssectionispresented.Measurementsarecomparedtonext-to-leadingordercalculations.

1 ]

11Introduction

VevG 1Theproductionofheavy avourintwo-/ b2pphotoncollisionsisdominatedbytwopro- [

1*Dp

9cesses,thedirectandthesingle-resolvedpro-d/0cess.Bothcontributeinequalsharestoσd00heavy avour nalstatesatLEPIIener-/gies.Thelargequarkmassallowsreliablehpperturbativecalculationsforthedirectcon--tribution.Thesingle-resolvedoneinadditionpedependsonthegluondensityofthephoton.

Inthisarticlethenewmeasurements:hvfromtheLEPexperimentsonheavy avouriXproductionandthecomparisonwithnext-to-leadingordercalculations2aresummarized.rT

aOnlythemainresultsaregiven.Fordetailsthereaderisreferredtotheoriginalpapers.Figure1.Di erentialcrosssectiondσ/dpD TversusthetransversemomentumpD ToftheD +.

2

HeavyQuarkIdenti cation

3

Di erentialCharmCrossSection

Aclear,non-ambiguoussignalforcharm

quarkproductionisthepresenceofaD +.ThegooddetectorresolutionandwiththeThisgold-platedsignaturehasbeenexploitedlowkineticenergyavailable,theD +methodbyallfourLEPcollaborations.Boththeallowsforameasurementofthedi erentialproductionprobabilityP(c→D +)andthecrosssectionintransversemomentum(seebranchingratiotoD0π+aswellastheD0Figure1)andpseudorapidity.Thethreeex-branchingratiosarereasonablywell-known.

periments,ALEPH,L3,OPAL,agreeamongTheleptonicdecayhasbeenusedbythemselvesandwiththetheoreticalexpec-ALEPH(µ±forcharm)andL3(µ±ande±tation,thatthedistributioninpseudorapid-bothforcharmandbottom).Thoughtheseityisaboutconstant.Intransversemomen-analysesrelyonthemomentumspectrumastumthemasslessapproachfollowstheOPALtheoreticalinput,thestatisticsissubstan-measurements,whilethemassivecalculationtiallyincreased.

isclosertotheALEPHdata.