- Email: [email protected]
A prototype of strip readout MRPC for CBM-TOF
Nuclear Instruments and Methods in Physics Research A 661 (2012) S125–S128
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
A prototype of strip readout MRPC for CBM-TOF Jingbo Wang a,b,n, Yi Wang a,b, Xianglei Zhu a,b, WeiCheng Ding a,b, Yuanjing Li a,b, Jianping Cheng a,b a b
Department of Engineering Physics, Tsinghua University, Beijing 100084, China Key Laboratory of Particle & Radiation Imaging, Ministry of Education, Tsinghua University, Beijing 100084, China
a r t i c l e in fo
abstract
Available online 29 September 2010
The time-of-flight (TOF) system of the CBM experiment is proposed to be assembled of Multi-gap Resistive Plate Chambers (MRPCs). A strip MRPC prototype with low-resistive silicate glass electrodes (bulk resistivity 1010 O cm) was developed suited for the high rate (up to 20 kHz/cm2) applications of CBM-TOF. Beam tests performed at GSI indicate time resolutions of about 70 ps with efficiencies larger than 95%. The beam position scan shows a crosstalk less than 25%. & 2010 Elsevier B.V. All rights reserved.
Keywords: MRPC Rate capability Time resolution Efficiency Crosstalk
1. Introduction Multi-gap Resistive Plate Chambers (MRPCs) are gas detectors with good time resolution, high efficiency and relatively low cost, firstly developed in 1996 [1]. Four years later, the development of MRPC [2] opened the possibility to build high resolution time of flight (TOF) system. At present, MRPCs have become favorite detectors for high-granularity large-area TOF systems in modern nuclear and particle physics experiments, such as ALICE, FOPI, HADES, HARP and STAR [3–7]. The Compressed Baryonic Matter (CBM) experiment, proposed at the future FAIR accelerator facility (GSI, Germany), is to investigate the strongly interacting matter under extremely high net baryon densities and moderate temperatures [8]. In the current design, the hadron identification is considered to use a time-of-flight (TOF) system based on MRPCs. However, considering the inner part of the TOF wall, high rate capability up to 20 kHz/cm2 is required for the MRPCs. To achieve this goal, we produced special low-resistive silicate glass with a bulk resistivity on the order of 1010 O cm (for more details, see Ref. [9]). In our previous study, a prototype of pad readout MRPC made of this type of silicate glass has shown satisfactory behavior in terms of efficiency and time resolution, at counting rates up to 25 kHz/cm2, thus fulfill the CBM requirement [9,10]. This paper presents results of a study of a strip MRPC prototype made of low-resistive silicate glass. The beam test was performed at GSI-Darmstadt, using secondary particles stemming from a 3 GeV proton beam in cave B. Limited by the mechanic system, it was impossible to achieve the high rate
n Corresponding author at: Department of Engineering Physics, Tsinghua University, Beijing 100084, China. Tel.: + 86 1062771960; fax: + 86 1062782658. E-mail address: [email protected] (J. Wang).
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.09.068
environment. Therefore, this paper focused explicitly on the multi-strip performance at low particle flux.
2. Experimental system 2.1. MRPC structure The basic structure of the strip readout MRPCs is depicted in Fig. 1, similar with that of the 10-gap MRPC tested for rate capability [9]. The high-voltage electrodes are covered by colloidal graphite spray with a surface resistivity about 2 MO/&. This mirror symmetrical structure has a same negative HV on the inner electrodes. The positive HV is applied to the outer electrodes. The gaps between the glass plates are ensured by 0.25 mm fishing lines. The readout strips have a 24 cm length and a 22 mm width. The intervals between the strips are 3 mm, in which grounded guard strips are printed in order to reduce the crosstalk. The cathode and anode signals are collected, respectively, by the inner and outer strips. The signals with the same polarity are joined together and differential signals are sent to the front end electronics (FEE) used for the STAR TOF prototype ‘‘TOFr’’ [11]. The detector is placed in a sealed iron box flushed with a gas mixture of 96.5% C2H2F4, 3% iso-C4H10 and 0.5% SF6 at atmospheric pressure. For the strip readout prototype studied in this paper, some samples of special silicate glass were produced for the construction of the high rate MRPC. This glass is characterized by electron conductivity and contains oxides of transition elements. It has a black color and is opaque to visible light, showing a relatively low bulk resistivity on the order of 1010 O cm. The long term stability test of the glass resistivity with large transported charges is shown in Ref. [9]. In this experiment, two MRPCs with the same structure were tested at the same time. MRPC#1 is made
S126
J. Wang et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S125–S128
100
130
90
120 Eff: MRPC#1
Efficiency (%)
80
Fig. 2. Beam test setup. All of the MRPCs and scintillators are movable along the vertical direction. The tracking information can be obtained from the silicon detectors.
of silicate glass electrodes with a relatively low resistivity ( 1010 O cm), while MRPC#2 is made of traditional float glass used as a reference counter.
110
Eff: MRPC#2 70
100
σdiff /P2
60
90
50
80
40
70
30 5.8
6.0
6.2
2.2. Beam test setup
6.4 6.6 6.8 High voltage (kV)
7.0
Time resolution (ps)
Fig. 1. Structure the MRPCs with strip readout.
60 7.2
Fig. 3. Efficiency and time resolution as a function of high voltage.
The beam test was performed under secondary particles scattering from 3 GeV proton collisions. The detectors were placed in a gas-tight box fixed on a moveable platform under the main beam and flushed with a continuous flow of 200 cm3/min, as shown in Fig. 2. Three scintillators read-out by photo multiplier tubes (PMs) were used to build a trigger system. The coincidence of all the PMT signals defined the direction of the scattered particles and gave the trigger for QDC and TDC crates. The size of the trigger area was 2 4 cm2, determined by the scintillators. Both the MRPCs and the scintillators were movable along the vertical direction, which allowed a low-resolution position scan across the MRPC strips. Using the tracking information from silicon detectors the particle position could be accurately confirmed.
1.5 Hz/cm2, while MRPC#2 made with silicate glass has a darkrate of 3.0 Hz/cm2. 3.1. HV scan To find the optimum operating voltage of the counters, the efficiency and time resolution were scanned as a function of the high voltage at low particle flux (less than 20 Hz/cm2). The efficiencies are always determined by the valid rates recorded by the scintillators as well as the MRPCs. The time resolution is calculated by characterizing the distribution of the time difference between the two MRPCs:
DTdiff ¼ TMRPC#1 TMRPC#2 3. Results and discussion Before starting the test, the MRPCs were conditioned under high voltage for a few hours in order to reach a stable, low darkrate working status. At high voltage of 76.8 kV and 50 mV threshold, for the reference float glass MRPC#1 the dark-rate is
The sdiff of a Gaussian fit within 72.0sdiff about the mean of the time distribution is considered as the combined resolution. Assuming that the resolution is equal forpboth MRPCs, the time ffiffiffi resolution for a single counter is sdiff = 2. These results are summarized in Fig. 3. It can be seen that for both MRPCs, time
J. Wang et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S125–S128
resolutions of 70 ps can be obtained with efficiencies larger than 95% at a working voltage of 76.8 kV.
S127
110 100 90
3.2. Beam position scan across the strips
or_eff
Using position information recorded by the mechanic system and the tracking information provided by the silicon detectors, time resolutions and efficiencies were scanned as a function of the transverse beam position across the strips (y-position). Fig. 4 shows the time resolution profile for both MRPCs. 70 ps is obtained in the middle of the strips with a position accuracy of 715 mm. Figs. 5 and 6 show the efficiency variations at different beam positions for MRPC#1 and MRPC#2, respectively. The overall efficiency, the efficiencies of each individual strip and
Efficiency (%)
80
eff1 eff2
70
eff3 eff1&2
60
eff2&3
2
1
50
3
40 30 20 10
120 strip1 115
0 50
55
60
strip2
65
70 75 80 85 90 y-position (mm)
95 100 105 110
110 strip3
Fig. 6. Efficiency profile of MRPC#2 across the strips.
Time resolution (ps)
105 100 95 90
1
2
3
85 80 75 70 65 60 50
55
60
65
70 75 80 85 y-position (mm)
90
95 100 105
Fig. 4. Time resolution profile across the strips.
4. Conclusion
110 100 90
or_eff
Efficiency (%)
80
eff1 eff2
70
eff3 eff1&2
60 1
50
2
eff2&3
3
40
the coincident efficiencies of neighboring strips are plotted. In order to keep an acceptable statistical precision, the position accuracy is set to 74 mm for the efficiency calculation. From Figs. 5 and 6, we can see an obvious efficiency drop for about 5% between the strips due to the effect of the guard strip. When trigged on the center of a strip (take strip2 for instance), the efficiency of the neighboring strip is caused by the crosstalk contribution. The crosstalk of MRPC#2 (reference counter made of float glass) is at the level of 3%. However, MRPC#1 shows larger values (10% on strip1 and 25% on strip3), and especially, the difference between the crosstalk on strip1 and that on strip3 is unexpected. These results are supposed to be caused by the electronic difference, or the intrinsic characters of the lowresistive glass. Future study and analysis are needed to search the exact reasons.
30
The TOF wall of the CBM spectrometer is proposed to use MRPCs. Simulations predict that the innermost part of the TOF system will be operated under particle fluxes of about 20 kHz/cm2, far beyond the reach of standard float-glass technology. In order to achieve this goal, a new type of low-resistive silicate glass has been developed. In our previous work, a pad readout MRPC made of silicate glass has an improved rate capability of up to 25 kHz/cm2. Based on the successful pad readout counter tested in the rate capability experiment, another MRPC prototype with strip readout was developed and tested in beam in GSI. The beam test focused on the multi-strip performance and has yield time resolutions of about 70 ps with efficiencies over 95%. Due to the effect of the guard strip, the efficiency drops obviously for about 5% between the strips. The beam position scan shows a crosstalk less than 25%.
20 10
Acknowledgments
0 50
55
60
65
70
75 80 85 90 y-position (mm)
95 100 105 110
Fig. 5. Efficiency profile of MRPC#1 across the strips.
We would like to thank the GSI test beam crew for providing us with excellent beam. This work is supported by the National Natural Science Foundation of China under Grant nos. 10620210287, 10610285, 10675072 and 10775082. This study is
S128
J. Wang et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S125–S128
also supported by the Ministry of Science and Technology under Grant no. 2008CB817707. References [1] E. Cerron Zeballos, et al., Nucl. Instr. and Meth. A NS374 (1996) 132. [2] P. Fonte, et al., Nucl. Instr. and Meth. A NS443 (2000) 201.
[3] [4] [5] [6] [7] [8] [9] [10] [11]
A. Akindinov, et al., Nucl. Instr. and Meth. A 602 (2009) 709. ¨ A. Schuttauf, et al., Nucl. Instr. and Meth. A NS533 (2004) 65. H. Alvarez-Pol, et al., Nucl. Instr. and Meth. A NS535 (2004) 277. A. Blanco, et al., Nucl. Instr. and Meth. A NS602 (2009) 691. Y. Wang, et al., Nucl. Instr. and Meth. A NS538 (2005) 425. Letter of Intent for the CBM Experiment, Darmstadt, Germany, 2004. J. Wang, et al., Nucl. Instr. and Meth. A . doi:10.1016/j.nima.2010.04.056. CBM Collaboration. CBM Progress Report 2009, March 2010, p. 37. F. Geurts, et al., Nucl. Instr. and Meth. A NS533 (2004) 60.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
A prototype of strip readout MRPC for CBM-TOF Jingbo Wang a,b,n, Yi Wang a,b, Xianglei Zhu a,b, WeiCheng Ding a,b, Yuanjing Li a,b, Jianping Cheng a,b a b
Department of Engineering Physics, Tsinghua University, Beijing 100084, China Key Laboratory of Particle & Radiation Imaging, Ministry of Education, Tsinghua University, Beijing 100084, China
a r t i c l e in fo
abstract
Available online 29 September 2010
The time-of-flight (TOF) system of the CBM experiment is proposed to be assembled of Multi-gap Resistive Plate Chambers (MRPCs). A strip MRPC prototype with low-resistive silicate glass electrodes (bulk resistivity 1010 O cm) was developed suited for the high rate (up to 20 kHz/cm2) applications of CBM-TOF. Beam tests performed at GSI indicate time resolutions of about 70 ps with efficiencies larger than 95%. The beam position scan shows a crosstalk less than 25%. & 2010 Elsevier B.V. All rights reserved.
Keywords: MRPC Rate capability Time resolution Efficiency Crosstalk
1. Introduction Multi-gap Resistive Plate Chambers (MRPCs) are gas detectors with good time resolution, high efficiency and relatively low cost, firstly developed in 1996 [1]. Four years later, the development of MRPC [2] opened the possibility to build high resolution time of flight (TOF) system. At present, MRPCs have become favorite detectors for high-granularity large-area TOF systems in modern nuclear and particle physics experiments, such as ALICE, FOPI, HADES, HARP and STAR [3–7]. The Compressed Baryonic Matter (CBM) experiment, proposed at the future FAIR accelerator facility (GSI, Germany), is to investigate the strongly interacting matter under extremely high net baryon densities and moderate temperatures [8]. In the current design, the hadron identification is considered to use a time-of-flight (TOF) system based on MRPCs. However, considering the inner part of the TOF wall, high rate capability up to 20 kHz/cm2 is required for the MRPCs. To achieve this goal, we produced special low-resistive silicate glass with a bulk resistivity on the order of 1010 O cm (for more details, see Ref. [9]). In our previous study, a prototype of pad readout MRPC made of this type of silicate glass has shown satisfactory behavior in terms of efficiency and time resolution, at counting rates up to 25 kHz/cm2, thus fulfill the CBM requirement [9,10]. This paper presents results of a study of a strip MRPC prototype made of low-resistive silicate glass. The beam test was performed at GSI-Darmstadt, using secondary particles stemming from a 3 GeV proton beam in cave B. Limited by the mechanic system, it was impossible to achieve the high rate
n Corresponding author at: Department of Engineering Physics, Tsinghua University, Beijing 100084, China. Tel.: + 86 1062771960; fax: + 86 1062782658. E-mail address: [email protected] (J. Wang).
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.09.068
environment. Therefore, this paper focused explicitly on the multi-strip performance at low particle flux.
2. Experimental system 2.1. MRPC structure The basic structure of the strip readout MRPCs is depicted in Fig. 1, similar with that of the 10-gap MRPC tested for rate capability [9]. The high-voltage electrodes are covered by colloidal graphite spray with a surface resistivity about 2 MO/&. This mirror symmetrical structure has a same negative HV on the inner electrodes. The positive HV is applied to the outer electrodes. The gaps between the glass plates are ensured by 0.25 mm fishing lines. The readout strips have a 24 cm length and a 22 mm width. The intervals between the strips are 3 mm, in which grounded guard strips are printed in order to reduce the crosstalk. The cathode and anode signals are collected, respectively, by the inner and outer strips. The signals with the same polarity are joined together and differential signals are sent to the front end electronics (FEE) used for the STAR TOF prototype ‘‘TOFr’’ [11]. The detector is placed in a sealed iron box flushed with a gas mixture of 96.5% C2H2F4, 3% iso-C4H10 and 0.5% SF6 at atmospheric pressure. For the strip readout prototype studied in this paper, some samples of special silicate glass were produced for the construction of the high rate MRPC. This glass is characterized by electron conductivity and contains oxides of transition elements. It has a black color and is opaque to visible light, showing a relatively low bulk resistivity on the order of 1010 O cm. The long term stability test of the glass resistivity with large transported charges is shown in Ref. [9]. In this experiment, two MRPCs with the same structure were tested at the same time. MRPC#1 is made
S126
J. Wang et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S125–S128
100
130
90
120 Eff: MRPC#1
Efficiency (%)
80
Fig. 2. Beam test setup. All of the MRPCs and scintillators are movable along the vertical direction. The tracking information can be obtained from the silicon detectors.
of silicate glass electrodes with a relatively low resistivity ( 1010 O cm), while MRPC#2 is made of traditional float glass used as a reference counter.
110
Eff: MRPC#2 70
100
σdiff /P2
60
90
50
80
40
70
30 5.8
6.0
6.2
2.2. Beam test setup
6.4 6.6 6.8 High voltage (kV)
7.0
Time resolution (ps)
Fig. 1. Structure the MRPCs with strip readout.
60 7.2
Fig. 3. Efficiency and time resolution as a function of high voltage.
The beam test was performed under secondary particles scattering from 3 GeV proton collisions. The detectors were placed in a gas-tight box fixed on a moveable platform under the main beam and flushed with a continuous flow of 200 cm3/min, as shown in Fig. 2. Three scintillators read-out by photo multiplier tubes (PMs) were used to build a trigger system. The coincidence of all the PMT signals defined the direction of the scattered particles and gave the trigger for QDC and TDC crates. The size of the trigger area was 2 4 cm2, determined by the scintillators. Both the MRPCs and the scintillators were movable along the vertical direction, which allowed a low-resolution position scan across the MRPC strips. Using the tracking information from silicon detectors the particle position could be accurately confirmed.
1.5 Hz/cm2, while MRPC#2 made with silicate glass has a darkrate of 3.0 Hz/cm2. 3.1. HV scan To find the optimum operating voltage of the counters, the efficiency and time resolution were scanned as a function of the high voltage at low particle flux (less than 20 Hz/cm2). The efficiencies are always determined by the valid rates recorded by the scintillators as well as the MRPCs. The time resolution is calculated by characterizing the distribution of the time difference between the two MRPCs:
DTdiff ¼ TMRPC#1 TMRPC#2 3. Results and discussion Before starting the test, the MRPCs were conditioned under high voltage for a few hours in order to reach a stable, low darkrate working status. At high voltage of 76.8 kV and 50 mV threshold, for the reference float glass MRPC#1 the dark-rate is
The sdiff of a Gaussian fit within 72.0sdiff about the mean of the time distribution is considered as the combined resolution. Assuming that the resolution is equal forpboth MRPCs, the time ffiffiffi resolution for a single counter is sdiff = 2. These results are summarized in Fig. 3. It can be seen that for both MRPCs, time
J. Wang et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S125–S128
resolutions of 70 ps can be obtained with efficiencies larger than 95% at a working voltage of 76.8 kV.
S127
110 100 90
3.2. Beam position scan across the strips
or_eff
Using position information recorded by the mechanic system and the tracking information provided by the silicon detectors, time resolutions and efficiencies were scanned as a function of the transverse beam position across the strips (y-position). Fig. 4 shows the time resolution profile for both MRPCs. 70 ps is obtained in the middle of the strips with a position accuracy of 715 mm. Figs. 5 and 6 show the efficiency variations at different beam positions for MRPC#1 and MRPC#2, respectively. The overall efficiency, the efficiencies of each individual strip and
Efficiency (%)
80
eff1 eff2
70
eff3 eff1&2
60
eff2&3
2
1
50
3
40 30 20 10
120 strip1 115
0 50
55
60
strip2
65
70 75 80 85 90 y-position (mm)
95 100 105 110
110 strip3
Fig. 6. Efficiency profile of MRPC#2 across the strips.
Time resolution (ps)
105 100 95 90
1
2
3
85 80 75 70 65 60 50
55
60
65
70 75 80 85 y-position (mm)
90
95 100 105
Fig. 4. Time resolution profile across the strips.
4. Conclusion
110 100 90
or_eff
Efficiency (%)
80
eff1 eff2
70
eff3 eff1&2
60 1
50
2
eff2&3
3
40
the coincident efficiencies of neighboring strips are plotted. In order to keep an acceptable statistical precision, the position accuracy is set to 74 mm for the efficiency calculation. From Figs. 5 and 6, we can see an obvious efficiency drop for about 5% between the strips due to the effect of the guard strip. When trigged on the center of a strip (take strip2 for instance), the efficiency of the neighboring strip is caused by the crosstalk contribution. The crosstalk of MRPC#2 (reference counter made of float glass) is at the level of 3%. However, MRPC#1 shows larger values (10% on strip1 and 25% on strip3), and especially, the difference between the crosstalk on strip1 and that on strip3 is unexpected. These results are supposed to be caused by the electronic difference, or the intrinsic characters of the lowresistive glass. Future study and analysis are needed to search the exact reasons.
30
The TOF wall of the CBM spectrometer is proposed to use MRPCs. Simulations predict that the innermost part of the TOF system will be operated under particle fluxes of about 20 kHz/cm2, far beyond the reach of standard float-glass technology. In order to achieve this goal, a new type of low-resistive silicate glass has been developed. In our previous work, a pad readout MRPC made of silicate glass has an improved rate capability of up to 25 kHz/cm2. Based on the successful pad readout counter tested in the rate capability experiment, another MRPC prototype with strip readout was developed and tested in beam in GSI. The beam test focused on the multi-strip performance and has yield time resolutions of about 70 ps with efficiencies over 95%. Due to the effect of the guard strip, the efficiency drops obviously for about 5% between the strips. The beam position scan shows a crosstalk less than 25%.
20 10
Acknowledgments
0 50
55
60
65
70
75 80 85 90 y-position (mm)
95 100 105 110
Fig. 5. Efficiency profile of MRPC#1 across the strips.
We would like to thank the GSI test beam crew for providing us with excellent beam. This work is supported by the National Natural Science Foundation of China under Grant nos. 10620210287, 10610285, 10675072 and 10775082. This study is
S128
J. Wang et al. / Nuclear Instruments and Methods in Physics Research A 661 (2012) S125–S128
also supported by the Ministry of Science and Technology under Grant no. 2008CB817707. References [1] E. Cerron Zeballos, et al., Nucl. Instr. and Meth. A NS374 (1996) 132. [2] P. Fonte, et al., Nucl. Instr. and Meth. A NS443 (2000) 201.
[3] [4] [5] [6] [7] [8] [9] [10] [11]
A. Akindinov, et al., Nucl. Instr. and Meth. A 602 (2009) 709. ¨ A. Schuttauf, et al., Nucl. Instr. and Meth. A NS533 (2004) 65. H. Alvarez-Pol, et al., Nucl. Instr. and Meth. A NS535 (2004) 277. A. Blanco, et al., Nucl. Instr. and Meth. A NS602 (2009) 691. Y. Wang, et al., Nucl. Instr. and Meth. A NS538 (2005) 425. Letter of Intent for the CBM Experiment, Darmstadt, Germany, 2004. J. Wang, et al., Nucl. Instr. and Meth. A . doi:10.1016/j.nima.2010.04.056. CBM Collaboration. CBM Progress Report 2009, March 2010, p. 37. F. Geurts, et al., Nucl. Instr. and Meth. A NS533 (2004) 60.