HowtoMakeMillionsinParticlePhysics

RobertHarrWayneStateUniversity

Outline• TheCMSgroupatWayneState• ThestandardmodelofparticlephysicsandtheHiggsBoson

• TheCMSExperiment• SearchesforNewPhysics• Confirmationanddiscussionofimplications

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CompactMuonSolenoid(CMS)• WayneStategroupconsistsof– Profs.PaulKarchinandRobHarr– ResearchengineerAlfredoGutierrez– PostdocDr.JustinSturdy– PhDstudents:ChrisClarke,KevinSiehl,Prakash Thapa,ShawnZaleski,Nabin Poudyal

• Weinteractwiththetheorygroupof– Profs.AlexeyPetrov, GilPaz,andNausheenShah

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THESTANDARDMODELOFPARTICLEPHYSICS

Inanutshell

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TheStandardModel• Thestandardmodelofparticlephysicsisthetheoryforthebehaviorofthefundamentalparticlesofnature.

• Itisextremely wellestablished.• TheHiggsBosoncompletedthemodel.• Wearenowlookingforphenomenabeyondwhatisinthestandardmodel:– supersymmetry,extradimensions,righthandedcurrents,preons,axions,andmany,manymore

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TheStandardModelofParticlePhysics

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StandardModel• TheSMisbuiltonprinciplesofgaugeinvariance.– physicsnotchangedbyashiftofpotentialenergy– slightlymorecomplexinparticlephysics

• Masstermsbreakgaugeinvariance– startwithmasslessparticlesand– usesymmetrybreakingtogeneratetherequiredmassterms.

• Soundscrazy,butthatiswhythere’saHiggs.18Nov.2013 PHY6991 7

GaugeTransformations• Thestandardmodelofparticlephysicsisbuiltontheideaofgaugesymmetries.– Recallfromelectromagnetismthatthescalarandvectorpotentialcanbetransformedaccordingto:

– TheMaxwellequationsremainunchanged.

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A� A +��

�� �� ���t

GaugeTransformations(2)• ThesameprocessisusedinQFT

• Aµ canbethefieldforphotons,gluons,orweakbosons(WandZ).

• ButtheWandZhavemass,andmasstermsbreaktheinvariance

• Symmetrybreakingcangenerateamassforaninitiallymasslessfield(c.f. superconductivity).

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Aµ ! Aµ + @µ⇤

mAµAµ

SymmetryBreaking• SymmetryisbrokenbyaHiggspotentialwhosegroundstatehasnon-zerofield– commonlypicturedwiththemexican hatpotential

• PredictstheexistenceofaHiggsBoson.18Nov.2013 PHY6991 10

ManyQuestionsRemain• Whatisdarkmatter?darkenergy?• Whataccountsforthepredominanceofmatterintheuniverse?

• Howdowesolvethehierarchyproblem?• Howmanygenerationsofquarksandleptons?• Aretheknownparticlesfundamentalorcomposite?• Arethereextradimensions?• Doessupersymmetryexist?Wherearethesuper-partners?

• AreneutrinosMajorana orDiracparticles?18Nov.2013 PHY6991 11

THECMSEXPERIMENT

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TheLHCandHiggsDetectors

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NoteonApparatus• LHCoperationispausedfromDecember2018toMarch2020.

• Improvementstotheacceleratorcomplexwillenableahigherrateofcollisions.

• TheWayneStategroupisworkingon– (Karchin)addingnewdetectorstothemuonsystemforcoverageatverysmallangles(nearthebeampipe),

– (Harr)buildinganewtrackertoreplacetheexistingone.

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SEARCHESFORNEWPHYSICS

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TwoWaystoSearch:• DirectSearch– Produceaparticleandobserveitsdecay.– Advantageofdirectlystudyingtheparticle.

• IndirectSearch– Observeeffectsproducedbynewparticlesinpreciselypredictedandmeasuredquantities.

– Advantageofsensitivitytomanykindsofnewparticlesinasinglemeasurement

– Thereisalonghistoryofindirectevidencefornewparticles

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TevatronWHandZHResults

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EvidenceforHiggsatabout3s

SensitivetotheHiggscouplingtobquarks.

DirectSearch:Hà Z*ZandHà gg

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Z*Zà 4l gg

Hà gg

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Hà gg

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Hà gg

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Hà ZZà4µ

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Hà ZZà2e2µ

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Hà ZZà2e2µ

IndirectSearch:MW vs Mtop

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IndirectSearch:MW vs Mtop

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SearchingforNewPhysics• Directsearchesarespecific,indirectsearchesarebroad.

• Todate,allresultsfromtheLHCareconsistentwiththestandardmodel.

• IwillsummarizetheworkgoingonbytheWayneStategroup.

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ContactInteractions• Karchinandstudentsaresearchingforsignsofnewinteractionsbetweenquarksandgluonsatveryshortdistances.

• Theylookforanexcessofµ+µ- pairswithveryhighinvariantmass.

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TripleandQuarticGaugeCouplings• W,Z,andg havetripleandquarticcouplings.• TheSMcouplingsarerestrictive,andnon-SMcouplingsaresignsofnewphysics.

• ThesisprojectforK.Siehl,N.Poudyal

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ExclusiveWBosonDecays• Wà ln hasamissingneutrino.• NoexclusiveWdecayhaseverbeenreconstructed!• SearchforWà csdecay.– triggeronDdecay– lookfor3tracks,netchargeof1,lowmass

• Usetomeasuremassandwidthdirectly.

• Veryspeculative18Nov.2013 PHY6991 31

Summary• SearchesfornewphysicsinCMSdata.• Bothdirectandindirectsearchesarepossible.• Wà J/y Ds maybethefirstexclusiveWdecaytobereconstructedandwillmakepossibleinterestingmass,width,andpolarizationmeasurements.

• TriplegaugecouplingsaresensitivetonewphysicsthateffectsthegaugeBosons

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