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91509ec6 | 1 | // $Id$ |
2 | ||
3 | /*! | |
4 | ||
5 | \page README_rec Reconstruction | |
6 | ||
b1fea02e | 7 | The reconstruction is a multistage process, driven by the AliMUONTracker and AliMUONReconstructor classes |
8 | via the AliReconstruction class, which is divided into three parts: | |
9 | - the digitization of the electronic response, | |
10 | - the clustering of the digits to locate the crossing point of the muon with the chamber, | |
11 | - the tracking to reconstruct the trajectory of the muon in the spectrometer from which we can extract the kinematics. | |
91509ec6 | 12 | |
b1fea02e | 13 | All the adjustable options and parameters used to tune the different part of the reconstruction are handled by the class AliMUONRecoParam. |
91509ec6 | 14 | |
91509ec6 | 15 | |
b1fea02e | 16 | \section rec_s1 Digitization |
91509ec6 | 17 | |
b1fea02e | 18 | - We read the RAW data, convert them (convert them back for simulated data) to digit (object inheriting from AliMUONVDigit |
19 | stored into containers inheriting from AliMUONVDigitStore). This conversion is performed by the class AliMUONDigitMaker. | |
20 | - We calibrate the digits, via AliMUONDigitCalibrator, by subtracting pedestals and multiplying by gains. All the calibration parameters | |
21 | (pedestals, gains, capacitances and HV) are read from the OCDB and stored into AliMUONCalibrationData objects. | |
22 | - We create the status of the digit (e.g. pedestal higher than maximum or HV switched off), using AliMUONPadStatusMaker. | |
23 | - We create the status map for each digit, i.e the global status (good/bad) of that digit and of its neighbords, using AliMUONPadStatusMapMaker. | |
24 | - Calibrated digits might be saved (back) to TreeD in MUON.Digits.root file. | |
fd3ef136 | 25 | |
fd3ef136 | 26 | |
b1fea02e | 27 | \section rec_s2 Clustering |
28 | ||
29 | - We convert the digits having a positive charge into pads (AliMUONPad objects), which also contain information about the digit geometrical | |
30 | position. | |
31 | - We loop over pads in the bending and non-bending planes of the DE to form groups of contiguous pads. We then merge the overlapping groups | |
32 | of pads from both cathodes to build the pre-clusters that are the objects to be clusterized. | |
33 | - We unfold each pre-cluster in order to extract the number and the position of individual clusters merged in it (complex pre-clusters are | |
34 | made of a superimposition of signals from muon from physical background (e.g. hadrons) and from electronic noise). | |
35 | ||
36 | Several versions of pre-clustering are available, all inheriting from AliMUONVClusterFinder, with different ways to loop over pads to form | |
37 | pre-clusters: | |
38 | - AliMUONPreClusterFinder | |
39 | - AliMUONPreClusterFinderV2 | |
40 | - AliMUONPreClusterFinderV3 | |
41 | ||
42 | Several version of clustering are available, all inheriting from AliMUONVClusterFinder, with different degrees of complexity: | |
43 | - AliMUONClusterFinderCOG simply compute the Center Of Gravity of the charge distribution in the pre-cluster. | |
44 | - AliMUONClusterFinderSimpleFit simply fit the charge distribution with a single 2D Mathieson function. | |
45 | - AliMUONClusterFinderMLEM uses the Maximum Likelihood Expectation Minimization algorithm. | |
46 | This is a recursive procedure which determines the number and the approximate position of clusters into the pre-cluster that are needed | |
47 | to reproduce the whole charge distribution. It assumes that the charge distribution of each single cluster follow a 2D Mathieson function. | |
48 | If the estimated number of clusters is too high (>3), the pre-cluster is split into several groups of 1-2 or 3 clusters selected having | |
49 | the minimum total coupling to all the other clusters into the pre-cluster. Each group of clusters is then fitted with a sum of 2D Mathieson | |
50 | functions to extract their exact position. | |
51 | - AliMUONClusterFinderPeakCOG is a simplified version of the MLEM clusterizer, without splitting and computing the Center Of Gravity of the | |
52 | local charge distribution to extract the position of every clusters found in the pre-cluster. | |
53 | - AliMUONClusterFinderPeakFit is another simplified version of the MLEM clusterizer again without splitting. The pre-cluster is fitted with | |
54 | a sum of 2D Mathieson if it contains less than 3 clusters or we switch to the above COG method. | |
55 | ||
56 | The cluster recontruction is driven by the class AliMUONSimpleClusterServer, inheriting from AliMUONVClusterServer. | |
57 | It can be performed either before or during the tracking. In the first case, all the chambers are fully clusterized and the clusters (objects | |
58 | inheriting from AliMUONVCluster stored into containers inheriting from AliMUONVClusterStore) are saved to TreeR in Muon.RecPoints.root file. | |
59 | We use the class AliMUONLegacyClusterServer (also inheriting from AliMUONVClusterServer) read back the TreeR and provide clusters to the tracking. | |
60 | In the second case, we clusterize the chambers only in the region where we are looking for new clusters to be attached to the track candidates. | |
61 | This makes the clustering faster but the clusters cannot be saved to the TreeR. | |
62 | ||
63 | ||
64 | \section rec_s3 Tracking | |
65 | ||
66 | The MUON code provides two different algorithms to reconstruct the muon trajectory. In both cases the general tracking procedure is the same, | |
67 | the only difference being the way the track parameters are computed from the cluster positions. The "Original" algorithm perform a fit of the | |
68 | track parameters using the MINUIT package of Root, while the "Kalman" algorithm compute them using analytical formulae. The classes driving | |
69 | the tracking are AliMUONTrackReconstructor and AliMUONTrackReconstructorK for the "Original" and the "Kalman" algorithms respectively, | |
70 | both inheriting from AliMUONVTrackReconstructor. The reconstructed muon tracks are objects of the class AliMUONTrack. | |
71 | ||
72 | The general tracking procedure is as follow: | |
73 | - Build primary track candidates using clusters on station 4 and 5: Make all combination of clusters between the two chambers of station 5(4). | |
74 | For each combination compute the local position and orientation of the track and estimate its bending momentum given the averaged magnetic field | |
75 | inside the dipole and assuming that the track is coming from the vertex. Then select pairs for which the estimated bending momentum and the | |
76 | non-bending slope are within given limits. Extrapolate the primary track candidates to station 4(5), look for at least one compatible cluster to | |
77 | validate them and recompute the track parameters. | |
78 | - Remove the identical track candidates, i.e. the ones sharing exactly the same clusters. | |
79 | - Propagate the track to station 3, 2 then 1 and, at each step, ask the "ClusterServer" to provide clusters in the region of interest, | |
80 | and select the one(s) compatible with the track. The track is validated if we find at least 1 cluster per station. | |
81 | - Remove the double tracks, i.e. the ones sharing more than half of their clusters, keeping the one with the larger number of cluster or the | |
82 | one with the lowest chi2 in case of equality. Then recompute the track parameters at each attached cluster (using the so called Smoother algorithm | |
83 | in the case of the "Kalman" tracking). | |
84 | - The reconstructed tracks are finally matched with the trigger tracks (reconstructed from the local response of the trigger) to identify the | |
85 | muon(s) that made the trigger. | |
86 | ||
87 | The new clusters to be attached to the track are selected according to their local chi2 (i.e. their transverse position relatively to the track, | |
88 | normalized by the convolution of the cluster resolution with the resolution of track extrapolated at the cluster location). | |
89 | If several compatible clusters are foundon the same chamber, the track candidate is duplicated to consider all the possibilities. | |
90 | ||
91 | The last part of the tracking is the extrapolation of the reconstructed tracks to the vertex of the collision. The vertex position is measured | |
92 | by the SPD (the Silicon Pixel layers of the ITS Detector). In order to be able to perform any kind of muon analysis, we need to compute the track | |
93 | parameters assuming the muon has been produced in the initial collision as well as the track parameters in the vertex plane. The first set of | |
94 | parameters is obtained by correcting for energy loss and multiple Coulomb scattering in the front absorber (we force the track to come from the | |
95 | exact vertex position (x,y,z) by using the Branson correction), while the second one is obtained by correcting for energy loss only. | |
96 | ||
97 | The final results of the reconstruction - from which we will perform the physical analyses, compute detector efficiencies and perform calibration | |
98 | checks - are stored in objects of the class AliESDMuonTrack and saved in AliESD.root file. Three kinds of track can be saved: a tracker track | |
99 | matched with a trigger track, a tracker track alone and a trigger track alone (unused data members are set to default in the last two cases). | |
100 | The complete list of MUON data saved into ESD is given in section @ref rec_s5. | |
101 | ||
102 | ||
103 | \section rec_s4 How to tune the muon reconstruction | |
104 | ||
105 | Several options and adjustable parameters allow to tune the entire reconstruction. These can be changed by adding the following lines in the | |
106 | reconstruction macro (runReconstruction.C): | |
107 | \verbatim | |
108 | AliMUONRecoParam *muonRecoParam = AliMUONRecoParam::Get...Param(); | |
fd3ef136 | 109 | muonRecoParam->Use...(); |
110 | muonRecoParam->Set...(); | |
111 | ... | |
112 | AliRecoParam::Instance()->RegisterRecoParam(muonRecoParam); | |
b1fea02e | 113 | \endverbatim |
114 | ||
115 | Three sets of default parameters are available: | |
116 | - <code>GetLowFluxParam()</code>: parameters for p-p collisions | |
117 | - <code>GetHighFluxParam()</code>: parameters for Pb-Pb collisions | |
118 | - <code>GetCosmicParam()</code>: parameters for cosmic runs | |
119 | ||
120 | Every option/parameter can also be set one by one. Here is the complete list of available setters: | |
121 | - <code>SetCalibrationMode("mode")</code>: set the calibration mode: NOGAIN (only do pedestal subtraction), | |
122 | GAIN (do pedestal subtraction and apply gain correction, but with a single capacitance value for all channels), | |
123 | GAINCONSTANTCAPA (as GAIN, but with a channel-dependent capacitance value). | |
124 | - <code>SetClusteringMode("mode")</code>: set the clustering (pre-clustering) mode: NOCLUSTERING, PRECLUSTER, PRECLUSTERV2, PRECLUSTERV3, COG, | |
125 | SIMPLEFIT, SIMPLEFITV3, MLEM:DRAW, MLEM, MLEMV2, MLEMV3. | |
126 | - <code>SetTrackingMode("mode")</code>: Set the tracking mode: ORIGINAL, KALMAN. | |
127 | - <code>CombineClusterTrackReco(flag)</code>: switch on/off the combined cluster/track reconstruction | |
128 | - <code>SaveFullClusterInESD(flag, % of event)</code>: save all cluster info (including pads) in ESD, for the given percentage of events | |
129 | (100% by default) | |
130 | - <code>SetMostProbBendingMomentum(value)</code>: set the most probable value (GeV/c) of momentum in bending plane (used when B=0) | |
131 | - <code>SetMinBendingMomentum(value)</code>: set the minimum acceptable value (GeV/c) of track momentum in bending plane | |
132 | - <code>SetMaxBendingMomentum(value)</code>: set the maximum acceptable value (GeV/c) of track momentum in bending plane | |
133 | - <code>SetMaxNonBendingSlope(value)</code>: set the maximum value of the track slope in non bending plane | |
134 | - <code>SetMaxBendingSlope(value)</code>: set the maximum value of the track slope in non bending plane (used when B=0) | |
135 | - <code>SetNonBendingVertexDispersion(value)</code>: set the vertex dispersion (cm) in non bending plane (used for original tracking only) | |
136 | - <code>SetBendingVertexDispersion(value)</code>: set the vertex dispersion (cm) in bending plane (used for original tracking only) | |
137 | - <code>SetMaxNonBendingDistanceToTrack(value)</code>: set the maximum distance to the track to search for compatible cluster(s) in non bending | |
138 | direction. This value is convoluted with the track resolution to define the region of interest. | |
139 | - <code>SetMaxBendingDistanceToTrack(value)</code>: set the maximum distance to the track to search for compatible cluster(s) in bending direction | |
140 | This value is convoluted with the track resolution to define the region of interest. | |
141 | - <code>SetSigmaCutForTracking(value)</code>: set the cut in sigma to apply on cluster (local chi2) and track (global chi2) during tracking | |
142 | - <code>ImproveTracks(flag, sigma cut)</code>: recompute the local chi2 of each cluster with the final track parameters and removed the ones that | |
143 | do not pass a new quality cut. The track is removed if we do not end with at least one good cluster per station. | |
144 | - <code>ImproveTracks(flag)</code>: same as above using the default quality cut | |
145 | - <code>SetSigmaCutForTrigger(value)</code>: set the cut in sigma to apply on track during trigger hit pattern search | |
146 | - <code>SetStripCutForTrigger(value)</code>: set the cut in strips to apply on trigger track during trigger chamber efficiency | |
147 | - <code>SetMaxStripAreaForTrigger(value)</code>: set the maximum search area in strips to apply on trigger track during trigger chamber efficiency | |
148 | - <code>SetMaxNormChi2MatchTrigger(value)</code>: set the maximum normalized chi2 for tracker/trigger track matching | |
149 | - <code>TrackAllTracks(flag)</code>: consider all the clusters passing the sigma cut (duplicate the track) or only the best one | |
150 | - <code>RecoverTracks(flag)</code>: if no cluster is found in a given station, we try it again after having removed the worst of the 2 clusters | |
151 | attached in the previous station (assuming it was a cluster from background). | |
152 | - <code>MakeTrackCandidatesFast(flag)</code>: make the primary track candidates formed by cluster on stations 4 and 5 assuming there is no | |
153 | magnetic field in that region to speed up the reconstruction. | |
154 | - <code>MakeMoreTrackCandidates(Bool_t flag)</code>: make the primary track candidate using 1 cluster on station 4 and 1 cluster on station 5 | |
155 | instead of starting from 2 clusters in the same station. | |
156 | - <code>ComplementTracks(Bool_t flag)</code>: look for potentially missing cluster to be attached to the track (a track may contain up to 2 | |
157 | clusters per chamber do to the superimposition of DE, while the tracking procedure is done in such a way that only 1 can be attached). | |
158 | - <code>UseSmoother(Bool_t flag)</code>: use or not the smoother to recompute the track parameters at each attached cluster | |
159 | (used for Kalman tracking only) | |
160 | - <code>UseChamber(Int_t iCh, Bool_t flag)</code>: set the chambers to be used (disable the clustering if the chamber is not used). | |
161 | - <code>RequestStation(Int_t iSt, Bool_t flag)</code>: impose/release the condition "at least 1 cluster per station" for that station. | |
de487b6e | 162 | - <code>BypassSt45(Bool_t st4, Bool_t st5)</code>: make the primary track candidate from the trigger track instead of using stations 4 and/or 5. |
b1fea02e | 163 | |
164 | We can use the method Print("FULL") to printout all the parameters and options set in the class AliMUONRecoParam. | |
165 | ||
166 | ||
167 | \section rec_s5 ESD content | |
168 | ||
169 | The final results of the reconstruction are stored in objects of the class AliESDMuonTrack. Those objects contain: | |
170 | - Tracker track parameters (x, theta_x, y, theta_y, 1/p_yz) at vertex (x=x_vtx; y=y_vtx) | |
171 | - Tracker track parameters in the vertex plane | |
172 | - Tracker track parameters at first cluster | |
173 | - Tracker track parameter covariances at first cluster | |
174 | - Tracker track global informations (chi2, number of clusters, cluster map) | |
175 | - TClonesArray of associated clusters stored in AliESDMuonCluster objects | |
176 | - Trigger track informations (local trigger decision, strip pattern, hit pattern) | |
177 | - Chi2 of tracker/trigger track matching | |
178 | ||
179 | Each AliESDMuonCluster object contain by default: | |
180 | - Cluster ID providing information about the location of the cluster (chamber ID and DE ID) | |
181 | - Cluster position (x,y,z) | |
182 | - Cluster resolution (sigma_x,sigma_y) | |
183 | ||
184 | More information about clusters can be stored in these objects for a given fraction of events: | |
185 | - Charge | |
186 | - Chi2 | |
187 | - TClonesArray of associated pads stored in AliESDMuonPad objects | |
188 | ||
189 | Each AliESDMuonPad object contain: | |
190 | - Digit ID providing information about the location of the digit (DE ID, Manu ID, Manu channel and cathode) | |
191 | - Raw charge (ADC value) | |
192 | - Calibrated charge | |
193 | ||
194 | ||
195 | \section rec_s6 Conversion between MUON/ESD objects | |
196 | ||
197 | Every conversion between MUON objects (AliMUOVDigit/AliMUONVCluster/AliMUONTrack) and ESD objects | |
198 | (AliESDMuonPad/AliESDMuonCluster/AliESDMuonTrack) is done by the class AliMUONESDInterface. There are 2 ways of using this class: | |
199 | ||
200 | 1) Using the static methods to convert the objects one by one (and possibly put them into the provided store): | |
201 | - Get track parameters at vertex, at DCA, ...: | |
202 | \verbatim | |
203 | ... | |
204 | AliESDMuonTrack* esdTrack = new AliESDMuonTrack(*(esd->GetMuonTrack(iTrack))); | |
205 | AliMUONTrackParam param; | |
206 | AliMUONESDInterface::GetParamAtVertex(*esdTrack, param); | |
207 | \endverbatim | |
208 | ||
209 | - Convert an AliMUONVDigit to an AliESDMuonPad: | |
210 | \verbatim | |
211 | ... | |
212 | AliMUONVDigit *digit = ...; | |
213 | AliESDMuonPad esdPad; | |
214 | AliMUONESDInterface::MUONToESD(*digit, esdPad); | |
215 | \endverbatim | |
216 | ||
217 | - Convert an AliMUONLocalTrigger to a ghost AliESDMuonTrack (containing only trigger informations): | |
218 | \verbatim | |
219 | ... | |
220 | AliMUONLocalTrigger* locTrg = ...; | |
221 | AliESDMuonTrack esdTrack; | |
222 | AliMUONESDInterface::MUONToESD(locTrg, esdTrack, trackId); | |
223 | \endverbatim | |
224 | ||
225 | - Convert an AliESDMuonTrack to an AliMUONTrack: | |
226 | \verbatim | |
227 | ... | |
228 | AliESDMuonTrack* esdTrack = new AliESDMuonTrack(*(esd->GetMuonTrack(iTrack))); | |
229 | AliMUONTrack track; | |
230 | AliMUONESDInterface::ESDToMUON(*esdTrack, track); | |
231 | \endverbatim | |
232 | ||
233 | - Add an AliESDMuonTrack into an AliMUONVTrackStore: | |
234 | \verbatim | |
235 | ... | |
236 | AliESDMuonTrack* esdTrack = new AliESDMuonTrack(*(esd->GetMuonTrack(iTrack))); | |
237 | AliMUONVTrackStore *trackStore = AliMUONESDInteface::NewTrackStore(); | |
238 | AliMUONESDInterface::Add(*esdTrack, *trackStore); | |
239 | \endverbatim | |
240 | ||
241 | 2) Loading an entire ESDEvent and using the finders and/or the iterators to access the corresponding MUON objects: | |
242 | - First load the ESD event: | |
243 | \verbatim | |
244 | AliMUONESDInterface esdInterface; | |
245 | esdInterface.LoadEvent(*esd); | |
246 | \endverbatim | |
247 | ||
248 | - Get the track store: | |
249 | \verbatim | |
250 | AliMUONVTrackStore* trackStore = esdInterface.GetTracks(); | |
251 | \endverbatim | |
252 | ||
253 | - Access the number of digits in a particular cluster: | |
254 | \verbatim | |
255 | Int_t nDigits = esdInterface.GetNDigitsInCluster(clusterId); | |
256 | \endverbatim | |
257 | ||
258 | - Find a particular digit using its ID: | |
259 | \verbatim | |
260 | AliMUONVDigit *digit = esdInterface.FindDigit(digitId); | |
261 | \endverbatim | |
262 | ||
263 | - Find a particular cluster in a given track using their IDs: | |
264 | \verbatim | |
265 | AliMUONVCluster* cluster = esdInterface.FindCluster(trackId, clusterId); | |
266 | \endverbatim | |
267 | ||
268 | - Iterate over all clusters of a particular track using an iterator: | |
269 | \verbatim | |
270 | TIterator* nextCluster = esdInterface.CreateClusterIterator(trackId); | |
271 | while ((cluster = static_cast<AliMUONVCluster*>(nextCluster()))) {...} | |
272 | \endverbatim | |
273 | ||
274 | Note: You can change (via static method) the type of the store this class is using: | |
275 | \verbatim | |
276 | AliMUONESDInterface::UseTrackStore("name"); | |
277 | AliMUONESDInterface::UseClusterStore("name"); | |
278 | AliMUONESDInterface::UseDigitStore("name"); | |
279 | AliMUONESDInterface::UseTriggerStore("name"); | |
280 | \endverbatim | |
281 | ||
282 | ||
283 | \section rec_s7 ESD cluster/track refitting | |
284 | ||
285 | We can re-clusterize and re-track the clusters/tracks stored into the ESD by using the class AliMUONRefitter. This class gets the MUON objects | |
286 | to be refitted from an instance of AliMUONESDInterface (see section @ref rec_s6), then uses the reconstruction framework to refit the | |
287 | objects. The reconstruction parameters are still set via the class AliMUONRecoParam (see section @ref rec_s5). The initial data are not changed. | |
288 | Results are stored into new MUON objects. The aim of the refitting is to be able to study effects of changing the reconstruction parameters or the | |
289 | calibration parameters without re-running the entire reconstruction. | |
fd3ef136 | 290 | |
b1fea02e | 291 | To use this class we first have to connect it to the ESD interface containing MUON objects: |
292 | \verbatim | |
293 | AliMUONRefitter refitter; | |
294 | refitter.Connect(&esdInterface); | |
295 | \endverbatim | |
fd3ef136 | 296 | |
b1fea02e | 297 | We can then: |
298 | - Re-clusterize the ESD clusters using the attached ESD pads (several new clusters can be reconstructed per ESD cluster): | |
299 | \verbatim | |
300 | AliMUONVClusterStore* clusterStore = refitter.ReClusterize(iTrack, iCluster); | |
301 | AliMUONVClusterStore* clusterStore = refitter.ReClusterize(clusterId); | |
302 | \endverbatim | |
303 | ||
304 | - Re-fit the ESD tracks using the attached ESD clusters: | |
305 | \verbatim | |
306 | AliMUONTrack* track = refitter.RetrackFromClusters(iTrack); | |
307 | AliMUONVTrackStore* trackStore = refitter.ReconstructFromClusters(); | |
308 | \endverbatim | |
309 | ||
310 | - Reconstruct the ESD tracks from ESD pads (i.e. re-clusterize the attached clusters). Consider all the combination of clusters and return only | |
311 | the best one: | |
312 | \verbatim | |
313 | AliMUONTrack* track = refitter.RetrackFromDigits(iTrack); | |
314 | AliMUONVTrackStore* trackStore = refitter.ReconstructFromDigits(); | |
315 | \endverbatim | |
fd3ef136 | 316 | |
b1fea02e | 317 | The macro MUONRefit.C is an example of using this class. The results are stored in a new AliESDs.root file. |
fd3ef136 | 318 | |
91509ec6 | 319 | |
aa36dc36 | 320 | This chapter is defined in the READMErec.txt file. |
91509ec6 | 321 | |
322 | */ |