Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 348.882 LHC PhysicsExperimental Methods and MeasurementsCharge Multiplicity Measurement[Lecture 5, February 18, 2009]C.Paus, LHC Physics: Charge Multiplicity Measurement 2Organizational Issues Recitation session this week●will be over video●format slightly different than last time●prepare questions for the session Charge Multiplicity Assignment●is already available on the web●start early to get a feel for how much work it is●pointer: http://www.cmsaf.mit.edu/twiki/bin/view/Class8882/NChargedDescription‘09The Physics Colloquium SeriesThursday, February 19 at 4:15 pm in room 34-101 Matthias BurkardtNew Mexico State University / Jefferson Lab "Nucleon Spin Physics" SpringFor a full listing of this semester’s colloquia, please visit our website at web.mit.edu/physicsColloquium SeriesPhysicsC.Paus, LHC Physics: Charge Multiplicity Measurement 4Lecture Outline Charge multiplicity measurements●observables and experimental status●CDF data and how they are organized●trigger conditions and information●contents of the “ntuple”●prototype analysis●main components for full analysis●pile up events●secondary interactionsC.Paus, LHC Physics: Charge Multiplicity Measurement 5General Scattering Considerations Why is the charge multiplicity interesting?●in classical collision: no new particles get created●one particle in, one particle out at angle θ●for particle physics new particle creation main purpose●inelastic collision●creation of new particles with available energy●some properties of newly created particles●how many?●type or mass●detailed kinematics●difficult to predict●low momentum regime●non-perturbative QCD●no high-profile measurement in HEPC.Paus, LHC Physics: Charge Multiplicity Measurement 6Charged Particles in Heavy Ions Very relevant●simple observable to characterize the fireball●identify state transition using charge multiplicity Compare interactions in HI collisions with proton-proton or proton-antiproton collisions → are HI interactions independent?C.Paus, LHC Physics: Charge Multiplicity Measurement 7CDF Charge Particle Multiplicity Figure●x axis: number of tracks in event, n●y axis: number of events over total events, Pn●various symmetric pseudorapidity intervals●at 1800 GeV (Run I)●careful, curves are artificially normalized to show them separatelyC.Paus, LHC Physics: Charge Multiplicity Measurement 8Fit Charge Multiplicity Distribution Fitting function, [2] TWiki●negative binomial distr. Two parameter function●<n> - average number of tracks●k - shape parameter Implementation in Ana/fit●negativeBinomial.C●assumes that you ran●Ana/script/runNTrks.CC.Paus, LHC Physics: Charge Multiplicity Measurement 9Multiplicities versus EnergyAdd one more point here (≈2 TeV)C.Paus, LHC Physics: Charge Multiplicity Measurement 10Some Jargon You Should Know Fill or store●when operators fill machine with a fresh set of protons and antiprotons (or protons and protons at LHC)●stores can take up to several days: luminosity drops exponentially in beginning, at some point one has to stop Run●at CDF: bunch of data with constant detector conditions●ideally just one per store, often many per store Luminosity section (LS)●smallest unit of data for which luminosity is determined●LS kept together in one file, consider asynchronous data takingC.Paus, LHC Physics: Charge Multiplicity Measurement 11Hadron Collider Triggers General●trigger is crucial in hadron collider●event rate: 3 (40 CMS) MHz, written to tape: 100-200 Hz●trigger significantly shapes kinematic of output events●problem: readout time of detector is long Rough overview of CDF Trigger●trigger system is pipelined and organized in levels●pipelines allow to process in parallel●levels allow to use increasing amount of information with increasing amount of decision time ●level 1: implemented in hardware, very fast (input 106)●level 2: implemented in firmware, pretty fast (input 104)●level 3: implemented in software, fast (input 103)C.Paus, LHC Physics: Charge Multiplicity Measurement 12CDF Trigger System OverviewProperly join levels●event needs to have fully defined level 1, 2, 3 sequence●sequence called path●path important for efficiency calculationOur trigger●minimum bias trigger●looks into forward region to trigger on some minimal activityC.Paus, LHC Physics: Charge Multiplicity Measurement 13Code Organization: BottomMods General●code sits in ~/8.882/614, please keep it there●AC++ is general CDF reconstruction software, you should have nothing to do with AC++ (you cannot even run it) BottomMods: a B reconstruction package●cands – reconstruction of particles purely AC++●mod – interface between AC++ and ntuple format ●stn – definition of the ntuple data blocks●ana – general analysis modules and other helpers●taggers – implementation of tagging algorithms●tools – generic independent tools Do not be afraid, just take a look at it!C.Paus, LHC Physics: Charge Multiplicity Measurement 14Organization of CDF Data Data in BStntuple format: a root TTree●all files are split into two main TTrees●event based information (most): “STNTUPLE”●run based information: “db”●run tree information●run number,●trigger table●beamline, etc.●event tree information●header and trigger info●“Pions”: all tracks reconstructed as if they were pions●“Muons”: tracks reconstructed as if they were muons●etc.C.Paus, LHC Physics: Charge Multiplicity Measurement 15The Header Block General idea●small datablock which contains very general event info●used to very quickly/roughly select events, always loaded TStnHeaderBlock●int EventNumber () const;●int RunNumber () const;●int SectionNumber() const;●int McFlag () const;●etc.C.Paus, LHC Physics: Charge Multiplicity Measurement 16The Trigger Word Block General idea●keep track of trigger decision at each level using the name of the trigger path TStnTrigWdBlock●int GetListOfPassedTriggers●(const TStnTriggerTable* Table, ● const char* Name, ● int Level, ● TObjArray* List); ●TStnTriggerTable connects trigger name with