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Search for Resonant Production of Top Antitop Pairs Decaying into Multi-Jets at the Collider Detector at Fermilab

Permanent Link: http://ufdc.ufl.edu/UFE0041141/00001

Material Information

Title: Search for Resonant Production of Top Antitop Pairs Decaying into Multi-Jets at the Collider Detector at Fermilab
Physical Description: 1 online resource (103 p.)
Language: english
Creator: Oksuzian, Iuri
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: Physics -- Dissertations, Academic -- UF
Genre: Physics thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: We performed a search for top-antitop resonances in the all jets final state channel. The main goal was to examine top-antitop invariant mass spectrum for the presence of narrow resonant states. The data analysis used 2.8/fb of CDF data; events were produced at the Tevatron collider in proton antiproton collisions with center-of-mass energy of 1.96 TeV. 2086 data events were analyzed and compared to Standard Model expectation. No evidence for new resonant production mechanisms was found. Upper limits were placed on the cross-section times branching ratio for resonance production at 805 GeV. For signal modeling we considered leptophobic Z' boson in a topcolor-assisted technicolor model with the width of 1.2% of its mass.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Iuri Oksuzian.
Thesis: Thesis (Ph.D.)--University of Florida, 2009.
Local: Adviser: Konigsberg, Jacobo.
Local: Co-adviser: Korytov, Andrey.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2010-06-30

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0041141:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041141/00001

Material Information

Title: Search for Resonant Production of Top Antitop Pairs Decaying into Multi-Jets at the Collider Detector at Fermilab
Physical Description: 1 online resource (103 p.)
Language: english
Creator: Oksuzian, Iuri
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: Physics -- Dissertations, Academic -- UF
Genre: Physics thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: We performed a search for top-antitop resonances in the all jets final state channel. The main goal was to examine top-antitop invariant mass spectrum for the presence of narrow resonant states. The data analysis used 2.8/fb of CDF data; events were produced at the Tevatron collider in proton antiproton collisions with center-of-mass energy of 1.96 TeV. 2086 data events were analyzed and compared to Standard Model expectation. No evidence for new resonant production mechanisms was found. Upper limits were placed on the cross-section times branching ratio for resonance production at 805 GeV. For signal modeling we considered leptophobic Z' boson in a topcolor-assisted technicolor model with the width of 1.2% of its mass.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Iuri Oksuzian.
Thesis: Thesis (Ph.D.)--University of Florida, 2009.
Local: Adviser: Konigsberg, Jacobo.
Local: Co-adviser: Korytov, Andrey.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2010-06-30

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0041141:00001


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Firstofall,Iwouldliketoexpressmysinceregratitudeanddeepappreciationtomyadvisors,Prof.JacoboKonigsbergandProf.AndreyKorytov,fortheirexpertise,constantguidance,support,encouragementandinspiringdiscussions.Inparticular,IwanttomentionAndrey'spricelesshelpintheearlyyearsofmygraduatestudiesandJacobo'sdedicationtohisworkandcommitmenttohisstudents.Thesepeopletremendouslyhelpedmetodevelopasthephysicist.IwouldliketotakethisopportunitytothankDr.RobertoRossinandDr.AlexanderSukhanovforsharingtheirknowledgeindetectoroperations.Withouttheirclearexplanationsandsupport,Iwouldnotbeabletoappreciatethebeautyofthehardwarepartinhighenergyphysics.Theyaswellcontributedindevelopingtools,whichwerewidelyusedinmyanalysis.IalsothankallmyfriendsfromTbilisiStateUniversityandfromhighschool,whoarenowscatteredallovertheworld,butstillkeepintouch.Inparticular,IwillbeforevergratefultoSergoJindarianiandNicholasSambelashvili,whohelpedinmanyaspects.Onlywiththeirhelpandsuggestions,IwasabletoentergraduateschoolatUniversityofFloridaandtohaveagreatopportunityworkonmyfavoritesubject.TheinuenceIreceivedfromthemhelpedmetodevelopasthebetterphysicistandpersoningeneral.IwouldliketomentionallthefriendsImetinGainesville,VictorBarashkoandArtemNahapetyaninparticular.DuringmytimeatCDF,IdrewmuchknowledgefrominteractingwithmanypeoplesuchasDr.FabrizioMargaroli,Dr.FlorenciaCanelli,Dr.DanielWhiteson,Dr.NathanGoldschmidt,Dr.AlexandrePronkoandDr.SongMingWang,whohelpedmegreatlygettinguptothespeedoftheexperimentalphysicsatCDF.AlsoIwanttomentionandthankJimLunguformanyinterestingdiscussionsduringourregularworkoutswehad. 4

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page ACKNOWLEDGMENTS ................................. 4 LISTOFTABLES ..................................... 8 LISTOFFIGURES .................................... 9 ABSTRACT ........................................ 11 CHAPTER 1INTRODUCTION .................................. 12 1.1HistoryofElementaryParticlePhysics .................... 12 1.2TheStandardModel .............................. 15 1.3BeyondtheStandardModel .......................... 17 1.4TopQuarkPhysics ............................... 18 2EXPERIMENTALAPPARATUS .......................... 25 2.1Accelerator ................................... 25 2.1.1ProtonSource .............................. 25 2.1.2MainInjector .............................. 26 2.1.3AntiprotonSource ............................ 26 2.1.4Tevatron ................................. 27 2.2TheCDFIIDetector .............................. 28 2.2.1TrackingandVertexingSystems .................... 29 2.2.2Calorimetry ............................... 33 2.2.3OtherSystems .............................. 34 2.2.4TriggerSystemandDataAcquisition ................. 38 2.2.5GoodRunRequirements ........................ 39 2.3JetReconstruction ............................... 40 2.3.1JetClustering .............................. 40 2.3.2JetCorrections ............................. 42 3DATASAMPLEANDEVENTSELECTION ................... 52 3.1DataandMonteCarloSamples ........................ 52 3.2EventSelection ................................. 53 3.2.1NeuralNet ................................ 56 3.2.2QCDBackgroundModeling ...................... 58 4FLAMEALGORITHM ............................... 70 4.1ConstructionoftheLikelihood ......................... 70 4.2TheMatrixElements(ME) .......................... 71 6

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.............. 73 4.4TransferFunctions ............................... 73 4.4.1MttReconstruction ........................... 74 4.4.2SignalandBackgroundTemplates ................... 75 5SENSITIVITY .................................... 78 5.1UpperLimitSettingandSensitivityCalculation ............... 78 5.2Method ..................................... 78 5.3Implementation ................................. 80 5.3.1Templates ................................ 80 5.3.2TemplatesWeighting .......................... 80 5.3.3Z'ContaminationinQCDTemplate .................. 81 5.3.4DataStructureandAlgorithm ..................... 81 5.3.5CalculationofPosterior ......................... 82 5.3.6CrossSectionMeasurement&LimitCalculation ........... 82 5.4SystematicErrorsAccounting ......................... 83 5.4.1ShapeSystematics ............................ 84 5.4.2JetEnergyScale ............................. 84 5.4.3ISR&FSR ............................... 84 5.4.4PDFsUncertainty ............................ 85 5.4.5OverallShapeSystematicUncertainties ................ 85 5.4.6IncorporatingtheShapeSystematics ................. 85 5.4.7ExpectedSensitivityWithShapeSystematics ............ 86 6RESULTS ....................................... 93 6.1Conclusion .................................... 94 REFERENCES ....................................... 99 BIOGRAPHICALSKETCH ................................ 103 7

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Table page 1-1Listofmostimportantparticlediscoveriesledtodeeperinsightintheunderstandingofnature ....................................... 23 1-2Threequarkgenerations ............................... 23 1-3Threeleptongenerations ............................... 23 1-4Forcecarriers ..................................... 24 2-1SummaryofthecurrentTevatronperformancecharacteristics. .......... 28 2-2SummaryofquantitiescharacterizingCDFcalorimetry. .............. 34 3-1ttdecaychannels.lcorrespondstoelectronormuononly ............ 52 3-2Numberofeventsinthemulti-jetdataaftertheclean-upcutsandtagging.TheintegratedluminosityisL=2.8fb1. ........................ 55 3-3NumberofeventsintheSMt tMonteCarlosample. ................ 56 3-4NumberofeventsintheMX0MonteCarlosamples. ................ 56 3-5TableofacceptancesforMX0MonteCarlosamples. ................ 58 4-1Denitionofthebinninginpartonpseudo-rapidityforthetransferfunctionsparame-terization. 74 8

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Figure page 1-1Negativelogprobability ............................... 22 2-1OverviewoftheFermilabacceleratorcomplex.Thechainconsistsofseveralindividualcomponents:ProtonSource(Cockcroft-Walton,LinacandBooster),MainInjector,AntiprotonSource(Debuncher,AccumulatorandRecycler)andtheTevatron.Thedetectors,CDFandD0,arealsoshown. .................... 43 2-2BeamstructureattheTevatron. ........................... 44 2-3ThetotalintegratedluminositydeliveredbytheTevatronfromthebeginningofRunIIwhichstartedinApril2001. ......................... 44 2-4Theschematiccross-sectionviewoftheCDFdetector. .............. 45 2-5Theschematicr{zviewofonequadrantoftheCDFtrackingsystem.Itscomponents:CentralOuterTracker(COT)andthesilicondetectors:Layer00(L00),SiliconVertexDetector(SVX),andIntermediateSiliconLayers(ISL)areshown. .... 46 2-6TransverseviewofthenominalcelllayoutforCOTsuperlayer2.Thearrowshowstheradialdirection.Theelectriceldisroughlyperpendiculartotheeldpanels.Themagneticeldisperpendiculartotheplane.Theanglebetweenwire-planeofthecentralcellandtheradialdirectionis35. ........... 47 2-71=6thoftheCOTeastendplate.Shownarethewire-planeslotsgroupedintoeightsuperlayers. ................................... 47 2-8SVXbulkheaddesign.Placementofladdersisshownintwoadjacentwedges. 48 2-9Schematicpictureofonequadrantoftheplugcalorimeterincludingtheelectromagneticandhadronicparts.Theplugcalorimeterhasfull2coverageandextendsto1:1
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.............................. 60 3-3Neuralnetinputvariables .............................. 61 3-4NeuralnetStructure ................................. 62 3-5Neuralnettraining .................................. 62 3-6Neuralnettraining .................................. 62 3-7Neuralnettraining .................................. 63 5-1Linearitytest.Thetopplotsshowtheinputversusthereconstructedcrosssectionafter1000PEsatintegratedluminosityRL=1000pb1.Bottomplotsshowsdeviationfromlinearityinexpandedscale.Weestimatethedeviationtobeabout2%(Reddottedline). ................................. 86 5-2Posteriorprobabilityfunctionforthesignalcrosssection.Themostprobablevalueisassumedasestimatorforthecrosssection.Fromtheposteriorwealsoextract95%CLupperlimitandlowerlimit.Theredarrowandthequotedvaluecorrespondtothe95%CLUL0. ........................... 87 5-3CrosssectionshiftduetoJESuncertaintyforluminosityscenariosRL=2:8fb1.TheshiftisassumedtobetheuncertaintyonthecrosssectionduetoJES. ..... 88 5-4CrosssectionshiftduetoISRandFSRuncertainties. ............... 89 5-5Totalshapesystematicuncertaintyversusinputsignalcrosssection. ....... 90 5-6Posteriorprobabilityfunctionforhesignalcrosssection.Thesmearedp.d.f.(green)showsalongertailthantheunsmearedone(black).AsaconsequencetheUL0quotedontheplotisshiftedtohighervalueswithrespecttotheonecalculatedonunsmearedposterior. ......................... 91 5-7Upperlimitsat95%CL.Thecurvesshowstheresultsfortwoluminosityscenariosandbothincludingorexcludingthecontributionfromshapesystematicuncertainties. 92 10

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1-1 15

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1-2 and 1-3 .Theforce-mediatingparticlesdescribedbytheStandardModelallhaveanintrinsicspinwhosevalueis1,makingthembosons.Asaresult,theydonotfollowthePauliExclusionPrinciple.Thephotonsmediatethefamiliarelectromagneticforcebetweenelectricallychargedparticles(thesearethequarks,electrons,muons,tau,W-boson).Theyaremasslessandaredescribedbythetheoryofquantumelectrodynamics.TheWandZgaugebosonsmediatetheweaknuclearinteractionsbetweenparticlesofdierentavors(allquarksandleptons).Theyaremassive,withtheZ-bosonbeingmoremassivethantheW-boson.Thesethreegaugebosonsalongwiththephotonsaregroupedtogetherwhichcollectivelymediatetheelectroweakinteractions,asdescribedbytheGlashow-Salam-Weinberg(GSW)theory.Eachquarkcarriesanyoneofthreecolorcharges-red,greenorblue,enablingthemtoparticipateinstronginteractionsmediatedbytheeightgluons.Gluonsaremassless.Theeight-foldmultiplicityofgluonsislabeledbyacombinationsofcolorandananticolorcharge.Becausethegluonhasaneectivecolorcharge,theycaninteractamongthemselves.Thegluonsandtheirinteractionsaredescribedbythetheoryofquantumchromodynamics(QCD).Thepropertiesofgaugebosonsaresummarizedinthetable 1-4 16

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1 ].Inthismechanism,thelocalSU(2)LU(1)Ysymmetryoftheelectroweakinteractionsisspontaneouslybroken.Thisaspectofthetheorycorrectlypredictstheexistenceoftheweakgaugebosonsaswellastheratiooftheirmasses.Italsopredictstheexistenceofaspin0particle:theHiggsboson.ThesearchfortheStandardModelHiggsbosonremainsoneofthetopprioritiesattheTevatronandthefutureLHCexperiments.Todate,almostallexperimentaltestsofthethreeforcesdescribedbytheStandardModelhaveagreedwithitspredictions.ThemostimpressiveistheagreementbetweenthepredictedandmeasuredvaluesoftheWandZgaugebosonsmasses.TheStandardModelpredictionshavealsoleadtothediscoveryoftopquarkattheTevatron.Still,theStandardModelfallsshortofbeingacompletetheoryoffundamentalinteractions,primarilybecauseofitslackofinclusionofgravity,butalsobecauseofthelargenumberofnumericalparameters(suchasmassesandcouplingconstants)thatmustbeput\byhand"intothetheoryratherthanbeingderivedfromrstprinciples. 17

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2 ].Theexistenceofanisospinpartnerfortheb-quarkisstronglymotivatedbyargumentsoftheoreticalconsistencyoftheStandardModel,absenceofavorchangingneutralcurrentinBmesondecaysandstudiesofZbosondecays[ 3 ].However,thelargemassofthetopquark,nearly175GeV/c2,wasinitselfasurpriseatthetime.Inthisregard,thetopquarkseparatesitselffromallotherquarks.Forexample,itisthemostmassivefermionbyafactorofnearly40(thebottombeingtheclosestcompetitor). 18

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36 ]of4.8pbat176GeV=c2.Theapparentdisagreementbetweentheoreticalandexperimentalvalueshasvanishedwiththemostrecenttheoreticalcalculationandthe2002-2009measurement(RunII)performedcombiningthevariousdecaymodes,ascanbeseeninFig. 1-1 10 ].ThetotalintegratedluminosityincludedinCDF'sanalysisis3.2fb1andD0'sanalysishas2.3fb1.ABayesiananalysisisusedtoextractthecrosssectionfromthedistributionsofmultivariatediscriminantsprovidedbythecollaborations.Foratopquarkmassmt=170GeV=c2,theymeasureacrosssectionof2:76+0:580:47pb.TheyextracttheCKMmatrixelementjVtbj=0:880:07witha95%C.L.lowerlimitofjVtbj>0:77. 19

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Figure1-1. CombinationofPreliminaryResultscomparedtotheoreticalpredictionsasafunctionoftopquarkmass.Atopquarkmassvalueof172.5GeVisassumedfortheexperimentalresult 22

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Year NobelPrize Method Thomson Dischargeingases Rutherford Naturalradioactivity Chadwick Naturalradioactivity Anderson CosmicRays Neddermeyer,Anderson CosmicRays Powell,Occhialini CosmicRays Powell CosmicRays Bjorklund Accelerator Armenteros CosmicRays Cowan,Reines Nuclearreactor Lederman Accelerator 1975 Ting,Richter Accelerator Perl Accelerator (bquark) 1977 none(E288collaboration) Accelerator Rubbia,vanderMeer Accelerator 1995 none(CDF&D0collaboration) Accelerator none(DONUT(E872)collaboration) Accelerator Table1-1. Listofmostimportantparticlediscoveriesledtodeeperinsightintheunderstandingofnature Quark Electriccharge(e) Mass(MeV=c2) +2/3 1.4-4 -1/3 4-8 -1/3 80-130 +2/3 1:151:35103 -1/3 4:14:9103 +2/3 173:1103 Threequarkgenerations Lepton Electriccharge(e) Mass(MeV=c2) 0.51099892 105.658369 1777 Table1-3. Threeleptongenerations 23

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Spin(e) Mass(GeV=c2) 0 1 0 80.40 91.188 graviton 2 ? 1 ? Table1-4. Forcecarriers 24

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2-1 25

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2-2 .Theantiprotonsareusuallyinjectedaftertheprotonsandtheirbunchensembleisthemirrorimageoftheprotonspacing.Therateofproducedeventsforaparticularprocessdirectlydependsoninstantaneousluminosity(i.e.theintensityofcollidingprotonandantiprotonbeams).Theinstantaneousluminosityisdened: whereNBisthenumberofbunches;NpandNparenumberofprotonsandantiprotonsperbunch,respectively;fisthebunchrevolutionfrequency;andpandparetheaveragecross-sectionalareasofthebunches.Makingp,psmallerandNp,Nplargerincreasestherateofcollisions.Itisachievedbyfocusingthebeamsdirectlybeforeimpact,usingthesocalledlow-betaquadrupolemagnets.Duringastoretheinstantaneousluminosityisdecreasingexponentiallyduetocollisionsandtransversespreadingofthebeamswhichleadstolossesofprotonsandanti-protons.Typicalstoredurationisabout20hours.SummaryofthecurrentTevatronperformancecharacteristicsisgiveninTable 2-1 .ThetotalintegratedluminositymeasuredatCDFisshowninFig. 2-3 fromthebeginning 27

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SummaryofthecurrentTevatronperformancecharacteristics. center-of-massenergy1.96TeVbunchcrossingseparation396nsnumberofprotonsperbunch240109numberofantiprotonsperbunch25109peakluminosity3501030cm2s1 22 ],whichisamulti-purposedetector;itisdesignedtostudyawiderangeofphysicsprocessesproducedatproton-antiprotoninteractionsandcharacterizedbynalstateswithhightransversemomentaparticles.Thedetectorisroughlycylindricallyandbackward-forwardsymmetricaroundthebeamaxis.Itisabout10metershigh,extendsabout27metersfromendtoend,andweightsover5000tons.ThelayoutofCDFisshowninFig. 2-4 .CDFhasthefollowingcoordinatesystem:thezaxiscoincideswiththedirectionoftheprotonbeam,thexaxispointsradiallyoutwardtheacceleratorring,andtheyaxispointsverticallyup.Thecenterofthecoordinatesystemroughlycoincideswiththecenterofthebeamcrossingpoint.Wecanaswellthemoreconvenientpolar(r;;)coordinatesystem,whereiscountedfromthepositivedirectionofthezaxis,andismeasuredwithrespecttothepositivedirectionofthexandyaxisrespectively.Commonly,isreplacedbythepseudo-rapidity,(): 28

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2lnE+pz isinvariantunderLorentztransformations.Intheultra-relativistic/masslessparticlelimit,therapiditycanbereplacedbythepseudo-rapidity. 29

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2-5 .Thecomponentsaredescribedindetailsbelow.CentralOuterTrackerTheCentralOuterTracker(COT)[ 23 ]isananchorofCDFstrackingsystem.Itisacylindricalopen-celldriftchamberwithalargetrackingvolume,designedtomeasurethethree-dimensionaltrajectoriesofchargedparticlesinthecentralregion,jj<1:0.TheCOToccupiestheradialregion40to138cm,andmeasures310cmalongthe^zaxis.Itislledwithwithfastgas(50%argon,50%ethane)tomakedrifttimessmallenoughsothatthehitscanbereadoutbetweeneachTevatronbunchcrossing.ThebasicelementoftheCOTisthecell,whichspansthelengthoftheCOT.Withineachcellarehigh-voltageeldpanels,potentialwiresandshaperwireswhichservetosupportaregularelectrostaticeld.Chargedparticlestravelingthroughthegasmixtureleaveatrailofionizationelectrons.Theseelectronsdrifttowardthesensewiresbyvirtueoftheelectriceldcreatedbytheeldpanelsandpotentialwires.Becauseofthemagneticeldalongthe^zaxis,thedriftisnotinthedirectionoftheelectriceld.Insuchcrossedeldselectronsmoveintheplaneperpendiculartothemagneticeldandatananglewithrespecttotheelectriceld.Thevaluesofdependsonthemagnitudeofbotheldsandthegasproperties,intheCOTitis35.Sincetheelectrondriftvelocityisknown,thepositionofthetrackcanbeaccuratelymeasuredbysimplyrecordingthetimeoftheresultingcurrentonthesensewires.AtransverseviewofatypicalcellwiththepositionsofindividualwiresisshowninFig. 2-6 .ThecellsoftheCOTarearrangedintoeightradiallyspacedsuperlayers.Fourofthemhavetheirwiresarrangedparalleltothe^zaxis,allowingtrackmeasurementsintherplane.Otherfoursuperlayershavetheirwirestiltedby2allowingtorecordstereoinformation,trackmeasurementsintherzplane.Thesuperlayergeometryisshownin 30

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2-7 .ThehitpositionresolutionofCOTisapproximately140m,whichtranslatesintothetransversemomentumresolutionpT 23 ].Theprimarypurposeofthesilicondetectorsistoprovideexcellentspatialresolutionforthecharged-particletracks.Thisiscrucialforreconstructionofthedisplacedsecondaryvertexes,and,therefore,identicationofbjets.Theprincipleonwhichthesilicontrackingisbasedissomewhatsimilartothatofthedriftchamber.Whenachargedparticlegoesthroughthesilicon,itionizestheatoms,producingelectronsandholes-theremainingsiliconatomsmissinganelectron.Intheelectriceldelectronstraveltoonesideandtheholesintheother,leavinganelectricsignalthatcanberecorded.Duetothenarrowwidthofthestrips,thesilicondetectorshavemuchbetterresolutionthanCOT.Toprovideexcellentspacialresolutionsilicondetectorshavetobepositionedasclosetothebeamaspossible,imposinganadditionalrequirement,thatthedetectorshouldbeabletowithstandlargedosesofradiationintheregionclosetothebeam-pipe.Layer00isasingle-sidedradiationhardsiliconmicrostripdetector.Itismounteddirectlyonthebeampipe,attheinnerradiusof1.15cmandanouterradiusof2.1cm,soastobeascloseaspossibletotheinteractionpoint.Itcoversjj<4:0.L00isdesignedtoenhancethetrackimpactparameterresolution(theimpactparameterd0isdenedastheshortestdistanceintherplanebetweentheinteractionpointandthetrajectoryoftheparticleobtainedbythetrackingalgorithmt).Therearesixreadoutmoduleswithtwosensorsbondedtogetherineachmodule.TheSiliconVertexDetectoriscomposedofvelayersofdouble-sidedsiliconmicrostripdetectors,itcoversradialcoveragefrom2.5to10.6cmandjj<2:0.SVXisbuiltinthreecylindricalbarrelseach29cmlong.Onesideofeachmicrostrip 31

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2-8 .TheprimarygoaloftheSVXistodetectsecondaryverticesfromheavyavordecays.ThesecondarygoalistomaximizetrackingperformancebycombiningtheCOTandSVXhitinformation.ThealignmentoftheSVXdetectorisveryimportantforthetrackreconstruction,everyeortismadetopositiontheSVXbarrelsinacoaxialmanner.TheprocessofcombinedCOTandSVXtrackreconstruction[ 24 ]startsinCOT.AfterCOT-onlytrackisreconstructed,itisextrapolatedthroughtheSVX.Becausethetrackparametersaremeasuredwithuncertainties,thetrackismorelikeatubeofcertainradius,determinedbytheerrorsontracksparameters.AteachSVXlayer,hitsthatarewithinacertainradiusareappendedtothetrackandthere-ttingisperformedtoobtainthenewsetofparametersforthetrack.InthisprocesstheremaybeseveraltrackcandidatesassociatedtotheoriginalCOT-onlytrack.Thebestoneintermsofthenumberofhitsandtqualityisselectedattheend.TheimpactparameterresolutionoftheSVXisabout40m.Theresolutioninzisabout70m.Inthecentralregion,asingleISLlayerisplacedataradiusof22cm.Intheplugregion,1:0
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2-9 ).ThecalorimetrydetectorsatCDF[ 23 ]aremechanicallysubdividedintothreeregions:central,wallandplug.Theyarelocatedjustoutsidethesolenoidmagnetinthecentralregion,andjustoutsidethetrackingvolumeintheplugregion.TheelectromagneticandhadroniccomponentsarecalledtheCentralElectro-Magnetic(CEM),CentralHadronic(CHA),WallHadronic(WHA),PlugElectromagnetic(PEM)andPlugHadronic(PHA)calorimeters.TheCEMisdividedinto15wedgesisazimuthalangleandintotentowerssubtending0.1unitsofpseudorapidity.Itconsistsofalternating1=8inchabsorberlayers,madeofaluminum-cledlead,and5mmlayersofpolystyrenescintillator,foratotaldepthof18radiationlengthsofmaterial.EmbeddedintheCEMattheapproximatedepthofmaximumshowerdevelopmentareproportionalwirechambers,CentralElectromagneticStrip(CES).Withthepositionresolutionof2mm,theycontributetoe=identication,usingthepositionmeasurementtomatchwithtracks.Asecondsetofproportionalchambers,theCentralPreshower(CPR),islocatedbetweentheCEMandthemagnetcoil,andprovidegreatlyenhancedphotonandsoftelectronidentication. 33

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SummaryofquantitiescharacterizingCDFcalorimetry. NameCoverageThicknessMaterialResolution(EinGeV) CEMjj<1:119X03mmPb,5mmScint.13:5%=p CHAjj<0:94.7025mmFe,10mmScint.75%=p TheCHAconsistofalternatinglayersofironabsorberandnaphthalenescintillator.TheyaresegmentedtomatchtheCEMtowers,0.1unitsofpseudorapiditypertowerand15ofazimuthperwedge,withatotalthicknessof4.7nuclearinteractionlengths.TheWHAisdesignedtocompensatethelimitedforwardcoverageoftheCHA,andcoverstheregion0:7
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23 ]:CentralMuonDetector(CMU),CentralMuonUpgrade(CMP),CentralMuonExtension(CMX)andIntermediateMuonDetector(IMU).TheCDFmuondetectorsconsistofstackedargon-ethanedrifttubes,somebackedupwithscintillatorcounters.Muonswhichpassthroughthedrifttubesleaveatrailofionizedgasalongtheirtrajectory;muonswhichpassthroughthescintillationpanelsinducelightpulseswhicharecollectedbyPMTs.TheCMUdetectorconsistsoffourlayerdriftchamberdirectlybehindthehadroniccalorimeter.Thelayersaredividedintorectangulardriftcellseachwithasinglesensewire.Thedetectorcoversjj<0:6anddetectsmuonswithaminimumpTof1.4GeV/c.TheCMPsitsbehindanadditional60cmlayerofsteelandisalsocomposedoffourlayersofindividualdriftcellscoveringjj<0:6.TheCMPdetectsmuonsdowntopTof2.2GeV/c.TheCMX,composedofconicalsectionsofdriftchambersandscintillationcounters,extendsthemuonjjcoveragefrom0.6to1.0,whilemeasuringmuonswithaminimumpTof1.4GeV/c.Finally,theIMU,whichwasapartofCDFRunIIupgrade,extendsmuoncoverageouttojj<1:5.TheIMUisalsocomposedofdriftcellsandscintillatorcounters,detectsmuonwithminimumtransversemomentum1:42:0GeV/c.Havingatracksegment(stub)inthemuonchambersisnotsucientformuondetection.Stubscanbeduetoahadronicpunch-throughorjustnoiseintheelectronics.OnlyifastubmatchesacertaintrackmeasuredbytheCOTthenthetwoarecombinedtomakeamuon.CherenkovLuminosityCounters

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25 ]atCDFinRunIIistomeasuretheluminosity.CLCsuccessfullyprovidesprecisemeasurementsatcurrentpeakinstantaneousluminositiesof31032cm2s1.TheCLCutilizestheeectknownasCherenkovradiation.Whenachargedparticletravelsinamediumfasterthespeedoflightinthismedium(i.e.when=v=c>1=n,wherenistherefractionindexofthemedium),itstartsemittinglightintoaconearounditsdirection.Cone'sopeningangledependsontheratioofthetwospeedsandtherefractionindex.Thedetectorconsistsoftwomodules(EastandWest)locatedwithinthe\3-degreeholes"insidetheforwardandbackwardcalorimeters,itcoverspseudorapidityrange3:75
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Theprobabilityofhavinganemptybunchcrossingisthen: Thus,measurementoftheprobabilityofhavinganemptycrossingisenoughtodeterminetheaveragenumberofinteractions,and,consequently,thevalueofinstantaneousluminosity.Thisprobabilityismeasuredbydividingthenumberofemptycrossings(correctedforthedetectoracceptance)bythetotalnumberofbunchcrossingsinacertaintimeinterval.ForacrossingtobeconsideredemptythereshouldbenohitsineitherEastorWestCLCmodules.Thedisadvantageofthismethodisthatatveryhighluminositiestheprobabilityofhavinganemptycrossingissmall,makingitdiculttomaintaingoodprecision.Time-of-FlightTheTime-of-Flightsystem(TOF)expandsCDFsparticleidenticationcapabilityinthelowpTregion.TOFmeasuresarrivaltimetofaparticlewithrespecttothecollisiontimet0.Theparticlemassmisthendeterminedusingtherelation: cr whereListhepathlengthandpisthemomentummeasuredbythetrackingsystem.TOFhascylindricalgeometrywith2coverageinandroughlyjj<1inpseudorapidity.Itconsistsof216scintillatorbarsinstalledataradiusofabout138cminthe4.7cmspacebetweentheoutershelloftheCOTandthecryostatofthe 37

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26 ]. 2-11 .Theelaboratedescriptionoftheentiresystemisgivenin[ 23 ].TheLevel-1(L1)isasynchronoussystemwithaneventreadinandanacceptorrejectdecisionmadeeverybunchcrossing.WithintheDAQelectronicsofeachdetectorcomponent,thereisa42\bucket"datapipeline.ThepipelineissynchronizedwiththeTevatronmasterclock,whichhasaperiodof132ns.Eventdatafromeachproton-antiprotonbunchcrossingentersthepipeline.Adecisionmustbemadebeforethedatareachestheendofthepipeline,otherwisethedataislost.ThedecisiontimeforL1is5.5sanditisbasedonthedatafromthecalorimeters,theCOTandthemuonchambers.Thecalorimeterstreamdecisionisbasedupontheenergydepositedincalorimetertowers,alongwiththemagnitudeofunbalancedtransverseenergy.TheExtremelyFastTracker(XFT)[ 27 ]usesinformationfromtheCOTtoreconstructtracks,eventsareacceptedorrejectedbasedonthetrackmultiplicityandtransversemomenta.ThemuonstreamusesinformationfromtheXFTtomatchtrackstohitsinthemuonchamberstoproducemuoncandidates.ThemaximumacceptrateforL1triggeris20kHz,afactoroffewhundredsmallerthantheinputrateof2.5MHz.EventswhichmeettherequirementsoftheL1triggerarepassedtotheLevel-2(L2).AtL2,aneventiswrittenintooneoffourbuerswithintheDAQelectronicsforeachdetectorcomponent.ThesebuersaredierentfromthedatapipelineusedinL1,thedatahereremainsinthebueruntilthedecisionismade.Whileeventdataarebeingprocessed,theycannotbeoverwrittenbyanothereventfromL1.IfanL1acceptoccurs 38

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39

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28 ],aconealgorithmcombiningobjectsbasedonrelativeseparationinspace;MidPoint,analgorithmsimilartoJetClubuthavingsomemodications;andKT[ 29 ],analgorithmcombiningobjectsbasedontheirrelativetransversemomentumaswellastheirrelativeseparationinspace.TheJetClualgorithmwasusedinthemeasurementspresentedinthisdissertation. 40

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Thetowercentroid(i;i)isobtainedby: whereEEMTiandEHATiaretransverseenergiesdepositedintheelectromagnetic(EM)andhadronic(HA)partsofthei-thcalorimetertower,respectively.Inthenextstep,alltowerswithET>0:1GeVwithinR=p 41

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where(i;i)istheangularpositionofthei-thcalorimetertower. 30 ].Therststepistocorrectforthe-dependenceofthecalorimeterresponse.Thiscorrectionisespeciallyimportantintheregionswithsignicantnon-uniformitiesanduninstrumentedregions,suchasbetweentwohalvesofthecentralcalorimeter,orbetweencentral,wallandplugcalorimeters.Thecorrectionisbasedonagoodunderstandingofthecentralregionofthecalorimeter.Theideasisthatinaneventwithonlytwojets,theirtransverseenergiesshouldbebalanced.ThepTofa\probe"jet,anywhereinthecalorimeteriscomparedtothepTofa\trigger"jetinthecentralregion,awayfromuninstrumentedregions,0:2
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OverviewoftheFermilabacceleratorcomplex.Thechainconsistsofseveralindividualcomponents:ProtonSource(Cockcroft-Walton,LinacandBooster),MainInjector,AntiprotonSource(Debuncher,AccumulatorandRecycler)andtheTevatron.Thedetectors,CDFandD0,arealsoshown. carefultuningofthedetectorsimulation,basedon\insitu"calibrationsusingdatatracksatlowenergiesandtestbeamdataathighenergies.ThecorrectionisafunctionofpT.Finally,thesocalled\out-of-cone"correctionaccountfortheparticle-levelenergyleakageofradiationoutsidetheclusteringcone.Itcorrectsthejetenergybacktotheparentpartonenergy.ThecorrectionisbasedontheratiosofjetandparentpartonenergiesobtainedfromtheMonteCarlo. 43

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BeamstructureattheTevatron. Figure2-3. ThetotalintegratedluminositydeliveredbytheTevatronfromthebeginningofRunIIwhichstartedinApril2001. 44

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Theschematiccross-sectionviewoftheCDFdetector. 45

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Theschematicr{zviewofonequadrantoftheCDFtrackingsystem.Itscomponents:CentralOuterTracker(COT)andthesilicondetectors:Layer00(L00),SiliconVertexDetector(SVX),andIntermediateSiliconLayers(ISL)areshown. 46

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TransverseviewofthenominalcelllayoutforCOTsuperlayer2.Thearrowshowstheradialdirection.Theelectriceldisroughlyperpendiculartotheeldpanels.Themagneticeldisperpendiculartotheplane.Theanglebetweenwire-planeofthecentralcellandtheradialdirectionis35. Figure2-7. 1=6thoftheCOTeastendplate.Shownarethewire-planeslotsgroupedintoeightsuperlayers. 47

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SVXbulkheaddesign.Placementofladdersisshownintwoadjacentwedges. 48

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Schematicpictureofonequadrantoftheplugcalorimeterincludingtheelectromagneticandhadronicparts.Theplugcalorimeterhasfull2coverageandextendsto1:1
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TheCherenkovLuminosityCounteratCDF.Thedetectormodulesarelocatedwithinthe\3-degreeholes"insidetheforwardandbackwardcalorimeters. 50

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FunctionalblockdiagramoftheCDFdataow.ThecrossingrateattheTevatronisactuallyonly2.5MHz,butthetriggersystemwasdesignedfortheoriginallyenvisioned7.5MHzcrossing. Figure2-12. Theratio=pprobeT=ptriggerToftransversemomentaofthe\probe"andthe\trigger"jetsusingthe70GeVjettrigger,obtainedusingtwodierentmethods(missingETprojectionfractionanddijetbalancing.The\probe"triggerjethastobeinacentralregion0:2
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Category Decayproducts Branchingratio Signature Dilepton 2ormorejets,oppositesideleptonsandmissing6ET 4ormorejets,1leptonandmissing6ET 6ormorejets Table3-1. Lepton+Jetsisconsideredtobethe\goldenchannel"toperformameasurementinTopPhysics.Ithasaverydistinguishedsignatureandfairlylargesample.Therefore,alltheprevioussearchesforttresonanceswereperformedinlepton+jetschannel.Comparingtoallhadronicchannel,thebiggestdisadvantageisoverwhelmingbackground,whichcomesdominantlyfromQCDmulti-jetproduction.Forthisreasonapowerfuleventselectionmustbeapplied,whichisdescribedbelow.ThedataeventsforthisanalysisareCDFRunIImulti-jeteventscollectedin2002-2008years(uptoperiod17).Duringthistime,CDFaccumulated2.8fb1.InoursearchweuseTOP MULTIJETtrigger,whichselectstheeventsofourinterestduringdata-taking.Ithascross-sectionof14nband85%eciencyonSMttallhadronicevents.TodescribeSMttandresonantttproductionweusestandardCDFMonteCarlosamples.AllsamplesweregeneratedusingPythiaeventgenerator,assumingtopmassof175GeVandMX0=f450;500;550;650;700;750;800;850;900gGeV=c2.Onthenal 52

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MULTIJETtriggerrequires: 6ETsignicance(6ET=p PET):<3

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54

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3-2 3-3 showthecomparisonof11variablesusedasaninputtoNeuralNet:backgrounddominateddataevents,SMttandMX0at500,700,900GeV.Theycorrespondtotheeventspassedtriggerandcleanupcuts.Asyoucanseefromtheplots,thereisaquitegoodseparationbetweenQCDdominateddataandttevents.Sointheend,wehaveallttsamplespeakedatNeuralNetoutputvalueequalto1,andQCDeventspeakedat0.ThemainideabehindNeuralNetisdescribedbelow.Intablestable 3-2 weshownumberofdataeventswehaveaftervariouscutsinouranalysis.Table 3-3 showsthesamenumbersforSMttsample.Additionally,wecalculateSMtt/QCD,usingthefollowingexpression:NexpSM=L,where-acceptance,L-totalintegratedluminosity(2800pb1),-SMtttheoreticalcross-section(6.7fb1).ThenumberofQCDeventsisthedierencebetweentheobservednumberofeventsinthedatashown 3-2 intableandthesignalexpectation.TheSVXb-taggerusedhasahighereciencyintheMonteCarlothaninthedata.ThereforeweneedtodegradethenumberoftaggedeventsaccordingtotheappropriatescalefactorwhichisSF=0:95. Table3-2. Numberofeventsinthemulti-jetdataaftertheclean-upcutsandtagging.TheintegratedluminosityisL=2.8fb1. CutEventsFraction(%) Initial24283816100TriggerandCleanupcuts1171953348.2Ntightjets=6;711600914.81tag1470760.602tag146560.061,2tagsandNNetcut31581.3e-02 55

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NumberofeventsintheSMt tMonteCarlosample. CutEventsFraction(%)ExpectedS/B Initial4719385100170001e-03TriggerandCleanupcuts187687439.770001e-03Ntightjets=6;793974119.937001/3201tag4167868.815701/902tag1738763.96901/201,2tagsandNNetcut1797813.86801/3 Table3-4. NumberofeventsintheMX0MonteCarlosamples. CutEvents(%)Events(%)Events(%) Initial531758100531968100531922100TriggerandCleanupcuts22520842.318960035.615026728.2Ntightjets=6;711756122.110219219.27806614.71tag517839.7441728.3326286.12tag213184.0163263.1105832.01,2tagsandNNetcut249314.7294415.5188393.5 66 ]),weconsiderinouranalysisisimplementedinROOT[ 67 ]throughtheclassTMultiLayerPerceptron.Thisisasimplefeed-forwardnetworkwithaninputlayer,severalhiddenlayersandanoutputnode.Thebestcongurationwefoundconsistsof2hiddenlayerswith20and10hiddennodesrespectivelyandasingleoutputnode.Theoutputnode,NNout,isthevariableusedtoplacethenalcutonanditrangesfrom0to1:0-background,1-signal.Fig. 3-4 showsthecongurationweuse.Thenextstepistotrainneuralnettodistinguishbetweensignalandbackground.Theaimofthetrainingprocessistominimizethetotalerroronasetofweightedexamples.Theerrorisdenedasthesuminquadrature,dividedbytwo,oftheerroroneachindividualoutputneurons(oneinourcase).TheTMultiLayerPerceptronC++classimplementsavarietyoflearningmethods,butweconsiderhereonlyBroyden,Fletcher,Goldfarb,Shanno(BFGS)methodwhichimpliesthecomputationofaNweightsNweightsmatrixandisconsideredtobemorepowerful. 56

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3-5 showsthatbotherrorsarealmostindistinguishable.Fromthesamepictureyoucanseethatlearningoftheneuralnetworkisthefastprocess;inlessthanabout20epochstheerrorsarestable.Theoutputoftheneuralnetwork,NNout,afterthetrainingisshowninFig. 3-6 asevaluatedonthetestsample.Thetrainingtookabout1000cpuminutesonastandardPC.TheoutcomeoftheneuralnetworktrainingisexportedasastandaloneC++class,containingalltheweightsforthenetwork.Whenweapplybacktheneuralnetworktothewholesampleof507thousandmulti-jeteventsandtothetteventsnormalizedtotheexpectationatthislevel,i.e.'2260events,weobtainthedistributionsof 3-7 .Theoptimizationofthecutwillbebasedonthemaximizationofthesignalstatisticalsignicance,S 3-7 suchamaximumisreachedat'0.93.Asyoucanseefromthesameplot,byintroducingFlameNNvariableintoneuralnetwegainafactorof'2inS/Bvalueforthesamesignaleciency.Inthetable 3-5 weshowlistofacceptancesforMX0samples.Asyoucanseefromthetable,eventhoughwetrainedneuralnetonSMtteventsassignal,forthesameneuralnetcutacceptancesvaluesforMX0andSMttarecomparable. 57

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3{4 )and( 3{5 )denetheprobabilityforeacheventtobesingleordoubletaggedrespectively.It'sworthmentioningthatdoubletagprobabilityequation( 3{5 )worksuptoaconstant,duetothefactthatmostofb-jetsareproducedinpairs.WeobtaintheconstantnormalizationfactorfromQCDdominatedregion. Table3-5. TableofacceptancesforMX0MonteCarlosamples. Mass acceptance 450 0.042 500 0.047 550 0.053 600 0.057 650 0.058 700 0.056 750 0.052 800 0.046 850 0.040 900 0.036 58

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3-8 3-13 showtagratematrixpredictionforthevariablesinseveralcontrolregions,usingeventswith6or7eventsaftercleanupcuts.Obviously,whenweusepre-taggeddatatopredictMX0spectrumforQCDwemayhavecontaminationinthatsamplecomingfromMX0aswellasSMttevents.Weaccountforthiseectbelow. Negativelogprobabilityvsmtop.Bluelinecorrespondstot tsampleofmtop=175GeV,whileredandblacklinesarethebackgroundsmodeledbyMCanddatarespectively 59

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Neuralnetinputvariables:QCDdominateddata-black,SMtt-red,500,700and900GeVttresonances-blue,magentaandgreenrespectively.Allhistogramsarenormalizedtounity 60

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Neuralnetinputvariables(MX0andNNetoutputforthereference):QCDdominateddata-black,SMtt-red,500,700and900GeVttresonances-blue,magentaandgreenrespectively.Allhistogramsarenormalizedtounity 61

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Neuralnetconguration.Synapsethicknessisproportionaltotheweight Neuralnettraining.Testing(red)andtraining(blue)errorsasafunctionoftrainingepochs. Neuralnetoutput.Signal(red)andbackground(blue). 62

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Neuralnetoutput.SignalisSMtt,normalizedtothenumberexpectedofevents.Signal(red)andbackground(blue).BottomfourplotsshowS/B,Eciency,SignicanceandEciencyvsS/BplotsforNeuralnetcongurationswith(red)andwithout(black)FlameNNvariable. 63

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Firstcontrolregion:0
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Firstcontrolregion:0
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Secondcontrolregion:0:25
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Secondcontrolregion:0:25
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Thirdcontrolregion:0:75
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Thirdcontrolregion:0:75
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71

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(pq+pq)2u(pu)(15)v(pd) 4-2 Thematrixelementneededinthecross-sectionformulaisjMggj2=1 64XcolorjA1+A2+A3j2whereAiaretheamplitudescorrespondingtothethreediagrams.Thecolorsumcoversallpossiblecolorcongurationsforthegluonsandquarks.ThisexpressionisnotoptimalwithregardtoCPUtimeifweweretodothesesumsastheystand.WecanrewriteitasjMggj2=1 64Xcolor(jA1j2+jA2j2+jA3j2+2RefA1A2g+2RefA1A3g+2RefA2A3g)ThisformisveryconvenientsincethecolorsumscanbeevaluatedforeachindividualtermregardlessofthekinematicsbecausetheamplitudesarefactorizedasA=AkinAcolorWecanwriteagain 72

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t(SMandZ')MonteCarlosamples.Moreexactly,ajetisassociatedtoapartonifitsdirectioniswithinaconeofR=0:4aroundthepartondirection.Wesaythatajetismatchedtothepartonifnootherjetshouldsatisfythisgeometricalrequirement.Wecallaneventasbeingamatchedeventifeachofthesixpartonsinthenalstatehasadierentjetmatchedtoit.Ofallthet tMonte 73

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Bin 0!0:2 2 0:2!0:6 3 0:6!0:9 4 0:9!1:4 5 1:4!2:0 Table4-1. 4-3 74

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4-4 showsactualsignaltemplatesusedinanalysis.Dataeventsareobviouslytreatedinthesamefashion. 75

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TreelevelFeynmandiagramfortheprocessqq!tt!bbqqqq Gluon-gluonLOcontributiontottproductioninppcollisions 76

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Light/Bquarkstransferfunctions(x=1Ej 77

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68 69 ]. 78

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79

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5.3.1TemplatesAspointedoutineq. 5{3 ,tobuildthelikelihoodfunctionweneedtoknowthetemplatedistributionsforthesignalandforthebackground.TocreatethetemplateswetakeocialTopgroupMonteCarlosamplesandPythiagenerated-showeredsamplesweproducedandsimulatedbyourselves.Thebackgroundsconsidered: 5{3 showsthatinordertobuildthelikelihoodweneedtoknowthenumberofbackgroundeventsNbjforeachbackground.SincethecrosssectionsfortheQCDprocessisunknownwedecidedtoestimatethenumberofeventsfromQCDasthebalancetothetotalnumberofobservedeventsinCDFaftersubtractingtheexpectednumberofsignal 80

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5{3 wehave,numberofeventsinbin\i": 81

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5{3 weneedtocalculatetheposteriordensityforsaccordingtoeqs. 5{1 5{2 5{1 accordingtoournotations. 69 ]page20,weimplementthe\Sample&Scan"method.Werepeatedly(1000times)samplethepriors(As)andj(Nbj),whicharetruncatedgaussianswithrespectivewidthsofAsandNbj.Thenwescan(200bins)thesuptosomevaluewheretheposteriorisnegligible.AteachscanpointweincrementthecorrespondingbininahistogramofswithaweightequaltoL(s;As;Nbjn)(sj;As;Nb).Thisyieldstheposteriordensityfors. 5-1 showstheresultsofthetestswithfakegaussiansignaltemplatesof800and900GeV=c2masses(60GeV=c2width)andwithFlaMEtemplatesforX0massesfrom650to900GeV=c2atanintegratedluminosityequaltoRL=1000pb1. 82

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5-2 showsanexampleofposteriorforaPEwithinputsignalof2pb,MX0=900GeV=c2andtotalintegratedluminosityRL=1000pb1.Werunmany(1000)PEsforeachconguration(MX0,integratedluminosity)andwethenllhistogramswiththeMPV,UL0,LLandUL;fortheMPV,UL0andULthemedianofthehistogramsarethenconsideredasourestimators,whilefortheLLwedenedthefractionofPEswithLL6=0asanestimationofthepowerofthealgorithmindiscriminatingthepresenceofasignaloutofthebackground. 5.2 ,isduetouncertaintyonthesignalacceptanceoronthebackgroundsacceptancesorcrosssectionsanddoesnotaectthetemplates.Theeectofthesekindofuncertaintieshasbeenincorporatedintothelikelihoodbyintroducingthenuisanceparameterspriorswhichreecttheiruncertaintyandthenintegratingoverthemasdescribedin 5.3.5 83

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70 ]. 5-3 84

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5-5 showstheshiftsforthevesignalmassesMX0=500:::900GeV=c2atanintegratedluminosityofRL=2:8pb1. 2X00 5-6 showstheeectofthesmearingonaposteriordistributionfunctions. 85

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5-7 showstheexpectedsensitivityforthetwointegratedluminosityscenariosR1000pb1. Figure5-1. Linearitytest.Thetopplotsshowtheinputversusthereconstructedcrosssectionafter1000PEsatintegratedluminosityRL=1000pb1.Bottomplotsshowsdeviationfromlinearityinexpandedscale.Weestimatethedeviationtobeabout2%(Reddottedline). 86

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Posteriorprobabilityfunctionforthesignalcrosssection.Themostprobablevalueisassumedasestimatorforthecrosssection.Fromtheposteriorwealsoextract95%CLupperlimitandlowerlimit.Theredarrowandthequotedvaluecorrespondtothe95%CLUL0. 87

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CrosssectionshiftduetoJESuncertaintyforluminosityscenariosRL=2:8fb1.TheshiftisassumedtobetheuncertaintyonthecrosssectionduetoJES. 88

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CrosssectionshiftduetoISRandFSRuncertainties. 89

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Totalshapesystematicuncertaintyversusinputsignalcrosssection. 90

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Posteriorprobabilityfunctionforhesignalcrosssection.Thesmearedp.d.f.(green)showsalongertailthantheunsmearedone(black).AsaconsequencetheUL0quotedontheplotisshiftedtohighervalueswithrespecttotheonecalculatedonunsmearedposterior. 91

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Upperlimitsat95%CL.Thecurvesshowstheresultsfortwoluminosityscenariosandbothincludingorexcludingthecontributionfromshapesystematicuncertainties. 92

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6-1 ,leftplot.19eventswerenotreconstructedwhichmeanstherewerenosolutionssatisfyingtheWandtopmassconstraints.ThetwotopquarksandW'sareforcedtobeonshell.Therightplotshowseventscontaining2b-taggedjetsonly,howevertheupperlimitswillbecalculatedusingeventswith1or2b-jets.Figure 6-3 showsthespectrumabovethe400GeVcuttogetherwiththeSMexpectation.The95%condencelevelupperlimitsonsignalcrosssectionfromdatatogetherwiththeSMexpectedupperlimitsareshowninFigure 6-4 .Thebandsdene68%and95%CLontheexpectedupperlimit.Thecentralvalueisthemedianofthehistogramofupperlimitsfrom1000pseudoexperiments,asmentionedbefore,andthebandsaredenedbyintegratinghalftheintervalonbothsides-i.e.34%oftheareaoneachsideofthemedianinthecaseofthe68%CLband. 93

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94

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ResonantproductionupperlimitsinCDFRun2data,2.8fb1

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[1] P.W.Higgs,Phys.Lett.12,132(1964). [2] F.Abeetal.,Phys.Rev.Lett.74,2626(1995);S.Abachietal.,Phys.Rev.Lett.74,2632(1995). [3] AdiscussionofthemotivationforatopquarkinsidetheStandardModelcanbefoundin:J.H.Kuhn,Lecturesdeliveredat23rdSLACSummerInstitute,(1995);hep-ph/9707321. [4] V.M.Abazovetal.(D0Collaboration),Phys.Rev.D67,012004(2003). [5] T.Aolderetal.(CDFCollaboration),Phys.Rev.D64,032002(2001);Erratum-ibid.D67,119901(2003). [6] D.Acostaetal.(CDFCollaboration),Phys.Rev.D71,052003(2005). [7] D.Acostaetal.(CDFCollaboration),Phys.Rev.D93,142001(2004). [8] D.Chakraborty,J.KonigsbergandD.L.Rainwater,Ann.Rev.Nucl.Part.Sci.53,301(2003). [9] M.Cacciarietal.,JHEP0404,068(2004);N.KidonakisandR.Vogt,Phys.Rev.D68,114014(2003). [10] [TevatronElectroweakWorkingGroup],(2009)[arXiv:hep-ex/0412071]. [11] S.L.Glashow,J.IliopoulosandL.Maiani,Phys.Rev.D2,1285(1970). [12] S.Eidelmanetal.,Phys.Lett.B592,1(2004). [13] F.Abeetal.(CDFCollaboration),Phys.Rev.Lett.79,3585(1997);B.Abbottetal.(D0Collaboration),Phys.Rev.Lett.82,4975(1999);T.Aolderetal.(CDFCollaboration),Phys.Rev.D62,012004(2000);V.M.Abazovetal.(D0Collaboration),Phys.Rev.Lett.88,151803(2002). [14] LEPElectroweakWorkingGroup,http://lepewwg.web.cern.ch/LEPEWWG/.Tobepublished(2005). [15] P.Azzietal.,CDFandD0CollaborationsandTheTevatronElectroweakWorkingGroup,hep-ex/0404010. [16] ALEPH,DELPHI,L3andOPALCollaborationsandTheLEPWorkingGroupforHiggsBosonSearches,Phys.Lett.B565,61(2003). 99

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IuriOksuzianwasborninTbilisi,GeorgiaonDecember16,1979.In1997IurisuccessfullygraduatedfromVekuaHighSchoolandappliedtotheDepartmentofPhysicsatTbilisiStateUniversity.In2001IurigraduatedwithhonorsfromTbilisiStateUniversitywithB.S.inPhysics,SummaCumLaude.Duringhisbachelorsstudies,IuritookaresearchassistantpositionattheJointInstituteofNuclearResearchinDubna,Russia.In2003IuriwasadmittedtograduateschoolatUniversityofFlorida.Aftercompletionofthecourserequirements,hemovedtoFermilabin2005forresearchwithintheCDFcollaborationunderthesupervisionofProf.JacoboKonigsberg.Hisresearchwasfocusedont=bartresonancesearchinmultijetsnalstate.HealsoplayedkeyroletotheoperationsoftheCherenkovLuminosityCounter(CLC)atCDF. 103