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Angular dependence of quartz fiber calorimeter response
CQ-s __
Nuclear Instruments and Methods in Physics Research A 360 (1995) 237-239
NUCLEAR INSTRUMENTS 8 METHOOS IN PHYSICS RESEARCH SectIonA
g iicl ELSEVIER
Angular dependence of quartz fiber calorimeter response G. Anzivino a, Yu. Chamorovskii b, A. Contin c,d, M. Danilov e, G. Dellacasa f, R. DeSalvo ‘, V. Gavrilov e, A. Golutvin e, P. Gorodetzky g,l, J.M. Helleboid g, V. Isaev b, K.F. Johnson h, P. Juillot g, S. Kuleshov e, G. Lacommare ‘, D. Lazic h, D. Litvintsev e, M. Lundin g,i32,M. Marino ‘, A. Musso f, F. Ratnikov e, V. Rusinov e, V. Stolin e, M. Vinogradov e
*,
aINFN Laboratori Nazionali di Frascati, Italy ’ IRE, Moscow, Russian Federation ’ CERN/LAA, Get&e, Switzerland ’ Universiry of Bologna and INFN Bologna, Italy e ITEP, Moscow. Russian Federation ’ University of Torino and INFN Torino, Italy g CRN, Strasbourg, France h Florida State Uniaersity Tallahassee, FL, USA i Universitt Louis Pasteur. Strasbourg, France
Abstract A small quartz fiber calorimeter prototype with copper absorber has been assembled and tested at ITEP as a first test of a “0 degree” component of the RD-40 R&D program. Calibration and monitoring of each tower response was performed using the positions of single photoelectron peaks as well as the response to minimum ionizing particles incident at an angle of 45”. The response of the prototype to 4 GeV electrons as a function of beam angle with respect to the quartz fibers was studied in the range from 0” to 90”. The test results are compared to the GEANT based Monte Carlo (MC) simulations.
1. Introduction
to beam the line and grouped into towers. Study of such a design was started by the GEM collaboration (see e.g. Ref.
Quartz fiber (QF) calorimetry [l] is a more than adequate technique for very forward calorimeters in LHC detectors. Cherenkov based QF calorimeters have proven to be fast, radiation resistant and insensitive to neutrons and radioactive background. It has to be shown that such a calorimeter can provide the required energy and spatial resolution for use in LHC experiments. Two main design concepts of QF calorimetry are under study: L A calorimeter where QFs are oriented with their longitudinal axis at an angle of 45” + 5” with respect to incoming particles in order to achieve the maximum Cherenkov light collection is discussed in more detail in Ref. [2]. - A coaxial calorimeter where QFs are oriented parallel
[311. - The combination of both designs, with coaxial fibers at the high pseudorapidity region where the highest channel occupancy is expected and with 45” QFs in the outer crown at intermediate rapidity, is considered by the Q-Cal collaboration to be the best option for very forward calorimetry [4]. The results reported here were obtained in the framework of the Q-Cal collaboration. The response of a QF calorimeter prototype with copper absorber as a function of the incident particle angle is reported.
1 At CERN from March 1994. ’ Partially supported by INFN Eloisatron * Corresponding author.
Project.
0168-9002/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIO168-9002(95)00113-l
2. Prototype design and test set-up A small QF calorimeter prototype with copper absorber has been assembled and tested at ITEP (Moscow). The prototype was assembled as a stack of 2 mm thick flat copper sheets (width 4.05 cm, length 30 cm) interleaved with QF layers forming a sensitive volume of 4.05 X 12.5 X 30 cm3. Radiation hard optical fibers with fused silica
V. TRENDS IN CALORIMETRY
core (diameter 300 Fmf, fluorine doped fused silica cladding (diameter 330 pm), and acrylate coating (diameter 420 km) were used. The numerical aperture of the QFs used here is equal to 0.22 and does not vary substantially as a function of light wavelength (A) in a wide range of A. The volume sampling fraction of this prototype is about 8%. Outside of the copper stack, the QF have been bundled and coupled to nine photomultiplier tubes (PMT) forming a matrix of 3 X 3 towers. Fused silica rods of 1 cm diameter and of 4 cm length placed between the end of each QF bundle and PMT window without optical contact served as light mixers. Hamamatsu R329 PMTs with good single photoelectron resolution were used as photodetectors. The use of PMTs which are insensitive to UV light results in a disadvantage in Cherenkov light collection but rather they limit the detection of light to a wavelength region where QFs keep their full transparency even after high dose irradiation. These tests, therefore, obtain a conservative estimate of the expected performance of a QF calorimeter operating under demanding irradiation conditions. The prototype has been tested using a 4 GeV test beam of the ITEP proton synchrotron. The beam was mainly negative pions with several percent of both electrons and muons. A gas threshold Cherenkov counter was used for electron identification. A scintillator counter placed downstream of the prototype was used for muon and non-interacting pion selections. Three double-coordinate multi-wire gas chambers were used to track the beam particles. The prototype was placed onto a swivel so that it could be rotated around the vertical axis. A scintillator finger counter of 2 cm width and of 5 cm height placed in front of the prototype served to cut off beam tails. The information from the multi-wire chambers’ hits and the prototype’s PMT pulse amplitudes were recorded and stored for each triggering beam particle (electron or non-interacting Minimum Ionizing Particle (MIP~).
BlrnOi:
z
800 -
600 -
50
loa
150
ml
250
ml
ADC channels
Fig. 1. Typical pulse height distribution near the single photoelectron peak. The ordinate scale for the first 80 ADC channels is suppressed by a factor of 100.
photoelectrons have been calculated tions in two different ways:
from these distribu-
- from the ratio of the average tower response to the SPE pulse height and, - from the formula ( Npe) = -1n W(O) where W(O) is the fraction of pedestal events co~esponding to the 0th photoelectron peak detected in a Poisson distribution.
3. Calibration and monitoring
The last method is well suited in the case where the sharp pedestal peak is clearly isolated from the signal of the first photoelectron and does not require scale calibration and linearity. Both methods yielded the same results for each tower within the accuracy of a few percent. The deviation of MIP responses of various channels from the average value was less than 20%. As a result the average response to MIPS passing through the QFs at the angle of 45” was found to be about of 0.45 photoelectrons per 1 mm particle path length in the fiber core.
Particular attention was paid to calibration and monitoring of each prototype tower response using beam events. First, all ADC scales were calibrated in units of photoelectrons using the position of Single PhotoElectron 6PE) peaks. A typical event distribution over ADC channel counts near the SPE peak is shown in Fig. 1. The variation of the position of the SPE peak during all test runs allowed the monitoring of PMT gains. The measurement of the response of each prototype tower to MIPS at the incident angle of 45” was used for the calibration of Cherenkov light collection efficiency and photocathode sensitivity. Fig. 2 shows the typical pulse height distribution for MIPS passing through the fiducial volume of the tower. The mean values for the number of
Fig. 2. Pulse height distribution MIP at 45”.
of the single tower response
to
G. Anziuino et al./Nucl.
239
Instr. and Meth. in Phys. Res. A 360 (1995) 237-239
The MC simulations of the prototype response to MIPS at 45” gives the value of 0.7 p.e./mm. The ratio of the measured and the calculated response for MIP at 45” provided the factor which was used for the normalization of MC results for electron shower detection.
4. Response to EM shower Fig. 3 shows the prototype response to 4 GeV electrons entering the calorimeter at an angle of 45” with respect to the QFs. This response function can be approximated by a Gaussian shape. The small fraction of events at the left of the main peak corresponds to the pion contamination in the triggered events. The position and the shape of these pion induced signals are similar to response for triggering MIPS at 45”. The position of the 4 GeV electron peak at 27 p.e. is in a good agreement with the MC results (taking into account the normalization factor measured using MIP). Having only about 12 radiation lengths for shower development, the prototype did not provide good shower containment. The MC simulations showed that the response of this prototype corresponds to 92% containment. Taking into account this 8% longitudinal leakage, the average value of 7.3 p.e./GeV was estimated. The width of the Gaussian in Fig. 3 corresponds to an energy resolution of u&E = 21%, which is determined mainly by photoelectron statistics (1,’ 6 = 0.19). Taking into account the sampling and leakage fluctuations the value of q/E = 21% is well reproduced. Fig. 4 shows the angular dependence of the peak position of the prototype response to 4 GeV electron showers. The solid curve is the result of MC simulations normalized using MIP. The position, height and width of e‘s0
I.
Oo
,
20
/
/
40
00
I
so
I 100
a*
Fig. 4. Dependence of the peak position of the prototype response to 4 GeV electrons as a function of beam angle with respect to QF. Crosses are experimental data points, curve is the MC prediction. the measured peak are in agreement with MC results. A deviation of MC prediction from data is observed at small angles.
5. Summary A QF calorimeter prototype with copper absorber and radiation hard quartz core and quartz clad optical fibers (volume filling ratio of 8%) has been assembled and tested at 4 GeV beam. ADC scale calibration and the PMTs’ gain monitoring were performed using the position of the single phot~lectron peaks. Calibration of the Cherenkov light collection was done using each tower response to MIPS for the incident angle of 45”. The response of the prototype to 4 GeV electron showers was measured as a function of the angle between beam and QF directions. With these fibers and this geometry the EM shower produces about 7 p.e./GeV for 45” and about 3 p.e./GeV near 0”. The electron energy resolution is determined mainly by photoelectron statistics. The test data are in good agreement with MC simulation results.
References
Fig. 3. The prototype response to 4 GeV electrons incident at an angle of 45” with respect to the QFs.
[I] G. Anzivino et al., Design of a quartz fiber calorimeter for a collider experiment, submitted to the Proc. 4th Int. Conf. on Calorimetry in High Energy Physics, Isola d’Elba, Italy, Sept. 19-2.5, 1993. [2] A. Contin et al., Development of quartz fiber calorimetry, CERN DRDC/94-4 (1994). [3] See, e.g., Workshop on the Forward Calorimetry, ITEP, Moscow, June 5, 1993; GEM TN-93-424. [4] G. Anzivino et al., presented at this Meeting (6th Pisa Meeting on Advanced Detector. La Biodola, Isola d’Elba, Italy, 1994).
V. TRENDS IN CALORIME~Y
Nuclear Instruments and Methods in Physics Research A 360 (1995) 237-239
NUCLEAR INSTRUMENTS 8 METHOOS IN PHYSICS RESEARCH SectIonA
g iicl ELSEVIER
Angular dependence of quartz fiber calorimeter response G. Anzivino a, Yu. Chamorovskii b, A. Contin c,d, M. Danilov e, G. Dellacasa f, R. DeSalvo ‘, V. Gavrilov e, A. Golutvin e, P. Gorodetzky g,l, J.M. Helleboid g, V. Isaev b, K.F. Johnson h, P. Juillot g, S. Kuleshov e, G. Lacommare ‘, D. Lazic h, D. Litvintsev e, M. Lundin g,i32,M. Marino ‘, A. Musso f, F. Ratnikov e, V. Rusinov e, V. Stolin e, M. Vinogradov e
*,
aINFN Laboratori Nazionali di Frascati, Italy ’ IRE, Moscow, Russian Federation ’ CERN/LAA, Get&e, Switzerland ’ Universiry of Bologna and INFN Bologna, Italy e ITEP, Moscow. Russian Federation ’ University of Torino and INFN Torino, Italy g CRN, Strasbourg, France h Florida State Uniaersity Tallahassee, FL, USA i Universitt Louis Pasteur. Strasbourg, France
Abstract A small quartz fiber calorimeter prototype with copper absorber has been assembled and tested at ITEP as a first test of a “0 degree” component of the RD-40 R&D program. Calibration and monitoring of each tower response was performed using the positions of single photoelectron peaks as well as the response to minimum ionizing particles incident at an angle of 45”. The response of the prototype to 4 GeV electrons as a function of beam angle with respect to the quartz fibers was studied in the range from 0” to 90”. The test results are compared to the GEANT based Monte Carlo (MC) simulations.
1. Introduction
to beam the line and grouped into towers. Study of such a design was started by the GEM collaboration (see e.g. Ref.
Quartz fiber (QF) calorimetry [l] is a more than adequate technique for very forward calorimeters in LHC detectors. Cherenkov based QF calorimeters have proven to be fast, radiation resistant and insensitive to neutrons and radioactive background. It has to be shown that such a calorimeter can provide the required energy and spatial resolution for use in LHC experiments. Two main design concepts of QF calorimetry are under study: L A calorimeter where QFs are oriented with their longitudinal axis at an angle of 45” + 5” with respect to incoming particles in order to achieve the maximum Cherenkov light collection is discussed in more detail in Ref. [2]. - A coaxial calorimeter where QFs are oriented parallel
[311. - The combination of both designs, with coaxial fibers at the high pseudorapidity region where the highest channel occupancy is expected and with 45” QFs in the outer crown at intermediate rapidity, is considered by the Q-Cal collaboration to be the best option for very forward calorimetry [4]. The results reported here were obtained in the framework of the Q-Cal collaboration. The response of a QF calorimeter prototype with copper absorber as a function of the incident particle angle is reported.
1 At CERN from March 1994. ’ Partially supported by INFN Eloisatron * Corresponding author.
Project.
0168-9002/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIO168-9002(95)00113-l
2. Prototype design and test set-up A small QF calorimeter prototype with copper absorber has been assembled and tested at ITEP (Moscow). The prototype was assembled as a stack of 2 mm thick flat copper sheets (width 4.05 cm, length 30 cm) interleaved with QF layers forming a sensitive volume of 4.05 X 12.5 X 30 cm3. Radiation hard optical fibers with fused silica
V. TRENDS IN CALORIMETRY
core (diameter 300 Fmf, fluorine doped fused silica cladding (diameter 330 pm), and acrylate coating (diameter 420 km) were used. The numerical aperture of the QFs used here is equal to 0.22 and does not vary substantially as a function of light wavelength (A) in a wide range of A. The volume sampling fraction of this prototype is about 8%. Outside of the copper stack, the QF have been bundled and coupled to nine photomultiplier tubes (PMT) forming a matrix of 3 X 3 towers. Fused silica rods of 1 cm diameter and of 4 cm length placed between the end of each QF bundle and PMT window without optical contact served as light mixers. Hamamatsu R329 PMTs with good single photoelectron resolution were used as photodetectors. The use of PMTs which are insensitive to UV light results in a disadvantage in Cherenkov light collection but rather they limit the detection of light to a wavelength region where QFs keep their full transparency even after high dose irradiation. These tests, therefore, obtain a conservative estimate of the expected performance of a QF calorimeter operating under demanding irradiation conditions. The prototype has been tested using a 4 GeV test beam of the ITEP proton synchrotron. The beam was mainly negative pions with several percent of both electrons and muons. A gas threshold Cherenkov counter was used for electron identification. A scintillator counter placed downstream of the prototype was used for muon and non-interacting pion selections. Three double-coordinate multi-wire gas chambers were used to track the beam particles. The prototype was placed onto a swivel so that it could be rotated around the vertical axis. A scintillator finger counter of 2 cm width and of 5 cm height placed in front of the prototype served to cut off beam tails. The information from the multi-wire chambers’ hits and the prototype’s PMT pulse amplitudes were recorded and stored for each triggering beam particle (electron or non-interacting Minimum Ionizing Particle (MIP~).
BlrnOi:
z
800 -
600 -
50
loa
150
ml
250
ml
ADC channels
Fig. 1. Typical pulse height distribution near the single photoelectron peak. The ordinate scale for the first 80 ADC channels is suppressed by a factor of 100.
photoelectrons have been calculated tions in two different ways:
from these distribu-
- from the ratio of the average tower response to the SPE pulse height and, - from the formula ( Npe) = -1n W(O) where W(O) is the fraction of pedestal events co~esponding to the 0th photoelectron peak detected in a Poisson distribution.
3. Calibration and monitoring
The last method is well suited in the case where the sharp pedestal peak is clearly isolated from the signal of the first photoelectron and does not require scale calibration and linearity. Both methods yielded the same results for each tower within the accuracy of a few percent. The deviation of MIP responses of various channels from the average value was less than 20%. As a result the average response to MIPS passing through the QFs at the angle of 45” was found to be about of 0.45 photoelectrons per 1 mm particle path length in the fiber core.
Particular attention was paid to calibration and monitoring of each prototype tower response using beam events. First, all ADC scales were calibrated in units of photoelectrons using the position of Single PhotoElectron 6PE) peaks. A typical event distribution over ADC channel counts near the SPE peak is shown in Fig. 1. The variation of the position of the SPE peak during all test runs allowed the monitoring of PMT gains. The measurement of the response of each prototype tower to MIPS at the incident angle of 45” was used for the calibration of Cherenkov light collection efficiency and photocathode sensitivity. Fig. 2 shows the typical pulse height distribution for MIPS passing through the fiducial volume of the tower. The mean values for the number of
Fig. 2. Pulse height distribution MIP at 45”.
of the single tower response
to
G. Anziuino et al./Nucl.
239
Instr. and Meth. in Phys. Res. A 360 (1995) 237-239
The MC simulations of the prototype response to MIPS at 45” gives the value of 0.7 p.e./mm. The ratio of the measured and the calculated response for MIP at 45” provided the factor which was used for the normalization of MC results for electron shower detection.
4. Response to EM shower Fig. 3 shows the prototype response to 4 GeV electrons entering the calorimeter at an angle of 45” with respect to the QFs. This response function can be approximated by a Gaussian shape. The small fraction of events at the left of the main peak corresponds to the pion contamination in the triggered events. The position and the shape of these pion induced signals are similar to response for triggering MIPS at 45”. The position of the 4 GeV electron peak at 27 p.e. is in a good agreement with the MC results (taking into account the normalization factor measured using MIP). Having only about 12 radiation lengths for shower development, the prototype did not provide good shower containment. The MC simulations showed that the response of this prototype corresponds to 92% containment. Taking into account this 8% longitudinal leakage, the average value of 7.3 p.e./GeV was estimated. The width of the Gaussian in Fig. 3 corresponds to an energy resolution of u&E = 21%, which is determined mainly by photoelectron statistics (1,’ 6 = 0.19). Taking into account the sampling and leakage fluctuations the value of q/E = 21% is well reproduced. Fig. 4 shows the angular dependence of the peak position of the prototype response to 4 GeV electron showers. The solid curve is the result of MC simulations normalized using MIP. The position, height and width of e‘s0
I.
Oo
,
20
/
/
40
00
I
so
I 100
a*
Fig. 4. Dependence of the peak position of the prototype response to 4 GeV electrons as a function of beam angle with respect to QF. Crosses are experimental data points, curve is the MC prediction. the measured peak are in agreement with MC results. A deviation of MC prediction from data is observed at small angles.
5. Summary A QF calorimeter prototype with copper absorber and radiation hard quartz core and quartz clad optical fibers (volume filling ratio of 8%) has been assembled and tested at 4 GeV beam. ADC scale calibration and the PMTs’ gain monitoring were performed using the position of the single phot~lectron peaks. Calibration of the Cherenkov light collection was done using each tower response to MIPS for the incident angle of 45”. The response of the prototype to 4 GeV electron showers was measured as a function of the angle between beam and QF directions. With these fibers and this geometry the EM shower produces about 7 p.e./GeV for 45” and about 3 p.e./GeV near 0”. The electron energy resolution is determined mainly by photoelectron statistics. The test data are in good agreement with MC simulation results.
References
Fig. 3. The prototype response to 4 GeV electrons incident at an angle of 45” with respect to the QFs.
[I] G. Anzivino et al., Design of a quartz fiber calorimeter for a collider experiment, submitted to the Proc. 4th Int. Conf. on Calorimetry in High Energy Physics, Isola d’Elba, Italy, Sept. 19-2.5, 1993. [2] A. Contin et al., Development of quartz fiber calorimetry, CERN DRDC/94-4 (1994). [3] See, e.g., Workshop on the Forward Calorimetry, ITEP, Moscow, June 5, 1993; GEM TN-93-424. [4] G. Anzivino et al., presented at this Meeting (6th Pisa Meeting on Advanced Detector. La Biodola, Isola d’Elba, Italy, 1994).
V. TRENDS IN CALORIME~Y