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 Tailing effect
68 The control to turn on/off the parametrized tailing effect:
70 AliMUON::SetTailEffect(Bool_t),
73 The parameter to tune increase/decrease the tailing effect is kept inside,
74 AliMUONResponseV0::DisIntegrate(). This parameter is an integer number
75 (excluding zero and four), the higher the value is the less is the tailing
80 Zero is excluded because it gives straight line transformation, and four
81 is excluded because the AliRoot simulation chain spends VERY VERY long
82 time in AliMUONResponseV0::DisIntegrate method, which reason was not yet
83 understood. The parameter for 1, 2, 3, 5, 6, 7, 8, 9, 10 were checked with
84 no slowing down problem, however parameters greater than 6 give almost no
85 tailing effect since they basically correspond to higher order polynomial
89 \section sim_s5 MUON cocktail generator
91 There is a MUON cocktail generator of the muon sources in the
92 EVGEN directory. This class derives from AliGenCocktail.
93 In the init of this class I have filled the cocktail with
94 the muon sources: J/Psi, Upsilon, Open Charm, Open Beauty,
95 Pion, Kaons. The code needs only the production cross section
96 at 4pi (for the moment this values are in the code since I
97 prefere them do not be modified), and the code calculates the
98 rate of particles in the acceptance, making the scaling based
99 on the number of collisions for the hard probes and on the
100 number of participants for soft sources: Pions and Kaons.
102 In the Genereate of this class all entries in the cocktail
103 are called and we define a "primordial trigger" with requires
104 a minimum number of muons above a Pt cut in the required acceptance.
105 In order to normalized to the real number of simulated events,
106 there are 2 data members in the class fNsuceeded adn fNGenerate
107 which tell us what is the biais source.
109 Enclose an example to use this generator:
111 AliGenMUONCocktail * gener = new AliGenMUONCocktail();
112 gener->SetPtRange(1.,100.); // Transverse momentum range
113 gener->SetPhiRange(0.,360.); // Azimuthal angle range
114 gener->SetYRange(-4.0,-2.4);
115 gener->SetMuonPtCut(1.);
116 gener->SetMuonThetaCut(171.,178.);
117 gener->SetMuonMultiplicity(2);
118 gener->SetImpactParameterRange(0.,5.); // 10% most centra PbPb collisions
119 gener->SetVertexSmear(kPerTrack);
120 gener->SetOrigin(0,0,0); // Vertex position
121 gener->SetSigma(0,0,0.0); // Sigma in (X,Y,Z) (cm) on IP position
125 \section sim_s6 How to simulate events with misaligned geometry in local CDB
127 If you want to use a misaligned geometry to simulate some
128 events you can use a local CDB. For this need to follow
131 - Generate misaligned data in local CDB.
132 You can use MUONGenerateGeometryData.C as described above in
133 the corresponding section. Let's assume you used the default
134 residual misalignment settings, then you have a local CDB in
135 your working directory called ResMisAlignCDB containing
136 misalignement data (ResMisAlignCDB/MUON/Align).
138 - Tell AliSimulation you want to use your local CDB for
140 To do this you need to instantiate the AliCDBManager, set the
141 default storage and set the specific storage for MUON/Align/Data,
142 before instantiating AliSimulation (see for example the commented
143 lines AlirootRun_MUONtest.sh).
146 aliroot -b >& testSim.out << EOF
147 AliCDBManager* man = AliCDBManager::Instance();
148 man->SetDefaultStorage("local://$ALICE_ROOT");
149 man->SetSpecificStorage("MUON/align/Data","local://ResMisAlignCDB");
150 AliSimulation MuonSim("$ALICE_ROOT/MUON/Config.C");
151 MuonSim.SetWriteRawData("MUON");
157 \section sim_s7 How to Merge events
159 You can merge 2 types of simulated events. For example,
160 you can simulate Hijing events, and then simulate muons
163 Merging is done at the sdigits level, so Kinematics files
164 of the merged events will just correspond to the
165 Config.C simulated file).
167 You must, first, do the Hijing simulation and store it
168 in directory $HIJING_SIM. Note that for merging you
169 won't need Kinematics files of the Hijing simulation...
175 AliSimulation HijingSim("$HIJING_SIM/YourConfigForHIJING.C")
181 You cand build YourConfigFroHIJING.C File from the
182 ConfigPPR file in AliRoot/macros module.
184 Then you can do muon simulation and reconstruction
185 merging both simulated events. In next example, we are
186 merging 20 times each Hijing event in order to simulate
187 100 muons merged with 5 Hijing events.
191 AliSimulation MuonSim("$ALICE_ROOT/MUON/Config.C")
192 MuonSim.MergeWith("$HIJING_SIM/galice.root",20) //parameters are the Hijing simulation file and the number of times we use each Hijing event
193 MuonSim.Run(100) // number of muon (Config.C) events
199 TPluginManager * pluginmanager = gROOT->GetPluginManager()
200 pluginmanager->AddHandler("AliReconstructor","MUON","AliMUONReconstructor","MUON","AliMUONReconstructor()")
201 AliReconstruction MuonRec("galice.root")
202 MuonRec.SetRunTracking("")
203 MuonRec.SetRunVertexFinder(kFALSE)
204 MuonRec.SetRunLocalReconstruction("MUON")
205 MuonRec.SetFillESD("MUON")
211 \section sim_s8 On track numbering
213 All generated particles, including primary and secondary
214 particles are put on the stack. The secondary particles are kept
215 in the stack only if they gave a hit in *any* of the ALICE detectors
216 The number of all particles placed on the stack for a given event
218 Int_t nPart = AliStack::GetNtrack();
219 Looping from 0 to nPart via AliStack::Particle(ipart)
220 gives the particle listing as obtained from the particle generator (primaries)
221 and Monte Carlo (secondaries).
223 The particle response in the detector, a hit, is registered
224 in the hits tree and the hits are filled with each primary track.
225 The total number of "tracks" (fills of the tree) can be obtained
226 with ntracks = AliMUONMCDataInterface::NumberOfTracks(event) and is usually smaller than "nPart".
227 Since particles can also deposit hits in other detectors than
228 the MUON spectrometer, there will be many "tracks" (fills) in the hit-tree
229 without a hit in MUON.
231 The correspondence between "track ID" in the hits-tree ("itr") and the
232 particle ID for particles on the stack (i.e. generated particles) can be
235 for (Int_t itr = 0; itr < ntracks; itr++) {
236 AliMUONVHitStore* hitStore = mcDataInterface.HitStore(event,itr);
237 //track "itr" of the hits-tree
238 Int_t nhitstot = hitStore->GetSize();
240 TIter next(hitStore->CreateIterator());
241 while ( ( mHit = static_cast<AliMUONHit*>(next()) ) )
243 Int_t id = mHit->Track(); //gives particle ID on stack
244 TParticle* particle = mcDataInterface.Stack(event)->Particle(id);
249 where mcDataInterface has been obtained by
250 AliMUONMCDataInterface mcDataInterface("galice.root");
252 During the procedure to go from hits to digits, the hits
253 are summed up such that more than one track can contribute
254 to a given digit. As a consequence the method
255 Int_t AliMUONDigit::Track(Int_t trackID)
256 takes an argument, where "trackID" runs from 0 to
257 AliMUONDigit::Ntracks() to provide the reference to *all*
258 tracks that contributed to it. The returned track ID is the one
259 referred to in the hit-tree. To know which is the generated particle
260 that deposited a given digit one has to follow the sequence of the kind:
261 (shown here using the simple, but not fast, DataInterface interfaces) :
264 AliMUONMCDataInterface mcdi("galice.root");
265 AliMUONDataInterface di("galice.root");
267 AliMUONVDigitStore* digitStore = di.DigitStore(event);
268 AliMUONVDigit* mDigit = ... get some digit from the digitStore
270 for (int tr = 0; tr < mDigit->Ntracks(); tr++)
272 Int_t hitTrackID = mDigit->Track(tr);
273 // get the hits corresponding to this trackID
274 AliMUONHitStore* hitStore = mcdi.HitStore(event,hitTrackID);
275 // loop over the hits
276 TIter hNext(hitStore->CreateIterator());
278 while ( ( mHit = static_cast<AliMUONHit*>(hNext()) ) )
280 Int_t numPart = mHit->Track(); //gives ID of particle on the stack
281 Int_t idTrack = mHit->Particle(); //gives flavour code of the particle
286 This chapter is defined in the READMEsim.txt file.