HBT Analyzer

1
HBT Analyzer
Piotr Krszysztof Skowronski for ALICE
Collaboration CERN/Warsaw Univ. of
Technology CHEP 2003
2
Correlation Function

• HBT analysis result is a Correlation Function
  (CF)
• Experimental CF of some variable Q(part1,part2,)
  is created by division of two histograms
• Numerator is a histogram obtained by calculating
  value of Q( part1n, part2n,) for particles
  coming from the same event
• Denominator is a combinatorial background
  obtained by histogramming Q(part1n,part2k,)
  value of particles coming from different events

3
Algorithm

• Algorithm itself is trivial
• Loop over events (I)
• Loop over events (II)
• Loop over particles from event (I)
• Loop over particles from event
  (II)
• Check cuts
• Calculate Q
• Fill numerator or denominator depending if
  event (I) event (I)

• However, we want to
• Calculate many CF in one analysis run
• Apply different cuts
• Have program as fast and robust as possible

4
Structure
fReader
fPairCut
fFirstPartCut fSecondPartCut
fBasePairCuts
5
AliHBTAnalysis

• This object performs looping
• User adds functions to it in a macro
• Track functions (One Pair Fctn)
• Particle functions (One Pair Fctn)
• Resolution functions (Two Pair Fctn)
• Track Monitor Functions
• Action is triggered by method Process(Option_t)
• Options can be
• Tracks (default) - process only tracks
• Particles - process only particles
• TracksParticles - process all functions

6
AliHBTAnalysis cont.

• Separate, specialized mixing algorithm for
  non-identical particles analysis
• Used automatically in case particle cuts in pair
  cut exclude each other
• i.e. different PID
• Events are filtered before mixing

7
Structure Functions
fReader
fPairCut
8
Structure Functions
9
Functions

• AliHBTOnePairFctn
• virtual void ProcessSameEventParticles(AliHBTPair
  pair) 0
• virtual void ProcessDiffEventParticles(AliHBTPair
  pair) 0
• AliHBTTwoPairFctn
• virtual void ProcessSameEventParticles(AliHBTPair
  trackpair, AliHBTPair partpair) 0
• virtual void ProcessDiffEventParticles(AliHBTPair
  trackpair, AliHBTPair partpair) 0
• AliHBTFunction, base pure virtual
• implements pair cut interface each function can
  have a different cut
• in one analysis it is possible to get the same
  function with different cuts
• some getters and setters
• (TH1 GetResult(), etc.)
• other common methods
• AliHBTOnePairFctn1D, uses TH1D
• AliHBTTwoPairFctn2D, uses TH2D
• etc...

10
Functions

• So creating a new type function is very
  easyclass AliHBTQInvCorrelFctn public
  AliHBTOnePairFctn1D //Q Invaraint Correlation
  Function public AliHBTQInvCorrelFctn()
  AliHBTQInvCorrelFctn(Int_t nbins,Double_t
  maxXval,Double_t minXval) virtual
  AliHBTQInvCorrelFctn() TH1
  GetResult()return GetRatio(Scale())
  protected Double_t GetValue(AliHBTPair
  pair)return pair-gtGetQInv() public
  ClassDef(AliHBTQInvCorrelFctn,1)

11
Monitoring Functions

• Monitor Fuctions are for controling single
  particle properties
• Spectra
• Resolutions
• Structure similar to correlation functions
• AliHBTMonitorFunction, base pure virtual
• AliHBTMonOneParticleFctn
• virtual void Process(AliHBTParticle pair) 0
• AliHBTMonTwoParticleFctn
• virtual void Process(AliHBTParticle
  trackparticle,
• AliHBTParticle partparticle)
  0
• AliHBTMonOneParticleFctn1D uses TH1D
• AliHBTMonOneParticleFctn2D uses TH2D
• etc...

12
AliHBTReader

• Pure virtual interface
• AliHBTEvent GetParticleEvent(Int_t)
• AliHBTEvent GetTrackEvent(Int_t)
• Int_t GetNumberOfPartEvents()
• Int_t GetNumberOfTrackEvents()
• Allows to implement buffering/non-buffering
  readers
• List of particle cuts (AliHBTPartCut) allows for
  filtering particles on the level of reading.
• In simple case no more cuts is needed
• Makes analysis faster
• User can specify list of directories to read
  events from
• Many AliHBTAnalysis objects can use the same
  instance of the reader
• It is very important feature, since reading is
  very time consuming - specially from the tape via
  RFIO.

13
Structure Particle Cut
PID
fBaseCuts
14
Particle Cut

• Applies cut on many particle properties
• Particle cut (AliHBTParticleCut) have an array of
  base cuts
• Base cut applies cut on one particle property
• Base cut (AliHbtBaseCut) implements setters and
  getters for max and min value and method
• inline Bool_tAliHbtBaseCutPass(AliHBTParticle
  p) if( (GetValue(p)gtfMin)
  (GetValue(p)ltfMax) ) return kFALSE
  //accepted else return kTRUE //rejected
• where GetValue(AliHBTParticle) is pure virtual
• Package implements set of base cuts, and
  AliHBTParticleCut has an comfortable interface
  methods to set them
• However, users will invent for new cuts...

15
Particle Cut

• But again, implementing new base cut is very
  easyclass AliHBTPtCut public AliHbtBaseCut
  public AliHBTPtCut(Double_t min,Double_tmax)
  AliHbtBaseCut(min,max,kHbtPt)
  virtual AliHBTPtCut() protected Double_t
  GetValue(AliHBTParticle p)return p-gtPt()
  ClassDef(AliHBTPtCut,1)
• There is implemented Empty Particle Cut
  (AliHBTEmptyParticleCut) , which accepts all
  particles
• All objects that have a particle cut as a member,
  creates by default empty cut

16
Pair Cut

• Applies cut on particle on different properties
  of a pair of particles
• Pair Cut has a two pointers for particle cut
• One for each particle in pair
• Both can point the same object, of course.
• By default they are empty cuts (accepting all
  particles)
• And a list of Base Pair Cuts (AliHbtBasePairCut)
• Implememnts cut on one particle pair property
• Implementation follows the idea described for
  Particle Cut
• An empty pair cut is implemented as well

17
AliHBTPair

• Just two pointers to particles and methods for
  calculating quantities (Qinv, Minv , etc., ...)
• But,
• Results of time consuming calculations are
  buffered
• For each such a variable exists buffer and
  Boolean flag
• Flags are set to false if new particles are set
  in pair
• Values are calculated on demand if flag "value
  calculated" is false.
• This solution speeds up the code more than twice

18
AliHBTPair

• AliHBTPair has a member variable of type
  AliHBTPair with swapped particles
• This is dictated by the way of mixing (looping)
• If pair is AB, there is not going to come BA
• In some analysis order of particles is important
• If Pair is not accepted by PairCut, swapped pair
  can be obtained and eventually (after passing
  cut) analyzed

19
Example Macro
AliHBTAnalysis analysis new
AliHBTAnalysis() AliHBTReader reader new
AliHBTReaderTPC() AliHBTParticleCut
readerpartcut new AliHBTParticleCut() readerpart
cut-gtSetPtRange(0.1,1.0) readerpartcut-gtSetPID(kP
iPlus) //read this particle type with this
cut reader-gtAddParticleCut(readerpartcut)
analysis-gtSetReader(reader)//Set Reader to
Analysis AliHBTPairCut paircut new
AliHBTPairCut() paircut-gtSetQInvRange(0.0,0.20)
analysis-gtSetGlobalPairCut(paircut) //pi pi
analysis AliHBTQInvCorrelFctn qinvcfT
new AliHBTQInvCorrelFctn("qinvcfP","Particle
(simulated) Qinv CF") AliHBTQInvCorrelFctn
qinvcfP new AliHBTQInvCorrelFctn("qinvcfT","T
rack (recontructed) Qinv CF") analysis-gtAddTrack
Function(qinvcfT) analysis-gtAddParticleFunction(q
invcfP) analysis-gtProcess("TracksAndParticles")
TFile histoOutput(outfile,"recreate") analysis-gt
WriteFunctions() histoOutput.Close()
20
http//alisoft.cern.ch/people/skowron