3 /*! \page README_sim Simulation
5 The simulation encompasses the following tasks :
7 - Generation of MC particles (the kinematics of the event ends up in the TreeK
10 - Tracking particles through the detector using
11 the Virtual Monte Carlo, producing AliMUONHit objects, that end up in
12 the TreeH of MUON.Hits#.root file(s). This part is steered by AliMUON and its child
15 - Converting MC hits into AliMUONVDigit, called SDigits, that end up in the TreeS
16 of the MUON.SDigits#.root file(s). A S(ummable)Digit is a pad with its associated
17 charge, but no noise or electronics response function applied. Steered by AliMUONSDigitizerV2 class.
19 - Converting SDigits into Digits, by applying electronics calibrations. Actually, we de-calibrate
20 the digits at this stage, by adding a pedestal and dividing by a gain, more or less. Steered
21 by AliMUONDigitizerV3 class. Digits end up in TreeD of MUON.Digits#.root file(s). In addition,
22 for the trigger, we create AliMUONLocalTrigger, AliMUONRegionalTrigger and AliMUONGlobalTrigger objects
23 at this stage, that ends up in TreeD as well.
25 - Convert the Digits into RAW data, in a format that should be exactly the same as real data from the
26 DAQ. Performed by AliMUONRawWriter.
28 From there on, the reconstruction can proceed, in the very same way for real or simulated data,
29 as long as they are in RAW format.
31 \section sim_s1 How to run a MUON generation
33 You only need to run the simulation part of the test script
34 AlirootRun_MUONtest.sh
37 \section sim_s2 Tracking parameters, cuts, energy loss and physics processes
39 Tracking parameters in MUON are automatically defined by GEANT
40 MUON takes the default values of CUTs and physics processes
41 defined by the Config files, except for the gas mixture medium
42 of the tracking chambers. The CUT's and physics processes of
43 the gas mixture medium is then defined in the galice.cuts file
44 in the data directory. In particular ILOSS parameter MUST be
45 equal unity (1) in order simulate a realistic energy loss
46 distribution (mean value and fluctuations) in the active gas.
48 \section sim_s3 Tracking of particle in the magnetic field
50 GEANT has two ways for tracking charged particles in the
51 magnetic field: HELIX et RKUTA.
52 HELIX is faster and works well if the gradient of magnetic
54 For MUON, HELIX is a not a good approximation and we must
55 use RKUTA to get the optimal mass resolution of the
56 spectrometer. The choice of HELIX or RKUTA is done in the
57 config file when the magnetic field is defined:
59 AliMagFMaps* field = new AliMagFMaps("Maps","Maps", TRACKING, FACTOR, MAXB, AliMagFMaps::k5kG);
60 gAlice->SetField(field);
62 TRACKING must be 1 for RKUTA and 2 for HELIX (the default value for aliroot is 2 (HELIX))
63 FACTOR allows you to set the magnetic field to 0, just putting FACTOR=0. Default value is 1.
64 MAXB is the maximum magnetic field which is 10.T
66 \section sim_s4 MUON cocktail generator
68 There is a MUON cocktail generator of the muon sources in the
69 EVGEN directory. This class derives from AliGenCocktail.
70 In the init of this class I have filled the cocktail with
71 the muon sources: J/Psi, Upsilon, Open Charm, Open Beauty,
72 Pion, Kaons. The code needs only the production cross section
73 at 4pi (for the moment this values are in the code since I
74 prefere them do not be modified), and the code calculates the
75 rate of particles in the acceptance, making the scaling based
76 on the number of collisions for the hard probes and on the
77 number of participants for soft sources: Pions and Kaons.
79 In the Genereate of this class all entries in the cocktail
80 are called and we define a "primordial trigger" with requires
81 a minimum number of muons above a Pt cut in the required acceptance.
82 In order to normalized to the real number of simulated events,
83 there are 2 data members in the class fNsuceeded adn fNGenerate
84 which tell us what is the biais source.
86 Enclose an example to use this generator:
88 AliGenMUONCocktail * gener = new AliGenMUONCocktail();
89 gener->SetPtRange(1.,100.); // Transverse momentum range
90 gener->SetPhiRange(0.,360.); // Azimuthal angle range
91 gener->SetYRange(-4.0,-2.4);
92 gener->SetMuonPtCut(1.);
93 gener->SetMuonThetaCut(171.,178.);
94 gener->SetMuonMultiplicity(2);
95 gener->SetImpactParameterRange(0.,5.); // 10% most centra PbPb collisions
96 gener->SetVertexSmear(kPerTrack);
97 gener->SetOrigin(0,0,0); // Vertex position
98 gener->SetSigma(0,0,0.0); // Sigma in (X,Y,Z) (cm) on IP position
102 \section sim_s5 How to simulate events with misaligned geometry in local CDB
104 If you want to use a misaligned geometry to simulate some
105 events you can use a local CDB. For this need to follow
108 - Generate misaligned data in local CDB.
109 You can use MUONGenerateGeometryData.C as described above in
110 the corresponding section. Let's assume you used the default
111 residual misalignment settings, then you have a local CDB in
112 your working directory called ResMisAlignCDB containing
113 misalignement data (ResMisAlignCDB/MUON/Align).
115 - Tell AliSimulation you want to use your local CDB for
117 To do this you need to instantiate the AliCDBManager, set the
118 default storage and set the specific storage for MUON/Align/Data,
119 before instantiating AliSimulation (see for example the commented
120 lines AlirootRun_MUONtest.sh).
123 aliroot -b >& testSim.out << EOF
124 AliCDBManager* man = AliCDBManager::Instance();
125 man->SetDefaultStorage("local://$ALICE_ROOT");
126 man->SetSpecificStorage("MUON/align/Data","local://ResMisAlignCDB");
127 AliSimulation MuonSim("$ALICE_ROOT/MUON/Config.C");
128 MuonSim.SetWriteRawData("MUON");
134 \section sim_s6 How to Merge events
136 You can merge 2 types of simulated events. For example,
137 you can simulate Hijing events, and then simulate muons
140 Merging is done at the sdigits level, so Kinematics files
141 of the merged events will just correspond to the
142 Config.C simulated file).
144 You must, first, do the Hijing simulation and store it
145 in directory $HIJING_SIM. Note that for merging you
146 won't need Kinematics files of the Hijing simulation...
152 AliSimulation HijingSim("$HIJING_SIM/YourConfigForHIJING.C")
158 You cand build YourConfigFroHIJING.C File from the
159 ConfigPPR file in AliRoot/macros module.
161 Then you can do muon simulation and reconstruction
162 merging both simulated events. In next example, we are
163 merging 20 times each Hijing event in order to simulate
164 100 muons merged with 5 Hijing events.
168 AliSimulation MuonSim("$ALICE_ROOT/MUON/Config.C")
169 MuonSim.MergeWith("$HIJING_SIM/galice.root",20) //parameters are the Hijing simulation file and the number of times we use each Hijing event
170 MuonSim.Run(100) // number of muon (Config.C) events
176 TPluginManager * pluginmanager = gROOT->GetPluginManager()
177 pluginmanager->AddHandler("AliReconstructor","MUON","AliMUONReconstructor","MUON","AliMUONReconstructor()")
178 AliReconstruction MuonRec("galice.root")
179 MuonRec.SetRunTracking("")
180 MuonRec.SetRunVertexFinder(kFALSE)
181 MuonRec.SetRunLocalReconstruction("MUON")
182 MuonRec.SetFillESD("MUON")
188 \section sim_s7 On track numbering
190 All generated particles, including primary and secondary
191 particles are put on the stack. The secondary particles are kept
192 in the stack only if they gave a hit in *any* of the ALICE detectors
193 The number of all particles placed on the stack for a given event
195 Int_t nPart = AliStack::GetNtrack();
196 Looping from 0 to nPart via AliStack::Particle(ipart)
197 gives the particle listing as obtained from the particle generator (primaries)
198 and Monte Carlo (secondaries).
200 The particle response in the detector, a hit, is registered
201 in the hits tree and the hits are filled with each primary track.
202 The total number of "tracks" (fills of the tree) can be obtained
203 with ntracks = AliMUONMCDataInterface::NumberOfTracks(event) and is usually smaller than "nPart".
204 Since particles can also deposit hits in other detectors than
205 the MUON spectrometer, there will be many "tracks" (fills) in the hit-tree
206 without a hit in MUON.
208 The correspondence between "track ID" in the hits-tree ("itr") and the
209 particle ID for particles on the stack (i.e. generated particles) can be
212 for (Int_t itr = 0; itr < ntracks; itr++) {
213 AliMUONVHitStore* hitStore = mcDataInterface.HitStore(event,itr);
214 //track "itr" of the hits-tree
215 Int_t nhitstot = hitStore->GetSize();
217 TIter next(hitStore->CreateIterator());
218 while ( ( mHit = static_cast<AliMUONHit*>(next()) ) )
220 Int_t id = mHit->Track(); //gives particle ID on stack
221 TParticle* particle = mcDataInterface.Stack(event)->Particle(id);
226 where mcDataInterface has been obtained by
227 AliMUONMCDataInterface mcDataInterface("galice.root");
229 During the procedure to go from hits to digits, the hits
230 are summed up such that more than one track can contribute
231 to a given digit. As a consequence the method
232 Int_t AliMUONDigit::Track(Int_t trackID)
233 takes an argument, where "trackID" runs from 0 to
234 AliMUONDigit::Ntracks() to provide the reference to *all*
235 tracks that contributed to it. The returned track ID is the one
236 referred to in the hit-tree. To know which is the generated particle
237 that deposited a given digit one has to follow the sequence of the kind:
238 (shown here using the simple, but not fast, DataInterface interfaces) :
241 AliMUONMCDataInterface mcdi("galice.root");
242 AliMUONDataInterface di("galice.root");
244 AliMUONVDigitStore* digitStore = di.DigitStore(event);
245 AliMUONVDigit* mDigit = ... get some digit from the digitStore
247 for (int tr = 0; tr < mDigit->Ntracks(); tr++)
249 Int_t hitTrackID = mDigit->Track(tr);
250 // get the hits corresponding to this trackID
251 AliMUONHitStore* hitStore = mcdi.HitStore(event,hitTrackID);
252 // loop over the hits
253 TIter hNext(hitStore->CreateIterator());
255 while ( ( mHit = static_cast<AliMUONHit*>(hNext()) ) )
257 Int_t numPart = mHit->Track(); //gives ID of particle on the stack
258 Int_t idTrack = mHit->Particle(); //gives flavour code of the particle
263 This chapter is defined in the READMEsim.txt file.