- Email: [email protected]
Upgrade of the KEDR tagging system
Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
Upgrade of the KEDR tagging system V.M. Aulchenko, A.E. Bondar, A.F. Buzulutskov, A.O. Poluektov, L.V. Romanov, L.I. Shekhtman, A.V. Sokolov, V.M. Titov, A.A. Vasiljev*, V.N. Zhilich, V.V. Zhulanov Budker Institute of Nuclear Physics, Acad. Lavrentiev Prospect 11, Novosibirsk 630090, Russia
Abstract An upgrade of a special system to tag scattered electrons from two-photon processes, based on triple-GEM detectors, is described. The system is intended for the experiments at the VEPP-4M storage ring. Tests of the detector prototype with two gas mixtures confirm the feasibility of the chosen upgrade layout. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40.Cs; 29.40.Gx Keywords: Triple-GEM; Multi-GEM; Micropattern detectors; KEDR; Two-photon processes
1. Introduction
*
The paper describes the upgrade of the detector KEDR Tagging System (TS). The TS is designed to study two-photon ðgn gn Þ interactions with the detector KEDR [1,2] at the VEPP-4M collider. In these interactions virtual photons produce a Ceven state X. The reaction kinematics is fixed by the final electron and positron which are called Scattered Electrons (SE). The SE angles are of the order of 1=g: The detection of both SEs (‘‘double-tag’’ experiment) determines the parameters of the gn gn system. This method is complementary to commonly used ‘‘no-tag’’ and ‘‘single-tag’’ approaches. The primary physics problems to investigate with the help of the TS are:
* *
study of the total cross-section of two photons into hadrons at low Q2 ; study of C-even resonances, search for exotic states.
The basic idea of the TS is to use accelerator quadrupole lenses as a part of the spectrometer as shown in Fig. 1. It allows to register SEs leaving interaction point at zero angle: lower energy SE is taken away from equilibrium orbit with a help of vertical magnetic field and then is detected in one of the four tagging system stations TS1 –TS4 : Due to the focusing properties of quadrupoles, a SE transverse coordinate at the place of detection does not depend on its initial angle. Measuring the coordinate one can unambiguously determine the particle energy without measuring its angle. 1.1. Tagging system requirements
*Corresponding author. E-mail address: [email protected] (A.A. Vasiljev).
The first factor demanding an upgrade is insufficient spatial resolution. The 300 mm
0168-9002/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 2 ) 0 1 4 7 4 - 2
242
V.M. Aulchenko et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
3GEM detectors TS upgrade TS4
TS3
KEDR
TS2 TS1 M2
M1
L2
L1
S i.p.
16.5 m
Fig. 1. One arm of the KEDR Tagging System. Here M1 and M2 are bending magnets; L1, L2—quadrupole lenses; S—compensating solenoid; TSs are Tagging Stations. Each TS is a one-coordinate drift tube module. TS upgrade includes 3GEM detectors placed in front of each module.
transverse coordinate resolution of the current TS is not sufficient to operate at the energy of the J=c-resonance. The resolution must be better than 100 mm: The second factor is a wish for better background suppression. The main source of background in the Tagging System is the process of single Bremsstrahlung (SBS) at the colliding beam. The angular distribution of SBS electrons is even more sharp compared to that of electrons in gn gn processes. Implementing 2D-readout at each TS station, one could improve the signal/background ratio by rejecting events with small vertical angles. The disadvantage of this method is a partial loss of detector efficiency. The new Tagging System requirements could be summarized as follows: *
*
*
*
*
*
the resolution in transverse coordinate must be better than 100 mm; reliable multitrack event recognition and reconstruction must be provided by TS design, the detection system has to operate at a total counting rate per station higher than 106 Hz; 2D-readout is desirable for better background suppression, entrance angle of the SE ought to be measured with the accuracy of sy r103 for some background suppression, sensitive area of the detection system should start as close as possible to the vacuum pipe.
Multi-GEM (Gas Electron Multiplier [3]) detectors placed in front of the current TS stations satisfy all these conditions.
∆ UD ∆ UGEM1 ∆ UT1 ∆ UGEM2 ∆ UT2 ∆ UGEM3 ∆ UI
Drift electrode
E D Drift gap Top GEM
E T1 Transfer gap 1 Middle GEM
E T2 Transfer gap 2 Bottom GEM
EI
Induction gap Readout strips
Read−out electronics Fig. 2. 3GEM detector layout. Transfer gaps are 1 mm wide, the induction gap is 2 mm wide and the drift gap is 3 mm wide.
2. Detector and system layout 2.1. Investigated prototype and future detector’s design Multi-GEM detectors [4] have been already proposed for LHCb [5] and COMPASS [6] projects. The triple-GEM configuration chosen for the TS upgrade is shown in Fig. 2. The gas amplification of ionization occurs in GEM holes, where the electrical field is rather strong. The appropriate potential distribution provides the ionization drift with successive amplification in each GEM. The amplified charge is collected on a Printed Circuit Board (PCB) and transferred to readout electronics. The PCB has two layers with straight and stereo strips (Fig. 3). Stereo strips have varying inclination (Fig. 4) in order to obtain better vertical resolution near the collider plane. This would allow fine adjustment of SBS background rejection
V.M. Aulchenko et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
criteria. The layout of the PCB was optimized to minimize strip capacitance and thus get the best noise performance [7].
2.2. DAQ The goal of the proposed DAQ system (Fig. 5) is to digitize a set of detectors signals and transfer the result via an Ethernet connection. Signal measurements from all strips of each PCB are performed simultaneously in one Premux
243
preamplifier-multiplexor chip [8]. Then analog signals stored in the Premux are read out in sequence. Sets of analog signals from all TS stations of one TS ‘‘arm’’ are to be concentrated and quantized at single CAMAC stand in parallel. Assuming 12 bits for each signal value, TS1 –TS3 of 512 channels each and TS4 of 1024 channels yield 3:75 kbytes of raw data for one TS arm per single event. Raw data transfer via 100 Mbit Ethernet connection determines a limit on the event rate at the level of 3:3 103 Hz: Implemented hardware zero suppression would further raise the limit on the event rate.
3. Experimental results 0.1mm 5mm, 1mm
500µ
60µ
500µ
100
512pitches x 0.25mm=128mm
20 x 1mm=20
8 x 5mm=40mm
Fig. 3. PCB in detail.
Tests of the 3GEM prototype TS station with two different gas mixtures, Ar=iso-C4 H10 (70:30) and Ar=CO2 (70:30), have been performed. Low saturated vapor pressure of iso-C4 H10 restricts the maximum pressure of Ar/iso-C4 H10 mixture in a bottle to 10 atm; making it less convenient to use. But at the same time the working voltage in this mixture is lower than that in Ar=CO2 ; thus the discharge probability is also lower. So if some problems with a discharge had occurred in Ar=CO2 ; the Ar=iso-C4 H10 mixture would has been considered as a back-up option. Both mixtures turned out to be robust. One can see an efficiency plateau in Fig. 6. Cluster width dependence on gain shown in Fig. 7 in both mixtures is the same, giving the same signal-tonoise ratio dependence, shown on Fig. 6. Charge correlation between straight and stereo strip planes (Fig. 8) allows to assemble ‘‘straight’’ and ‘‘stereo’’ track components during the reconstruction procedure in the case of a multitrack event.
5 15
4. Conclusion
512pitches x 0.2mm=102mm Fig. 4. PCB layout.
While testing a 3GEM station prototype, gains up to 2 104 were obtained. At these gains an efficiency plateau is already achieved. Signal-tonoise ratio at the beginning of the plateau is about 20–30. Stable work of the installation with Ar=iso-
3 GEM
3 GEM
PREMUX
PREMUX
PREMUX
PREMUX
ADC
ADC
ADC
3 GEM
ADC
3 GEM
ADC
V.M. Aulchenko et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
244
Primary trigger
Controller
Secondary trigger Ethernet
Buffer / Filter
Digital/Analog output
Readout control Premux service signals
Fig. 5. DAQ scheme of 3GEM part of TS.
BINP Novosibirsk, Jan 2002
100
300
BINP Novosibirsk, Jan 2002
4
80
40 20
S/N
0
Ar/C4 H10- i (70:30) Ar/C4 H10-i (70:30) Ar/CO2 (70:30) Ar/CO2 (70:30)
-20 -40 3
4
3x10
10
Ar/CO2 (70:30) Ar/C4H10-i (70:30)
Cluster width (pitch)
Efficiency (%)
100
Signal-to-noise ratio
3GEM + stereo-PCB
Eff. 60
3
10 4 2x10
Gain Fig. 6. Efficiency (right axis) and signal-to-noise ratio (left axis) gain dependences in Ar=iso-C4 H10 and Ar=CO2 :
2 3 3x10
4
10
4
2x10
Gain Fig. 7. Cluster width dependences in Ar=iso-C4 H10 and Ar=CO2 :
C4 H10 (70:30) and Ar=CO2 (70:30) was shown. It allows to choose the more convenient Ar=CO2 gas as a working mixture. Straight and stereo planes charge correlation allows to satisfy 2D-multitrack readout requirements.
At the present time works on electronic equipment are on the way; detector mounting and testing procedures are planned for the fall of the year.
V.M. Aulchenko et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
245
Fig. 8. Charge correlation between straight and stereo strip planes.
References [1] V.M. Aulchenko, et al., Nucl. Instr. and Meth. A 355 (1995) 261. [2] V.M. Aulchenko, et al., Nucl. Instr. and Meth. A 379 (1996) 360. [3] F. Sauli, Nucl. Instr. and Meth. A 386 (1997) 531. [4] C. Buttner, . et al., Nucl. Instr. and Meth. A 409 (1998) 79. [5] M. Ziegler, et al., A triple GEM detector for LHCb, LHCb 99-024 TRAC, http://doc.cern.ch//archive/electronic/cern/ others/LHB/public/lhcb-99-024.ps.gz.
[6] B. Ketzer, Micro-pattern gas detectors in COMPASS, talk on the Eighth International Conference on Instrumentation for Colliding Beam Physics. http://www.inp.nsk.su/events/ confs/instr2002/talks/020301/ketzer.pdf. [7] A.E. Bondar, et al., Performance of the triple-GEM detector with optimized 2-D readout in high intensity hadron beam, BINP 2001-60, http://www.inp.nsk.su/publications/preps/oldwww/texts/p2001-60.ps. [8] L. Jones, PreMUX128 specification V2.3, Ruthenford Appleton Laboratory internal document, 1995, http:// hep.uia.ac.be/wimb/archive/forwardelectronics/PREMUX spec v2.3.ps.
Upgrade of the KEDR tagging system V.M. Aulchenko, A.E. Bondar, A.F. Buzulutskov, A.O. Poluektov, L.V. Romanov, L.I. Shekhtman, A.V. Sokolov, V.M. Titov, A.A. Vasiljev*, V.N. Zhilich, V.V. Zhulanov Budker Institute of Nuclear Physics, Acad. Lavrentiev Prospect 11, Novosibirsk 630090, Russia
Abstract An upgrade of a special system to tag scattered electrons from two-photon processes, based on triple-GEM detectors, is described. The system is intended for the experiments at the VEPP-4M storage ring. Tests of the detector prototype with two gas mixtures confirm the feasibility of the chosen upgrade layout. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40.Cs; 29.40.Gx Keywords: Triple-GEM; Multi-GEM; Micropattern detectors; KEDR; Two-photon processes
1. Introduction
*
The paper describes the upgrade of the detector KEDR Tagging System (TS). The TS is designed to study two-photon ðgn gn Þ interactions with the detector KEDR [1,2] at the VEPP-4M collider. In these interactions virtual photons produce a Ceven state X. The reaction kinematics is fixed by the final electron and positron which are called Scattered Electrons (SE). The SE angles are of the order of 1=g: The detection of both SEs (‘‘double-tag’’ experiment) determines the parameters of the gn gn system. This method is complementary to commonly used ‘‘no-tag’’ and ‘‘single-tag’’ approaches. The primary physics problems to investigate with the help of the TS are:
* *
study of the total cross-section of two photons into hadrons at low Q2 ; study of C-even resonances, search for exotic states.
The basic idea of the TS is to use accelerator quadrupole lenses as a part of the spectrometer as shown in Fig. 1. It allows to register SEs leaving interaction point at zero angle: lower energy SE is taken away from equilibrium orbit with a help of vertical magnetic field and then is detected in one of the four tagging system stations TS1 –TS4 : Due to the focusing properties of quadrupoles, a SE transverse coordinate at the place of detection does not depend on its initial angle. Measuring the coordinate one can unambiguously determine the particle energy without measuring its angle. 1.1. Tagging system requirements
*Corresponding author. E-mail address: [email protected] (A.A. Vasiljev).
The first factor demanding an upgrade is insufficient spatial resolution. The 300 mm
0168-9002/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 2 ) 0 1 4 7 4 - 2
242
V.M. Aulchenko et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
3GEM detectors TS upgrade TS4
TS3
KEDR
TS2 TS1 M2
M1
L2
L1
S i.p.
16.5 m
Fig. 1. One arm of the KEDR Tagging System. Here M1 and M2 are bending magnets; L1, L2—quadrupole lenses; S—compensating solenoid; TSs are Tagging Stations. Each TS is a one-coordinate drift tube module. TS upgrade includes 3GEM detectors placed in front of each module.
transverse coordinate resolution of the current TS is not sufficient to operate at the energy of the J=c-resonance. The resolution must be better than 100 mm: The second factor is a wish for better background suppression. The main source of background in the Tagging System is the process of single Bremsstrahlung (SBS) at the colliding beam. The angular distribution of SBS electrons is even more sharp compared to that of electrons in gn gn processes. Implementing 2D-readout at each TS station, one could improve the signal/background ratio by rejecting events with small vertical angles. The disadvantage of this method is a partial loss of detector efficiency. The new Tagging System requirements could be summarized as follows: *
*
*
*
*
*
the resolution in transverse coordinate must be better than 100 mm; reliable multitrack event recognition and reconstruction must be provided by TS design, the detection system has to operate at a total counting rate per station higher than 106 Hz; 2D-readout is desirable for better background suppression, entrance angle of the SE ought to be measured with the accuracy of sy r103 for some background suppression, sensitive area of the detection system should start as close as possible to the vacuum pipe.
Multi-GEM (Gas Electron Multiplier [3]) detectors placed in front of the current TS stations satisfy all these conditions.
∆ UD ∆ UGEM1 ∆ UT1 ∆ UGEM2 ∆ UT2 ∆ UGEM3 ∆ UI
Drift electrode
E D Drift gap Top GEM
E T1 Transfer gap 1 Middle GEM
E T2 Transfer gap 2 Bottom GEM
EI
Induction gap Readout strips
Read−out electronics Fig. 2. 3GEM detector layout. Transfer gaps are 1 mm wide, the induction gap is 2 mm wide and the drift gap is 3 mm wide.
2. Detector and system layout 2.1. Investigated prototype and future detector’s design Multi-GEM detectors [4] have been already proposed for LHCb [5] and COMPASS [6] projects. The triple-GEM configuration chosen for the TS upgrade is shown in Fig. 2. The gas amplification of ionization occurs in GEM holes, where the electrical field is rather strong. The appropriate potential distribution provides the ionization drift with successive amplification in each GEM. The amplified charge is collected on a Printed Circuit Board (PCB) and transferred to readout electronics. The PCB has two layers with straight and stereo strips (Fig. 3). Stereo strips have varying inclination (Fig. 4) in order to obtain better vertical resolution near the collider plane. This would allow fine adjustment of SBS background rejection
V.M. Aulchenko et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
criteria. The layout of the PCB was optimized to minimize strip capacitance and thus get the best noise performance [7].
2.2. DAQ The goal of the proposed DAQ system (Fig. 5) is to digitize a set of detectors signals and transfer the result via an Ethernet connection. Signal measurements from all strips of each PCB are performed simultaneously in one Premux
243
preamplifier-multiplexor chip [8]. Then analog signals stored in the Premux are read out in sequence. Sets of analog signals from all TS stations of one TS ‘‘arm’’ are to be concentrated and quantized at single CAMAC stand in parallel. Assuming 12 bits for each signal value, TS1 –TS3 of 512 channels each and TS4 of 1024 channels yield 3:75 kbytes of raw data for one TS arm per single event. Raw data transfer via 100 Mbit Ethernet connection determines a limit on the event rate at the level of 3:3 103 Hz: Implemented hardware zero suppression would further raise the limit on the event rate.
3. Experimental results 0.1mm 5mm, 1mm
500µ
60µ
500µ
100
512pitches x 0.25mm=128mm
20 x 1mm=20
8 x 5mm=40mm
Fig. 3. PCB in detail.
Tests of the 3GEM prototype TS station with two different gas mixtures, Ar=iso-C4 H10 (70:30) and Ar=CO2 (70:30), have been performed. Low saturated vapor pressure of iso-C4 H10 restricts the maximum pressure of Ar/iso-C4 H10 mixture in a bottle to 10 atm; making it less convenient to use. But at the same time the working voltage in this mixture is lower than that in Ar=CO2 ; thus the discharge probability is also lower. So if some problems with a discharge had occurred in Ar=CO2 ; the Ar=iso-C4 H10 mixture would has been considered as a back-up option. Both mixtures turned out to be robust. One can see an efficiency plateau in Fig. 6. Cluster width dependence on gain shown in Fig. 7 in both mixtures is the same, giving the same signal-tonoise ratio dependence, shown on Fig. 6. Charge correlation between straight and stereo strip planes (Fig. 8) allows to assemble ‘‘straight’’ and ‘‘stereo’’ track components during the reconstruction procedure in the case of a multitrack event.
5 15
4. Conclusion
512pitches x 0.2mm=102mm Fig. 4. PCB layout.
While testing a 3GEM station prototype, gains up to 2 104 were obtained. At these gains an efficiency plateau is already achieved. Signal-tonoise ratio at the beginning of the plateau is about 20–30. Stable work of the installation with Ar=iso-
3 GEM
3 GEM
PREMUX
PREMUX
PREMUX
PREMUX
ADC
ADC
ADC
3 GEM
ADC
3 GEM
ADC
V.M. Aulchenko et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
244
Primary trigger
Controller
Secondary trigger Ethernet
Buffer / Filter
Digital/Analog output
Readout control Premux service signals
Fig. 5. DAQ scheme of 3GEM part of TS.
BINP Novosibirsk, Jan 2002
100
300
BINP Novosibirsk, Jan 2002
4
80
40 20
S/N
0
Ar/C4 H10- i (70:30) Ar/C4 H10-i (70:30) Ar/CO2 (70:30) Ar/CO2 (70:30)
-20 -40 3
4
3x10
10
Ar/CO2 (70:30) Ar/C4H10-i (70:30)
Cluster width (pitch)
Efficiency (%)
100
Signal-to-noise ratio
3GEM + stereo-PCB
Eff. 60
3
10 4 2x10
Gain Fig. 6. Efficiency (right axis) and signal-to-noise ratio (left axis) gain dependences in Ar=iso-C4 H10 and Ar=CO2 :
2 3 3x10
4
10
4
2x10
Gain Fig. 7. Cluster width dependences in Ar=iso-C4 H10 and Ar=CO2 :
C4 H10 (70:30) and Ar=CO2 (70:30) was shown. It allows to choose the more convenient Ar=CO2 gas as a working mixture. Straight and stereo planes charge correlation allows to satisfy 2D-multitrack readout requirements.
At the present time works on electronic equipment are on the way; detector mounting and testing procedures are planned for the fall of the year.
V.M. Aulchenko et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 241–245
245
Fig. 8. Charge correlation between straight and stereo strip planes.
References [1] V.M. Aulchenko, et al., Nucl. Instr. and Meth. A 355 (1995) 261. [2] V.M. Aulchenko, et al., Nucl. Instr. and Meth. A 379 (1996) 360. [3] F. Sauli, Nucl. Instr. and Meth. A 386 (1997) 531. [4] C. Buttner, . et al., Nucl. Instr. and Meth. A 409 (1998) 79. [5] M. Ziegler, et al., A triple GEM detector for LHCb, LHCb 99-024 TRAC, http://doc.cern.ch//archive/electronic/cern/ others/LHB/public/lhcb-99-024.ps.gz.
[6] B. Ketzer, Micro-pattern gas detectors in COMPASS, talk on the Eighth International Conference on Instrumentation for Colliding Beam Physics. http://www.inp.nsk.su/events/ confs/instr2002/talks/020301/ketzer.pdf. [7] A.E. Bondar, et al., Performance of the triple-GEM detector with optimized 2-D readout in high intensity hadron beam, BINP 2001-60, http://www.inp.nsk.su/publications/preps/oldwww/texts/p2001-60.ps. [8] L. Jones, PreMUX128 specification V2.3, Ruthenford Appleton Laboratory internal document, 1995, http:// hep.uia.ac.be/wimb/archive/forwardelectronics/PREMUX spec v2.3.ps.