- Email: [email protected]
A liquid argon calorimeter prototype for forward region at the LHC
a
Nuclear Instruments and Methods in Physics Research A 370 (1996) 425-428
* __ __
NUCLEAR IN_NlS &METNoDs IN PHVSICS REsEAw)I
@ ELSEVIER
SectionA
A liquid argon calorimeter
prototype for forward region at the LHC
A. Artamonov, V. Epstein, P. Gorbunov, V. Jemanov, V. Khovansky”, A. Kuchenkov, S. Kruchinin, A. Maslennikov, M. Rjabinin, P. Shatalov, V. Vinogradov, V. Zaitsev, S. Zeldovich, I. Zuckerman ITEP. Mo.mw, Russian Federation
Received 29 May 1995: revised form received 4 August 1995 Abstract We report on the design and on beam test results of a liquid argon calorimeter prototype. This technology was proposed as an option for the forward region of an experiment at the future Large Hadron Collider (LHC) at CERN. The measurements were performed using electrons from the ITEP PS with an energy range of I to 5 GeV.
1. Introduction The main challenge for a forward calorimeter in a LHC experiment is the high radiation dose it must withstand, up to I MGy/yr at 1~1= 5, for an integrated luminosity of 10’ pb- ’ [I]. The calorimeter will have to function at luminosities up to 2 X 10s4 cm-‘s-l. Fast time response is therefore of importance. As far as the energy resolution is concerned, Monte Carlo simulations show that a modest hadronic energy resolution of about lOO%/ j/@z)@lOo/ c IS sufficient to accomplish the task [1,2]. Liquid argon is one of the technologies suitable for the forward region calorimetry at the LHC. Liquid argon is known to be radiation hard. Also, high speed is achievable by means of electronic shaping, provided that a short charge transfer time is ensured by the detector geometry. In this paper we report on a liquid argon calorimeter prototype with coaxial cylindrical electrodes, built at ITEP in 1993 and tested in the electron beam at the ITEP PS in 1994.
narrow, reducing the effect of positive ion build-up. This results in lower fabrication cost. In our prototype the desired gap between the rod and the tube is maintained by spacers. The rod-tube assemblies are embedded into an absorber matrix, thus forming a homogeneous structure with a line lateral granularity. By varying the number of tubes in a leadout cell one can form equal cells in 71X 4 space. This provides a flexibility which is of particular importance for the forward region where r] varies rapidly with the angle. Rods, tubes and an absorber matrix of the prototype are made of stainless steel. The absorber consists of a stack of plates with drilled holes, forming a hexagonal array with a centre-to-centre distance of 1 I mm. The tubes have an inner diameter of 9 mm. The rod diameter is 6 mm. The rod and the tube are separated by a liquid argon gap of 1.5 mm. The rods have in one end holes with soldered copper wire pins. The resulting calorimeter sampling fraction is 8%. The prototype has a cylindrical shape with a little top segment cut away to leave space for a heat exchanger coil. It has a radius of 35 mm (1.3 Molikre radii) and is 450 mm ( 17X,,) long. A schematic view of the prototype is given in Fig. I.
2. Prototype design The basic elements of the design are rods inserted in tubes running parallel (or nearly parallel) to the beam. This geometry has two important advantages compared to parallel plate geometry. First, the charge transfer is faster due to lower inductance of the circuit formed by the electrodes, which act as signal transmission lines. Second, cylindrical parts can be routinely produced with tolerances of tens of microns so that the active gap may be kept * Corresponding
author. E-mail [email protected]
0168-9002/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 016%9002(95)00833-O
3. Readout electronics A total of 29 rod-tubes assemblies were used in the prototype. Each has capacitance of 1 IOpF and wave impedance 20 R. High voltage is applied to the absorber matrix to avoid blocking capacitors in signal lines. The operational voltage was about 900 V. The rods are grouped in 15 readout channels (I4 pairs + I single) on the interconnection board mounted on the back face of the
A. Artamonov
426
et al. I Nucl. Instr. and Meth. in Phys. Res. A 370 (1996) 425-428 PCB
ROD
ABSORBER @=70mm
35 30
25 20 15 10 5
Fig.3
Fig. 3. Pulse height distribution histogram is for the pedestals.
Fig. I. Schematic view of the prototype. prototype. Signals exit the cryostat through cold feedthroughs. Connections to a PCB with front-end electronics are done through 40cm long 100 I2 twisted pairs. Two different readout schemes were used for two modes of operation. In the “MIP mode” when the response to cosmic muons is measured signals are grouped together right after a connector and fed into a charge sensitive preamplifier. In the “calorimeter mode” each of 15 signals is fed into a common base transistor. Transistor collectors are ganged together and the output signal is fed into a current preamplifier. In both cases the electronic chain is completed by a shaper and ADC readout located remotely. For the “MIP mode” a peaking time was set to 3 ps to optimize the signal to noise ratio which is of concern because of small signals generated by muons. The shaper integration time constant is 2 p.s and the differentiation constant is 5 ps. For the “calorimeter mode” we used a shaper producing a bipolar signal with a peaking time of 30 ns with a tail of opposite polarity defined by electrons drift time. The signal is sampled at its peak and digitized by FADC. The dispersion is switching time was less than 1 ns. The block diagram of readout electronics is given in
Fig. 2. readout
muons. The dashed
4. Tests with cosmic muons Operational tests of the prototype were performed with cosmic muons. The shaper output signal was gated by a coincidence of the two scintillating counters installed above and below the prototype positioned horizontally. The signal distribution at the drift field of 6.7 kV/cm is shown in Fig. 3. The mean measured charge is 7 X 1O’e which corresponds to 4 MeV of deposited energy. From the observed pedestal fluctuations (see Fig. 3) the electronic noise was found to be 5 X 1O’e (about 0.3 MeV). Fig. 4 shows the collected charge as a function of the drift field.
5. Beam tests The prototype was exposed to electron beam with energies l-5 GeV at the ITEP PS. It was installed on a rotatable support. A rotation around the vertical axis of 23” was controlled with a precision of 0.1”. The beam spot on the prototype face was 10 X 10 mm2. The beam divergence was less than 0.5”. It is known that the resolution of calorimeters with
channel
:........_..._.................. J Fig. 2. Block diagram
for cosmic
aDt ctwnnc,:.
of readout electronics.
A. Artamonov
0
90
8
80
7 0
et al. I Nucl. Instr. and Meth. in Phys. Res. A 370 (1996) 425-428
427
70 60 50 40 30 20
---l
I-.-u-
10 0
10' Fig. 4. The
E,“jCAO’
-5
-4
-3
-2
-1
0
1
2
An@: (de&es
collected charge as a function of the drift field. Fig. 6. The resolution
active elements arranged along the beam direction deteriorates significantly at zero angle [3] because of channeling. The angular scan was taken at 3.3 GeV. The signal distributions at different angles are shown in Fig. 5. The distributions have nearly a Gaussian shape and agree well with GEANT predictions. The low signal tail present at all the angles is due to material in the beam line. Fig. 6 presents the angular dependence of the resolution obtained from a Gaussian fit to experimental distributions within k2.5~ around the maximum. The data shows a small rise towards zero angle. The resolution varies by -20% which is quite acceptable for the forward calorimeter.
for electrons
as a function
of the incidence
angle.
The energy dependence of the response was studied at 0 = 2” which is the mean angle for the forward calorimeter coverage at the LHC. Data was taken at beam momenta 1.1, 2.2. 3.3 and 5.0 GeVlc. At each momentum the response was calculated as a peak value of a Gaussian fit to the signal distribution. It was further corrected for the energy leakage calculated by GEANT (-14%). The data shows a good linearity with energy (Fig. 7a). The resulting resolution was parameterized by a(E)IE = aJ/& $ b @c/
___
v)250 ‘;e 225
lf?200 ,/o
d. = 3”
175
150 125 100 75 50 25 ~,,,s
0
I’: ,,,,,,,,,L,
50
100
IS0
j
200
,v,,;L 0
50
FADC channels
0
50
100
150
FADC charm
/
,,,,,(,,
FSC
0
50
100
cl%
150
200
FADC channels
Fig. 5. Signal distributions for 3.3 GeV electrons at different incidence angles. The solid histograms are for data and the dashed histograms are Monte Carlo predictions.
Fig. 7. Electron energy response and resolution as a function of the energy at 13= 2”. Circles are for data and squares are Monte Carlo predictions.
A. Artanwnov
428
et al. I Nucl. Insir. and Meth. in Phys. Res. A 370 (1996) 425-428
E, where E is in GeV. The noise constant c was measured to be 340220 MeV. The fit with two parameters yields (r(E)IE = (26.4+3.5)%Ifi@(6.8~3.6)@(0.340+0.020)/E, in reasonable 7b).
agreement
with GEANT predictions
(see Fig.
6. Conclusions We have build a liquid argon calorimeter prototype with a cylindrical geometry of electrodes, equipped with fast readout electronics based on shaping technique. The prototype was tested with electrons. Tests demonstrated that the calorimeter response depends weakly on the incidence angle. The measured performance together with other attractive features of the proposed concept makes this technology a good candidate for a forward calorimeter at the LHC.
Acknowledgements We would like to thank D. Fournier, l? Jenni and J. Rutherfoord for fruitful conversations. The research described in this publication was made possible in part by Grant No. MBGOOO from the International Science Foundation.
References [l] ATLAS, Letter of Intent for a General-Purpose pp Experiment at the LHC at CERN, CERNILHCC192-4, LHCC/I 2. [2] SDC Collaboration, Technical Design Report, SDC-92-201. [3] D. Acosta et al., Nucl. Instr. and Meth. A 308 (1991) 481.
Nuclear Instruments and Methods in Physics Research A 370 (1996) 425-428
* __ __
NUCLEAR IN_NlS &METNoDs IN PHVSICS REsEAw)I
@ ELSEVIER
SectionA
A liquid argon calorimeter
prototype for forward region at the LHC
A. Artamonov, V. Epstein, P. Gorbunov, V. Jemanov, V. Khovansky”, A. Kuchenkov, S. Kruchinin, A. Maslennikov, M. Rjabinin, P. Shatalov, V. Vinogradov, V. Zaitsev, S. Zeldovich, I. Zuckerman ITEP. Mo.mw, Russian Federation
Received 29 May 1995: revised form received 4 August 1995 Abstract We report on the design and on beam test results of a liquid argon calorimeter prototype. This technology was proposed as an option for the forward region of an experiment at the future Large Hadron Collider (LHC) at CERN. The measurements were performed using electrons from the ITEP PS with an energy range of I to 5 GeV.
1. Introduction The main challenge for a forward calorimeter in a LHC experiment is the high radiation dose it must withstand, up to I MGy/yr at 1~1= 5, for an integrated luminosity of 10’ pb- ’ [I]. The calorimeter will have to function at luminosities up to 2 X 10s4 cm-‘s-l. Fast time response is therefore of importance. As far as the energy resolution is concerned, Monte Carlo simulations show that a modest hadronic energy resolution of about lOO%/ j/@z)@lOo/ c IS sufficient to accomplish the task [1,2]. Liquid argon is one of the technologies suitable for the forward region calorimetry at the LHC. Liquid argon is known to be radiation hard. Also, high speed is achievable by means of electronic shaping, provided that a short charge transfer time is ensured by the detector geometry. In this paper we report on a liquid argon calorimeter prototype with coaxial cylindrical electrodes, built at ITEP in 1993 and tested in the electron beam at the ITEP PS in 1994.
narrow, reducing the effect of positive ion build-up. This results in lower fabrication cost. In our prototype the desired gap between the rod and the tube is maintained by spacers. The rod-tube assemblies are embedded into an absorber matrix, thus forming a homogeneous structure with a line lateral granularity. By varying the number of tubes in a leadout cell one can form equal cells in 71X 4 space. This provides a flexibility which is of particular importance for the forward region where r] varies rapidly with the angle. Rods, tubes and an absorber matrix of the prototype are made of stainless steel. The absorber consists of a stack of plates with drilled holes, forming a hexagonal array with a centre-to-centre distance of 1 I mm. The tubes have an inner diameter of 9 mm. The rod diameter is 6 mm. The rod and the tube are separated by a liquid argon gap of 1.5 mm. The rods have in one end holes with soldered copper wire pins. The resulting calorimeter sampling fraction is 8%. The prototype has a cylindrical shape with a little top segment cut away to leave space for a heat exchanger coil. It has a radius of 35 mm (1.3 Molikre radii) and is 450 mm ( 17X,,) long. A schematic view of the prototype is given in Fig. I.
2. Prototype design The basic elements of the design are rods inserted in tubes running parallel (or nearly parallel) to the beam. This geometry has two important advantages compared to parallel plate geometry. First, the charge transfer is faster due to lower inductance of the circuit formed by the electrodes, which act as signal transmission lines. Second, cylindrical parts can be routinely produced with tolerances of tens of microns so that the active gap may be kept * Corresponding
author. E-mail [email protected]
0168-9002/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 016%9002(95)00833-O
3. Readout electronics A total of 29 rod-tubes assemblies were used in the prototype. Each has capacitance of 1 IOpF and wave impedance 20 R. High voltage is applied to the absorber matrix to avoid blocking capacitors in signal lines. The operational voltage was about 900 V. The rods are grouped in 15 readout channels (I4 pairs + I single) on the interconnection board mounted on the back face of the
A. Artamonov
426
et al. I Nucl. Instr. and Meth. in Phys. Res. A 370 (1996) 425-428 PCB
ROD
ABSORBER @=70mm
35 30
25 20 15 10 5
Fig.3
Fig. 3. Pulse height distribution histogram is for the pedestals.
Fig. I. Schematic view of the prototype. prototype. Signals exit the cryostat through cold feedthroughs. Connections to a PCB with front-end electronics are done through 40cm long 100 I2 twisted pairs. Two different readout schemes were used for two modes of operation. In the “MIP mode” when the response to cosmic muons is measured signals are grouped together right after a connector and fed into a charge sensitive preamplifier. In the “calorimeter mode” each of 15 signals is fed into a common base transistor. Transistor collectors are ganged together and the output signal is fed into a current preamplifier. In both cases the electronic chain is completed by a shaper and ADC readout located remotely. For the “MIP mode” a peaking time was set to 3 ps to optimize the signal to noise ratio which is of concern because of small signals generated by muons. The shaper integration time constant is 2 p.s and the differentiation constant is 5 ps. For the “calorimeter mode” we used a shaper producing a bipolar signal with a peaking time of 30 ns with a tail of opposite polarity defined by electrons drift time. The signal is sampled at its peak and digitized by FADC. The dispersion is switching time was less than 1 ns. The block diagram of readout electronics is given in
Fig. 2. readout
muons. The dashed
4. Tests with cosmic muons Operational tests of the prototype were performed with cosmic muons. The shaper output signal was gated by a coincidence of the two scintillating counters installed above and below the prototype positioned horizontally. The signal distribution at the drift field of 6.7 kV/cm is shown in Fig. 3. The mean measured charge is 7 X 1O’e which corresponds to 4 MeV of deposited energy. From the observed pedestal fluctuations (see Fig. 3) the electronic noise was found to be 5 X 1O’e (about 0.3 MeV). Fig. 4 shows the collected charge as a function of the drift field.
5. Beam tests The prototype was exposed to electron beam with energies l-5 GeV at the ITEP PS. It was installed on a rotatable support. A rotation around the vertical axis of 23” was controlled with a precision of 0.1”. The beam spot on the prototype face was 10 X 10 mm2. The beam divergence was less than 0.5”. It is known that the resolution of calorimeters with
channel
:........_..._.................. J Fig. 2. Block diagram
for cosmic
aDt ctwnnc,:.
of readout electronics.
A. Artamonov
0
90
8
80
7 0
et al. I Nucl. Instr. and Meth. in Phys. Res. A 370 (1996) 425-428
427
70 60 50 40 30 20
---l
I-.-u-
10 0
10' Fig. 4. The
E,“jCAO’
-5
-4
-3
-2
-1
0
1
2
An@: (de&es
collected charge as a function of the drift field. Fig. 6. The resolution
active elements arranged along the beam direction deteriorates significantly at zero angle [3] because of channeling. The angular scan was taken at 3.3 GeV. The signal distributions at different angles are shown in Fig. 5. The distributions have nearly a Gaussian shape and agree well with GEANT predictions. The low signal tail present at all the angles is due to material in the beam line. Fig. 6 presents the angular dependence of the resolution obtained from a Gaussian fit to experimental distributions within k2.5~ around the maximum. The data shows a small rise towards zero angle. The resolution varies by -20% which is quite acceptable for the forward calorimeter.
for electrons
as a function
of the incidence
angle.
The energy dependence of the response was studied at 0 = 2” which is the mean angle for the forward calorimeter coverage at the LHC. Data was taken at beam momenta 1.1, 2.2. 3.3 and 5.0 GeVlc. At each momentum the response was calculated as a peak value of a Gaussian fit to the signal distribution. It was further corrected for the energy leakage calculated by GEANT (-14%). The data shows a good linearity with energy (Fig. 7a). The resulting resolution was parameterized by a(E)IE = aJ/& $ b @c/
___
v)250 ‘;e 225
lf?200 ,/o
d. = 3”
175
150 125 100 75 50 25 ~,,,s
0
I’: ,,,,,,,,,L,
50
100
IS0
j
200
,v,,;L 0
50
FADC channels
0
50
100
150
FADC charm
/
,,,,,(,,
FSC
0
50
100
cl%
150
200
FADC channels
Fig. 5. Signal distributions for 3.3 GeV electrons at different incidence angles. The solid histograms are for data and the dashed histograms are Monte Carlo predictions.
Fig. 7. Electron energy response and resolution as a function of the energy at 13= 2”. Circles are for data and squares are Monte Carlo predictions.
A. Artanwnov
428
et al. I Nucl. Insir. and Meth. in Phys. Res. A 370 (1996) 425-428
E, where E is in GeV. The noise constant c was measured to be 340220 MeV. The fit with two parameters yields (r(E)IE = (26.4+3.5)%Ifi@(6.8~3.6)@(0.340+0.020)/E, in reasonable 7b).
agreement
with GEANT predictions
(see Fig.
6. Conclusions We have build a liquid argon calorimeter prototype with a cylindrical geometry of electrodes, equipped with fast readout electronics based on shaping technique. The prototype was tested with electrons. Tests demonstrated that the calorimeter response depends weakly on the incidence angle. The measured performance together with other attractive features of the proposed concept makes this technology a good candidate for a forward calorimeter at the LHC.
Acknowledgements We would like to thank D. Fournier, l? Jenni and J. Rutherfoord for fruitful conversations. The research described in this publication was made possible in part by Grant No. MBGOOO from the International Science Foundation.
References [l] ATLAS, Letter of Intent for a General-Purpose pp Experiment at the LHC at CERN, CERNILHCC192-4, LHCC/I 2. [2] SDC Collaboration, Technical Design Report, SDC-92-201. [3] D. Acosta et al., Nucl. Instr. and Meth. A 308 (1991) 481.