LC上对e+e-→ W+W+b-b-过程的一圈QCD修正

我们研究了标准模型下在ILC上$e^+e^- \to W^+ W^- b\bar b$过程在领头阶(LO)和QCD修正的次领头(NLO)的所有贡献。为了处理共振问题,我们在树图和一圈图的微扰计算中采用了复质量方案。我们得到的数值结果表明在$\sqrt{s}$从$360~GeV$到$1.5~TeV$时,K因子从$1.501$变化到$

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One-loopQCDcorrectionstothee+e →W+W b¯bprocessatthe

ILC

GuoLei,MaWen-Gan,ZhangRen-You,andWangShao-Ming

DepartmentofModernPhysics,UniversityofScienceandTechnology

ofChina(USTC),Hefei,Anhui230027,P.R.China

Abstract

Westudythefullcontributionsattheleadingorder(LO)andQCDnext-to-leadingor-der(NLO)tothecrosssectionofthee+e →W+W b¯bprocessinthestandardmodel(SM)attheILC.Indealingtheresonanceproblemweadoptedthecomplexmassschemeinbothtree-levelandone-looplevelperturbative√calculations.OurnumericalresultsshowthattheK-factorvariesfrom1.501to0.847whengoesupfrom360GeVto1.5TeV.Weinvestigatethe

+ + ¯dependenceofthe√LOandQCDNLOcorrectedcrosssectionsofprocessee→WWbbon

collidingenergyandHiggs-bosonmass.WealsopresenttheresultsoftheLOandQCDNLOcorrecteddistributionsofthetransversemomentaof nalparticles,andtheinvariantmassesofWb-,b¯b-andWW-pair.

Keywords: ILC，QCD，Top-quark，Higgs-boson

PACS:13.66.Jn,14.65.Ha,14.80.Bn,12.38.Bx

SuppportbyNationalNaturalScienceFoundationofChina:10575094,10575095,10675110andSpecialized

ResearchFundfortheDoctoralProgramofHigherEducation:20050358063

我们研究了标准模型下在ILC上$e^+e^- \to W^+ W^- b\bar b$过程在领头阶(LO)和QCD修正的次领头(NLO)的所有贡献。为了处理共振问题,我们在树图和一圈图的微扰计算中采用了复质量方案。我们得到的数值结果表明在$\sqrt{s}$从$360~GeV$到$1.5~TeV$时,K因子从$1.501$变化到$

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I.Introduction

TheHiggsboson,whichgivesmassestotheweakvectorbosonsandfermions,playsanimportantroleinthestandardmodel(SM).Unfortunately,ithasnotbeendirectlydetectedyetinexperiments.SearchingforHiggsbosonwithinthestandardmodel(SM)andstudythephenomenologyconcerningHiggspropertiesaretheimportanttasksatthepresentandupcominghighenergycolliders.LEPIIexperimentshaveprovidedthelowerlimitontheSMHiggsmassas114.4GeVatthe95%con dencelevel,whichisextractedfromtheresultsofsearchesfore+e →Z0H0production[1,2].WhiletheindirectevidencesoftheSMHiggsmassthroughelectroweakprecisionmeasurementsindicatethe95%C.L.upperboundasmH 182GeV,whenthelowerlimitonmHisusedindeterminationofthisupperlimit[2].Ontheotherhand,theheavytop-quarkpracticallyplaysacentralandcrucialroleinprobingtheelectroweaksymmetrybreakingaswellasthe avorprobleminalltheextendedmodelsbeyondtheSMwhichaddressthehierarchyproblem.Recently,anewdatumoftop-quarkmasshasbeenalreadypresentedbytheCDFandD0experimentsatFermilab,andthepreliminaryworldaveragemassofthetop-quarkisknownasmt=172.5±1.3(stat)±1.9(syst)GeV,whichcorrespondstoa20%precisionimprovementrelativetothepreviouscombination[3].

ThefutureInternationalLinearCollider(ILC)isproposedbytheparticlephysicscommunity

√

withtheentirecollidingenergyintherangeof200GeV<<500GeVandanintegrated

√

luminosityofaround500(fb) 1infouryears.Themachineshouldbeupgradeableto～1TeV

withanintegratedluminosityof1(ab) 1inthreeyears[4].MostofthemainphysicstopicswithintheSMoritsbeyondatTeVenergyscalecanbeexploredatsuchamachine.Emphasisisgiventothestudyoftop-quarkphysics,electroweakphysicsintheSM,andthemeasurementsintheextendedSM,suchassupersymmetry.

Comparedwiththehadroncolliders,suchastheTevatronandtheCERNLargeHadronCol-lider(LHC),theILCcanproducetopandHiggsbosonsignaleventsmoreeasilyresolvedfrombackgrounds.Therefore,theILCisanidealfacilitytostudytopandHiggsphysicswithmuchmoreprecisemeasurementfortheirparameters.AttheILCwecanalsocarryoutthestudyofgaugebosoninteractions,andthedelicatecancellationswhicharerelatedtothegaugestructureofthetheoryandessentialtopreserveunitarity.Furthermore,theILCexperimentmightbeableto

我们研究了标准模型下在ILC上$e^+e^- \to W^+ W^- b\bar b$过程在领头阶(LO)和QCD修正的次领头(NLO)的所有贡献。为了处理共振问题,我们在树图和一圈图的微扰计算中采用了复质量方案。我们得到的数值结果表明在$\sqrt{s}$从$360~GeV$到$1.5~TeV$时,K因子从$1.501$变化到$

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explorethesignatureofthenewphysics,iftheSMisreallyonlyane ectivetheoryatlowenergy.

¯isagoodwaytostudyAttheILC,detectingthetop-quarkpairproductionprocesse+e →tt

thetop-quarkproperties,andtheassociatedHiggsproductionwithZ0bosone+e →H0Z0isoneofthecleanestsignatureindiscoveringHiggsbosonifthetheb-quarktriggersystemhashighperformancesexceptvertexdetectors[5].Theformerprocesswillbefollowedbythesubsequential¯→W+W b¯decaythroughttb[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.Intheprecisemeasurementsofthesignalsof¯pairandH0Z0associatedproductionprocesses,therelevantirreduciblebackgroundboththett

frome+e →W+W b¯bshouldbecarefullyinvestigated.

¯InRefs.[6,8,9,10,11,12]theNLOelectroweakandQCDcorrectionstotheprocesse+e →ttanddecayt→W+bhavebeenalreadyextensivelystudied.Andthenon-relativistice ectnearthe¯productionisalsostudiedcarefullyinRef.[13],whichcannotbereliablydescribedthresholdoftt

with xedQCDordersinperturbativetheory.TheHiggs-strahlungBjorkenprocesse+e →H0Z0¯→W+W b¯wasinvestigatedinRef.[14],andtheprocesse+e →ttb→6fwithsixfermion nalstatesafterWpairdecayshas …… 此处隐藏：23850字，全部文档内容请下载后查看。喜欢就下载吧 ……