- Email: [email protected]
Pre-installation tests and calibration of the ALICE TOF modules
Nuclear Instruments and Methods in Physics Research A 661 (2012) S106–S109
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Pre-installation tests and calibration of the ALICE TOF modules A. Akindinov a, A. Alici b,c, P. Antonioli c, S. Arcelli b,c, Y.W. Baek d, M. Basile b,c, G. Cara Romeo c, L. Cifarelli b,c, F. Cindolo c, A. De Caro e, D. De Gruttola e, S. De Pasquale e, M. Fusco Girard e, Yu. Grishuk a, D. Hatzifotiadou c, H.T. Jung d, W.W. Jung d, D.S. Kim d, D.W. Kim d, H.N. Kim d, J.S. Kim d, S. Kiselev a, G. Laurenti c, K. Lee d, S.C. Lee d, D. Malkevich a,, A. Margotti c, R. Nania c, A. Nedosekin a, F. Noferini c,1, P. Pagano e, A. Pesci c, O. Pinazza c, R. Preghenella c,2, M. Ryabinin a, E. Scapparone c, G. Scioli b,c, A. Silenzi b,c, K. Voloshin a, M.C.S. Williams c, C. Zampolli f,1, A. Zichichi b,c,2 a
Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia Dipartimento di Fisica dell’Universita , Bologna, Italy Sezione INFN, Bologna, Italy d Department of Physics, Gangneung-Wonju National University, Gangneung, South Korea e Dipartimento di Fisica dell’Universita and INFN, Salerno, Italy f CERN, Geneva, Switzerland b c
a r t i c l e in f o
a b s t r a c t
Available online 27 August 2010
Before installation into the ALICE experiment, all 87 modules of the TOF system had to undergo a series of tests. Initial check-ups included control of the gas tightness, readout connections quality, and highvoltage tests. Further tests were performed on a specially constructed Cosmic Ray Test Facility, where main characteristics of the modules were scanned under the working high voltage by means of cosmic muons. All TOF channels proved to provide the detection efficiency of more than 97% and time resolution of 80–110 ps, which complies with the ALICE requirements. & 2010 Elsevier B.V. All rights reserved.
Keywords: MRPC ALICE TOF START Cosmic rays
1. Introduction A new method of particle identification based on the time-offlight (TOF) measurements by gaseous chambers of parallel-plate geometry has made a big progress during the last 15 years [1–4]. It has been practically proven, in the ALICE experiment at LHC [5], that this technique may be used to build large TOF arrays covering up to hundreds of square meters, providing near 100% detection efficiency and time resolution of about 50 ps. The ALICE TOF system [6] is constructed of strips of Multigap Resistive Plate Chambers (MRPC). It comprises almost 153 000 readout channels and covers an area of about 150 m2 [7]. MRPC strips, each containing 96 readout pads, are installed inside gas-tight TOF modules of different types, 15 or 19 strips per module. The ALICE-TOF R&D program and tests of the pilot TOF modules had been for the most part performed at the T10 testbeam facility at the CERN Proton Synchrotron [7]. However, construction of a large-scale system required an implementation
Corresponding author.
E-mail address: [email protected] (D. Malkevich). Also at INFN-CNAF, Bologna, Italy. 2 Also at Museo Storico della Fisica e Centro Studi e Ricerche ‘‘Enrico Fermi’’, Roma, Italy. 1
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.08.031
of new adequate assembling and testing techniques. In particular, mass beam tests of the ALICE TOF modules appeared to be very time- and cost-consuming. As an alternative, tests with cosmic particles were suggested. For this purpose, a special test area, capable of simultaneous testing and storing of up to 12 TOF modules, was arranged at CERN, with a Cosmic Ray Test Facility (CRTF) being its key element. Presented in this report are the test area description, test procedure, and main test results.
2. Test setup The ALICE TOF test area at CERN was equipped with two metal frames, each capable to accommodate six TOF modules. The storage frame (Fig. 1a) was used for preliminary tests of newly arrived modules, as well as for storing already tested modules on their way to the assembly area [8]. The other one, holding the CRTF proper (Fig. 1b), was intended for continuous tests of the TOF modules with cosmic particles. Both frames provided gas, low- and high-voltage supply. To facilitate positioning of the modules, a special loading platform (shown in Fig. 1a) and roller mechanisms were used. In CRTF, cosmic particles were triggered by two planes of Scintillation Counters with MRS APD Light Readout (START) [9]
A. Akindinov et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S106–S109
S107
Fig. 2. Distribution of gas leakage in TOF modules.
Fig. 1. Test area at CERN: (a) the storage frame with a loading platform, (b) CRTF with five TOF modules under test.
positioned at the top and at the bottom of the frame. These counters demonstrated a high level of stability during 3 years of CRTF operation [10]. The readout, low-voltage and high-voltage control systems used for TOF modules in CRTF were identical to those currently used in the ALICE experiment. Along with the tests at CRTF, the software involved was being debugged and finalized for further use in the ALICE environment. The DATE package [11] was used for readout control, PVSS-II [12]—for slow control, and MOOD [13]—for system monitoring.
3. Preliminary tests Upon arrival at CERN, the TOF modules were placed into the storage farm, where they gradually passed tests on gas tightness, quality of the connections between detecting pads and readout sockets, and measurements of leakage currents on the highvoltage channels. To check the gas tightness, the tested modules were inflated to an overpressure of 10–15 mbar, after which the pressure was monitored for 12–15 h. In case a significant leakage was found, the gas inputs and outputs were additionally sealed. In four cases, gaskets under the bottom module covers had to be reinstalled. As a result, the leakage values for all modules were found to be below 1 mbar/h, as shown in the distribution in Fig. 2. At the next step, the connections between MRPC pads and readout electronics were checked. For this purpose, each TOF module was equipped with a special connector for feeding pulser signals to the capacitances of all detecting pads. These signals
passed through the readout chain: strip connectors, flat cables, transmission cards (implemented as elements of top module covers) and output connectors of the modules [6]. Output signals were then sent to the readout electronics with the intrinsic timing jitter of 20 ps. During the tests, the pulser signals were simultaneously sent to 3 or 4 MRPC strips inside a tested module. A difference between the pulser synchronization signal and the logical signal of the readout electronics was measured for each individual channel with an oscilloscope. In case the signals were not observed, the corresponding flat cables were reconnected. As a result, the timing jitters of all channels were found to be below 30 ps. Finally, the modules were put under high-voltage tests. The chambers were filled with the working gas mixture [14] after which a bi-polar voltage of 1 kV was applied. The leakage currents in all TOF modules were found to be below 5 mA.
4. Tests at CRTF After preliminary tests five TOF modules (to form a single Super Module at a later stage [10]) were loaded into the CRTF frame, where they were connected to the readout electronics, gas, low- and high-voltage supplies. The gas system had five independent lines with the total flux of 10 l/h. During one week following the installation of the modules into CRTF, the high voltage was slowly raised on both polarities to reach 6.5 kV. The data were then taken independently with four different positions of the connected readout cards, as illustrated in Fig. 3. Cosmic particles were triggered by coincidence of signals coming from two STARTs (from the top and bottom layers) within a 40 ns time window. The cosmic trigger was being controlled and configured with a trigger configuration system specifically designed for CRTF (see the screenshot in Fig. 4). The system allowed for including or excluding any START counter in/from the trigger configuration. In most cases, two trigger configurations were used during the data taking, ‘left’ or ‘right’. In each of them, only one-half of START counters (left or right parts of the top and bottom layers) was included in the trigger. The ‘left’ configuration was used with the
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A. Akindinov et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S106–S109
Fig. 5. Example of a track triggered with two STARTs and corresponding hits in MRPC strips.
Fig. 3. The four connection positions of the readout cards (marked with numbers 1–4) and the corresponding trigger configurations (‘left’ and ‘right’).
Fig. 4. Screenshot of the trigger configuration interface.
readout cards in positions 1 or 2, the ‘right’ one—with the positions 3 and 4, see Fig. 3 for explanation. Due to the symmetric geometry and identical solid angles, the equal amounts of data obtained with the ‘left’ and ‘right’ trigger configurations, could be summed up to produce the data for the whole system.
5. Results In accordance with the ALICE TOF design [6], MRPC strips are inclined inside TOF modules in different ways, depending on the module type. Therefore, for geometrical reasons, cosmic particles
Fig. 6. Comparison of the efficiency obtained from simulation results (top) and from real measurements (bottom).
triggered with CRTF can pass through TOF modules without hits (see Fig. 5). To account for this effect, a Monte-Carlo simulation of the CRTF operation was performed for a part of a random TOF module under test, corresponding to one position of the readout cards. The TOF efficiency was then estimated by comparing the measured response with the simulation results, as shown in Fig. 6. The resulting TOF detecting efficiency for this particular module was found to be about 98%.
A. Akindinov et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S106–S109
S109
channels, where the CRTF acceptance was significantly lower. After applying the slewing correction, the width of the distribution t1–t3 was calculated (Fig. 7b). Assuming that pads 1 and 3 have close characteristics, the time resolution of a single channel pffiffiffi could be estimated as this width divided by 2. The resulting values of the time resolution were found in the range 80–100 ps. This is worse than 50 ps obtained previously during the beam tests [7] and may be explained by the uniform distribution of the hits over the sensitive areas of the pads (hit-position correction could not be performed because of poor tracking precision in CRTF) and by various inclination angles of the MRPC strips. Those pads for which the slewing correction could not be applied had a time resolution of about 110 ps, which agrees with the beam test results without slewing and hit-position corrections. These characteristics, both with and without slewing correction, were similar for all 87 tested TOF modules which proved that the mass assemblage procedure used for MRPC in ALICE TOF was adequate and effective.
40 Entries 926
20 0 −20 −40 −60 −80 −100
6. Conclusion
−120 200
400
600
800
1000
1200
1400
(t1−t2) vs. a1 [HPTDC bins]
All 87 modules of the ALICE TOF system passed a multi-step test procedure at a specially equipped area at CERN. The tests included complete inspection of the readout connections, troubleshooting and all necessary repairing, as well as measurements and calibration with cosmic particles. After tests, all modules had a gas leakage below 1 mbar/h and the leakage current in high voltage below 5 mA. The detection efficiency of the whole system was found to be above 97%, the time resolution — in the range 80–110 ps (without hit-position correction) — which meets the requirements of the ALICE experiment. These results were confirmed later, after installation of the TOF system, during continuous cosmic runs in 2008–2009 and during first pp collisions at the end of 2009 [15,16]. The equipment and methods used in the tests proved to be reliable and may be exploited in the future for tests and calibration of similar TOF systems, e.g. in the CBM (FAIR) or MPD (NICA) experiments.
Acknowledgements This work was partially supported from the RFBR Grant 08-0291011-CERN_a and from the funding program LHC-2 of the Russian Federal Agency of Atomic Energy (Rosatom). References
Fig. 7. Estimation of the time resolution (see Section 5 for details): (a) slewing correction, (b) time distribution.
Estimation of the time resolution was done by selecting events with tracks hitting pads positioned above each other on one vertical line, as shown in Fig. 5. Suppose we have three pads in such an event set (marked as 1, 2, 3 in Fig. 5). The slewing functions for pads 1 and 3 were calculated by plotting (t1 t2) vs. a1 and (t3 t2) vs. a3 distributions, with t staying for time, and a staying for TOT (signal trailing edge duration) data (Fig. 7a). This procedure required large statistics of more than 1000 events, and as a result it could not be performed for the most peripheral
[1] P. Fonte, A. Smirnitsky, M.C.S. Williams, Nucl. Instr. and Meth. A 443 (2000) 201. [2] A. Akindinov, et al., Nucl. Instr. and Meth. A 456 (2000) 16. [3] A. Akindinov, et al., Nucl. Instr. and Meth. A 494 (2002) 474. [4] A. Akindinov, et al., IEEE Trans. Nucl. Sci. NS-48 (5) (2001) 1658. [5] K. Aamodt, et al., ALICE Collaboration, JINST 0803 (2008) S08002. [6] ALICE Collaboration, Time-of-flight System, Addendum to ALICE TDR 8, CERN/ LHCC 2002-16. [7] A. Akindinov, et al., Nucl. Phys. Proc. Suppl. 158 (2006) 60. [8] A. Akindinov, et al., Nucl. Instr. and Meth. A 602 (2009) 709. [9] A. Akindinov, et al., Nucl. Instr. and Meth. A 539 (2005) 172. [10] A. Akindinov, et al., Nucl. Instr. and Meth. A 610 (2009) 431. [11] ALICE DAQ Project, ALICE-INT-2005-015. [12] /http://www.etm.at/index_e.asp?sname=div_siemens_faq_e.htmS. [13] R. Brun, et. al., ROOT /http://root.cern.chS. [14] A.N. Akindinov, et al., Nucl. Instr. and Meth. A 532 (2004) 562. [15] A. Akindinov, et al., Nucl. Instr. and Meth. A 615 (2010) 37. [16] A. Alici, et al., Nucl. Instr. and Meth. A, this issue.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Pre-installation tests and calibration of the ALICE TOF modules A. Akindinov a, A. Alici b,c, P. Antonioli c, S. Arcelli b,c, Y.W. Baek d, M. Basile b,c, G. Cara Romeo c, L. Cifarelli b,c, F. Cindolo c, A. De Caro e, D. De Gruttola e, S. De Pasquale e, M. Fusco Girard e, Yu. Grishuk a, D. Hatzifotiadou c, H.T. Jung d, W.W. Jung d, D.S. Kim d, D.W. Kim d, H.N. Kim d, J.S. Kim d, S. Kiselev a, G. Laurenti c, K. Lee d, S.C. Lee d, D. Malkevich a,, A. Margotti c, R. Nania c, A. Nedosekin a, F. Noferini c,1, P. Pagano e, A. Pesci c, O. Pinazza c, R. Preghenella c,2, M. Ryabinin a, E. Scapparone c, G. Scioli b,c, A. Silenzi b,c, K. Voloshin a, M.C.S. Williams c, C. Zampolli f,1, A. Zichichi b,c,2 a
Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia Dipartimento di Fisica dell’Universita , Bologna, Italy Sezione INFN, Bologna, Italy d Department of Physics, Gangneung-Wonju National University, Gangneung, South Korea e Dipartimento di Fisica dell’Universita and INFN, Salerno, Italy f CERN, Geneva, Switzerland b c
a r t i c l e in f o
a b s t r a c t
Available online 27 August 2010
Before installation into the ALICE experiment, all 87 modules of the TOF system had to undergo a series of tests. Initial check-ups included control of the gas tightness, readout connections quality, and highvoltage tests. Further tests were performed on a specially constructed Cosmic Ray Test Facility, where main characteristics of the modules were scanned under the working high voltage by means of cosmic muons. All TOF channels proved to provide the detection efficiency of more than 97% and time resolution of 80–110 ps, which complies with the ALICE requirements. & 2010 Elsevier B.V. All rights reserved.
Keywords: MRPC ALICE TOF START Cosmic rays
1. Introduction A new method of particle identification based on the time-offlight (TOF) measurements by gaseous chambers of parallel-plate geometry has made a big progress during the last 15 years [1–4]. It has been practically proven, in the ALICE experiment at LHC [5], that this technique may be used to build large TOF arrays covering up to hundreds of square meters, providing near 100% detection efficiency and time resolution of about 50 ps. The ALICE TOF system [6] is constructed of strips of Multigap Resistive Plate Chambers (MRPC). It comprises almost 153 000 readout channels and covers an area of about 150 m2 [7]. MRPC strips, each containing 96 readout pads, are installed inside gas-tight TOF modules of different types, 15 or 19 strips per module. The ALICE-TOF R&D program and tests of the pilot TOF modules had been for the most part performed at the T10 testbeam facility at the CERN Proton Synchrotron [7]. However, construction of a large-scale system required an implementation
Corresponding author.
E-mail address: [email protected] (D. Malkevich). Also at INFN-CNAF, Bologna, Italy. 2 Also at Museo Storico della Fisica e Centro Studi e Ricerche ‘‘Enrico Fermi’’, Roma, Italy. 1
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.08.031
of new adequate assembling and testing techniques. In particular, mass beam tests of the ALICE TOF modules appeared to be very time- and cost-consuming. As an alternative, tests with cosmic particles were suggested. For this purpose, a special test area, capable of simultaneous testing and storing of up to 12 TOF modules, was arranged at CERN, with a Cosmic Ray Test Facility (CRTF) being its key element. Presented in this report are the test area description, test procedure, and main test results.
2. Test setup The ALICE TOF test area at CERN was equipped with two metal frames, each capable to accommodate six TOF modules. The storage frame (Fig. 1a) was used for preliminary tests of newly arrived modules, as well as for storing already tested modules on their way to the assembly area [8]. The other one, holding the CRTF proper (Fig. 1b), was intended for continuous tests of the TOF modules with cosmic particles. Both frames provided gas, low- and high-voltage supply. To facilitate positioning of the modules, a special loading platform (shown in Fig. 1a) and roller mechanisms were used. In CRTF, cosmic particles were triggered by two planes of Scintillation Counters with MRS APD Light Readout (START) [9]
A. Akindinov et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S106–S109
S107
Fig. 2. Distribution of gas leakage in TOF modules.
Fig. 1. Test area at CERN: (a) the storage frame with a loading platform, (b) CRTF with five TOF modules under test.
positioned at the top and at the bottom of the frame. These counters demonstrated a high level of stability during 3 years of CRTF operation [10]. The readout, low-voltage and high-voltage control systems used for TOF modules in CRTF were identical to those currently used in the ALICE experiment. Along with the tests at CRTF, the software involved was being debugged and finalized for further use in the ALICE environment. The DATE package [11] was used for readout control, PVSS-II [12]—for slow control, and MOOD [13]—for system monitoring.
3. Preliminary tests Upon arrival at CERN, the TOF modules were placed into the storage farm, where they gradually passed tests on gas tightness, quality of the connections between detecting pads and readout sockets, and measurements of leakage currents on the highvoltage channels. To check the gas tightness, the tested modules were inflated to an overpressure of 10–15 mbar, after which the pressure was monitored for 12–15 h. In case a significant leakage was found, the gas inputs and outputs were additionally sealed. In four cases, gaskets under the bottom module covers had to be reinstalled. As a result, the leakage values for all modules were found to be below 1 mbar/h, as shown in the distribution in Fig. 2. At the next step, the connections between MRPC pads and readout electronics were checked. For this purpose, each TOF module was equipped with a special connector for feeding pulser signals to the capacitances of all detecting pads. These signals
passed through the readout chain: strip connectors, flat cables, transmission cards (implemented as elements of top module covers) and output connectors of the modules [6]. Output signals were then sent to the readout electronics with the intrinsic timing jitter of 20 ps. During the tests, the pulser signals were simultaneously sent to 3 or 4 MRPC strips inside a tested module. A difference between the pulser synchronization signal and the logical signal of the readout electronics was measured for each individual channel with an oscilloscope. In case the signals were not observed, the corresponding flat cables were reconnected. As a result, the timing jitters of all channels were found to be below 30 ps. Finally, the modules were put under high-voltage tests. The chambers were filled with the working gas mixture [14] after which a bi-polar voltage of 1 kV was applied. The leakage currents in all TOF modules were found to be below 5 mA.
4. Tests at CRTF After preliminary tests five TOF modules (to form a single Super Module at a later stage [10]) were loaded into the CRTF frame, where they were connected to the readout electronics, gas, low- and high-voltage supplies. The gas system had five independent lines with the total flux of 10 l/h. During one week following the installation of the modules into CRTF, the high voltage was slowly raised on both polarities to reach 6.5 kV. The data were then taken independently with four different positions of the connected readout cards, as illustrated in Fig. 3. Cosmic particles were triggered by coincidence of signals coming from two STARTs (from the top and bottom layers) within a 40 ns time window. The cosmic trigger was being controlled and configured with a trigger configuration system specifically designed for CRTF (see the screenshot in Fig. 4). The system allowed for including or excluding any START counter in/from the trigger configuration. In most cases, two trigger configurations were used during the data taking, ‘left’ or ‘right’. In each of them, only one-half of START counters (left or right parts of the top and bottom layers) was included in the trigger. The ‘left’ configuration was used with the
S108
A. Akindinov et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S106–S109
Fig. 5. Example of a track triggered with two STARTs and corresponding hits in MRPC strips.
Fig. 3. The four connection positions of the readout cards (marked with numbers 1–4) and the corresponding trigger configurations (‘left’ and ‘right’).
Fig. 4. Screenshot of the trigger configuration interface.
readout cards in positions 1 or 2, the ‘right’ one—with the positions 3 and 4, see Fig. 3 for explanation. Due to the symmetric geometry and identical solid angles, the equal amounts of data obtained with the ‘left’ and ‘right’ trigger configurations, could be summed up to produce the data for the whole system.
5. Results In accordance with the ALICE TOF design [6], MRPC strips are inclined inside TOF modules in different ways, depending on the module type. Therefore, for geometrical reasons, cosmic particles
Fig. 6. Comparison of the efficiency obtained from simulation results (top) and from real measurements (bottom).
triggered with CRTF can pass through TOF modules without hits (see Fig. 5). To account for this effect, a Monte-Carlo simulation of the CRTF operation was performed for a part of a random TOF module under test, corresponding to one position of the readout cards. The TOF efficiency was then estimated by comparing the measured response with the simulation results, as shown in Fig. 6. The resulting TOF detecting efficiency for this particular module was found to be about 98%.
A. Akindinov et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S106–S109
S109
channels, where the CRTF acceptance was significantly lower. After applying the slewing correction, the width of the distribution t1–t3 was calculated (Fig. 7b). Assuming that pads 1 and 3 have close characteristics, the time resolution of a single channel pffiffiffi could be estimated as this width divided by 2. The resulting values of the time resolution were found in the range 80–100 ps. This is worse than 50 ps obtained previously during the beam tests [7] and may be explained by the uniform distribution of the hits over the sensitive areas of the pads (hit-position correction could not be performed because of poor tracking precision in CRTF) and by various inclination angles of the MRPC strips. Those pads for which the slewing correction could not be applied had a time resolution of about 110 ps, which agrees with the beam test results without slewing and hit-position corrections. These characteristics, both with and without slewing correction, were similar for all 87 tested TOF modules which proved that the mass assemblage procedure used for MRPC in ALICE TOF was adequate and effective.
40 Entries 926
20 0 −20 −40 −60 −80 −100
6. Conclusion
−120 200
400
600
800
1000
1200
1400
(t1−t2) vs. a1 [HPTDC bins]
All 87 modules of the ALICE TOF system passed a multi-step test procedure at a specially equipped area at CERN. The tests included complete inspection of the readout connections, troubleshooting and all necessary repairing, as well as measurements and calibration with cosmic particles. After tests, all modules had a gas leakage below 1 mbar/h and the leakage current in high voltage below 5 mA. The detection efficiency of the whole system was found to be above 97%, the time resolution — in the range 80–110 ps (without hit-position correction) — which meets the requirements of the ALICE experiment. These results were confirmed later, after installation of the TOF system, during continuous cosmic runs in 2008–2009 and during first pp collisions at the end of 2009 [15,16]. The equipment and methods used in the tests proved to be reliable and may be exploited in the future for tests and calibration of similar TOF systems, e.g. in the CBM (FAIR) or MPD (NICA) experiments.
Acknowledgements This work was partially supported from the RFBR Grant 08-0291011-CERN_a and from the funding program LHC-2 of the Russian Federal Agency of Atomic Energy (Rosatom). References
Fig. 7. Estimation of the time resolution (see Section 5 for details): (a) slewing correction, (b) time distribution.
Estimation of the time resolution was done by selecting events with tracks hitting pads positioned above each other on one vertical line, as shown in Fig. 5. Suppose we have three pads in such an event set (marked as 1, 2, 3 in Fig. 5). The slewing functions for pads 1 and 3 were calculated by plotting (t1 t2) vs. a1 and (t3 t2) vs. a3 distributions, with t staying for time, and a staying for TOT (signal trailing edge duration) data (Fig. 7a). This procedure required large statistics of more than 1000 events, and as a result it could not be performed for the most peripheral
[1] P. Fonte, A. Smirnitsky, M.C.S. Williams, Nucl. Instr. and Meth. A 443 (2000) 201. [2] A. Akindinov, et al., Nucl. Instr. and Meth. A 456 (2000) 16. [3] A. Akindinov, et al., Nucl. Instr. and Meth. A 494 (2002) 474. [4] A. Akindinov, et al., IEEE Trans. Nucl. Sci. NS-48 (5) (2001) 1658. [5] K. Aamodt, et al., ALICE Collaboration, JINST 0803 (2008) S08002. [6] ALICE Collaboration, Time-of-flight System, Addendum to ALICE TDR 8, CERN/ LHCC 2002-16. [7] A. Akindinov, et al., Nucl. Phys. Proc. Suppl. 158 (2006) 60. [8] A. Akindinov, et al., Nucl. Instr. and Meth. A 602 (2009) 709. [9] A. Akindinov, et al., Nucl. Instr. and Meth. A 539 (2005) 172. [10] A. Akindinov, et al., Nucl. Instr. and Meth. A 610 (2009) 431. [11] ALICE DAQ Project, ALICE-INT-2005-015. [12] /http://www.etm.at/index_e.asp?sname=div_siemens_faq_e.htmS. [13] R. Brun, et. al., ROOT /http://root.cern.chS. [14] A.N. Akindinov, et al., Nucl. Instr. and Meth. A 532 (2004) 562. [15] A. Akindinov, et al., Nucl. Instr. and Meth. A 615 (2010) 37. [16] A. Alici, et al., Nucl. Instr. and Meth. A, this issue.