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The Semiconductor Tracker performance in the ATLAS Combined Testbeam 2004
Nuclear Physics B (Proc. Suppl.) 172 (2007) 64–66 www.elsevierphysics.com
The Semiconductor Tracker performance in the ATLAS Combined Testbeam 2004. S. Gonzalez-Sevillaa∗ , M.J. Costaa and S. Marti i Garciaa a Instituto de F´ısica Corpuscular (IFIC), Universitat de Val`encia/CSIC, Edificios de Investigaci´on de Paterna, P.O.Box 22085, Valencia, E-46071, Spain.
The performance of the Semiconductor Tracker in the ATLAS Combined Testbeam 2004 is presented. The setup and DAQ system, data quality and software framework are described. Results of spatial resolution, efficiency and noise occupancy are shown.
1. Introduction The Inner Detector (ID) is the internal tracker of the ATLAS experiment.The Semiconductor Tracker (SCT) [1] is one of the three sub-systems of the ID. The SCT is made of 4088 silicon microstrip modules, distributed in four layers in a barrel region and nine disks in two identical endcaps. More details about the characteristics of the SCT modules can be found in [2,3]. A full barrel slice of the ATLAS detector was tested at the CERN H8 testbeam facility during 2004 in the so-called Combined Testbeam (CTB). Detectors from all the different ATLAS subsystems were integrated in a common Data Acquisition (DAQ) system and the full offline chain was comissioned with a real data-taking environment. Figure 1. SCT setup in the CTB. 2. Setup of the SCT in the CTB Eight endcap outer modules were arranged by pairs in four layers (see Figure 1). The distance between consecutive layers and the overlaps between modules within the same layer reproduced the arrangement of barrel modules in the cylindrical structures of the real ATLAS SCT detector. A single carbon fibre plate held one pair of modules and was equipped with a cooling circuit and services for the readout. The supporting plates were placed vertically inside a light-tight thermally insulating box, flushed with cold ni∗ Corresponding
author (on behalf of the SCT Collab.)
0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.07.029
trogen in order to ensure a dry atmosphere. A water-ethanol mixture flowing at 5 ◦ C was used as the coolant needed to dissipate the heat generated by the 7W per module from the electrical power consumption. The modules were kept at a fixed nominal discriminator threshold of 1 fC (charge deposited from a mip is ∼ 3.6 fC). The modules were located perpendicularly to the incoming particle beam. The whole SCT testbox was put inside a magnet providing a magnetic field up to 1.4 T parallel to the strips. The DAQ system of the SCT was made of a
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in the front-side respect to the channel hit in the back-side of the same SCT modules was lost (see Figure 3). This problem was tackled in field-off runs, where the beam had an almost constant perpendicular incidence respect to the detecting modules. Some chips were delivering the binary information with one event shift. The correlation was recovered after offline correction.
Figure 2. SCT DAQ system and data-flow.
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first revision of final VME electronic modules that will be used in the real experiment. A schema of the SCT DAQ is shown in Figure 2. A clock of the same frequency as the LHC Bunch Crossing (40.08 MHz) clock was used for buffering the data in the FIFOs of the front-end chips. A Level 1 Accept trigger (made of the coincidence of several scintillators along the beamline and the Busy signals of all sub-detectors) was used for the readout of the data through optical fibres. Event fragments from the different detectors were sent to external farms for event-building and offline triggering. Complete events were transfered to a mass storage system (CASTOR) and archived for subsequent offline analysis. 3. Data quality and software framework A variety of runs of different particles (e, π, μ and γ), energies (varying from 3 up to 180 GeV/c2 ) and magnetic field configurations were recorded. A total of 22 Million events with all three ID subsystems were validated as usable for offline analysis. However, due to the complexity of the setup and the test-phase of the final DataFlow, some problems arose during data taking. In some runs, the expected correlation between the channel hit
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Figure 3. Correlation between channels hit in front and back-side for the as-recorded data (left) and after offline correction (right). Horizontal and vertical axis are respectively the channel hit in front and back-side of the same module. The offline reconstruction chain was implemented in the new ATLAS Event Data Model under the Athena software framework. A large number of tools and algorithms, developed for the Inner Detector [4] were used successfully in the CTB profitting from a flexible and modular design. The CTB extensively exercised the usage of different databases, crucial for the large scale experiment. As an example, the dead and/or noisy channels of the SCT modules were stored in the Conditions Database (the ATLAS offline database holding non-event data) and accessible from the different algorithms during the data reconstruction phase. 4. Alignment The alignment strategy followed in the CTB was to self-align the silicon detectors (Pixels and
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0.98 0.97
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SCT) without any external reference and then align the TRT using extrapolated silicon tracks. The non-uniform illumination of the SCT modules resulted in a non-sensitivity for some degrees of freedom.
Efficiency
S. Gonzalez-Sevilla et al. / Nuclear Physics B (Proc. Suppl.) 172 (2007) 64–66
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Figure 4. Residual distribution after alignment one SCT plane in the CTB. The outlined histogram corresponds to single-strip clusters and filled histogram to two-strip clusters. An example of residuals after alignment is shown in Figure 4. The spatial resolution due to single-strip clusters is given by the RMS of a uniform distribution with a width equal to the √ pitch: σ = p/ 12. For the two planes shown in Figure 4, the mean pitch hit by the beam was ∼ 77 m, resulting in σ ∼ 22 m in good agreement with the results obtained from data. 5. Efficiency and noise occupancy The tracking efficiency and noise occupancy of the SCT modules have been studied in the CTB (see Figure 5). For that, single track events were selected. A hit cluster was considered to be efficient if found 100 m close to the extrapolated track, and was counted as noise when found more than 500 m apart from the predicted track position. The plane under study was eliminated from the tracking in each case. All SCT planes were found to meet the ATLAS specifications in terms of efficiency and noise
Figure 5. Efficiency (left axis) and noise occupancy (right axis) for all SCT planes. Plane 10 was not working during the whole CTB. The upper and lower horizontal lines are the ATLAS specifications at nominal comparator threshold (1fC) for efficiency (>99%) and noise occupancy (<5×10−4) respectively.
occupancy at nominal threshold value. More details about the performance of the ID in the CTB are presented in [5]. 6. Conclusions The ATLAS 2004 CTB was a success for the SCT community. For the first time, a common data taking was possible with all the different subdetectors using the final offline reconstruction chain. 7. Acknowledgments The work presented here is the result of the dedicated efforts of both the ID software group and of the hardware experts during the CTB. REFERENCES 1. ATLAS ID TDR 2, CERN/LHCC/97-17. 2. R. Nisisus, Nucl. Instrum. Meth. A530, (2004) 44-49. 3. H. Fox, these proc. 4. W. Liebig and M. Elsing, these proc. 5. T. Cornelissen and W. Liebig, these proc.
The Semiconductor Tracker performance in the ATLAS Combined Testbeam 2004. S. Gonzalez-Sevillaa∗ , M.J. Costaa and S. Marti i Garciaa a Instituto de F´ısica Corpuscular (IFIC), Universitat de Val`encia/CSIC, Edificios de Investigaci´on de Paterna, P.O.Box 22085, Valencia, E-46071, Spain.
The performance of the Semiconductor Tracker in the ATLAS Combined Testbeam 2004 is presented. The setup and DAQ system, data quality and software framework are described. Results of spatial resolution, efficiency and noise occupancy are shown.
1. Introduction The Inner Detector (ID) is the internal tracker of the ATLAS experiment.The Semiconductor Tracker (SCT) [1] is one of the three sub-systems of the ID. The SCT is made of 4088 silicon microstrip modules, distributed in four layers in a barrel region and nine disks in two identical endcaps. More details about the characteristics of the SCT modules can be found in [2,3]. A full barrel slice of the ATLAS detector was tested at the CERN H8 testbeam facility during 2004 in the so-called Combined Testbeam (CTB). Detectors from all the different ATLAS subsystems were integrated in a common Data Acquisition (DAQ) system and the full offline chain was comissioned with a real data-taking environment. Figure 1. SCT setup in the CTB. 2. Setup of the SCT in the CTB Eight endcap outer modules were arranged by pairs in four layers (see Figure 1). The distance between consecutive layers and the overlaps between modules within the same layer reproduced the arrangement of barrel modules in the cylindrical structures of the real ATLAS SCT detector. A single carbon fibre plate held one pair of modules and was equipped with a cooling circuit and services for the readout. The supporting plates were placed vertically inside a light-tight thermally insulating box, flushed with cold ni∗ Corresponding
author (on behalf of the SCT Collab.)
0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.07.029
trogen in order to ensure a dry atmosphere. A water-ethanol mixture flowing at 5 ◦ C was used as the coolant needed to dissipate the heat generated by the 7W per module from the electrical power consumption. The modules were kept at a fixed nominal discriminator threshold of 1 fC (charge deposited from a mip is ∼ 3.6 fC). The modules were located perpendicularly to the incoming particle beam. The whole SCT testbox was put inside a magnet providing a magnetic field up to 1.4 T parallel to the strips. The DAQ system of the SCT was made of a
65
S. Gonzalez-Sevilla et al. / Nuclear Physics B (Proc. Suppl.) 172 (2007) 64–66
in the front-side respect to the channel hit in the back-side of the same SCT modules was lost (see Figure 3). This problem was tackled in field-off runs, where the beam had an almost constant perpendicular incidence respect to the detecting modules. Some chips were delivering the binary information with one event shift. The correlation was recovered after offline correction.
Figure 2. SCT DAQ system and data-flow.
750
750
700
700
650
650
600
600
550
550 550
first revision of final VME electronic modules that will be used in the real experiment. A schema of the SCT DAQ is shown in Figure 2. A clock of the same frequency as the LHC Bunch Crossing (40.08 MHz) clock was used for buffering the data in the FIFOs of the front-end chips. A Level 1 Accept trigger (made of the coincidence of several scintillators along the beamline and the Busy signals of all sub-detectors) was used for the readout of the data through optical fibres. Event fragments from the different detectors were sent to external farms for event-building and offline triggering. Complete events were transfered to a mass storage system (CASTOR) and archived for subsequent offline analysis. 3. Data quality and software framework A variety of runs of different particles (e, π, μ and γ), energies (varying from 3 up to 180 GeV/c2 ) and magnetic field configurations were recorded. A total of 22 Million events with all three ID subsystems were validated as usable for offline analysis. However, due to the complexity of the setup and the test-phase of the final DataFlow, some problems arose during data taking. In some runs, the expected correlation between the channel hit
600
650
700
750
550
600
650
700
750
Figure 3. Correlation between channels hit in front and back-side for the as-recorded data (left) and after offline correction (right). Horizontal and vertical axis are respectively the channel hit in front and back-side of the same module. The offline reconstruction chain was implemented in the new ATLAS Event Data Model under the Athena software framework. A large number of tools and algorithms, developed for the Inner Detector [4] were used successfully in the CTB profitting from a flexible and modular design. The CTB extensively exercised the usage of different databases, crucial for the large scale experiment. As an example, the dead and/or noisy channels of the SCT modules were stored in the Conditions Database (the ATLAS offline database holding non-event data) and accessible from the different algorithms during the data reconstruction phase. 4. Alignment The alignment strategy followed in the CTB was to self-align the silicon detectors (Pixels and
66
1
1 0.99
10-1
0.98 0.97
10-2
0.96
Noise Occupancy
SCT) without any external reference and then align the TRT using extrapolated silicon tracks. The non-uniform illumination of the SCT modules resulted in a non-sensitivity for some degrees of freedom.
Efficiency
S. Gonzalez-Sevilla et al. / Nuclear Physics B (Proc. Suppl.) 172 (2007) 64–66
-3
0.95
10
0.94 10-4
0.93 0.92 600
RMS(single-strip)=23 um σ(double-strip)=14 um
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Figure 4. Residual distribution after alignment one SCT plane in the CTB. The outlined histogram corresponds to single-strip clusters and filled histogram to two-strip clusters. An example of residuals after alignment is shown in Figure 4. The spatial resolution due to single-strip clusters is given by the RMS of a uniform distribution with a width equal to the √ pitch: σ = p/ 12. For the two planes shown in Figure 4, the mean pitch hit by the beam was ∼ 77 m, resulting in σ ∼ 22 m in good agreement with the results obtained from data. 5. Efficiency and noise occupancy The tracking efficiency and noise occupancy of the SCT modules have been studied in the CTB (see Figure 5). For that, single track events were selected. A hit cluster was considered to be efficient if found 100 m close to the extrapolated track, and was counted as noise when found more than 500 m apart from the predicted track position. The plane under study was eliminated from the tracking in each case. All SCT planes were found to meet the ATLAS specifications in terms of efficiency and noise
Figure 5. Efficiency (left axis) and noise occupancy (right axis) for all SCT planes. Plane 10 was not working during the whole CTB. The upper and lower horizontal lines are the ATLAS specifications at nominal comparator threshold (1fC) for efficiency (>99%) and noise occupancy (<5×10−4) respectively.
occupancy at nominal threshold value. More details about the performance of the ID in the CTB are presented in [5]. 6. Conclusions The ATLAS 2004 CTB was a success for the SCT community. For the first time, a common data taking was possible with all the different subdetectors using the final offline reconstruction chain. 7. Acknowledgments The work presented here is the result of the dedicated efforts of both the ID software group and of the hardware experts during the CTB. REFERENCES 1. ATLAS ID TDR 2, CERN/LHCC/97-17. 2. R. Nisisus, Nucl. Instrum. Meth. A530, (2004) 44-49. 3. H. Fox, these proc. 4. W. Liebig and M. Elsing, these proc. 5. T. Cornelissen and W. Liebig, these proc.