Searches for Supersymmetry at the Tevatron

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SEARCHESFORSUPERSYMMETRYATTHETEVATRON

ELSELYTKEN
(fortheCDFandDØcollaborations)
DepartmentofPhysics,PurdueUniversity
525NorthwesternAvenue,WestLafayette,Indiana,USA

TheresultsforsearchesforSupersymmetryattheTevatronCollideraresummarizedinthis
paper.Wefocushereonsearchesforchargino/neutralinoandthelighteststop,aswellas
scenarioswithR-parityviolationandsplitsupersymmetry.Nosignificantexcesseswithrespect
totheStandardModelwereobservedandconstraintsaresetontheSUSYparameterspace.

1Introduction
Supersymmetry(SUSY),anattractiveextensionoftheStandardModel(SM),isbasedonanew
symmetrybetweenfermionsandbosons.EachStandardModelparticleacquiresasupersymmet-
ricpartnerwith∆spin=1/2.MostoftheSUSYmodelsconsideredassumetheconservation
ofaquantumnumber,R-paritya,resultinginastablelightestsupersymmetricparticle,the
LSP.Thisstable,weaklyinteractingparticlewouldescapedetectionandgiverisetomissing
transverseenergy,ET.Inminimalsupergravitymodelsthelightestsupersymmetricparticle
isusuallythelightestneutralino,˜χ01.Thenon-excludedmassesfortheproposedsuperpartners
aretypicallyoftheorderof100GeV/c2andabove,thuspotentiallyaccessibleattheTevatron.
ThetwoTevatronexperiments,DØandCDFhavesuccessfullybeentakingdataat

aRP=(1)3(B−L)+2s
allthesquarks,thusmakingitveryfavorabletosearchforattheTevatron.Recentlyasearch
forlightstopquarksinfinalstateswithe±µ∓+b¯b+ETwascompletedwiththeDØdetector.
Thisisthesignatureof˜t1pairproduction,followedby˜t1→bℓ˜ν,whichisexpectedtobethe
dominantdecaymodewhenm˜ν∼mW.Theanalysisdefines3regions,eachoptimizedfora
particularmassdifference,∆M=m˜t1−m˜ν.TheresultsareshowninTable1below.

Table1:DØresultsonthesearchfor˜t1˜¯t1→e±µ∓+b¯b+ET(350pb−1)
∆MObserved

22.99±3.10
34.63±3.96
40.66±4.38
˜χ01’sandtheneutrino.VeryfewSMprocessescontributetosuchasignature,thedominant
beingDrell-Yanplusamisidentifiedjetoraγ→e+e−conversion,andrealWZproduction.
CDFpresentednewresultsontrileptonslookingatmanydifferentdecaychannels.Resultsare
summarizedinTable2.TheETspectrumfortheµµchannelisillustratedinFigure3.No
significantexcessisobservedandlimitsaresetontheχ±1massinminimalmodels.Aprevious
DØanalysis3setsalimitofmχ±1≥117GeV/c2form˜ℓ∼m˜χ02.

Table2:CDFresultsofsearchfor˜χ±1˜χ02→ℓℓ+X(∗=lowpTtriggers)
Channelµµ+ℓ∗ee+trackℓ±ℓ
±
L745pb−1607pb−1704pb
−1
0.17±0.050.78±0.110.13±0.03
000
tobothλ121andλ122couplings.Theobservationiscompatiblewithexpectationgiventhe
uncertaintiesin346pb−1ofdata.Boththe3and4leptonsignatureswereinvestigatedand
combinedtosetlimitsonthecouplings:σ<0.21pbforλ121>0and0.11pbforλ122>0.

4.2Long-livedLSP
DØlookedforthedecayoftheneutralinotoleptonsandaneutrinoin383pb−1ofdata.The
analysisfocusesonthescenariowheretheRPcouplingisweakandtheLSPwouldtravel≥5
cmbeforedecaying.Thispossibilitywasinspiredbyanexcessindimuoneventsreportedby
NuTeV4.Noeventsareobservedwithanexpectationof0.8±1.1±1.1frombackgroundsand
thelimitset(Figure5)excludesthepossibilitythattheNuTeVeventsareduetoneutralino
decay.

Figure5:Redcurveisthe95%CLlimitonpair
productionofneutral,long-livedparticles.

ObsObs
0.88±0.300.39±0.21
1.86±0.340.59±0.21