Start Detector for ALICE Experiment
Development and Design of Start Detector for Trigger and Time-of-Flight Systems for the ALICE Experiment at CERN, LHC
Tech Area / Field
- INS-DET/Detection Devices/Instrumentation
- PHY-PFA/Particles, Fields and Accelerator Physics/Physics
8 Project completed
Senior Project Manager
Lapidus O V
Russian Academy of Sciences / Institute of Nuclear Research, Russia, Moscow
- MIFI, Russia, Moscow\nKurchatov Research Center, Russia, Moscow\nNIIIT (Pulse Techniques), Russia, Moscow
- University of Jyväskylä, Finland, Jyväskylä\nCERN, Switzerland, Geneva
Project summaryThe aim of the project is to design, manufacture and study the prototypes of the TO starting trigger detector, intended to generate the starting signal for the time-of-flight system, and the zero level trigger for a number of other detector subsystems of the ALICE installation at the Large Hadron Collider (LHC) at CERN, Geneva. At the given installation there will be carried out fundamental researches on finding and studying a new form of nuclear matter – quark-gluon plasma, which in accordance with contemporary knowledge must be formed at collisions of opposing beams of super-high energy heavy nuclei. At present the experiments with collisions of relativistic heavy ions are conducted at the RHIC accelerator, Brookhaven, USA (STAR, PHENIX and oth.). First results have shown, that the energy of the RHIC accelerator is insufficient to achieve that level of nuclear matter’s energy density, at which the quark-gluon plasma is generated, and only the ALICE experiment at the LHC accelerator, having a substantially greater energy, can answer on this principal question and lead to the revelation of quark-gluon plasma and quark deconfinement.
The TO detector is very significant for the operation of the whole ALICE installation. It determines the instant, when the opposing accelerated particles collide, with an accuracy of 50 ps, that allows to carry out the identification of secondary particles, born in the collision, by the time-of-flight technique, using the time-of-flight detector, being a part of the installation. Besides that, the TO detector determines the point of collision with an accuracy of ~ 1 cm, thereby choosing the events, occurring in the installation’s aperture, and the multiplicity of particles, born in the collision, thereby generating signals, allowing event registration, – “experiment triggers”.
The detector design should consist of two assemblages of 12 Cherenkov detectors in each, placed coaxially around the beam pipe, unsymmetrically relative to the center of colliding beams interaction. The Cherenkov counters, as the majority of ALICE detectors, are placed inside a magnet with a field of 0.4 Tesla. Therefore the Cherenkov counters should be based on the modern unique magnet-resistant PMTs FEU-187. Those PMTs have not been used in accelerator experiments yet. Their close analogs Hamamatsu R5506 have been successfully employed in the PHENIX experiment, but the conditions of the ALICE experiment substantially differ from those of PHENIX, same as the functions of detectors on their basis. The parameters of an experimental batch of FEU-187 were thoroughly studied in MEPhI, and their adequacy to the experiment conditions was shown. Particularly, the Cherenkov counters on their basis allowed to achieve the required temporal resolution of 50 ps for solitary relativistic particles.
The physical characteristics of the collider experiment’s detector can not be directly measured in the experiment with a fixed target. Therefore they must be simulated by the Monte-Carlo technique. Experienced specialists from INR and MEPhI are invited to conduct those simulations.
The development of unique fast analog and trigger electronics for the TO detector is the most important part of the given project. Electronics should provide the detector’s temporal resolution on the order of 50 ps at a dynamic range of detector signals around 1:1000, thereat the dead time should be less than 25 ns and a high parameter stability in time should be provided. Those requirements are caused by the wide range of multiplicity in proton-proton and ion-ion collisions, as well as by the bunch period of accelerator. Such high demands to the detector electronics are unprecedented. Standard commercial electronics of the best worlds manufacturers does not provide such a wide dynamic range and small dead time. Experienced specialists from MEPhI, the Kurchatov Institute and INR RAS are invited to design and create the prototypes of electronic modules.
The 24 timing channels of the TO detector should provide a temporal resolution of the whole system in the order of 50 ps during the whole time of the experiment (10 years).
That requires the constance of signal delays in all timing channels with an accuracy of ±10 ps. The inevitable pergence of delays in the course of service requires their periodical correction by means of controlled digital delay lines. With this purpose, as well as for detector adjustment and calibration before its installation in the ALICE system, there will be created a special system of laser calibration, for which development there are invited the specialists of NIIIT and MEPhI. The laser calibration system should include a pulse laser with a duration of light pulse within 100 ps (for instance, PIL40G of Advanced Photonics Systems) and an optical fiber system with an optical attenuator, allowing to feed light pulses to the all 24 counters in a wide range of amplitudes.
For the creation of the detector’s mechanical part the topical requirement is to minimize the amount of matter at the specified rigidity of the structure. An additional term consists in the radiation hardness of the used materials and their long-time stability. The engineering solutions, based both on already existing and recently developed in CCBM (St.Petersbourg) technologies of light-weight thermo- and mechano-stable monolithic structures of carbo-composites, will allow to solve successfully the task of creating the TO detector. For the solution of that part of the task there have been involved the members of CCBM staff, who participated in the ISTC projects ## 345, 1666, 1999 and have an experience in designing, conducting mechanical and thermal simulations, calculations and tests of the developed technologies of working the high-module dry carbo-fibers and finished carbo-prepregs.
INR of RAS is the chief institution of the given project, which has a great experience of participating in a number of major international experiments on studying nuclear matter in nuclei-nuclear interactions, such as NA50 in CERN, HADES in GSI (Darmstadt, Germany) and which currently participates in the preparation of ALICE experiment. In the given project INR will coordinate its fulfilment and participate in all its tasks, carry out the integration of detector in the ALICE installation at CERN.
The qualification of the project executants from the five mentioned institutes is fairly high. Well known Russian specialists, including 4 doctors and 11 candidates of sciences, having large experiences of works on the project’s subjects, will participate in it.
The given project meets the ISTC objectives. Namely it does: promote the integration of Russian scientists in the international scientific community, re-orient the efforts of Russian weapon specialists toward peaceful activities (labour expenses of weapon specialists make up over 65% of those of all project participants), support fundamental and applied research and the development of modern technologies in the field of elementary particle physics. Besides that, the development of unique electronic, optical and mechanical units of the detector, being created, will further allow to solve the problems, linked with the transition of the teams, participating in the project, to market economy.
The consent on being foreign collaborators of the given project has been expressed in writing by CERN (Switzerland) and University of Jyvaskyla (Finland), which will participate in the composition of work plans, exchange of information, expert evaluation of work results, presentation of expensive beam time and modern equipment for tests, arrangement of scientific meetings and publications on the project’s subjects.
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