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18<FONT FACE="Albany, sans-serif"><FONT SIZE=4>============================================================================</FONT></FONT></P>
19<P STYLE="margin-top: 0.17in; margin-bottom: 0.2in; page-break-after: avoid">
20<FONT FACE="Albany, sans-serif"><FONT SIZE=4>Description of ALICE
21Silicon Strip Detector (SSD) Code (May 7, 2008, Enrico Fragiacomo)</FONT></FONT></P>
22<P STYLE="margin-top: 0.17in; margin-bottom: 0.2in; page-break-after: avoid">
23<FONT FACE="Albany, sans-serif"><FONT SIZE=4>============================================================================</FONT></FONT></P>
24<P STYLE="margin-bottom: 0in"><A NAME="Content"></A><STRONG><FONT SIZE=4 STYLE="font-size: 16pt">Content</FONT></STRONG>
25</P>
26<P STYLE="margin-bottom: 0in"><BR>
27</P>
28<OL>
29 <LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 1">Geometrical
30 description of the SSD module</A></P>
31 <LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 2">Detector
32 response simulation</A></P>
33 <LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 3">Cluster finding
34 and local reconstruction</A></P>
35 <LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 4">Calibration
36 files (OCDB)</A></P>
37 <LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 5">ECS Run types
38 and DAs</A></P>
39</OL>
40<P STYLE="margin-bottom: 0in"><BR>
41</P>
42<P STYLE="margin-top: 0.17in; margin-bottom: 0.2in; page-break-after: avoid">
43<FONT SIZE=4><FONT FACE="Albany, sans-serif">============================================================================</FONT></FONT></P>
44<P><STRONG><A HREF="#Content" NAME="punto 1">Geometrical description
45of the SSD module</A></STRONG></P>
46<P STYLE="margin-bottom: 0in"><BR>
47</P>
48<P STYLE="margin-bottom: 0in">Each of the 1698 SSD modules (748 on
49layer5 and 950 on layer6, module index ranging 500-2198) is a
50double-sided silicon strip detector.
51</P>
52<P STYLE="margin-bottom: 0in">Both P- and N-side has 768 strips,
53strip numbering ranging 0-767. Strip 0 on Pside is opposite to strip
540 on Nside (note that hardware numbering ranges 0-1535, with strip
551535, on Nside, opposite to strip 0 on Pside. This leads to
56conversions of the type strip=1535-strip for Nside, e.g. in the
57streamer class for rawdata decoding, see below).</P>
58<P STYLE="margin-bottom: 0in"><BR>
59</P>
60<P STYLE="margin-bottom: 0in">P- and N-stereo angles are 7.5
61milliradiant and 27.5 milliradiant, respectively, leading to a P-to-N
62stereo angle of 35 milliradiant. This small value eventually
63decreases the resolution (750 microns) along the z-coordinate
64parallel to the strips but reduces the number of fake intersections
65(ghosts). The resolution along the x-coordinate, perpendicular to the
66strips, is down to 20 microns.</P>
67<P STYLE="margin-bottom: 0in"><BR>
68</P>
69<P STYLE="margin-bottom: 0in">Detector size along x (r-phi): 72960
70microns</P>
71<P STYLE="margin-bottom: 0in">Detector size along z: 40000 microns</P>
72<P STYLE="margin-bottom: 0in">Detector thickness (local y): 300
73microns</P>
74<P STYLE="margin-bottom: 0in">Strip pitch: 95 microns</P>
75<P STYLE="margin-bottom: 0in"><BR>
76</P>
77<P STYLE="margin-bottom: 0in">Stereo angles, detector sizes and
78number of channels are controlled via the <B>AliITSsegmentationSSD</B>
79class, which also provides the tools for system frame conversion
80(local to global and viceversa).
81</P>
82<P STYLE="margin-bottom: 0in"><BR>
83</P>
84<P STYLE="margin-bottom: 0in">Each SSD module is readout by 12 chips,
856 on P- and 6 on N-side, each of them reading 128 strips. Conversion
86from local coordinates to chip index is also provided by
87AliITSsegmentationSSD for dead area recovery during tracking (if the
88track misses the point, the tracker checks if the area is readout by
89a dead chip).</P>
90<P STYLE="margin-bottom: 0in"><BR>
91</P>
92<P STYLE="margin-bottom: 0in"><BR>
93</P>
94<P STYLE="margin-bottom: 0in">=================================================================================================================</P>
95<P STYLE="margin-bottom: 0in"><BR>
96</P>
97<P><A NAME="punto 2"></A><STRONG><A HREF="#Content" NAME="punto 2">Detector
98response simulation</A></STRONG></P>
99<P STYLE="margin-bottom: 0in"><BR>
100</P>
101<P STYLE="margin-bottom: 0in">The SSD response simulation and
102digitization proceeds via the <B>AliITSsimulationSSD</B> class with
103the method DigitiseModule(), which in turn is called for each module
104by the HitsToDigits method of AliITS. Calibration and segmentation
105information are obtained via the <B>AliITSDetTypeSim</B> class.</P>
106<P STYLE="margin-bottom: 0in"><BR>
107</P>
108<P STYLE="margin-bottom: 0in"> DigitiseModule calls:
109</P>
110<P STYLE="margin-bottom: 0in"><BR>
111</P>
112<OL>
113 <LI><P STYLE="margin-bottom: 0in">HitsToAnalogDigits, which
114 provides the analog strip signal from the energy release of the
115 particle passing through the module. The step between two geant hits
116 (tipically, one entering and one exiting the module for
117 perpendicular tracks) is further divided into 25 microns step to
118 allow for a better geometrical description of the charge
119 distribution in the silicon. From the energy release in the step a
120 certain amount of charge is produced (as electron-holes pairs
121 generated in the middle of the step) which drifts as gaussian clouds
122 to the two sides of the detector (electrons to the P- and holes to
123 the N-side). The width of the cloud (which eventually determines the
124 number of strips involved by the cloud) depends on the drift
125 constant D and on the drift time, which in turn depends on the drift
126 velocity and the generation point. Both D and drift velocity differ
127 for the two types of carriers. The percentage of the charge gaussian
128 cloud which spatially corresponds to a strip is given to that strip.
129 </P>
130 <P STYLE="margin-bottom: 0in"></P>
131 <LI><P STYLE="margin-bottom: 0in">SdigitToDigit, which in turn:
132 </P>
133 <OL>
134 <LI><P STYLE="margin-bottom: 0in">distributes the signal to the
135 neighbouring strips according to the capacitive coupling,
136 </P>
137 <LI><P STYLE="margin-bottom: 0in">adds the electronic noise
138 (modeled as a gaussian distribution) to each strip (noise values
139 are taken from the OCDB via AliITSCalibrationSSD);</P>
140 <LI><P STYLE="margin-bottom: 0in">kills dead strips;</P>
141 <LI><P STYLE="margin-bottom: 0in">zero-suppresses those strips with
142 signal below 3*sigma_noise.</P>
143 <LI><P STYLE="margin-bottom: 0in">signal is finally converted to
144 ADC units and uncalibrated for the gain (with values from the
145 OCDB).</P>
146 </OL>
147</OL>
148<P STYLE="margin-bottom: 0in"><BR>
149</P>
150<P STYLE="margin-bottom: 0in"><BR>
151</P>
152<P STYLE="margin-bottom: 0in">========================================================================================================================</P>
153<P STYLE="margin-bottom: 0in"><BR>
154</P>
155<P><A NAME="punto 3"></A><STRONG><A HREF="#Content" NAME="punto 3">Cluster
156finding and local reconstruction</A></STRONG></P>
157<P STYLE="margin-bottom: 0in"><BR>
158</P>
159<P STYLE="margin-bottom: 0in">Cluster finding and local
160reconstruction in the SSD proceeds via the AliITSClusterFinderV2SSD
161class. As AliReconstruction::RunLocalEventReconstruction calls
162AliITSReconstructor::Reconstruct for the ITS and in turn
163AliITSDetTypeRec::DigitsToRecPoints, two differents methods of
164AliITSClusterFinderV2SSD (FindRawClusters or RawdataToClusters) can
165be called for each SSD module depending whether the input is a digits
166file (essentially from simulation) or a rawdata file (from real
167data).
168</P>
169<P STYLE="margin-bottom: 0in"><BR>
170</P>
171<P STYLE="margin-bottom: 0in"><BR>
172</P>
173<P STYLE="margin-bottom: 0in"><BR>
174</P>
175<P STYLE="margin-bottom: 0in">===============================================================================================================================</P>
176<P STYLE="margin-bottom: 0in"><BR>
177</P>
178<P><A NAME="punto 4"></A><STRONG><A HREF="#Content" NAME="punto 4">Calibration
179Files (OCDB)</A></STRONG></P>
180<P STYLE="margin-bottom: 0in"><BR>
181</P>
182<P STYLE="margin-bottom: 0in">There are 4 directories in ITS/Calib
183with calibration data to be used in SSD reconstruction</P>
184<P STYLE="margin-bottom: 0in"><BR>
185</P>
186<OL>
187 <LI><P STYLE="margin-bottom: 0in">NoiseSSD</P>
188 <LI><P STYLE="margin-bottom: 0in">PedestalSSD</P>
189 <LI><P STYLE="margin-bottom: 0in">BadChannelsSSD</P>
190 <LI><P STYLE="margin-bottom: 0in">GainSSD</P>
191</OL>
192<P STYLE="margin-bottom: 0in"><BR>
193</P>
194<P STYLE="margin-bottom: 0in"><BR>
195</P>
196<P STYLE="margin-bottom: 0in">========================================================================================================================</P>
197<P STYLE="margin-bottom: 0in"><BR>
198</P>
199<P><A NAME="punto 5"></A><STRONG><A HREF="#Content" NAME="punto 5">ECS
200Run Types amd DA</A></STRONG></P>
201<P STYLE="margin-bottom: 0in"><BR>
202</P>
203<P STYLE="margin-bottom: 0in">1) STANDALONE</P>
204<P STYLE="margin-bottom: 0in">- for test purposes</P>
205<P STYLE="margin-bottom: 0in">- no DA launched at EOR</P>
206<P STYLE="margin-bottom: 0in"><BR>
207</P>
208<P STYLE="margin-bottom: 0in">2) PEDESTAL</P>
209<P STYLE="margin-bottom: 0in"><BR>
210</P>
211<P STYLE="margin-bottom: 0in">3) PHYSICS</P>
212<P STYLE="margin-bottom: 0in">Nothing done for now.</P>
213<P STYLE="margin-bottom: 0in"><BR>
214</P>
215<P STYLE="margin-bottom: 0in"><BR>
216</P>
217<P STYLE="margin-bottom: 0in">===========================================================================================================================</P>
218<P STYLE="margin-bottom: 0in"><BR>
219</P>
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