LC上对e+e-→ W+W+b-b-过程的一圈QCD修正

One-loopQCDcorrectionstothee+e−→W+W−b¯bprocessattheILC∗GuoLei,MaWen-Gan,ZhangRen-You,andWangShao-MingDepartmentofModernPhysics,UniversityofScienceandTechnologyofChina(USTC),Hefei,Anhui230027,P.R.ChinaAbstractWestudythefullcontributionsattheleadingorder(LO)andQCDnext-to-leadingor-der(NLO)tothecrosssectionofthee+e−→W+W−b¯bprocessinthestandardmodel(SM)attheILC.Indealingtheresonanceproblemweadoptedthecomplexmassschemeinbothtree-levelandone-looplevelperturbativecalculations.OurnumericalresultsshowthattheK-factorvariesfrom1.501to0.847when√sgoesupfrom360GeVto1.5TeV.WeinvestigatethedependenceoftheLOandQCDNLOcorrectedcrosssectionsofprocesse+e−→W+W−b¯boncollidingenergy√sandHiggs-bosonmass.WealsopresenttheresultsoftheLOandQCDNLOcorrecteddistributionsofthetransversemomentaoffinalparticles,andtheinvariantmassesofWb-,b¯b-andWW-pair.PACS:13.66.Jn,14.65.Ha,14.80.Bn,12.38.Bx∗SuppportbyNationalNaturalScienceFoundationofChina:10575094,10575095,10675110andSpecializedResearchFundfortheDoctoralProgramofHigherEducation:200503580631，QCD，Top-quark，Higgs-bosonI.IntroductionTheHiggsboson,whichgivesmassestotheweakvectorbosonsandfermions,playsanimportantroleinthestandardmodel(SM).Unfortunately,ithasnotbeendirectlydetectedyetinexperiments.SearchingforHiggsbosonwithinthestandardmodel(SM)andstudythephenomenologyconcerningHiggspropertiesaretheimportanttasksatthepresentandupcominghighenergycolliders.LEPIIexperimentshaveprovidedthelowerlimitontheSMHiggsmassas114.4GeVatthe95%confidencelevel,whichisextractedfromtheresultsofsearchesfore+e−→Z0H0production[1,2].WhiletheindirectevidencesoftheSMHiggsmassthroughelectroweakprecisionmeasurementsindicatethe95%C.L.upperboundasmH.182GeV,whenthelowerlimitonmHisusedindeterminationofthisupperlimit[2].Ontheotherhand,theheavytop-quarkpracticallyplaysacentralandcrucialroleinprobingtheelectroweaksymmetrybreakingaswellastheflavorprobleminalltheextendedmodelsbeyondtheSMwhichaddressthehierarchyproblem.Recently,anewdatumoftop-quarkmasshasbeenalreadypresentedbytheCDFandD0experimentsatFermilab,andthepreliminaryworldaveragemassofthetop-quarkisknownasmt=172.5±1.3(stat)±1.9(syst)GeV,whichcorrespondstoa20%precisionimprovementrelativetothepreviouscombination[3].ThefutureInternationalLinearCollider(ILC)isproposedbytheparticlephysicscommunitywiththeentirecollidingenergyintherangeof200GeV√s500GeVandanintegratedluminosityofaround500(fb)−1infouryears.Themachineshouldbeupgradeableto√s∼1TeVwithanintegratedluminosityof1(ab)−1inthreeyears[4].MostofthemainphysicstopicswithintheSMoritsbeyondatTeVenergyscalecanbeexploredatsuchamachine.Emphasisisgiventothestudyoftop-quarkphysics,electroweakphysicsintheSM,andthemeasurementsintheextendedSM,suchassupersymmetry.Comparedwiththehadroncolliders,suchastheTevatronandtheCERNLargeHadronCol-lider(LHC),theILCcanproducetopandHiggsbosonsignaleventsmoreeasilyresolvedfrombackgrounds.Therefore,theILCisanidealfacilitytostudytopandHiggsphysicswithmuchmoreprecisemeasurementfortheirparameters.AttheILCwecanalsocarryoutthestudyofgaugebosoninteractions,andthedelicatecancellationswhicharerelatedtothegaugestructureofthetheoryandessentialtopreserveunitarity.Furthermore,theILCexperimentmightbeableto2ffectivetheoryatlowenergy.AttheILC,detectingthetop-quarkpairproductionprocesse+e−→t¯tisagoodwaytostudythetop-quarkproperties,andtheassociatedHiggsproductionwithZ0bosone+e−→H0Z0isoneofthecleanestsignatureindiscoveringHiggsbosonifthetheb-quarktriggersystemhashighperformancesexceptvertexdetectors[5].Theformerprocesswillbefollowedbythesubsequentialdecaythrought¯t→W+W−b¯b[6],whilethelaterprocessgoesviaH0Z0→W+W−b¯bthroughdecaysH0→W+W−andZ0→b¯biftheHiggsbosonmassislargerthan2mW[7].Therefore,thesignatureofe+e−→W+W−b¯battheILCservesasnon-resonantbackgroundtobothtop-quarkpairproductionandassociatedproductionofHiggsbosonwithZ0boson.WecanseethatitiscrucialtoseparatethetopandHiggssignaturesfromtheotherW+W−b¯bproductionbackgroundsinILCexperimentaldataanalyzing.Intheprecisemeasurementsofthesignalsofboththet¯tpairandH0Z0associatedproductionprocesses,therelevantirreduciblebackgroundfrome+e−→W+W−b¯bshouldbecarefullyinvestigated.InRefs.[6,8,9,10,11,12]theNLOelectroweakandQCDcorrectionstotheprocesse+e−→t¯tanddecayt→W+bhavebeenalreadyextensivelystudied.Andthenon-relativisticeffectnearthethresholdoft¯tproductionisalsostudiedcarefullyinRef.[13],whichcannotbereliablydescribedwithfixedQCDordersinperturbativetheory.TheHiggs-strahlungBjorkenprocesse+e−→H0Z0wasinvestigatedinRef.[14],andtheprocesse+e−→t¯t→W+W−b¯b→6fwithsixfermionfinalstatesafterWpairdecayshasbeenalsocalculatedatthelowestorderinRef.[15].Theevaluationofthee+e−→W+W−b¯bprocesswithfinitewidthmethodatthetree-levelisalsopresentedinRef.[7,16].Allthosestudiesindicatethatthepreciseinvestigationsofthecharacteristicsoftop-quarkandtheHiggs-bosonaresignificantforthefuturee+e−ILCexperiments.Inthispaperwepresentthecalculationsofthecrosssectionoftheprocesse+e−→W+W−b¯battheleadingorder(LO)an