- Email: [email protected]
CMS quartz fiber calorimeter
Nuclear Instruments and Methods in Physics Research A 453 (2000) 242}244
CMS quartz "ber calorimeter V. Gavrilov* ITEP B. Cheremushkinskaya ulitsa 25, RU-117 259, Moscow, Russia Accepted 19 June 2000
Abstract The CMS will be a general purpose detector for the Large Hadron Collider at CERN. Its quartz "ber calorimeter is designed to provide hermetic measurement of energy #ow in the forward rapidity region. The calorimeter must operate under extremely hard radiation conditions and almost without maintenance. Several prototypes have been constructed and tested at the CERN high-energy beam. The cost e!ective technology of manufacturing of "ne sampling absorber modules has been developed. 2000 Published by Elsevier Science B.V. All rights reserved.
1. Introduction The Large Hadron Collider will operate at high energies and luminosities ((s"14 GeV and ¸"10 cm\ s\). For the general purpose detector CMS the hermetic calorimetry coverage up to "g""5 will be required for the measurement of missing transverse energy and for detection of high-energy hadron jets. The most severe operation conditions are expected at the region of the small angles with respect to the colliding beams. The CMS forward calorimeters will cover the rapidity region of 3("g"(5 and will be installed at about 11 m from the interaction point [1]. The radiation doses and the neutron #uxes at that region will reach 50}100 MRaD/yr and 10 n cm\ s\ respectively. The main requirements to the CMS Forward Calorimeters are as follows: E High radiation resistance. E Limited maintenance.
* Tel.: #7-095-123-9447; fax: #7-095-883-9592. E-mail address: [email protected] (V. Gavrilov).
E Fast signal collection. E Low sensitivity to neutrons. 2. Quartz 5ber calorimetry The CMS forward calorimeters will consist of optical quartz "bers embedded in an absorber matrix. The "bers run along the beam direction, i.e. approximately in the same direction as the incoming particle. This "ber arrangement allows the build up of readout cells by grouping "bers from the desired areas. The basic features of the quartz "ber calorimeter are as follows: E Quartz "bers keep transparency to visible light being irradiated up to doses of GRaD [2]. E No maintenance in the hot zone will be required because the active element of the calorimeter will be inert. E Due to Cherenkov nature of the signal the calorimeter will be sensitive only to relativistic charged particles and therefore its sensitivity to neutron induced reactions will be very low.
0168-9002/00/$ - see front matter 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 0 ) 0 0 6 3 9 - 2
V. Gavrilov / Nuclear Instruments and Methods in Physics Research A 453 (2000) 242}244
E Due to instantaneous nature of Cherenkov light the calorimeter signal will be very fast [3]. E Light output of this type of calorimeters will be extremely low due to several reasons: E 䡩 Only a small faction of particle energy loss comes to Cherenkov light production. E䡩 Volume fraction of quartz "bers in the calorimeter should be very low (about 1%) to keep the overall cost of the calorimeter at an a!ordable level. E䡩 Only small faction of produced photons will be trapped in the "bers and transported to photodetectors. E䡩 Attempts to increase a number of photoelectrons using UV-sensitive photodetectors will not help in this case because the "ber transparency to UV light will be lost rapidly after the beginning of operation in a hard radiation environment. E This type of calorimeters is not compensating, i.e. the signal for high-energy hadron is considerably lower (by a factor of about 1.5 [3]) than the signal for electron (or photon) of the same energy. E The visible radius of a hadronic shower detected in the quartz "ber calorimeter is much smaller with respect to a radius of a hadronic shower detected in an ionizing or in a scintillating calorimeter [4].
3. Prototypes and expected performance Several prototypes of the quartz "ber hadron calorimeter has been assembled and tested at the CERN test beam. Calorimeters contained quartz "bers of 0.30 mm core diameter. The absorber of the "rst prototype [3] was made of copper. Fiber volume fraction was 1.5%. The length was 135 cm and the sensitive transversal area was about 16;16 cm. In the case of electrons, a good energy linearity of the signal was observed. The energy resolution for electrons was determined by statistical #uctuations of a number of photoelectrons. The output signal for that prototype was about 0.5 p.e./GeV and the electron energy resolution was pE/E"1.37/(E. For the charged pion showers the substantial energy non-linearity was observed.
243
In the high-energy range (200}375 GeV), the number of p.e. per GeV for pions was about of that for electrons. It was observed that the hadron energy resolution of quartz "ber calorimeter was determined predominantly by intrinsic #uctuations of hadron shower development rather than the statistical #uctuations of a number of photoelectrons. The purpose of the CMS quartz "ber calorimeter will be to measure the energy #ow in the forward rapidity region and the energy of forward hadron jets. In both cases, the fraction of energy carried by gammas (from decays of neutral pions and other hadrons) will #uctuate. Therefore an equalization of signals from hadronic and e.m. showers of the same energy will improve the calorimeter performance. Partial equalization could be achieved using longitudinal segmentation of the calorimeter where a sampling fraction in the front (`e.m.a) section will be lower with respect to the rear (`hadronica) section. This approach was tested using the prototype with two longitudinal segments [5]. The hadronic section was modeled with the above-described copper prototype and another copper prototype of 33 cm length with the same transversal structure as the hadronic section was assembled for the front e.m. section. The results of the beam test of the prototype with two longitudinal segments were used to simulate the response of the calorimeter to high-energy hadron jets. It was shown that the optimal jet energy resolution will be achieved in the quartz "ber calorimeter in which the e.m. section will have sampling fraction of with respect to that of the hadronic section. For such a calorimeter the full equalization of signals for hadronic and e.m. showers will not be achieved, but it will be optimal to minimize both #uctuations of photon content in the jets and a deterioration of hadron energy resolution due to longitudinal non-uniformity of such a calorimeter. The simulations of the performance of the CMS forward calorimeter for the detection of hadronic jets allowed to optimize the main parameters of calorimeter on the basis of the cost vs. performance balance. E Steel was chosen as the absorber material. The forward calorimeter will be placed outside the
6. CALORIMETERS
244
V. Gavrilov / Nuclear Instruments and Methods in Physics Research A 453 (2000) 242}244
magnet yoke of the CMS magnet, therefore the magnetic properties of its absorber are not so important. E The segmentation of read-out towers were chosen to be equal to dg;d "0.175;0.175. This tower will be two times larger than the tower of the central part of the CMS hadron calorimeter, but this segmentation will not compromise the jet transverse energy resolution and the e$ciency of the jet reconstruction. E The "ber spacing was chosen to be equal to 2.5;2.5 mm. This spacing will provide the "ber volume fraction of 0.55% for the e.m. section and of 0.85% for the hadronic section. Even for such low sampling fraction the jet energy resolution will not be dominated by the photoelectron statistical #uctuation. In order to test the performance of the quartz "ber calorimeter with the steel absorber and with the chosen sampling fractions for the longitudinal segments, the new prototype of the length of 165 cm has been assembled and tested at the CERN highenergy beam in September 1999. The beam test results are being analyzed.
4. Technology of absorber modules manufacturing The manufacturing of the calorimeter absorber with the "ne structure of tiny holes for the quartz "ber insertion will not be an easy task. There is no available standard industrial technology which could be used for that purpose. The absorber will be assembled of the modules of the sizes of 24;24;165 cm. The technology of module manufacturing was developed at the Russian Federal Nuclear Center VNIITF (Snezhinsk) in collabora-
tion with ITEP (Moscow). It consists of the following basic stages: E Cold rolling of steel plates with grooves for "bers. E Di!usion welding of the plate stack to form a monolithic structural element. E Machining of the module to provide the required outer shape. The di!usion welding will be the key stage of the absorber module manufacturing. The special equipment was designed, manufactured and commissioned for the di!usion welding of the modules. In order to test technology, the full size preproduction absorber module has been manufactured, mechanically tested and delivered to CERN in July 1999 for an inspection and the assembly of the preproduction prototype of the calorimeter module. As it was mentioned, this prototype was recently tested at the CERN high-energy beam. Acknowledgements The "nancial support from the ISTC Project 728 was crucial for the development of the technology of the manufacturing of the absorber modules for the CMS quartz "ber calorimeters. References [1] CMS, The Hadron Calorimeter Technical Design Report. CERN/LHCC 97-31, 1997. [2] V. Gavrilov et al., Prib. i Tech. Exper. 4 (1997) 23 (in Russian). [3] N. Akchurin et al., Nucl. Instr. and Meth. A 399 (1997) 202. [4] N. Akchurin et al., Nucl. Instr. and Meth. A 379 (1996) 526. [5] N. Akchurin et al., Nucl. Instr. and Meth. A 409 (1998) 593.
CMS quartz "ber calorimeter V. Gavrilov* ITEP B. Cheremushkinskaya ulitsa 25, RU-117 259, Moscow, Russia Accepted 19 June 2000
Abstract The CMS will be a general purpose detector for the Large Hadron Collider at CERN. Its quartz "ber calorimeter is designed to provide hermetic measurement of energy #ow in the forward rapidity region. The calorimeter must operate under extremely hard radiation conditions and almost without maintenance. Several prototypes have been constructed and tested at the CERN high-energy beam. The cost e!ective technology of manufacturing of "ne sampling absorber modules has been developed. 2000 Published by Elsevier Science B.V. All rights reserved.
1. Introduction The Large Hadron Collider will operate at high energies and luminosities ((s"14 GeV and ¸"10 cm\ s\). For the general purpose detector CMS the hermetic calorimetry coverage up to "g""5 will be required for the measurement of missing transverse energy and for detection of high-energy hadron jets. The most severe operation conditions are expected at the region of the small angles with respect to the colliding beams. The CMS forward calorimeters will cover the rapidity region of 3("g"(5 and will be installed at about 11 m from the interaction point [1]. The radiation doses and the neutron #uxes at that region will reach 50}100 MRaD/yr and 10 n cm\ s\ respectively. The main requirements to the CMS Forward Calorimeters are as follows: E High radiation resistance. E Limited maintenance.
* Tel.: #7-095-123-9447; fax: #7-095-883-9592. E-mail address: [email protected] (V. Gavrilov).
E Fast signal collection. E Low sensitivity to neutrons. 2. Quartz 5ber calorimetry The CMS forward calorimeters will consist of optical quartz "bers embedded in an absorber matrix. The "bers run along the beam direction, i.e. approximately in the same direction as the incoming particle. This "ber arrangement allows the build up of readout cells by grouping "bers from the desired areas. The basic features of the quartz "ber calorimeter are as follows: E Quartz "bers keep transparency to visible light being irradiated up to doses of GRaD [2]. E No maintenance in the hot zone will be required because the active element of the calorimeter will be inert. E Due to Cherenkov nature of the signal the calorimeter will be sensitive only to relativistic charged particles and therefore its sensitivity to neutron induced reactions will be very low.
0168-9002/00/$ - see front matter 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 0 ) 0 0 6 3 9 - 2
V. Gavrilov / Nuclear Instruments and Methods in Physics Research A 453 (2000) 242}244
E Due to instantaneous nature of Cherenkov light the calorimeter signal will be very fast [3]. E Light output of this type of calorimeters will be extremely low due to several reasons: E 䡩 Only a small faction of particle energy loss comes to Cherenkov light production. E䡩 Volume fraction of quartz "bers in the calorimeter should be very low (about 1%) to keep the overall cost of the calorimeter at an a!ordable level. E䡩 Only small faction of produced photons will be trapped in the "bers and transported to photodetectors. E䡩 Attempts to increase a number of photoelectrons using UV-sensitive photodetectors will not help in this case because the "ber transparency to UV light will be lost rapidly after the beginning of operation in a hard radiation environment. E This type of calorimeters is not compensating, i.e. the signal for high-energy hadron is considerably lower (by a factor of about 1.5 [3]) than the signal for electron (or photon) of the same energy. E The visible radius of a hadronic shower detected in the quartz "ber calorimeter is much smaller with respect to a radius of a hadronic shower detected in an ionizing or in a scintillating calorimeter [4].
3. Prototypes and expected performance Several prototypes of the quartz "ber hadron calorimeter has been assembled and tested at the CERN test beam. Calorimeters contained quartz "bers of 0.30 mm core diameter. The absorber of the "rst prototype [3] was made of copper. Fiber volume fraction was 1.5%. The length was 135 cm and the sensitive transversal area was about 16;16 cm. In the case of electrons, a good energy linearity of the signal was observed. The energy resolution for electrons was determined by statistical #uctuations of a number of photoelectrons. The output signal for that prototype was about 0.5 p.e./GeV and the electron energy resolution was pE/E"1.37/(E. For the charged pion showers the substantial energy non-linearity was observed.
243
In the high-energy range (200}375 GeV), the number of p.e. per GeV for pions was about of that for electrons. It was observed that the hadron energy resolution of quartz "ber calorimeter was determined predominantly by intrinsic #uctuations of hadron shower development rather than the statistical #uctuations of a number of photoelectrons. The purpose of the CMS quartz "ber calorimeter will be to measure the energy #ow in the forward rapidity region and the energy of forward hadron jets. In both cases, the fraction of energy carried by gammas (from decays of neutral pions and other hadrons) will #uctuate. Therefore an equalization of signals from hadronic and e.m. showers of the same energy will improve the calorimeter performance. Partial equalization could be achieved using longitudinal segmentation of the calorimeter where a sampling fraction in the front (`e.m.a) section will be lower with respect to the rear (`hadronica) section. This approach was tested using the prototype with two longitudinal segments [5]. The hadronic section was modeled with the above-described copper prototype and another copper prototype of 33 cm length with the same transversal structure as the hadronic section was assembled for the front e.m. section. The results of the beam test of the prototype with two longitudinal segments were used to simulate the response of the calorimeter to high-energy hadron jets. It was shown that the optimal jet energy resolution will be achieved in the quartz "ber calorimeter in which the e.m. section will have sampling fraction of with respect to that of the hadronic section. For such a calorimeter the full equalization of signals for hadronic and e.m. showers will not be achieved, but it will be optimal to minimize both #uctuations of photon content in the jets and a deterioration of hadron energy resolution due to longitudinal non-uniformity of such a calorimeter. The simulations of the performance of the CMS forward calorimeter for the detection of hadronic jets allowed to optimize the main parameters of calorimeter on the basis of the cost vs. performance balance. E Steel was chosen as the absorber material. The forward calorimeter will be placed outside the
6. CALORIMETERS
244
V. Gavrilov / Nuclear Instruments and Methods in Physics Research A 453 (2000) 242}244
magnet yoke of the CMS magnet, therefore the magnetic properties of its absorber are not so important. E The segmentation of read-out towers were chosen to be equal to dg;d "0.175;0.175. This tower will be two times larger than the tower of the central part of the CMS hadron calorimeter, but this segmentation will not compromise the jet transverse energy resolution and the e$ciency of the jet reconstruction. E The "ber spacing was chosen to be equal to 2.5;2.5 mm. This spacing will provide the "ber volume fraction of 0.55% for the e.m. section and of 0.85% for the hadronic section. Even for such low sampling fraction the jet energy resolution will not be dominated by the photoelectron statistical #uctuation. In order to test the performance of the quartz "ber calorimeter with the steel absorber and with the chosen sampling fractions for the longitudinal segments, the new prototype of the length of 165 cm has been assembled and tested at the CERN highenergy beam in September 1999. The beam test results are being analyzed.
4. Technology of absorber modules manufacturing The manufacturing of the calorimeter absorber with the "ne structure of tiny holes for the quartz "ber insertion will not be an easy task. There is no available standard industrial technology which could be used for that purpose. The absorber will be assembled of the modules of the sizes of 24;24;165 cm. The technology of module manufacturing was developed at the Russian Federal Nuclear Center VNIITF (Snezhinsk) in collabora-
tion with ITEP (Moscow). It consists of the following basic stages: E Cold rolling of steel plates with grooves for "bers. E Di!usion welding of the plate stack to form a monolithic structural element. E Machining of the module to provide the required outer shape. The di!usion welding will be the key stage of the absorber module manufacturing. The special equipment was designed, manufactured and commissioned for the di!usion welding of the modules. In order to test technology, the full size preproduction absorber module has been manufactured, mechanically tested and delivered to CERN in July 1999 for an inspection and the assembly of the preproduction prototype of the calorimeter module. As it was mentioned, this prototype was recently tested at the CERN high-energy beam. Acknowledgements The "nancial support from the ISTC Project 728 was crucial for the development of the technology of the manufacturing of the absorber modules for the CMS quartz "ber calorimeters. References [1] CMS, The Hadron Calorimeter Technical Design Report. CERN/LHCC 97-31, 1997. [2] V. Gavrilov et al., Prib. i Tech. Exper. 4 (1997) 23 (in Russian). [3] N. Akchurin et al., Nucl. Instr. and Meth. A 399 (1997) 202. [4] N. Akchurin et al., Nucl. Instr. and Meth. A 379 (1996) 526. [5] N. Akchurin et al., Nucl. Instr. and Meth. A 409 (1998) 593.