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2.LargeHadronCollider,CompactMuonSolenoid,anditsforwarddetectors
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Figure2.1.TheCERNacceleratorsanddetectorscomplex.
•Instantaneousluminosity(Linst),aquantityproportionaltotheoverlapintegralofthedensities
ofthetwocollidingbeams.Itisexpressedin[cm12·511]unitsanddefinedforeachsinglecrossing
ofprotonbunches.Theexpectednumberofeventsofagivenkind,e.g.MinimumBias(MB)
events,inasinglecrossingcanbecalculatedmultiplyingcorrespondingcrosssectionandLinst.
AsthestructureofbuncheschangesduringtheLHCoperation,Linstisafunctionoftime.
Moreover,itisalsochangingduringoneLHCfillasthenumberofprotonsdeteriorateswith
thetimeelapsedsincethebeginningofthecollisionsinagivenfill.
•Integratedluminosity(Lint)–itisaninstantaneousluminosityintegratedovertimeofthedata
taking:Lint1∫Linstdt.
•Pile-up(P)referstoadditionalindependentproton–protoninteractionsinagivenbunchcross-
ing.ItgrowswithLinst.
•Betafunction(β(z))describesatransversesizeofabeamatagivenpoint(z)alongthebeam
trajectory.Thewidthofthebeam(σ(z)),whichisassumedtohaveaGaussianshapeisrelated
toβasσ(z)1dćβ(z),wherećisthebeamemittance.Theemittanceisameasureofan
averagespreadofbeamparticlesinposition-momentumspace.Fortheinteractionpoint,z10,
betafunctionisdenotedasβ∗.Smallerβ∗correspondstostrongerbeamcollimationatthe
interactionpointandthereforelargerLinst.
2.1.1.LargeHadronColliderinRun1
ThemaingoaloftheNovemberandDecember2009LHCrunningwastocommissionthemachine
andtocheckitsprotectionsystem.However,asmallnumberofeventswasrecordedbytheex-
periments.AtfirsttheLHCdelivered∼10pb11ofintegratedluminositytoeachofthefourlarge
