[u/mrichter/AliRoot.git] / ITS / doc / doc_ssd.html

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<FONT FACE="Albany, sans-serif"><FONT SIZE=4>============================================================================</FONT></FONT></P>
<P STYLE="margin-top: 0.17in; margin-bottom: 0.2in; page-break-after: avoid">
<FONT FACE="Albany, sans-serif"><FONT SIZE=4>Description of ALICE
Silicon Strip Detector (SSD) Code (May 7, 2008, Enrico Fragiacomo)</FONT></FONT></P>
<P STYLE="margin-top: 0.17in; margin-bottom: 0.2in; page-break-after: avoid">
<FONT FACE="Albany, sans-serif"><FONT SIZE=4>============================================================================</FONT></FONT></P>
<P STYLE="margin-bottom: 0in"><A NAME="Content"></A><STRONG><FONT SIZE=4 STYLE="font-size: 16pt">Content</FONT></STRONG>
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<OL>
	<LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 1">Geometrical
	description of the SSD module</A></P>
	<LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 2">Detector
	response simulation</A></P>
	<LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 3">Cluster finding
	and local reconstruction</A></P>
	<LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 4">Calibration
	files (OCDB)</A></P>
	<LI><P STYLE="margin-bottom: 0in"><A HREF="#punto 5">ECS Run types
	and DAs</A></P>
</OL>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-top: 0.17in; margin-bottom: 0.2in; page-break-after: avoid">
<FONT SIZE=4><FONT FACE="Albany, sans-serif">============================================================================</FONT></FONT></P>
<P><STRONG><A HREF="#Content" NAME="punto 1">Geometrical description
of the SSD module</A></STRONG></P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">Each of the 1698 SSD modules (748 on
layer5 and 950 on layer6, module index ranging 500-2198) is a
double-sided silicon strip detector. 
</P>
<P STYLE="margin-bottom: 0in">Both P- and N-side has 768 strips,
strip numbering ranging 0-767. Strip 0 on Pside is opposite to strip
0 on Nside (note that hardware numbering ranges 0-1535, with strip
1535, on Nside, opposite to strip 0 on Pside. This leads to
conversions of the type strip=1535-strip for Nside, e.g. in the
streamer class for rawdata decoding, see below).</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">P- and N-stereo angles are 7.5
milliradiant and 27.5 milliradiant, respectively, leading to a P-to-N
stereo angle of 35 milliradiant. This small value eventually
decreases the resolution (750 microns) along the z-coordinate
parallel to the strips but reduces the number of fake intersections
(ghosts). The resolution along the x-coordinate, perpendicular to the
strips, is down to 20 microns.</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">Detector size along x (r-phi): 72960
microns</P>
<P STYLE="margin-bottom: 0in">Detector size along z: 40000 microns</P>
<P STYLE="margin-bottom: 0in">Detector thickness (local y): 300
microns</P>
<P STYLE="margin-bottom: 0in">Strip pitch: 95 microns</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">Stereo angles, detector sizes and
number of channels are controlled via the <B>AliITSsegmentationSSD</B>
class, which also provides the tools for system frame conversion
(local to global and viceversa). 
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">Each SSD module is readout by 12 chips,
6 on P- and 6 on N-side, each of them reading 128 strips. Conversion
from local coordinates to chip index is also provided by
AliITSsegmentationSSD for dead area recovery during tracking (if the
track misses the point, the tracker checks if the area is readout by
a dead chip).</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">=================================================================================================================</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P><A NAME="punto 2"></A><STRONG><A HREF="#Content" NAME="punto 2">Detector
response simulation</A></STRONG></P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">The SSD response simulation and
digitization proceeds via the <B>AliITSsimulationSSD</B> class with
the method DigitiseModule(), which in turn is called for each module
by the HitsToDigits method of AliITS. Calibration and segmentation
information are obtained via the <B>AliITSDetTypeSim</B> class.</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in"> DigitiseModule calls: 
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<OL>
	<LI><P STYLE="margin-bottom: 0in">HitsToAnalogDigits, which 
	provides the analog strip signal from the energy release of the
	particle passing through the module. The step between two geant hits
	(tipically, one entering and one exiting the module for
	perpendicular tracks) is further divided into 25 microns step to
	allow for a better geometrical description of the charge
	distribution in the silicon. From the energy release in the step a
	certain amount of charge is produced (as electron-holes pairs
	generated in the middle of the step) which drifts as gaussian clouds
	to the two sides of the detector (electrons to the P- and holes to
	the N-side). The width of the cloud (which eventually determines the
	number of strips involved by the cloud) depends on the drift
	constant D and on the drift time, which in turn depends on the drift
	velocity and the generation point. Both D and drift velocity differ
	for the two types of carriers. The percentage of the charge gaussian
	cloud which spatially corresponds to a strip is given to that strip.
		</P>
	<P STYLE="margin-bottom: 0in"></P>
	<LI><P STYLE="margin-bottom: 0in">SdigitToDigit, which in turn: 
	</P>
	<OL>
		<LI><P STYLE="margin-bottom: 0in">distributes the signal to the
		neighbouring strips according to the capacitive coupling, 
		</P>
		<LI><P STYLE="margin-bottom: 0in">adds the electronic noise
		(modeled as a gaussian distribution) to each strip (noise values
		are taken from the OCDB via AliITSCalibrationSSD);</P>
		<LI><P STYLE="margin-bottom: 0in">kills dead strips;</P>
		<LI><P STYLE="margin-bottom: 0in">zero-suppresses those strips with
		signal below 3*sigma_noise.</P>
		<LI><P STYLE="margin-bottom: 0in">signal is finally converted to
		ADC units and uncalibrated for the gain (with values from the
		OCDB).</P>
	</OL>
</OL>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">========================================================================================================================</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P><A NAME="punto 3"></A><STRONG><A HREF="#Content" NAME="punto 3">Cluster
finding and local reconstruction</A></STRONG></P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">Cluster finding and local
reconstruction in the SSD proceeds via the AliITSClusterFinderV2SSD
class. As AliReconstruction::RunLocalEventReconstruction calls
AliITSReconstructor::Reconstruct for the ITS and in turn
AliITSDetTypeRec::DigitsToRecPoints, two differents methods of
AliITSClusterFinderV2SSD (FindRawClusters or RawdataToClusters) can
be called for each SSD module depending whether the input is a digits
file (essentially from simulation) or a rawdata file (from real
data). 
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">===============================================================================================================================</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P><A NAME="punto 4"></A><STRONG><A HREF="#Content" NAME="punto 4">Calibration
Files (OCDB)</A></STRONG></P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">There are 4 directories in ITS/Calib
with calibration data to be used in SSD reconstruction</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<OL>
	<LI><P STYLE="margin-bottom: 0in">NoiseSSD</P>
	<LI><P STYLE="margin-bottom: 0in">PedestalSSD</P>
	<LI><P STYLE="margin-bottom: 0in">BadChannelsSSD</P>
	<LI><P STYLE="margin-bottom: 0in">GainSSD</P>
</OL>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">========================================================================================================================</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P><A NAME="punto 5"></A><STRONG><A HREF="#Content" NAME="punto 5">ECS
Run Types amd DA</A></STRONG></P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">1) STANDALONE</P>
<P STYLE="margin-bottom: 0in">- for test purposes</P>
<P STYLE="margin-bottom: 0in">- no DA launched at EOR</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">2) PEDESTAL</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">3) PHYSICS</P>
<P STYLE="margin-bottom: 0in">Nothing done for now.</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
<P STYLE="margin-bottom: 0in">===========================================================================================================================</P>
<P STYLE="margin-bottom: 0in"><BR>
</P>
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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
	21	Silicon 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
	45	of 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
	49	layer5 and 950 on layer6, module index ranging 500-2198) is a
	50	double-sided silicon strip detector.
	51	</P>
	52	<P STYLE="margin-bottom: 0in">Both P- and N-side has 768 strips,
	53	strip numbering ranging 0-767. Strip 0 on Pside is opposite to strip
	54	0 on Nside (note that hardware numbering ranges 0-1535, with strip
	55	1535, on Nside, opposite to strip 0 on Pside. This leads to
	56	conversions of the type strip=1535-strip for Nside, e.g. in the
	57	streamer 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
	61	milliradiant and 27.5 milliradiant, respectively, leading to a P-to-N
	62	stereo angle of 35 milliradiant. This small value eventually
	63	decreases the resolution (750 microns) along the z-coordinate
	64	parallel to the strips but reduces the number of fake intersections
65	(ghosts). The resolution along the x-coordinate, perpendicular to the
66	strips, 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
70	microns</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
73	microns</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
78	number of channels are controlled via the <B>AliITSsegmentationSSD</B>
79	class, 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,
85	6 on P- and 6 on N-side, each of them reading 128 strips. Conversion
86	from local coordinates to chip index is also provided by
87	AliITSsegmentationSSD for dead area recovery during tracking (if the
88	track misses the point, the tracker checks if the area is readout by
89	a 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
98	response simulation</A></STRONG></P>
99	<P STYLE="margin-bottom: 0in"><BR>
100	</P>
101	<P STYLE="margin-bottom: 0in">The SSD response simulation and
102	digitization proceeds via the <B>AliITSsimulationSSD</B> class with
103	the method DigitiseModule(), which in turn is called for each module
104	by the HitsToDigits method of AliITS. Calibration and segmentation
105	information 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
156	finding 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
160	reconstruction in the SSD proceeds via the AliITSClusterFinderV2SSD
161	class. As AliReconstruction::RunLocalEventReconstruction calls
162	AliITSReconstructor::Reconstruct for the ITS and in turn
163	AliITSDetTypeRec::DigitsToRecPoints, two differents methods of
164	AliITSClusterFinderV2SSD (FindRawClusters or RawdataToClusters) can
165	be called for each SSD module depending whether the input is a digits
166	file (essentially from simulation) or a rawdata file (from real
167	data).
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
179	Files (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
183	with 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
200	Run 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>
220	</BODY>
221	</HTML>