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Space and energy resolutions in a liquid krypton e.m. calorimeter
Nuclear Instruments and Methods in Physics Research A315 (1992) 491-493 North-Holland
INSTR IN P1111rSIC5 RE Secton A
Space and energy resolutions in a liquid krypton e .m. calorimeter Presented by P.L. Frabetti
P. Canteni, P.L. Frabetti and L. Stagni
Dipartimento di Fisica dell'Universith e Seziene INFN, Bologna, Italy
F. Lanni, G. Lo Bianco, B. Maggi, F. Palembo and A. Sala Dipartimento di Fisica dell'Università e Seziene INFN, Milano, Italy
V.M. Aulchenko, S.G. Klimenke, G.M. Kolachev, L.A. Leentiev, A.P. Onuchin, V.S. Panin, Yu.V. Pril, V.A. Redyakin, A.G. Shamev, Yu.I. Skovpen, V.A. Tayursky, Yu.A. Tikhonov and V.I. Yurchenko Institute of Nuclear Physics, Novosibirsk, USSR
P .F. Manfredi, V. Re and V. Speziali
Dipartimento di Elettonica dell'Universitb di Pavia e Seziene INFN, Milano, Italy
Results of the experimental measurement of space and energy resolutions of a liquid krypton (LKr) e.m. calorimeter are presented . A prototype has been exposed to a positron test-beam in the energy range 130-1300 MeV at the VEPP-3 storage ring. 1. Introduction An e.m. calorimeter based on liquid krypton is now under construction for the KEDR detector. It will be used at the e'-e - collider VEPP-4M with a maximum energy of 6 GeV [1] . The KEDR LKr calorimeter is a set of ionization chambers operating in the electronpulse regime with low-noise charge-sensitive amplifiers. The electrode thickness (0.5 mm of G10 + 2 x 18 Wm of Cu) is such that the calorimeter can be considered practically homogeneous in contrast with the usual liquid argon one where the energy resolution is determined mainly by the sampling fluctuations . We have studied the characteristics of liquid krypton as a calorimeter medium with two different prototypes . A small prototype (7 kg of LKr) was used for the first tests and for the measurements of space resolution using cosmic particles. We obtained a space resolution o,x = 3 mm in the anode readout mode and Qx = 0.4 mm in the cathode readout, using the centre of gravity method . Details of this experiment are described elsewhere [2] . Another prototype (400 kg of LKr) was used for the measurement of energy resolution on a positron beam in the energy region 130-1300 MeV. Details of this measurements can be found elsewhere [2].
A new test-experiment with the prototype-400 was performed, using an electrode system with strips and towers similar to the final KEDR calorimeter and reading the signals from both sides of the ioniation chambers. In this paper we present the results of this test-experiment . 2. Test-experiment with the prototype400 The prototype-400 was used in a new test-experiment for the measurement of space and energy resolutions on a positron beam in the energy region 130-1300 MeV. The electrodes system contained strips and towers. The high-voltage electrodes are divided into eight pads forming towers in the beam direction (z-axis). In this direction the towers are divided into three sections. Six grounded electrodes of the first section are divided into strips, 10 mm wide, oriented along the x-axis in three electrodes and along the y-axis in the other three. The thickness of the entrance window is 0.13 Xo (2 mm Fe). The capacitance of each strip channel is about 50 pF and the capacitance of each tower is about 250 pF. The signal was processed by charge-sensitive preampli-
0168-9002/92/$05 .00 0 1992 - Elsevier Science Publishers B.V. All rights reserved
IX. HIGH PRECISION DETECTORS
P. Cantoni et al. / Liquid krypton e.m . calorimeter
492
150 c w 100 c0r
W
50 0
0 10 20 -10 Ay (MM) Fig. 1. Space resolution of the LKr chamber, measured with positrons of 1.3 GeV. Solid line is a Chebychev polynomial fit. -20
Piers based on the FET SNJ903L and a RC--2CR shaper with a time constant of 0.8 Ws. In this case 10% of the total charge is collected . The charge was read from both the anode and cathode electrodes. The equivalent noise charge (rms) is (ENC) = 750 + 3.2 C (pF) units of electron charge. Preamplifiers and shapers are located on the flange of the cryostat and signals are transported to 12 bits peak ADCs by coaxial cables [3]. The result of the space resolution measurement with positrons of 1.3 GeV is shown in fig . 1. 0y is the difference between the centre of gravity coordinate measured in one ionization chamber and the coordinate obtained extrapolating the information of the magnetic spectrometer wire chambers (o"X - 0.3 mm). Fig . 2 shows the space resolution measurements for different energies. The solid line in the figure is the estimated contamination of the multiple scattering in a scintillator 5 mm Lhick, placed at 740 mm from the LKr prototype . The dashed line is the expected space resolution for anode read-out without multiple scattering.
Ecal - Ebeam(MeV)
Fig. 3. Distribution of the difference between the energy obtained from the calorimeter and the beam energy at Ebeam =1 .3 GeV. Solid line is a Chebychev polynomial fit .
10
KEDR LKr prototype preliminary
8 E
v 0
W w
W
6
Itl
4
0
2 0
0
0
0
0
200 400 600 800 1000 1200 1400 E(MeV)
Fig. 4. Energy resolution (rms) of the prototype-400.
10 8 6 E E v v 4 2 0
0
200 400 600 800 1000 1200 1400 E (MeV)
Fig. 2. Space resolution measurements at different e + energies. 40 HV of 0 .25 kV ; O HV of 1 kV .
Fig. 5. Energy' resolution. Electronics and radioactive noises for 1 tower vs time constant .
P. Cantoni et al. / Liquid krypton em . calorimeter
15
^ 10 m v
w w u
5
10
30
100 200 1000 Ey (MeV) Fig. 6. Resulting energy resolution in the Monte Carlo simula tion : ® sum of the amplitudes from 27 towers; o sum of the optimal number of towers amplitudes for each energy . Two sets of measurements were done, using voltages of 0.25 kV and 1 kV. The distribution of the difference between the energy obtained by the calorimeter and the beam energy at Ebeam =1 .3 GeV is shown in fig. 3. Results of the energy resolution measurements are shown in fig . 4. Details of this experiment can be found in ref. [4] . 3. Monte Carlo simulation Showers produced in liquid krypton have been simulated for the real structure of the calorimeter. The
493
following effects, determining the energy resolution of the LKr calorimeter, have been studied: longitudinal and transverse fluctuations of the energy leakage, sampling fluctuations in the dead material, geometric effect, electronics noise, LKr radioactivity, variation of the gap size, calibration inaccuracy, electronics instability and algorithm of energy reconstruction. The electronics and radioactive noise contribution as a function of the time constant of the RC-2CR shaper is presented in fig. 5. The calculation was performed for a tower channel with an electric capacitance of 250 pF and a LKr volume equal to 5000 cm 3. The equivalent noise of 1 tower is 1.0 MeV, the time constant is 1 Ws. The energy resolution, obtained taking into account all the above mentioned effects, as a function of the photon energy is shown in fig . 6. Two different -jgorithms were used for the energy reconstruction: in the first one the amplitudes of 27 towers (total size 30 x 30 x 70 cm3) were summed while in the other one the optimal number of towers for each energy was summed.
References [1] V.V. Anashin et al., Proc. Int. Symp. on Position Detectors in High Energy Physics, Dubna, 1988, ed. I.A. Golutvin (SINR) p. 58. [2] V.M. Aulchenko et al., Nucl. Instr. and Meth. A289 (1990) 68. [3] V.M. Aulchenko, S.E. Baru and G.A. Savinov, Proc. Int. Symp. on Position Detectors in High Energy Physics, Dubna, 1988, ed. I.A. Golutvin (SINR) p. 371. [4] V.M. Aulchenko et al., Conf. on Calorimetry in High Energy Physics, FNAL, 1990, eds. F. Anderson, M. Derrich, H.E. Fisk, A. Para and C.M. Sazama (World Scientific) p. 233.
IX. HIGH PRECISION DETECTORS
INSTR IN P1111rSIC5 RE Secton A
Space and energy resolutions in a liquid krypton e .m. calorimeter Presented by P.L. Frabetti
P. Canteni, P.L. Frabetti and L. Stagni
Dipartimento di Fisica dell'Universith e Seziene INFN, Bologna, Italy
F. Lanni, G. Lo Bianco, B. Maggi, F. Palembo and A. Sala Dipartimento di Fisica dell'Università e Seziene INFN, Milano, Italy
V.M. Aulchenko, S.G. Klimenke, G.M. Kolachev, L.A. Leentiev, A.P. Onuchin, V.S. Panin, Yu.V. Pril, V.A. Redyakin, A.G. Shamev, Yu.I. Skovpen, V.A. Tayursky, Yu.A. Tikhonov and V.I. Yurchenko Institute of Nuclear Physics, Novosibirsk, USSR
P .F. Manfredi, V. Re and V. Speziali
Dipartimento di Elettonica dell'Universitb di Pavia e Seziene INFN, Milano, Italy
Results of the experimental measurement of space and energy resolutions of a liquid krypton (LKr) e.m. calorimeter are presented . A prototype has been exposed to a positron test-beam in the energy range 130-1300 MeV at the VEPP-3 storage ring. 1. Introduction An e.m. calorimeter based on liquid krypton is now under construction for the KEDR detector. It will be used at the e'-e - collider VEPP-4M with a maximum energy of 6 GeV [1] . The KEDR LKr calorimeter is a set of ionization chambers operating in the electronpulse regime with low-noise charge-sensitive amplifiers. The electrode thickness (0.5 mm of G10 + 2 x 18 Wm of Cu) is such that the calorimeter can be considered practically homogeneous in contrast with the usual liquid argon one where the energy resolution is determined mainly by the sampling fluctuations . We have studied the characteristics of liquid krypton as a calorimeter medium with two different prototypes . A small prototype (7 kg of LKr) was used for the first tests and for the measurements of space resolution using cosmic particles. We obtained a space resolution o,x = 3 mm in the anode readout mode and Qx = 0.4 mm in the cathode readout, using the centre of gravity method . Details of this experiment are described elsewhere [2] . Another prototype (400 kg of LKr) was used for the measurement of energy resolution on a positron beam in the energy region 130-1300 MeV. Details of this measurements can be found elsewhere [2].
A new test-experiment with the prototype-400 was performed, using an electrode system with strips and towers similar to the final KEDR calorimeter and reading the signals from both sides of the ioniation chambers. In this paper we present the results of this test-experiment . 2. Test-experiment with the prototype400 The prototype-400 was used in a new test-experiment for the measurement of space and energy resolutions on a positron beam in the energy region 130-1300 MeV. The electrodes system contained strips and towers. The high-voltage electrodes are divided into eight pads forming towers in the beam direction (z-axis). In this direction the towers are divided into three sections. Six grounded electrodes of the first section are divided into strips, 10 mm wide, oriented along the x-axis in three electrodes and along the y-axis in the other three. The thickness of the entrance window is 0.13 Xo (2 mm Fe). The capacitance of each strip channel is about 50 pF and the capacitance of each tower is about 250 pF. The signal was processed by charge-sensitive preampli-
0168-9002/92/$05 .00 0 1992 - Elsevier Science Publishers B.V. All rights reserved
IX. HIGH PRECISION DETECTORS
P. Cantoni et al. / Liquid krypton e.m . calorimeter
492
150 c w 100 c0r
W
50 0
0 10 20 -10 Ay (MM) Fig. 1. Space resolution of the LKr chamber, measured with positrons of 1.3 GeV. Solid line is a Chebychev polynomial fit. -20
Piers based on the FET SNJ903L and a RC--2CR shaper with a time constant of 0.8 Ws. In this case 10% of the total charge is collected . The charge was read from both the anode and cathode electrodes. The equivalent noise charge (rms) is (ENC) = 750 + 3.2 C (pF) units of electron charge. Preamplifiers and shapers are located on the flange of the cryostat and signals are transported to 12 bits peak ADCs by coaxial cables [3]. The result of the space resolution measurement with positrons of 1.3 GeV is shown in fig . 1. 0y is the difference between the centre of gravity coordinate measured in one ionization chamber and the coordinate obtained extrapolating the information of the magnetic spectrometer wire chambers (o"X - 0.3 mm). Fig . 2 shows the space resolution measurements for different energies. The solid line in the figure is the estimated contamination of the multiple scattering in a scintillator 5 mm Lhick, placed at 740 mm from the LKr prototype . The dashed line is the expected space resolution for anode read-out without multiple scattering.
Ecal - Ebeam(MeV)
Fig. 3. Distribution of the difference between the energy obtained from the calorimeter and the beam energy at Ebeam =1 .3 GeV. Solid line is a Chebychev polynomial fit .
10
KEDR LKr prototype preliminary
8 E
v 0
W w
W
6
Itl
4
0
2 0
0
0
0
0
200 400 600 800 1000 1200 1400 E(MeV)
Fig. 4. Energy resolution (rms) of the prototype-400.
10 8 6 E E v v 4 2 0
0
200 400 600 800 1000 1200 1400 E (MeV)
Fig. 2. Space resolution measurements at different e + energies. 40 HV of 0 .25 kV ; O HV of 1 kV .
Fig. 5. Energy' resolution. Electronics and radioactive noises for 1 tower vs time constant .
P. Cantoni et al. / Liquid krypton em . calorimeter
15
^ 10 m v
w w u
5
10
30
100 200 1000 Ey (MeV) Fig. 6. Resulting energy resolution in the Monte Carlo simula tion : ® sum of the amplitudes from 27 towers; o sum of the optimal number of towers amplitudes for each energy . Two sets of measurements were done, using voltages of 0.25 kV and 1 kV. The distribution of the difference between the energy obtained by the calorimeter and the beam energy at Ebeam =1 .3 GeV is shown in fig. 3. Results of the energy resolution measurements are shown in fig . 4. Details of this experiment can be found in ref. [4] . 3. Monte Carlo simulation Showers produced in liquid krypton have been simulated for the real structure of the calorimeter. The
493
following effects, determining the energy resolution of the LKr calorimeter, have been studied: longitudinal and transverse fluctuations of the energy leakage, sampling fluctuations in the dead material, geometric effect, electronics noise, LKr radioactivity, variation of the gap size, calibration inaccuracy, electronics instability and algorithm of energy reconstruction. The electronics and radioactive noise contribution as a function of the time constant of the RC-2CR shaper is presented in fig. 5. The calculation was performed for a tower channel with an electric capacitance of 250 pF and a LKr volume equal to 5000 cm 3. The equivalent noise of 1 tower is 1.0 MeV, the time constant is 1 Ws. The energy resolution, obtained taking into account all the above mentioned effects, as a function of the photon energy is shown in fig . 6. Two different -jgorithms were used for the energy reconstruction: in the first one the amplitudes of 27 towers (total size 30 x 30 x 70 cm3) were summed while in the other one the optimal number of towers for each energy was summed.
References [1] V.V. Anashin et al., Proc. Int. Symp. on Position Detectors in High Energy Physics, Dubna, 1988, ed. I.A. Golutvin (SINR) p. 58. [2] V.M. Aulchenko et al., Nucl. Instr. and Meth. A289 (1990) 68. [3] V.M. Aulchenko, S.E. Baru and G.A. Savinov, Proc. Int. Symp. on Position Detectors in High Energy Physics, Dubna, 1988, ed. I.A. Golutvin (SINR) p. 371. [4] V.M. Aulchenko et al., Conf. on Calorimetry in High Energy Physics, FNAL, 1990, eds. F. Anderson, M. Derrich, H.E. Fisk, A. Para and C.M. Sazama (World Scientific) p. 233.
IX. HIGH PRECISION DETECTORS