Anomalous Single Production of the Fourth Generation Quarks at the LHC

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

8

002 lJu 72 ]hp-eph[ 1v1924.708:0viXraAnomalousSingleProductionoftheFourthGenerationQuarks

attheLHC

R.C¸ift¸ci

Dept.ofEng.ofPhysics,FacultyofEng.,AnkaraUniversity,06100Tandogan,Ankara,Turkey

(Dated:July27,2008)

Abstract

ly,pp→u4(d4)Xwithsubsequentu4→bW+processfollowedbyleptonicdecayofWbosonandd4→bγ(anditsh.c.)decaychannelareconsidered.Signaturesoftheseprocessesandcorrespondingstandardmodelbackgroundsarediscussedindetail.Discoverylimitsforquarkmassandachievablevaluesofanomalouscouplingstrengtharedetermined.

PACSnumbers:12.60.-i,14.65.-q,13.38.Be

Keywords:Anomalousinteractions;colliders;fourthgenerationquarks.

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

I.INTRODUCTION

ThenumberoffundamentalfermiongenerationsisnotpredictedbytheStandardModel(SM).ThisnumberisrestrictedfrombelowwithLEPIdataoninvisibledecaysofZbosonasng≥3[1].Ontheotherhand,theasymptoticfreedomofQCDenforcesthenumberofgenerationstobelessthan9.TherecentprecisionelectroweakdataareequallyconsistentwithexistenceofthreeorfourSMgenerations[2,3,4].

The avordemocracyisanaturalhypothesisintheframeworkofSMaswellasanumberofmodelsdealingwithnewphysics(seereview[5]andreferencestherein).The avordemocracyhypothesisinSMpredictstheexistenceofthefourthSMgeneration[6,7,8].Tevatronexperimentsgive250GeVoflowerboundonthemassofthefourthgenerationquarks[9].Howeveritdoesnot xthemassesandmixingsofthenewfermions.Anotherpredictionofthe avordemocracyisthemassesofthefourthgenerationfermionstobenearlydegenerateandliebetween300and700GeV,whereas,themassesofknownfermionsbelongingtolighterthreegenerationsappearduetosmalldeviationsofthedemocracy[10,11,12].Thelastvalueisclosetotheupperlimitonheavyquarkmasses,whichfollowsfrompartial-waveunitaryathighenergies[13].ThequarkmassesandCabibboKobayashiMaskawa(CKM)matrixforcertainparametrizationofmassmatrixaregiveninRefs.[10,11].Ref.[12]givesbothmassesandCKMmatrix(MakiNakagawaSakata(MNS)matrixforleptons)forbothquarksandleptonsforanotherparametrization.

AnewerainHighEnergyPhysicswillbeopenedwiththeconstructionofTeVscalecolliders[14].Obviously,TeVenergycollidersareneededfordiscoveryofthefourthSMgenerationfermions.The rstofthesuchcollidersistheLargeHadronCollider(LHC)with14TeVcenterofmassenergy.ThefourthgenerationquarksispredictedtobecopiouslyproducedinpairsattheLHC[15,16].Recently,thisprocessisproposedasthebestscenario(afterHiggs)fordiscoveryattheLHC[17,18,19].Also,aseriouscontributionsofanomalousinteractionsfortheproductionofthefourthgenerationfermionscanbeexpected.Suchanomalousinteractionsseemstobequitenaturalduetolargemassesofthefourthgenerationfermions(seeargumentationforanomalousinteractionfortquarkpresentedinref.[20]).Theseanomalousinteractionscouldprovidealsosingleproductionofthefourthgenerationfermions.Theanomaloussingleproductionofthefourthgenerationfermionsisconsideredinanumberofpapers[21,22,23,24].Recently,anomalousproductionofthe

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

100

(GeV)

10

1

200300400500600700800

m(GeV)

d(a)

BR (%)

200300400500600700800

m(GeV)

d(b)

FIG.1:(a)Thetotaldecaywidthofthefourthgenerationdowntypequarkand(b)thebranchingratios(%)dependingonthemassofthequark.

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

fourthgenerationchargedleptonandneutrinoatfutureepcollidersisconsideredin[25]and[26],respectively.ThispaperisdevotedtostudytheanomaloussingleproductionofthefourthgenerationupanddowntypequarksattheLHC.

InsectionIItheLagrangianforSMandtheanomalousinteractionsofthefourthgen-erationquarksispresented;thedecaywidthandbranchingratiosofthefourthgenerationquarksareevaluated.ProductionsofthefourthgenerationquarksattheLHCarestudiedinsectionIII:pp→d4X→bγX(anditsh.c.)andpp→u4X→bW+X→bν +XprocessesaswellastheirSMbackgroundsareconsidered.Thestatisticalsigni canceofthesignalandachievablevaluesofanomalouscouplingstrengtharegivenwithconcludingremarksinSectionIV.

II.ANOMALOUSINTERACTIONSOFTHEFOURTHGENERATIONQUARKS

Thee ectiveLagrangianfortheanomalousinteractionsofu4andd4quarkscanberewrittenfrom[22,27]withminormodi cationsas:

qL=

κγ

i2Λ

gZq¯4σµνqiZ

µν

+

κqg

i

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

100

(GeV)

10

1

200300400500600700800

m(GeV)

u(a)

BR (%)

200300400500600700800

m(GeV)

u(b)

FIG.2:(a)Thetotaldecaywidthofthefourthgenerationuptypequarkand(b)thebranchingratios(%)dependingonthemassofthequark.

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

(pb)

200300400500600700800

m(GeV)

4

¯FIG.3:Thetotalproductioncross-sectionsofthepp→u4(u¯4)Xandpp→d4(d4)XprocessesattheLHC.

widthΓofthefourthgenerationquarksandtherelativebranchingratiosarepresentedinFig.1andFig.2for(κ/Λ)=1TeV 1.Concerningtheanomalouscouplingstrength,thevalue(κ/Λ)=1TeV 1isratherconservative(themassscaleisorderofelectroweakscale).Consequently,Ihaveusedthisvalueatrestofmycalculations.

III.ANOMALOUSSINGLEPRODUCTIONOFTHEFOURTHGENERATION

QUARKSATLHC

IhavecalculatedtheanomaloussingleproductioncrosssectionsofthefourthSMgen-erationquarksattheLHCusingCompHEPwithCTEQ6L1partondistributionfunctions[29].Contributionstosingleproductionofu4comefromguandgcprocesses.Similarcon-tributionsforpp→d4Xcomefromprocessesofgd,gsandgb.TheresultsareshowninFig.3for(κ/Λ)=1TeV 1.

Varioussignaturesforanomalousinteractionsofthefourthgenerationquarksmightbeconsidered.Onecangroupthesesignaturesas

Anomalousproductionfollowedbyanomalousdecaysuchaspp→d4X→gbX,

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

(pb/10 GeV)

dm

b

d

20040060080010001200

m(GeV)

b

(a)

1

m= 400 GeV

(pb/10 GeV)

m= 600 GeV

m= 800 GeV

0,1Signal + total SM back.

dm

b

0,01

d

1E-3

20040060080010001200

m(GeV)

b

(b)

FIG.4:InvariantmassdistributionsofthefourthgenerationdowntypequarksignalforthreeselectedmassvaluesandcorrespondingSMbackgroundsattheLHC(withcutSelection3giveninTableI):(a)separatedand(b)summed.

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

TABLEI:CutselectioncriteriaandcorrespondingsignalandSMbackgroundcrosssectionsforpp→d4X→bγXprocess(anditsh.c.)(at(κ/Λ)=1TeV 1)

Signalcrosssections(pb)

300400500600700800

38.5422.2614.499.937.085.19

22.8916.1211.368.196.034.52

12.829.036.364.583.382.53

pp→bγX+h.c.pp→cγX+h.c.pp→jlightγX

Total

5.60×1033.42×1041.58×1051.98×105

1.25×1017.96×1012.83×1023.75×102

7.017.962.8317.80

pp→d4X→ZbX,pp→d4X→γbX,pp→u4X→gtXandpp→u4X→γtX AnomalousproductionfollowedbySMdecaysuchaspp→u4X→bW+Xandpp→d4X→tW X.

Inthisstudy,ly,pp→d4X→γbXfrom”anomalousproduction-anomalousdecay”groupandpp→u4X→bW+Xfrom”anomalousproduction-SMdecay”grouparechosentoinvestigateindetailsbecauseoftheirrelativesimplicity.Whilethecrosssectionofthe rstgroupisproportionalwith(κ/Λ)4,theof(κ/Λ)and|Vu4b|determinewhichgroupofsignatureisimportantfortheobservatibility.crosssectionofthesecondgroupisproportionalwith(κ/Λ)2and|Vu4b|2.Therefore,valuesFirst,pp→d4X→bγXprocess(anditsh.c.)isconsideredassignatureofanomalous

interactionsofthefourthgenerationdowntypequark.TheSMbackgroundforthisprocessispotentiallymuchlargerthanthesignal.However,somekinematiccutshavebeenapplied

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

(fb/10 GeV)

bW

dm

d

(fb/10 GeV)

ddm

bW

m(GeV)

bW

(b)

FIG.5:Invariantmassdistributionsofthefourthgenerationuptypequarksignalforsomemassand|Vu4b|valuesandcorrespondingSMbackgroundsattheLHC(withcutSelection1giveninTableIIandb-tag+mistag):(a)separatedand(b)summed.

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

TABLEII:Cutselectioncriteriaforpp→u4X→bν +Xprocess

Selection1

Selection2

Selection3

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

TABLEIII:SignalandSMbackgroundcrosssectionsforpp→u4X→bν +XprocesswithcutselectionsgiveninTableII(at(κ/Λ)=1TeV 1)SelectionCriterionSelection1

init

10· Vu4b 4.64·10 12.43·10 11.34·10 18.69·10 24.04·10 22.86·10 2

SMbackgroundcrosssections(pb)

0.23

pp→jlightν +X

1.69·102

Total

Selection2

init

10· Vu4b 3.78·10 12.01·10 11.11·10 17.15·10 23.79·10 22.41·10 2

SMbackgroundcrosssections(pb)

1.11·10 31.17·10 39.16·10 46.95·10 45.89·10 45.51·10 4

pp→jlightν +X

0.96

Total

1.04

0.83

0.64

0.55

0.51

Selection3

init

10· Vu4b 2.12·10 11.13·10 16.22·10 24.00·10 22.12·10 21.35·10 2

SMbackgroundcrosssections(pb)

6.22·10 46.55·10 45.13·10 43.89·10 43.30·10 43.10·10 4

pp→jlightν +X

9.62·10 21.04·10 18.35·10 26.38·10 25.48·10 25.47·10 2

Total

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

TABLEIV:Statisticalsigni cances(SS)foranomalousinteractionsofthefourthgenerationupanddowntypequarksattheLHCwithintegratedluminosityof100fb 1

SSforpp→d4X→bγX

SSforpp→u4X→bν +X

300400500600700800

960677477343253190

82.341.024.417.69.76.2

23011468492717

92045627219610869

criteriaarelistedinTableII.ThecalculatedsignalandSMbackgroundcrosssectionsafteralltheseselections,arepresentedinTableIII.InSelection1,oneisolatedlepton(e+orµ+)isidenti edandusedastrigger.Inaddition,W+bosonisreconstructedbytakingthemissingtransversemomentumastheneutrinomomentum,andis xedthelongitudinalcomponentbyMW.Themostofthecontributiontobackgroundcrosssectioncomesfromjetsoflightquarksandgluon.InSelection2,Irequire|Mjν Mu4|<2ΓTot,whereΓTotisgiveninFig.2a.Withthiscut,thebackgroundisdecreasedbymorethanafactorof100.InSelection3,b-quarkjetistaggedwithe ciencyof56%,and1%oflightjets(foru,

¯,sd,s,u¯,d¯andg)and10%ofc-quarkjetsaremistaggedasb-jetinadditiontoSelection2.ThesecutsgivefurtherdecreaseonSMbackgroundcrosssectionbyalmostafactorof100.Intotal,cutselectionsdecreasebackgroundbyafactorof105withrespecttono-cutcase.Thecalculatedsignalandbackgroundcrosssections,areplottedinFig.5asafunctionofthereconstructedbν invariantmass.Itisdrawnforsome|Vu4b|andmassvaluesofthefourthgenerationquarkforillustration.

IV.CONCLUSION

Thestatisticalsigni cance(SS)values,evaluatedfromSS=(σS/

√

Lint,where

Lintistheintegratedluminosityofthecollider,forbothsignalprocessesattheLHCwithintegratedluminosityof100fb 1arepresentedinTableIV.Achievablevaluesofanomalous

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

(

(TeV)

300400500600700800

m(GeV)

4

FIG.6:Observationreachat3σforanomalouscouplingstrengthasafunctionofthefourthgenerationquarkmassforpp→u4X→bν +Xandpp→d4X→bγXprocessesattheLHC.

couplingstrengthasafunctionofthefourthgenerationquarkmassforprocessesunderconsiderationareshowninFig.6.ForbothprocessesSS≥3istakenasanobservationcriterion.Onecanseethatvaluesaslowas0.24(0.35)TeV 1arereachablefor(κ/Λ)atm4=300(800)GeVfordowntypequark”anomalousproduction-anomalousdecay”groupprocess(asmentionedabove).Whileanomalousinteractionofthefourthgenerationuptypequarkisnotobservablewith”anomalousproduction-SMdecay”typeprocessatbecomesbetterbelow400GeVmassofu4fortopp→d4X→bγXprocess.Forprocess.

init

Vu4b ×10

init

Vu4b ×6.

init Vu4b ,

TeV 1atm4=300(800)GeVforuptypequark”anomalousproduction-SMdecay”groupAsaresultofthisstudy,possibleanomalousinteractionsofthefourthgenerationquarksLHCinafewyears.

atthegivenrangeofthequarkmass,|Vu4b|and(κ/Λ)willbeobservedorexcludedatthe

getsmoreobservablebelow700GeVmassoffourthgenerationquarkcompare

init

Vu4b ×20,

reachablevaluesfor(κ/Λ)are0.057(0.21)

pp→u4X→bν +Xprocessfor

it

Possible anomalous single productions of the fourth standard model generation up and down type quarks at CERN Large Hadron Collider are studied. Namely, $p p \to u_4 (d_4) X$ with subsequent $u_4\to bW^{+}$ process followed by leptonic decay of $W$ boson a

Acknowledgments

IwouldliketothankA.K.C¸ift¸ci,S.SultansoyandG.Unelformanyhelpfulconversationsanddiscussions,andacknowledgeforsupportfromtheTurkishScienti candTechnicalResearchCouncil(TUBITAK)BIDEB-2218grant.ThisworkwasalsosupportedinpartbytheTurkishAtomicEnergyAuthority(TAEA)via”Turkish-ATLASproject”.

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