Missing energy look-alikes with 100 pb $^{-1} $ at the CERN LHC

48 Pages·2013·0.62 MB·English

FERM ILAB-PUB-08-012-T
ANL-HEP-PR-08-30
M issing energy look-alikeswith 100 pb(cid:0)1 atthe LH C
Jay Hubisz(cid:3)
High Energy PhysicsDivision,ArgonneNationalLaboratory,Argonne,IL 60439,USA
Joseph Lykkeny
FermiNationalAcceleratorLaboratory,P.O.Box 500,Batavia,IL 60510,USA
M aurizio Pieriniz and M aria Spiropulux
PhysicsDepartment,CERN,CH 1211 Geneva 23,Switzerland
(Dated:April18,2013)
A missingenergydiscoveryispossibleattheLHC withthe(cid:12)rst100pb(cid:0)1 ofunderstooddata.W e
presentarealisticstrategytorapidlynarrow thelistofcandidatetheoriesat,orcloseto,themoment
8
ofdiscovery.Thestrategyisbasedonrobustratiosofinclusivecountsofsimplephysicsobjects.W e
0
studyspeci(cid:12)ccasesshowingdiscrimination oflook-alikemodelsin simulated datasetsthatareat
0
least10to100timessmallerthanusedinpreviousstudies.W ediscriminatesupersymmetrymodels
2
from non-supersymmetriclook-alikeswith only100pb(cid:0)1 ofsimulated data,usingcombinationsof

l observablesthattracebacktodi(cid:11)erencesinspin.
u
J
PACSnumbers:11.30.Pb,14.80.Ly,12.60.Jv
0
3
I. INTRODUCTION immediatefollow-upofanearlyLHC discovery.
]
h W henN islarge,itisnotaviablestrategytodiscrim-
p inatebetweenN alternativeexplanationsbyperforming
A. Twenty questionsatthe LHC
- N tests.However,asthegame\twentyquestions"illus-
p
trates,awell-designedseriesofsimpletestscan identify
e
M any well-motivated theoretical frameworks make
h thecorrectalternativeinoforderlog(N )steps,proceed-
dramatic predictionsforthe experimentsatthe Large
[ ingalongadecisiontreesuchthat,ateachbranching,of
Hadron Collider.Theseframeworksaregenerallybased
orderhalfoftheremainingalternativesareeliminated.
2
upon assumptions about new symmetries, as is the
AddressingtheLHC InverseProblem impliesdesigning
v
caseforsupersymmetry (SUSY)[1,2]and littleHiggs
8 and implementingthisseriesofsimpletestsin theLHC
(LH)[3,4],orupon assumptionsaboutnew degreesof
9 experiments,so thatwith high con(cid:12)dencea signi(cid:12)cant
3 freedom such asextralarge[5]orwarped [6]spatialdi- fraction ofthe remaining theory space isruled outat
2 mensions. W ithin each successfulframework,one can eachstep.Theresultsofthe(cid:12)rstfew testswillshapethe
. constructalargenumberofqualitativelydi(cid:11)erentmod-
5 requirementsforfuturetests,sotheimmediateneedisto
elsconsistentwith allcurrentdata. Collectively these
0 developthestrategyfortheearlytests.Inthispaperwe
8 modelspopulatethe\theory space" ofpossiblephysics providethisstrategyforthecaseofanLHC discoveryin
0 beyond theStandard M odel. TheBSM theory spaceis
theinclusivemissingenergysignature.
: many dimensional,and the numberofdistinctmodels
v
i within itisformally in(cid:12)nite. Since the data willnot
X provideadistinctionbetweenmodelsthatdi(cid:11)erbysu(cid:14)-
B. M issing energy atthe LHC
r cientlytinyorexperimentallyirrelevantdetails,in(cid:12)nity,
a
in practice,becomessomelarge(cid:12)nitenumberN . The
Theexistenceofdarkmatterprovidesapowerfulmo-
mappingoftheseN modelsintotheirexperimentalsig-
tivationtoexploremissingenergysignaturesattheLHC,
naturesatthe LHC,though stillincomplete,hasbeen
undertheassumption thatasigni(cid:12)cantfraction ofdark
exploredingreatdetail.
mattermayconsistofweaklyinteractingthermalrelics.
AssoonasdiscoveriesaremadeattheLHC,physicists
M issingenergyattheLHC isexperimentallychallenging.
willface the LHC Inverse Problem: given a (cid:12)nite set
M ostoftheenergyof14TeV ppcollisionsiscarried o(cid:11)
ofmeasurementswith (cid:12)nite resolutions,how doesone
byundetectedremnantsoftheunderlyingevent,somiss-
mapback[7]-[9]totheunderlyingtheoryresponsiblefor
ingenergy searchesactually look formissingtransverse
the new phenomena? So far,notenough progresshas
energy(Emiss)ofthepartonicsubprocess.Emisssearches
beenmadeonthisproblem,especiallyasitrelatestothe T T
areplagued by instrumentaland spuriousbackgrounds,
including cosmicrays,scattering o(cid:11) beam halo and jet
mismeasurement. Standard M odelprocessescreatean
irreducibleEmissbackgroundfrom processessuchasthe
(cid:3)Electronicaddress:[email protected] Z boson decaTy to neutrinosand tt(cid:22)production followed
yElectronicaddress:[email protected]
zElectronicaddress:M [email protected] bysemileptonicdecaysofthetop.
xElectronicaddress:[email protected] Inmanytheoreticalframeworkswithdarkmattercan-
2
didates,there are heavy strongly interacting particles btaggingin multijet(cid:12)nalstateswillbein development
withthesameconservedchargeorparitythatmakesthe during the100 pb(cid:0)1 era. In many smalldata samples
darkmatterparticlestable.Thesecoloredparticleswill peaksandedgesininvariantmassdistributionsmaynot
bepair-producedattheLHC withcrosssectionsroughly bevisible,and mostobservablesrelated todetailed fea-
intherange0.1to100pb.Theirsubsequentdecayswill turesoftheeventswillberatelimited.Theobservables
produceStandard M odelparticlesalong with a pairof thatare availableto discriminatethelook-alikesin the
undetected dark matterparticles.Thusthegenericex- veryearlyrunningwillbestronglycorrelatedbyphysics
perimentalsignatureisboth simpleand inclusive:large and systematicsmaking itimprudentto combinethem
Emissaccompaniedbymultipleenergeticjets.A detailed inamultivariateanalysis.
T
strategyforearlydiscoverywith theinclusiveEmisssig-
T
naturewaspresentedintheCM SPhysicsTechnicalDe-
sign Report[10]-[12]and studied with fullsimulation of D. IsitSUSY?
theCM Sdetector.Afteraseriesofcleanupandanalysis
cutson a simulated Emiss triggersampletargeting the
T Byfocusingonthediscriminationoflook-alikes,weare
reduction oftheinstrumentaland physicsbackgrounds,
pursuingastrategyofsimplebinarychoices:isM odelA
thesignale(cid:14)ciencyremainedashighas25%.Thesere-
a signi(cid:12)cantly betterexplanation ofthediscovery data
sultsindicatethat,forsignalcrosssectionsaslow asa
setthan M odelB? Each answercarrieswith ita few
few pb,an Emiss discoverycould bemadewith the(cid:12)rst
T bitsofimportantfundamentalinformationaboutthenew
100pb(cid:0)1 ofunderstoodLHC data1.Inourstudyweas-
physicsprocessresponsibleformissingenergy.Obviously
sumeasthestartingpointthatagreaterthan5(cid:27) excess
wewillneed to makemany distinctlook-alikecompar-
ofeventswillbeseen in a14TeV LHC datasampleof
isonsbeforewecanhopetobuildupaclearpicturefrom
100pb(cid:0)1 with an inclusivemissingenergyanalysis.For
theseindividualbits.
invariability and comparability wee(cid:11)ectively adoptthe
Considerhow thisstrategymightplayoutforanswer-
fullanalysispathandrequirementsusedin[10].
ingthebasicquestion\isitSUSY?"Itmaynotbepos-
sibletoanswerthisquestionconclusivelyduringthe100
pb(cid:0)1 era.Ourstrategywillconsistofaskingaseriesof
moremodestquestions,someofthem oftheform:\does
C. Look-alikesatthe m om entofdiscovery
SUSY M odelA giveasigni(cid:12)cantlybetterexplanationof
thediscoverydatasetthan non-SUSY M odelB?"None
Atthemomentofdiscoveryalargenumberoftheory
oftheseindividualbitsofinformationbyitselfisequiva-
modelswillbe immediately ruled outbecause,within
lenttoanswering\isitSUSY?"Howeverwedemonstrate
conservativeerrors,theygivethewrongexcess.However
thatwecan build up apicturefrom thedatathatcon-
alargenumberofmodelswillremain asmissingenergy
nectsbacktofeaturesoftheunderlyingtheory.
look-alikes,de(cid:12)ned asmodelsthatpredictthesamein-
Furthermore,wedemonstrateaconcretemethodtoob-
clusivemissingenergyexcess,within sometolerance,in
tainindirectinformationaboutthespinofthenew par-
thesameanalysisin thesamedetector,fora given in-
ticles.W eestablish how todiscriminatebetween anon-
tegratedluminosity.Theimmediatechallengeisthen to
SUSY modelanditsSUSY look-alikes.Eventhoughwe
begindiscriminatingthelook-alikes.
cannotmeasurethespinsoftheexoticparticlesdirectly,
Thelook-alikeproblem wasstudied in [9]asitmight
spin hassigni(cid:12)cante(cid:11)ectson production crosssections,
apply toalatermaturephaseoftheLHC experiments.
kinematic distributionsand signale(cid:14)ciencies. W e are
Evenrestrictedtothesliceoftheoryspacepopulatedbya
thusable to discriminate SUSY from non-SUSY using
partialscanoftheM SSM ,ignoringSM backgroundsand
combinationsofobservablesthattracebacktodi(cid:11)erences
systematicerrors,and applying an uncorrelated (cid:31)2-like
inspin.Ourstudyshowsthatinfavorablecasesthiscan
statisticalanalysisto 1808 correlated observables,this beaccomplishedwithdatasetsassmallas100pb(cid:0)1.
studyfoundthatalargenumberoflook-alikesremained
unresolvedinasimulationequivalentto10fb(cid:0)1.A more
recentanalysis[13]attemptstoresolvetheselook-alikes
E. Outline
inasimulationofafuturelinearcollider.
Atthe momentofan early discovery the look-alike
InsectionIIwereview indetailthemissingenergydis-
problem willbequalitatively di(cid:11)erent. Thedata sam-
covery path,including theexperimentalissuesand sys-
pleswillbemuch smaller,with a limited paletteofro-
tematicsthatlimitourabilitytofullyreconstructevents
bustreconstructed physicsobjects. Forexample,(cid:28) or
from thediscovery dataset. W eexplain how themiss-
ing energy signalsaresimulated,and theuncertainties
associatedwith thesesimulations.In section IIIwedis-
cusstheproblem ofpopulating thepartsofthetheory
1 The(cid:12)rst100pb(cid:0)1 ofunderstoodLHC datawillnotbethe(cid:12)rst
spacerelevantto a particularmissing energy discovery.
100pb(cid:0)1 ofdatawrittentotape.The10TeV datacollectedin
InsectionIV weintroducetwogroupsoflook-alikemod-
theearlyrunningwillbeusedforcalibrationsandunderstanding
ofbenchmarkStandardM odelprocesses. elsrelativeto two di(cid:11)erentmissing energy signals. For
3
modelsdi(cid:11)eringonlybyspins,wediscusshow crosssec- and misreconstruction oftheprimaryvertex.Eliminat-
tions,kinematicdistributionsande(cid:14)cienciescanbeused ingthesesourcesrequiresunbiased(cid:12)ltersbasedonclean
to distinguish them,drawing from formulae developed de(cid:12)nitionsofeventquality.
in theAppendix. In section V wede(cid:12)neallofthero- Todesign amissingenergyanalysis,weneed tohave
bustobservablesthatweusetodiscriminateamongthe someideaofthesourceoftheEmiss in thesignal.The
T
look-alikes,and in section VIwedescribethelook-alike possibilitiesinclude:
analysisitselfandhow wecomputethesigni(cid:12)canceofthe
discriminations.SectionsVIIandVIIIgiveasummaryof (cid:15) TheETmiss isentirely from neutrinos. Thiscould
ourresults,withdetailsrelegatedtofurtherAppendices. arisefrom thedirectdecayofnew heavyparticles
FinallysectionIX describesthestepswearefollowingto to neutrinos,ordecaysofnew heavy particlesto
improvethisanalysisforusewithrealdata. top,W ’s,Z’sor(cid:28)’s. One appropriatediscovery
strategyforthiscaseistolookforanomaliesinthe
energetictailsofdatasetswith reconstructedtop,
W ’sorZ’s.
II. DISCOVERY ANALYSIS FOR M ISSING
ENERGY (cid:15) TheEmissoriginatesfrom asingleweaklyinteract-
T
ing exoticparticlein the(cid:12)nalstate. An example
ofthispossibilityisgravitonproductioninmodels
M issingenergyhadroncolliderdatahasbeenusedpre-
withlargeextradimensions[20].Ifstrongproduc-
viously forsuccessfulmeasurementsofStandard M odel
processeswith energeticneutrinos;theseincludetheZ0 tionoccurs,thesignalwillconsistpredominatelyof
monojetsand largeEmiss. Successfulanalysesfor
boson invisibledecayrates,thetop quarkcrosssection, T
thiscasewerecarriedoutattheTevatron[21,22].
searchesfortheHiggsboson[14]andapreciseextraction
Othersignalsthat(cid:12)tthiscasearisefrom unpar-
oftheW massfrom thereconstruction oftheW trans-
ticlemodels[23]and from modelswith s-channel
versemass[15].Pioneeringsearchesfornew phenomena
resonancesthathaveinvisibledecays.
in missingenergydatasetsattheTevatron [16]-[19]led
tothedevelopmentandunderstandingofthebasictech-
(cid:15) The Emiss originatesfrom many weakly interact-
niquesthatwillbeusedinmissingenergysearchesatthe T
ingexoticparticles.Thiscanbethecaseinhidden
LHC.
valleymodels[24],wheretheweaklyinteractingex-
Inanidealdetector,withhermetic4(cid:25) solidanglecov-
oticsarelightpionsofthehiddensector.Thiscase
erageand excellentcalorimeterresolution,themeasure-
isexperimentallychallenging.
mentofmissing energy isthemeasurementoftheneu-
trinoenergyandtheenergyofanyotherneutralweakly (cid:15) TheEmiss originatesfrom two weakly interacting
T
interactingparticles.In arealdetectoritisalsoamea- exoticparticlesin the(cid:12)nalstate.Thisisthecase
surementofthe energy thatescapes detection due to forsupersymmetry modelswith conserved R par-
uninstrumented regionsand otherdetectore(cid:11)ectssuch ity,wheretheweaklyinteractingparticlesareneu-
asimperfectcalorimeterresponse. M uonsare sources tralinoLSPs.Italsoappliesformoregenericmod-
ofmissing energy sincea muon typically depositsonly elswithW IM P darkmattercandidates.
ofordera few GeV ofitstotalenergy in thecalorime-
ters2. QCD jetsproducerealEmiss from semileptonic W efocusonadiscoveryanalysisdevelopedforthelast
T
decaysofheavy (cid:13)avor,and fake Emiss from detector- case. Thusweareinterested in signaleventswith two
T
induced mismeasurements.ThustheEmiss distribution heavy W IM Ps in the (cid:12)nalstate. For early discovery
T
ofa pureQCD multijetsamplehasa long tailrelated attheLHC,thesignaleventsshould havestrong pro-
to non-Gaussian tails in the detector response. This duction crosssections;wewillassumethateach W IM P
givesrisetoanimportantbackgroundtomissingenergy arisesfrom thedecayofastronglyinteractingheavypar-
searchesthatisdi(cid:14)culttoestimatepriortodata.Atthe entparticle.Themostgenericsignatureisthereforelarge
Tevatronithasbeenshownthatthisbackgroundcanbe ETmissinassociationwithatleasttwohighET jets.There
broughtundercontrolbyexploitingthefactthatthefake willbeadditionaljetsiftheW IM P isnotproducedina
Emissfrom jetmismeasurementsishighlycorrelatedwith 2-bodydecayoftheparentparticle.Furthermore,there
T
theazimuthaldirectionsoftheleadingjets[16]. isasigni(cid:12)cantprobabilityofan extrajetfrom QCD ra-
There are other important sourcesoffake Emiss at diation,dueto thelargephasespace. Thusitisonly
hadroncolliders,includingbeam haloinducedEmiTss,cos- slightly lessgeneric to design an inclusive analysisfor
T largeEmiss in association with threeormoreenergetic
mic ray muons,noise in the data acquisition system, T
jets.W ewillrefertothisastheinclusivemissingenergy
signature3.
2 Theenergylossofmuonsismostlyduetoionizationuptomuon
energiesof100GeV.Above100GeV bremsstrahlungandnuclear
lossescan causeasingle\catastrophic"energy losscomparable 3 Therequirementofathirdenergeticjetgreatlyreducesthesize
tothetotalmuonenergy. andcomplexityoftheStandardM odelbackgrounds.Thuswhile
4
In the basic 2 ! 2 hard scattering,the heavy par- missingtransverseenergyEmiss(cid:21) 200GeV and atleast
T
entparticlesofthesignalwillbeproducedback-to-back threejetswithE (cid:21) 30GeV withinpseudorapidityj(cid:17)j<
T
in the partonic subprocesscenter-of-massframe;typi- 3. These requirementsdirectly de(cid:12)ne the missing en-
callytheywillhavep roughlycomparabletotheirmass ergy signalsignature. In addition theleading jetisre-
T
m .TheW IM Psofmassm resultingfrom theparent quired to bewithin thecentraltracker(cid:12)ducialvolume
p dm
particledecayswillfailtodepositenergy(cid:21) m in the i.e. j(cid:17)j< 1:7. Everywherein thispaper\jets" means
dm
calorimeters;iftheW IM PS havefairly largep ,a sig- uncorrected (raw)jetswith E > 30 GeV and j(cid:17)j< 3
T T
ni(cid:12)cantfraction ofthisenergycontributestotheEmiss. asmeasured in thecalorimeters;thejetreconstruction
T
Thuseitherlargem orlargem leadstolargeEmiss. iswithasimpleiterativeconealgorithm witha0.5cone
p dm T
NotetheazimuthaldirectionsoftheW IM PS areanti- sizeinthe(cid:17)(cid:0)(cid:30)space.Themissingenergyisuncorrected
correlated,afeatureinheritedfrom theirparents,sothe forthepresenceofmuonsintheevent.
magnitudeofthetotalEmiss tendsto belessthan the The rest ofthe analysis path is designed based on
T
magnitudeofthelargestsinglecontribution. elimination ofthemajorbackgrounds.TheQCD back-
At the LHC,the most important Standard M odel ground from mismeasured jets isreduced by rejecting
sourcesoflargerealEmiss willbett(cid:22),singletop,W and eventswheretheEmissistoocloselycorrelatedwiththe
T T
Z plusjetsassociated production,dibosonsand heavy azimuthaldirectionsofthejets.Toreducethelargeback-
(cid:13)avordecays. M ostoftheseprocessesproducea hard ground from W (! ‘(cid:23))+jets,Z(! ‘‘)+jetsand tt(cid:22)pro-
lepton in association with theEmiss from an energetic ductionanindirectlepton veto(ILV)schemeisdesigned
T
neutrino. Theexception isZ ! (cid:23)(cid:23)(cid:22). Even with a per- thatusesthetrackerand thecalorimeters.TheILV re-
fectdetector,Z ! (cid:23)(cid:23)(cid:22) plusjetsisan irreduciblephysics tainsalargesignale(cid:14)ciencywhileachievingafactorof
background. two rejection ofthe remaining W and tt(cid:22)backgrounds.
Theveto isindirectbecausewedon’tidentify leptons{
insteadeventsarerejectediftheelectromagneticfraction
ofoneofthetwoleadingjetsistoolarge,orifthehighest
A. Analysispath
p trackoftheeventisisolated.Thesignalsweareinter-
T
ested in arecharacterized by highlyenergeticjetswhile
In therealdata thissearch willbeperformed start-
leptonsinthesignaloriginatefrom cascadedecaysofthe
ingfrom aprimary datasetthatincludesrequirements
parentsorsemileptonicB decaysin thejets;thuseven
ofmissingenergy,jetsand generalcalorimetricactivity
when a signaleventhasleptonsitisrelatively unlikely
atthetriggerpath;thetriggere(cid:14)ciencyshouldbemea-
toberejected by theILV.Forthemodelsin ourstudy,
suredinotherdatasamples.
approximately85% ofallsignaleventsand70% ofsignal
For the o(cid:15)ine analysis,we willadoptthe inclusive
eventswithmuonsortauspasstheILV cut.
missingenergybenchmarkanalysisstudiedwith thefull
The (cid:12)nalselectionsrequire thatthe leading jethas
detectorsimulation fortheCM S PhysicsTechnicalDe-
E > 180GeV,and thatthesecond jethasE > 110
signReport[10,11]. T T
GeV.W ealsorequireH > 500GeV,where
The (cid:12)rstphase isa preselection based on the event T
quality.Thepurposeofthisprimarycleanupistodiscard
eventswith fakeEmiss from sourcessuch asbeam halo, X4
T H = Ei + Emiss; (1)
dataacquisition noiseand cosmicraymuons.Toelimi- T T T
natethesetypesofbackgroundsthebenchmarkanalysis i=2
usesjetvariables,averagesthem overtheeventto de-
where the E issummed overthe second,third and
(cid:12)necorrespondingeventvariables,andusesthesetodis- T
fourth (ifpresent)leading jets. These cuts selectfor
criminaterealEmiss+ multijeteventsfrom spuriousback-
T highlyenergeticevents,greatlyfavoringeventswithnew
grounds.Theeventelectromagneticfraction(EEM F)is
heavyparticlesovertheStandardM odelbackgrounds.
de(cid:12)ned tobetheE weighted jetelectromagneticfrac-
T
TableIsummarizesthebenchmarkanalysispath.The
tion. W e de(cid:12)ne an eventcharged fraction (ECHF)as
tableliststhecumulativee(cid:14)cienciesaftereachselection
theeventaverageofthejetchargedfraction (de(cid:12)ned as
P
fora benchmark signalmodeland theStandard M odel
theratioofthe p ofthetracksassociatedwithajet
T
backgrounds. ThesignalmodelistheCM S supersym-
overthetotalcalorimetricjetE ).Thepreselectionalso
T
metry benchmark modelLM 1,which hasagluinowith
hasaqualityrequirementforthereconstructedprimary
mass611GeV andsquarkswithmassesaround560GeV.
vertex.
Thelastlineofthetableshowstheexpected numberof
Eventsthatareaccepted by thepreselection require-
eventsthatsurvivetheselectioninadatasetcorrespond-
mentsproceed through the analysispath ifthey have
ingto1000pb(cid:0)1 ofintegratedluminosity.FortheQCD
backgroundandthesingletopbackground,whicharenot
shown in thetable,theestimated numberofremaining
eventsis107 and 3,respectively. Thusthe totalesti-
matureLHC analyseswillexplorethefullyinclusiveEmisssig-
T matedStandardM odelbackgroundafterallselectionsis
nature,weassumeherethatanearlydiscoverywillbebasedon
amultijet+ Emiss datasample. 245eventsper1000pb(cid:0)1.
T
5
TABLE I:Cumulativeselection e(cid:14)ciencyaftereach requirementin theE miss+ multijetsanalysispath foralow massSUSY
T
signalandthemajorStandardM odelbackgrounds(EW K referstoW =Z,W W =ZZ=ZW ),see[10,11]).
Cut/Sample Signal tt(cid:22)Z(! (cid:23)(cid:23)(cid:22))+ jetsEW K + jets
All(%) 100 100 100 100
Trigger 92 40 99 57
Emiss> 200GeV 54 0.57 54 0.9
T
PV 53.8 0.56 53 0.9
N (cid:21)3 39 0.36 4 0.1
j
j(cid:17)j1j(cid:21) 1:7 34 0.30 3 0.07
d
EEM F (cid:21) 0.175 34 0.30 3 0.07
ECHF (cid:21) 0.1 33.5 0.29 3 0.06
QCD angular 26 0.17 2.5 0.04
Isoleadtrk = 0 23 0.09 2.3 0.02
EM F(j1);
EM F(j2)(cid:21) 0:9 22 0.086 2.2 0.02
ET;1 > 180GeV,
ET;2 > 110GeV 14 0.015 0.5 0.003
H > 500GeV 13 0.01 0.4 0.002
T
eventsremainingper1000pb(cid:0)1
6319 54 48 33
B. Triggersand \boxes" (cid:15) The M uon20 trigger requires an energetic muon
thatisnotnecessarilyisolated.Thetriggeris88%
e(cid:14)cientformuonswithp = 20GeV/c,asymptot-
Havingestablishedabenchmarkanalysispath,wealso T
ingto95% asseeninFigure4.
need to de(cid:12)nebenchmark data samples. W ith thereal
LHC datathesewillcorrespondtodatastreamsanddata
Afterapplying theselection requirements,thesefour
pathsfrom varioustriggers. Forthe inclusive missing
triggersde(cid:12)nefourpotentialdiscoverydatasets.In our
energy signaturerelevanttriggersaretheEmiss and jet
T simulationtheDiJet,TriJet,andM uon20datasets,after
triggers.A singlelepton triggerisalsoofinterest,since
theinclusivemissingenergyanalysispathisapplied,are
many models produce energetic leptons in association
allsubsetsoftheM ET sample,apartfrom oneortwo
with largeEmiss. Forourstudy wehavechosen simple
T eventsper1000pb(cid:0)1 5. ThustheM ET isthelargest,
butreasonable[25,26]parametrizationsofthe trigger
mostinclusivesample.W eperform onecompleteanaly-
e(cid:14)cienciesde(cid:12)ningourfourbenchmarktriggers 4 :
sisbased on theM ET trigger.Theotherthreetriggers
arethentreatedasde(cid:12)ningthreemoreboxes,i.e.experi-
(cid:15) TheM ET triggerisapureinclusiveEmisstrigger.
T mentallywell-de(cid:12)nedsubsetsoftheM ET discoverydata
Itis50% e(cid:14)cientforE miss> 80 GeV,asseen in
T set. Thesimplestphysicsobservablesarethecountsof
Figure1.
eventsineachbox.
(cid:15) TheDiJettriggerrequirestwoveryhighE jets.It
T
is50% e(cid:14)cientforuncorrected jetE > 340GeV,
T
C. Backgroundsand system atics
asseeninFigure2.
IntheCM SstudythetotalnumberofStandardM odel
(cid:15) TheTriJettriggerrequiresthreehigh E jets. It
T
background eventsremaining afterallselectionsis245
is50% e(cid:14)cientforuncorrected jetE > 210GeV,
T per1000 pb(cid:0)1 foran Emiss triggersample. Theerror
asseeninFigure3. T
on thisestimateisdominated by i)theuncertainty in
how wellthedetectorsimulation softwaresimulatesthe
4 Thesearemade-up triggersforthepurposesofourstudy.The
guidanceon ourparametrizationsisfrom thepublished trigger
andphysicsreportsoftheCM Sexperiment.W eexpectthatthe 5 A perfectlydesignedtriggertablewillgiverisetooverlapsamong
triggertablesoftheLHC experimentswillincludecorresponding datasetsfrom di(cid:11)erenttriggerpathsdue to both physicsand
triggerpaths,richerandbetterintermsofthephysicscapture. slow/non-sharptriggere(cid:14)ciencyturn-ons(resolution).
6
y y
nc 1 nc 1
e e
ci ci
effi effi
r r
e 0.8 e 0.8
g g
g g
ri ri
T T
0.6 0.6
0.4 0.4
0.2 0.2
0 0
0 50 100 150 200 250 300 100 150 200 250 300 350
Emiss (GeV) E (GeV)
T T
FIG.1:TheEmisstriggere(cid:14)ciency. FIG.3:TheTriJettriggere(cid:14)ciency.
T
y y 1
nc 1 nc
e e
ci ci
r effi r effi 0.8
e 0.8 e
g g
g g
ri ri
T T
0.6
0.6
0.4
0.4
0.2 0.2
0 0
300 310 320 330 340 350 360 370 380 390 400 0 10 20 30 40 50 60
E (GeV) p (GeV/c)
T T
FIG.2:TheDiJettriggere(cid:14)ciency. FIG.4:TheM uon20triggere(cid:14)ciency.
responseoftheactualCM S detector,and ii)theuncer- overallsystematicerror.Thelook-alikeanalysiswillbe
taintyonhow welltheStandardM odeleventgenerators degraded,however,intheeventthattheStandardM odel
emulateQCD,top production,and W =Z plusjetspro- backgroundsturn outto be much largerthan current
duction. Detailed studiesoftherealLHC data willbe estimates.
required in orderto producereliableestimatesofthese Priortodata,itisalsodi(cid:14)culttomakeareliableesti-
uncertainties. mateofthemainsystematicuncertaintiesthatwilla(cid:11)ect
Priortodataweassignconservativeerrorbarsonthese theinclusivemissingenergyanalysis.Systematicuncer-
backgroundprojections.W ehavecheckedthat100pb(cid:0)1 taintieswilldecreaseovertime,asthedetectorsarebet-
ofdatain theM ET triggersampleissu(cid:14)cientfora5(cid:27) terunderstood,calibration studiesare performed,and
discovery fortheeightmodelsin ourstudy,even ifwe StandardM odelphysicsisanalyzedwiththeLHC data.
triplethebackgroundsquoted aboveand includea15% Forourstudy wehaveassumed that,atthemomentof
7
discovery,thedominantsystematicerrorsinthefulldis- W eperformed apreliminarystudy by comparingPGS
coverydatasetwillcomefrom threesources: results to the fullsimulation results reported for the
SUSY benchmark modelLM 1 [10,11]. W efound that
(cid:15) Luminosity uncertainty:ita(cid:11)ectsthecountingof
PGS jetsare nota good approximation ofuncorrected
events.Thissystematicuncertainty isprocessin-
jetsin thefullsimulation,even forthemostbasicprop-
dependent.
ertiessuchastheE spectrum.Varyingtheparameters
T
andaddingsimpleimprovements,suchastakingintoac-
(cid:15) Detectorsimulation uncertainty:itmainly a(cid:11)ects
countthe4Tesla(cid:12)eldinthebarrel,didnotchangethis
calorimetry-related variablesin ourstudy,in par-
conclusion. PGS jetshavea behavior,notsurprisingly,
ticularjetcounting and themissing energy. This
thatisintermediatebetweengeneratorleveljetsandun-
systematicispartiallyprocessdependent.
correctedfullsimulationjets.
(cid:15) QCD uncertainty: it includes the uncertainties W e developed a modi(cid:12)ed simulation called PGSCMS
from thepartondistributionfunctions,higherorder with the geometry and approximate magnetic (cid:12)eld of
matrixelements,andlargelogarithms.Thisuncer- the CM S detector. The PGS Gaussian smearing and
taintya(cid:11)ectseventcounting,jetcountingand the uninstrumentede(cid:11)ectsinthecalorimetersareturnedo(cid:11).
shapesofkinematic distributions. Itispartially Electrons,muonsandphotonsareextractedatgenerator
processdependent. level,andPGStaureconstructionisnotused.Trackinfor-
mationisextractedasinthestandardPGS.Thecalorime-
Note that,since weuse uncorrected jets,we do not
teroutputimprovesonageneratorlevelanalysisinthat
have a systematic from the jet energy scale. This is
weincludeapproximationstothee(cid:11)ectsofsegmentation
traded fora portion ofthe detectorsimulation uncer-
and the4Tesla(cid:12)eld,aswellasan (cid:17) correction derived
tainty,i.e. how wellwecan map signaleventsintoun-
from thezvalueoftheprimaryvertex.W eparameterized
correctedjetsaswouldbemeasuredintherealdetector.
thedetectorresponsein a limited setoflook-up tables
asafunctionofthegenerator-levelquantities.
Attheanalysislevelweapply parameterized correc-
D. Sim ulation ofthe signals
tionsandreconstructione(cid:14)cienciesinspiredbythepub-
lished CM S detectorperformance[29].Forthejets,we
A realistic study oflook-alikesrequiresfulldetector
applyanE and(cid:17)dependentrescalingoftheirE ,tuned
T T
simulation.Fortheinitialphaseofthisworkagenera-
toreproducethefullsimulation LM 1resultsin [10,11].
torlevelanalysisisattractive,beingcomputationallyless
Thisrescalingmakesthejetssofter(i.e. takesinto ac-
intensiveandprovidingaclearlinkbetweenobservables
countthedetectorreconstruction):a50GeV generator
andtheunderlyingtheorymodels6.
leveljetbecomesanapproximately30GeV raw jetinour
Inageneratorlevelanalysis,jetsarereconstructedby
analysis.
applying a standard algorithm to particlesratherthan
The Emiss reconstructed from PGSCMS is essentially
to calorimetertowers. Thisobviously doesnotcapture T
identical,modulosmallcalorimetersegmentatione(cid:11)ects,
thee(cid:11)ectsofarealisticcalorimeterresponse,calorimeter
toaageneratorlevelanalysis,i.e.ourEmissisvirtually
segmentation,and energy lossesdueto materialin the T
indistinguishablefrom theM onteCarlotruth Emiss ob-
trackeraswellasmagnetic(cid:12)elde(cid:11)ects. T
tainedfrom minusthevectorsum oftheE ofneutrinos,
A compromisebetweenthefullsimulationandagener- T
muonsand theotherweakly interactingparticles(such
atorlevelanalysisisaparameterizeddetectorsimulation.
astheLSP).W edid notattemptto rescaletheEmiss;
FortheLHC thepubliclyavailablesoftwarepackagesin- T
thisisa complicated task since Emiss isa vectorand
cludeAcerDET[27],and PGS[28].In such asimulation, T
in generalenergy losses,calorimeterresponseand mis-
electrons,muonsand photonscan bereconstructed us-
measurementstend todecreasethereallargeEmisstails
ing parameterized e(cid:14)cienciesand resolutionsbased on T
whileincreasingtheEmisstailsinthedistributionofnon-
abstractbuteducated rules-of-thumb formodern mul- T
realEmiss events. Instead ofattempting to rescalethe
tipurposedetectors. Jetsarereconstructed in a virtual T
Emiss eventby event,we raised the Emiss cut in our
calorimeter,from particleenergiesdepositedincellsthat T T
benchmarkanalysisto220GeV7.
roughly mimic the segmentation ofa realcalorimeter.
Becauseofthelimitationsofourfastsimulation,we
Calorimeterresponseisapproximated by performing a
Gaussiansmearingontheseenergydeposits.TheEmissis alsosimpli(cid:12)edpartsofthebenchmarkanalysis.The(cid:12)rst
T phaseprimary cleanup isdropped sinceitisrelated to
reconstructedfrom thesmearedenergiesinthesevirtual
supressionofspuriousprocessesthatwedonotsimulate,
towers.
anditisnearly100% e(cid:14)cientforthesignal.W ealsodrop
thejetelectromagneticfractioncutsoftheILV,because
6 ThefullGEANT4-basedsimulationistooslow toadequatelysam-
ple the entire theory space. Having completed the (cid:12)rst ex-
ploratory phaseofthiswork,wearerepeating theanalysisto 7 Inarealisticfullsimulationstudywiththe(cid:12)rstjetdatainhand,
validatetheseresultswiththefullexperimentalsimulation. ourEmissanalysiswillavoidsuchcompromises.
T
8
theyarenearly100% e(cid:14)cientforthesignal. A. SUSY
Theresulting performanceofourparameterized fast
simulationfortheSUSY benchmarkmodelLM 1isshown In a largeclassofsupersymmetry modelswith con-
inTableII.Theagreementwiththefullsimulationstudy servedR parity,notnecessarilyrestrictedtotheM SSM ,
isvery good. Thelargestsinglecutdiscrepancy is2%; theLSP iseitherthelightestneutralinooraright-handed
thisoccursfortheQCD angularcuts,re(cid:13)ectingtheex- sneutrino8.
pected factthatourfastsimulation doesnotaccurately
In addition, if the NLSP is a neutralino or sneu-
reproduce jetmismeasuremente(cid:11)ects. Since the (cid:12)nal trino and the LSP isa gravitino,the Emiss signature
T
e(cid:14)cienciesagreetowithin 7%,itisplausiblethatlook-
isthesame.M odelsbased on gravity-mediated,gauge-
alikesde(cid:12)ned in ourfastsimulation study willremain
mediated oranomaly-mediated SUSY breaking allpro-
look-alikesinourupcomingfullsimulationstudy.
videmanycandidatemodels.
Itisimportantto notethatthisfastsimulation does BecausethisrelevantportionofSUSY theoryspaceis
notreproducetheStandard M odelbackground e(cid:14)cien- alreadysovast,thereisatemptationtoreducethescope
ciesshown in TableI. In factthediscrepanciesin the oftheLHC InverseProblem by making explicitorim-
totale(cid:14)cienciescan approach an orderofmagnitude. plicittheoreticalassumptions.Totakean extreme,one
Thisisto be expected. W e are cutting very hard on couldapproachanearlyLHC discoveryintheEmisschan-
T
theStandardM odelevents,thustheeventsthatpassare nelhavingalreadymadetheassumptionsthat(i)thesig-
very atypical. Thisisin contrastto thesignalevents, nalisSUSY,(ii)ithasaminimalHiggssector(M SSM ),
wherethefraction thatpassarestillfairly generic,and (iii)ithasgravity-mediated SUSY breaking(SUGRA),
theirET andETmissspectranearthecutsarelesssteeply (iv)thebreakingisminimal(mSUGRA)and (v)100%
falling than thoseofthe background. Since SM back- ofdarkmatteristhermalrelicLSPswith anabundance
groundscannotbeestimated from aPGS levelanalysis, given by extrapolatingstandard cosmology back to the
wetakeourbackgroundsfrom thestate-of-the-artanaly- decouplingepoch.W edon’twanttomakeanysuch as-
sisin[10];thisapproachonlyworksbecausewehavealso sumptions;ratherwewanttotesttheoreticalhypotheses
matchedtheanalysispathusedin[10]. intheLHC discoverydatasetcombinedwithothermea-
Thefullsoftwarechainsweusein ourstudyaresum- surements.
marized in TableIII.Allofthesimulated datasetsin- ForSUSY wehavethebene(cid:12)tofmorethanonespec-
cludean averageof5 pileup eventsadded to each sig- trum calculatorthatcan handle generalmodels,more
nalevent,correspondingtolow luminosityLHC running thanonematrixelementcalculatorandeventgeneration
((cid:24) 1033 cm(cid:0)2s(cid:0)1). scheme,and astandardized interfaceviatheSUSY Les
HouchesAccord(SLHA)[32].Therearestillafew bugs
in thisgrandedi(cid:12)ce,buttheexistingfunctionalitycom-
bined with theability to perform multiplecross-checks
III. POPULATING THE THEORY SPACE putsuswithin sightofwhereweneed to bewhen the
dataarrives.
In Section IIwegavea partialclassi(cid:12)cation ofBSM
modelsaccording to how many new weakly interacting
particlesappearinatypical(cid:12)nalstate.Ourbenchmark B. Little Higgs
Emiss analysisis optimized for the case oftwo heavy
T
weaklyinteractingparticlesperevent,asappliestoSUSY
LittleHiggsmodelsareapromisingalternativetoweak
modelswithconservedR parity,littleHiggsmodelswith
scalesupersymmetry[33]-[37].InlittleHiggsmodels,the
conservedT parityandUniversalExtraDimensionsmod-
Higgsisan approximateGoldstoneboson,with global
elswith conserved K K parity.Thisstudy isa (cid:12)rstat-
symmetriesprotectingitsmass(whichoriginatesfrom a
temptatconstructinggroupsoflook-alikemodelsdrawn
quantum levelbreakingofthesesymmetries)from large
from thisratherlargefractionoftheBSM theoryspace,
radiativecorrections.M anyoftheseLH modelsrequire
and developing strategiesto discriminate them shortly
anapproximateT paritydiscretesymmetrytoreconcile
afteraninitialdiscovery.
LH with electroweak precision data. Thissymmetry is
Onecaveatisthatmodelsfrom othercornersofthe similartoR parity in SUSY models.Thenew LH par-
theoryspacemayalsobelook-alikesoftheonesconsid- ticlesthatwouldbeproducedattheLHC wouldbeodd
eredhere.Forexample,modelswithstrongproductionof underthissymmetry,enforcingthestabilityofthelight-
heavyparticlesthatdecaytoboostedtopquarkscanpro- estparticlethatisoddunderT parity.Thisnew particle
ducehigherET jetsandlargerETmissfrom neutrinosthan isweaklyinteractingandwouldmanifestitselfasmissing
doesStandard M odeltop production. Such look-alike
possibilitiesalsorequirestudy,buttheyarenotamajor
worrysinceourresultsshow thatwehavesomeabilityto
discriminateheavyW IM PSfrom neutrinoseveninsmall 8 Recentanalyses[30,31]haveargued forthephenomenological
datasets. viabilityofsneutrinodarkmatter.
9
TABLE II:Comparison ofcut-by-cutselection e(cid:14)cienciesforourE missanalysisappliedtotheSUSY benchmarkmodelLM 1.
T
\Full"referstothefullsimulationstudy[10,11];\Fast"iswhatweobtainfrom ourparameterized fastsimulation.
Cut/Software Full Fast
Triggerand
Emiss> 200GeV 53.9% 54.5%
T
N (cid:21)3 72.1% 71.6%
j
j(cid:17)j1j(cid:21) 1:7 88.1% 90.0%
d
QCD angular 75.6% 77.6%
Isoleadtrk = 0 85.3% 85.5%
ET;1 > 180GeV,
ET;2 > 110GeV 63.0% 63.0%
H > 500GeV 92.8% 93.9%
T
Totale(cid:14)ciency 12.9% 13.8%
TABLE III:Summaryofsoftwarechainsused in thisstudy.ThelittleHiggsspectrum isbased on [38].PGSCMSisavariation
ofPGS v4[28].
Software/M odels Group1models Group2models
Spectrum generator Isajet v7.69[39]or privatelittleHiggs
orSUSY-HIT v1.1[40]orSuSpect v2.34[41]
M atrixelementcalculator Pythia v6.4[42] MadGraph v4[43]
Eventgenerator Pythia v6.4 MadEvent v4[44]
withBRIDGE[45]
Showeringandhadronization Pythia v6.4 Pythia v6.4
Detectorsimulation PGSCMS v1.2.5 PGSCMS v1.2.5
plusparameterized plusparameterized
corrections corrections
energyattheLHC9. assinglets.ThelightestT oddparticleinthismodelwe
Justasin SUSY,new colored particlesarethedom- labelAH .Itisaheavygaugebosonthatisanadmixture
inantproduction modes. These particlessubsequently ofa heavy copy ofthehyperchargegaugeboson and a
generate high multiplicity (cid:12)nal states through decay heavyW 3 boson.
chainsthatend with thelightestT odd particle.In LH Foreventgeneration,weuseaprivateimplementation
models,thestronglycoupledparticlesareT odd quarks ofthelittlestHiggsmodelwithin MadGraph.Thereisa
(TOQ’s),analogoustothesquarksofSUSY.Theweakly needtogeneralizethistoawiderclassofmodels.
coupledanaloguesofthegauginosareT oddspinonevec-
torbosons(TOV’s). In themodelsconsidered to date,
thereisnoanalogofthegluino:thisisanimportantcon- C. Universalextra dim ensions
sideration in constructingsupersymmetriclook-alikesof
LH models. Universalextradimensionsmodelsarebased on orb-
Inthisstudy,weworkwithaminimalimplementation ifolds ofone or two TeV(cid:0)1 size extra spatialdimen-
ofalittleHiggsmodelwithT paritythatisknownasthe sions[49]-[56]. The(cid:12)ve-dimensionalversion ofUED is
littlestHiggsmodelwith T parity.Thismodelisbased the simplest. Atthe (cid:12)rstlevelofKaluza-Klein (K K )
onaSU(5)=SO(5)patternofglobalsymmetrybreaking. excitations,each Standard M odelboson hasan associ-
EachSM particleexceptthegluonhasanassociatedLH atedpartnerparticle,andeachStandardM odelfermion
partnerodd underT parity.Thereisalsoan extrapair hastwo associated partnerparticles(i.e. a vector-like
oftoppartners,oneT oddandtheotherT even,aswell pair).TheseK K partnersareodd underaK K parity,
theremnantofthebrokentranslationalinvariancealong
the(cid:12)fth dimension.Thisparityisassumedtobeanex-
actsymmetry.Aftertakingintoaccountmasssplittings
9 Thissymmetry may beinexact,orviolated by anomalies[46]. dueto Standard M odelradiativecorrections,one(cid:12)nds
Suchpossibilitiesaremodeldependent[47,48]. thatthelightestK K oddpartnerisnaturallytheweakly
10
interacting partnerofthehyperchargegaugeboson. A benchmarkmodelLM 2;LM 2phasaslightlylargervalue
widevarietyofspectrafortheK K oddpartnerscanbe ofm (360versus350GeV)thanLM 2,whichmakesit
1=2
obtained byintroducingadditionalinteractionsthatare moreofalook-alikeoftheotherGroup1models.
localized attheorbifold (cid:12)xed points;thesechoicesdis-
tinguish genericUED from theoriginalminimalmodel
TABLE IV: Input parameters for the mSUGRA models
of[49].ThesemodelsresembleSUSY.
LM 2p,LM 5and LM 8.Thenotation comformsto[39].The
A publiceventgeneration codebased on a modi(cid:12)ca-
massparametersand trilinearA0 parameterhave unitsof
tionofPythiaisavailableforgeneric5-dimensionalUED
GeV.
models[57].Thereisaneedtogeneralizethistoawider
LM 2p LM 5 LM 8
classofmodels,e.g. 6-dimensionalUED.In ourstudy
wehavenotusedanyUED examples,butwewillinclude m0 185 230 500
them inthefuture. m1=2 360 360 300
A0 0 0 -300
tan(cid:12) 35 10 10
IV. DESCRIPTION OF THE M ODELS sign((cid:22)) + + +
A. Group 1
The(cid:12)velook-alikemodelsofGroup 1 areallM SSM
TABLE V:InputparametersfortheM SSM modelsCS4dand
models.Twoofthem (LM 5 and LM 8)areCM S SUSY
CS6.Thenotationconformsto[40,41].Themassparameters
benchmarkmodels,whileanother(LM 2p)isaslightvari-
andtrilinearA parametershaveunitsofGeV.
ationofaCM S benchmark.Itisasoberingcoincidence
CS4d CS6
thatthesearelook-alikesoftheEmissanalysis,sincethe
T
benchmarksweredevelopedbyCM Stocoverdi(cid:11)erentex- M 1 620 400
perimentalsignatures,notproducelook-alikes.Toround M 2 930 600
outGroup1wefoundtwootherM SSM look-alikeswhose M 3 310 200
spectraanddecaychainsareasdi(cid:11)erentfrom eachother A ;A ;A ;A ;A ;A -400 -300
(cid:28) t b e u d
and from thethreeCM S benchmarksaswecould make
M ;M ;M 340 2000
them. QL tR bR
M ;M ;M 340 2000
Themodelsareconsistentwithallcurrentexperimen- qu uR dR
M ;M ;M ;M 340 340
talconstraints,butdo notallgive the \correct" relic (cid:28)L (cid:28)R eL eR
density ofdark matter. Any comparison ofrelicdensi- M h2u;M h2d 115600 115600
tiestotheso-calledW M AP constraintsassumesatleast tan(cid:12) 10 10
threefactsnotyetinevidence:(i)thatdarkmatterisa sign((cid:22)) + +
thermalrelic,(ii)thatthereisonlyonesigni(cid:12)cantspecies
ofdarkmatterand(iii)thatcosmologicalevolutionwas
entirelyradiation-dominatedfrom thetimeofdarkmat- TheGroup 1modelsCS4d and CS6arenotminimal
terdecouplinguntilthetimeofBigBangnucleosynthe- supergravity;they are more generalhigh scale M SSM
sis.A missingenergydiscoveryattheLHC willhelp us modelsbasedon thecompressedsupersymmetryideaof
testwhethertheseassumptionshaveany validity. For M artin [63,64]. The high scale inputparametersare
example,modelLM 8 producesa relicdensity an order shown in Table V. W e have used m = 175 GeV
top
ofmagnitudelargerthantheW M AP upperbound;thus andthespectrum generatorcombinationSuSpect v2.34
discriminating LM 8 asa morelikely explanation ofan with SUSY-HIT v1.1 [40,41]. M odelCS4d isin fact
early missing energy discovery would callinto question partofthecompressedSUSY modellinede(cid:12)nedin[63].
[58,59]assumptions(i)and(iii),orcouldbeahintthat M odelCS6isamodi(cid:12)cationofcompressedSUSY where
thelightestneutralinoisnotabsolutelystable. allofthesquarkshavebeenmadeveryheavy,>(cid:24) 2TeV.
LM 2p,LM 5and LM 8areminimalsupergravitymod- ThesuperpartnermassspectraoftheGroup1models
els[60]-[62]. They arespeci(cid:12)ed by theusualhigh scale aredisplayedinFigure5.Onenotesimmediatelythatall
mSUGRA inputparametersasshown in TableIV;be- ofthemSUGRA modelsaremoresimilartoeach other
causetheresultingsuperpartnerspectradependstrongly thantheyaretoeitherofthemoregeneralM SSM mod-
onRGE runningfrom thehighscale,acompletespeci(cid:12)- elsCS4dandCS6;thisshowsthelimitationsoftheusual
cation ofthemodelsalso requires(cid:12)xing thetop quark SUSY analysesthat do notgo beyond mSUGRA.As
mass and the particular spectrum generator program theirnameimplies,thecompressed SUSY modelsCS4d
used. W ehaveused m = 175 GeV and theISAJET andCS6haveacompressedgauginospectrum relativeto
top
v7.69generator[39],inordertomaintaincompatibility mSUGRA;thisproduceseitheralightgluino(asinCS6)
withtheCM SPhysicsTDR [10].M odelsLM 5andLM 8 oraheavyLSP (asinCS4d).
arethenidenticaltothemSUGRA benchmarkmodelsof The relative frequency ofvariousLHC superpartner
theCM SPhysicsTDR,whileLM 2pisalmostidenticalto productionprocessesissummarizedinTableVI,forthe