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

11

+ 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.”