news from ictp 133 new boson brought to light · particle, whether it’s the higgs boson the...
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rulingitoutwouldhaveprovenanexcitingdevelopmentthatwouldeitherconfirmalltheirworkthusfaroropenthedoortoanewworldforphysics.Newdatashouldpourin
throughout2012,asthepreliminaryresultsannounced4Julycontainonlyone-thirdof thedataexpectedfromtheLHCatCERNthisyear.ThefindinghasalsopromptedCERNscientiststokeepthecolliderrunninganotherthreemonthsbeforeitsscheduledshutdownin2013forapowerupgrade.CERNphysicistshopetofindoutmoreaboutthenewparticle,whetherit’stheHiggsBosontheStandardModelpredicts,oravariantof somekind.“Withmoredata,if theHiggs
bosonwerethere,wewouldbeabletoconfirmwhetherit’stheStandardModelHiggsbosonortheHiggsbosonof arichertheory,”saidAcharya,addingthatthefindingistremendouslyexciting.“ItprobablyistheHiggs,whichrepresentstheendtoasearchthathasgoneonfordecadestofindthemissingpieceof theStandardModelpuzzle,”hesaid.“ForICTPthisisanincrediblyimportantresultgiventhefundamentalrolethatAbdusSalamplayedinthedevelopmentof theStandardModelof ParticlePhysics.”Salam,aNobellaureatein
1979,wasthefounderof ICTP.Salam’smostfamousworkwasontheinteractionbetweentheelectromagneticandweaknuclear
NEWS from ICTP 133
HIGGS
New Boson Brought to Light
FINDINg OF LIkELy HIggs PaRTICLE a majOR mILEsTONE IN PHysICs
TheStandardModelof ParticlePhysicslookslikeakeeper.ScientistsatCERNhavefoundanewparticlelikelytobetheHiggsBoson,thelong-soughtparticlethatcompletestheStandardModelandwouldexplaintheoriginof massintheelementaryparticlesthatmakeupallmatter.ThroughresearchcoordinatedandfundedbytheItalianNationalInstitute
of NuclearPhysics(INFN),ICTPandtheUniversityof Udinehaveplayedanimportantroleinthediscovery.Thatrolestartedin1996whentheUniversityof UdinejoinedCERN’sATLASexperiment,withICTPcomingin10yearslater.LedbyMarinaCobalof theUniversityof UdineandICTPparticle
physicistBobbyAcharya,andincludingparticipantsfromtheUniversityof TriesteandSISSA,theresearchgrouphasexaminedthedebrisof particlecollisionsattheLargeHadronCollider(LHC)todiscovernewparticlessuchastheHiggsboson.
ThenewparticleappearswheretheStandardModelpredictstheHiggsbosonshouldbe,thoughtheexactpropertiesof theparticleareyetunknown.TheHiggsbosondecayssofastthatitisimpossibletodetectdirectly.But
itsdecaygeneratesotherparticles,thatphysicistscanusetoinferitsexistence.Thiswouldbeaneasysignforphysiciststopickup,exceptthattherearealsootherparticlesthatareheavyandshort-livedliketheHiggsthatoftendecayintotheexactsameparticles.Forexample,theHiggsdecaysintotwo“Wbosons,”particlesthatcarrytheweaknuclearforce.Wbosonsarealsoleftbehindbythedecayof atopquarkandanti-topquarkcombined.Thisnon-Higgsdata,called“background”byphysicistsatCERN,getsinthewayof pinpointingtheHiggs,ratherlikehowstaticcanobscurearadiosignal.Soscientistshavetodeterminethesubtledifferencesinthesedecaysequences.ThisknowledgeallowsCERNphysiciststoscreenthebackgrounddataandremoveit,exposingthenewlyfoundparticleliketheonetheydiscoveredthisyear.TheStandardModelof ParticlePhysicsdetailstheelementarycomponents
of matterandenergyintheuniverseandhasthusfarbeentestedsuccessfullybythousandsof experimentalmeasurements.If experimentsatCERNfailedtofindtheHiggsoranythingclosetoit,theStandardModelwouldhavehadtoberethoughtcompletely.Soformanyphysicists,bothfindingitor
force,whichiswidelyregardedasthecoreof theStandardModelof ParticlePhysics.Thetheorypredictedtheexistenceof WandZbosons,whichcarrytheweaknuclearforce,andwerediscoveredexperimentallyatCERNin1974.Regardlessof whetherthenew
particleisexactlytheHiggspredictedbytheStandardModelornot,itisatleastcertainthatanewbosonparticlehasbeenfound,whichisamilestoneforthe27-kilometerLHCundergroundinGeneva,Switzerland.Thediscoverywasturnedupbytwoof thedetectorsatthecollider,
+ Peter Higgs (right) at ICTP with B. Richter and L. Lederman, during the Summer Workshop in High Energy Physics and Cosmology, July 1987
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+ These diagrams show how the Higgs boson and the combination of a top quark and anti-top quark decay into similar particles. Scientists from ICTP and the University of Udine at CERN worked together to filter out the remnants of top/anti-top quark pairs to help hunt for the Higgs
+ Bobby Acharya in the ATLAS pit of the Large Hadron Collider (LHC) at CERN, Geneva, May 2007 (photo Marina Cobal)
+ Marina Cobal (courtesy Marina Cobal)
CMSandATLAS,andtheirfindingsweredeliveredintwoback-tobacklecturesaspartof ageneralannouncementbyCERN.Whenthepresentationsrevealedthedatashowinganewparticle,physicistswatchingthroughoutCERNburstintoenthusiasticapplause,includingPeterHiggs,whoseworkpredictedtheboson.CERNphysicistJoeIncandelaeven
hadamomentof pauseduringhispresentationontheCMSdetector’sfindings.Heflippedtotheslidedisplayingthebumpinthedatashowingthatanewparticleexisted,
andhadtroublewillinghimself tomoveontothenextslide.“That’sfairlysignificant,”hesaid.“It’shardtoleavethat,actuallyforme.Iwaslostforamoment.”Incandelasaidthebosonisa
profounddiscoverybecauseitisnotjustaboutanelementaryparticle.“We’rereachingintothefabricof theuniverseonalevelwe’veneverbeenbefore,”saidIncandela.“We’vekindof completedonepartof thestory.We’reonthefrontiersnow.”
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