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ForwardPhysics–anewwindowonhighenergyinteractions
experimentswithbeamssettotheenergyof0.45TeV(√s10.9TeV).Itcorrespondstoapproxi-
mately200000minimumbiaseventsrecordedatCMS.Thenthebeamenergywasincreasedupto
Theintegratedluminosityforthisenergywas∼0.4pb11whichcorrespondstoroughly10000mini-
mumbiaseventsrecordedatCMS.Inthisperiodthepile-upwasnegligible.
In2010,afterashortperiodofdatatakingat√s1900GeV,energiesofthebeamswere
ramped-upto3.5TeV.On30thMarchthefirstcollisionsat√s17TeVtookplace.Theinitial
numberofbuncheswas2,whilethenumberattheendoftheyearwas368.Theinitialintensitywas
around1010particlesperbunch.InJuneitwasincreasedtothenominalvalueofaround1011.It
wasfurtherincreasedto1.2×1011attheendofthedatatakingin2010.Theβ∗wasintherange
of2.0–3.5m.Theaveragenumberofcollisionsperbunchcrossingevolvedwiththeβ∗andintensity,
reaching4attheendofthedatataking.Thepeakluminosityin2010was2.1×1032cm12·511while
thetotalintegratedluminositydeliveredtoCMSwasaround0.04fb11.
In2011thebeamenergywasthesame,3.5TeV,whilethenumberofbuncheswasstrongly
increased.InJuneitraisedto1380bunches,themaximumpossiblenumberwithabunchspacing
of50ns(in2010thebunchspacingwas150ns).Theintensitywasslightlyincreasedto1.45×1011,
whileβ∗wasintherange1.0–1.5m.Alltheseimprovementsledtoalargeincreaseinthepeak
luminositywhichreached3.7×1033cm12·511.Themaximalmeannumberofcollisionspersingle
bunchcrossingin2011was17.Thetotalintegratedluminositydeliveredin2011toCMSwasaround
5.6fb11,thatisroughly140timeslargerthanin2010.
InthelastyearofRun1,2012,thebeamenergywasincreasedto4TeV(√s18TeV).The
numberofbunches(aftertwoweeksofdatataking)wassetto1380andthetransversesizeof
thebeamsattheinteractionpointwasfurthersqueezedtoβ∗10.6m.Thislastimprovementwas
achievedthankstotightercollimatorsettings.Thishoweverrequiredanimprovementintheorbit
stabilityduringthesqueeze.Itwasperformedintroducingadditionalcorrectionstothesqueeze
functions.Thecorrectionswereobtainedwithdedicatedtestrunswithlowintensityduringwhich
squeezesandorbitswerecloselymonitored.Thepeakluminosityraisedto7.7×1033cm12·511and
themaximalmeannumberofeventsperbunchcrossingreached37.The2012proton–protondata
luminositywasdeliveredbytheLHCperweekofthedatataking,whichallowedtorecord23.3fb11
atbothCMSandATLAS.
respectively[12].
2.2.CompactMuonSolenoid
CompactMuonSolenoid(CMS)isoneofthetwogeneralpurposedetectorslocatedattheLHC
collider.Itis21.6mlongand15minadiameter.Itweights14000tonnes.Itisplacedintheunder-
groundcavernunderCessyvillageinFranceneartheJuramountains,inalocationcalledPoint5.
ThecoordinatesysteminwhichallthephysicsobservablesatCMSarequotediscenteredat
thenominalpointofthecollisions,inthemiddleoftheCMSdetector.They-axispointsupward,
thex-axispointstothecenteroftheLHCring,whilethez-axisissetalongthebeamdirection
towardtheJuramountains.Inthexyplanetheazimuthalangleφisdefined.Itismeasuredstarting
fromthexdirection.Thepolarangleθismeasuredfromzdirection.Itcanbetranslatedinto
pseudorapidityvia:n1−ln[tan(θ/2)].
Beingageneralpurposedetector,CMShastomeetgoalsofabroadphysicsprogramme.This
setsanumberofstrongrequirementsontheconstructionandperformanceofthedetector.First,
averygoodidentificationandmomentumresolutionformuonsinawidekinematicrange(upto
