Technicolor leptoquarks and the excess of NC and C

arXiv:hep-ph/9709324v112Sep1997TechnicolorleptoquarksandtheexcessofNCandCCeventswithhigh-Q2atHERAZhenjunXiao∗RutherfordAppletonLaboratory,Chilton,OXON,OX110QX,UK†DepartmentofPhysics,HenanNormalUniversity,Xinxiang,453002P.R.China.‡February1,2008RAL-TR-97-043HEP-PH/9709xxxAbstractInthispaperwepursueaconsistentleptoquarkinterpretationforHERAanomaliesintheframeworkofTechnicolor.Wefindthat:(a)oneF=0scalarTechnicolorleptoquarkP′3withamassof200GeVcanprovidetherequiredcon-tributionstoaccountfortheexcessofbothneutralandchargedcurrenteventswithhigh-Q2atHERA;(b)thecurrentdatastillallowthecoexistenceofP′3withm(P′3)=200GeVandP03withm(P03)=225GeV,theycouldcontributeeffec-tivelytoe+pcollisionprocessandmayberesponsiblefortheapparentsplittingofaveragemassofH1andZEUSNCeventswithhigh-Q2.∗Email:[e-mail]†Mailingaddressbefore17Oct.1997‡Permanentaddress11.IntroductionInthisFebruary,thetwoHERAcollaborationsH1[1]andZEUS[2]reportedtheexcessofneutralcurrent(NC)eventswithhigh-Q2(Q215000GeV2)comparedwiththeStandardModel(SM)expectations,basedontheir1994-96e+pdata.ThisobservationhastriggeredextensiveinvestigationsaboutthepossiblenewmechanismsbeyondtheSMresponsibleforthisexcess[3].Amongmanypossiblesolutions,themostfavoredoneistheresonantproductionofnewbosonicparticlewithamassofabout200GeV,namelytheLeptoquark(LQ)[4,5]predictedbyTechnicolor(TC)andothernewphysicstheories[5]ortheSquarks(˜tand/or˜c)intheMinimalSupersymmetricStandardModel(MSSM)withRpviolatinginteractions[6,7].Butthenewestexperimentalresultsseemtodisfavortheleptoquarkinterpretationbasedonthepopularleptoquarkscenario[8].Firstly,theCDF[9]andD0[10]collaborationsreportedtheirnewlowermassboundsonscalarleptoquarks(andRpviolating˜q’s)veryrecently,basedontheirnegativesearchesforthepairproductionoffirstgenerationscalarleptoquarksusingthefullRUNIdatasetandthenewNLOtheoreticalcrosssection[11].Assumingβ=Br(S→eq)=1,theCDFandD0limitisMS≥213GeV[9]andMS≥225GeV[10]respectively,andthecombinedlimitisMS≥240GeV[12].Thecorrespondinglowermassboundsonvectorleptoquarksaswellassquarksareingeneralsignificantlyhigherthanthatforscalarleptoquarksbecausethecorrespondingproductioncrosssectionsfortheseparticlesaremuchmorelargerthanthatforscalarleptoquarks.Secondly,H1andZEUSCollaborations[13,14]reportedmorehigh-Q2neutralcur-rentandchargecurrent(CC)eventsatthe1997Lepton-PhotonconferenceaccordingtotheirnewdataobtainedthroughJune1997.Withacombinedluminosityof57.2Pb−1theformerreportedexcessofhigh-Q2NCeventsissupportedbythenewdata,andacleartendencyfortheCCdatatobeabovetheSMdeepinelasticscattering(DIS)expectationsatlargeQ2wasfoundbyH1andZEUScollaborations[13,14].ForQ2104GeV2,theyobserved28CCeventswhere17.7±4.3areexpected.WenowhavetoexplaintheexcessforbothNCandCCeventssimultaneously.Moreover,theinvariantmassdistributionsofthehigh-Q2NCeventsofH1andZEUSareratherdifferent.Forthe1994-96e+pdata,the7H1eventsappearclusteredaroundM≈200GeV,whilethe5ZEUSeventsclusteredatM≈220GeV.Recent2studies[15,13]showedthatthissplittingcannotbeaccountedforeitherbyinitialstateradiation(ISR)orbydetectoreffects,anditisunlikelythatexcessesobservedbyH1andZEUScouldbecausedbytheproductionanddecayofasinglenarrowresonance[13].Althoughascalarleptoquarkwithamassofabout200GeVisstillallowedbytheTevatrondataifitcandecaytootherchannels,buttheF=0scalarleptoquarksRand˜RintheBuchmuller,R¨ukleandWyler(BRW)leptoquarkscenario[8]couldnotdecaytobothe+dandνuchannelsandthereforecannotcontributetobothNCandCCprocessesatHERAsimultaneously.InordertoprovideaconsistentinterpretationforHERAanomalies,onehastostudysomethingnewbeyondtheclassicBRWleptoquarkscenario[16,17,18].Inthispaper,wewillconsider:(a)mixedstatesofcolor-tripletpseudo-Goldstonebosons,(b)morethanoneTCleptoquarkscontributeeffectively,intheframeworkofTechnicolor[19,20].WewillcalculatethecontributionstobothNCandCCe±pcollisionprocessesatHERAfromtheF=0scalarTechnicolor(TC)leptoquarkP′3andP03,themixedstatesofcolor-tripletpseudo-GoldstonebosonsPUNandPDE.Wefindthat:(a)oneP′3withmassof200GeVcanprovidetherequiredextracontributionstoaccountfortheHERAanomalies.ForQ2min=15000GeV2,wehaveσNCLQ=0.216pbandσCCLQ=0.306pbassumingm(P′3)=200GeV,F2L=0.02andβNC=0.7;(b)thecurrentdatastillallowthecoexistenceofaP′3withm(P′3)=200GeVandaP03withm(P03)=225GeV,theycouldcontributetherequiredextracrosssectionstobothNCandCCprocessesandmayberesponsiblefortheapparentsplittingofaveragemassofH1andZEUSNCeventswithveryhighQ2.WealsoestimatedthepossiblecontributionsfromotherheavierF=0scalarTCleptoquarks.Thispaperisorganizedasfollows.inSec.2webrieflyreviewthemassesandthecouplingsofTCleptoquarksandtherelevantexperimentalconstraints.InSec.3wecalculatethecontributionstothee±pcollisionprocessesfromtheF=0scalarTClep-toquarksandpresentthenumericalresults.Section4containstheconclusionanddiscussions.32.Technicolorleptoquarks,massesandcouplingsAsiswellknown,thecolortripletpseudo-Goldstonebosons(i.e.theleptoquarksinTCmodels)appearedinalmostallnon-minimalTCmodelswhichincludeonegenerationormoretechnifermions,suchastheonegenerationTCmodel[19],one-familySU(2)TCmod