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HADES upgrade
Subproject coordinator: Joachim StrothThe HADES spectrometer is a dedicated instrument to study rare leptonic decays of mesons produced in nuclear reactions. Of particular interest are meson decays occurring during the early stage of reactions of very heavy ions. The electron pairs emitted through such decays allow studying the properties of dense and hot nuclear matter. In its first configuration, HADES is now taking data since late 2002. At present part of the detector system does not yet have sufficient granularity to cope with particle multiplicities apparent in collisions of very heavy ions. Moreover, high particle multiplicities also produce large event sizes. To accomplish high data taking rates, the bandwidth of the data acquisition system has to be increased. In the past four years of operation the physics program therefore was focused on 12C+12C and 40Ar+KCl collisions as well as on p+p reactions.
With the current upgrade program, which is part of this CNI, the HADES spectrometer will be upgraded to fulfill all requirements to run experiments with high particle multiplicities and at sufficiently high event rates. The two major projects in this respect are the replacement of the inner time-of-flight (TOF) system by a novel detector system exploiting resistive plate technology (HADES-1), and the upgrade of the data acquisition system (HADES-3), which includes the replacement of several processor boards and the modification of HADES trigger bus. The spectrometer will also be complemented by a scintillating hodoscope placed at very forward angles, a region which so far was not covered by any detector. This detector system will add capabilities to reconstruct the reaction plane and thus will permit studying azimuthal emission patterns.
Besides activities covered by this construction task, other activities by HADES collaboration members complement the upgrade project (see below). The final goal is to have the spectrometer ready for high multiplicity experiments early 2009. As was shown in simulations, the spectrometer will then also be well equipped to cope with heavy ion reactions using SIS100 beams. The current planning foresees to continue the experimental program at SIS18 until all cave installation at the new experimental site is ready. The transfer of the spectrometer from the current experimental site to the new CBM cave will take about 1.5 years including commissioning of all detector elements after transport.
- HADES-1 / task 8
The replacement of the inner TOF system will add sufficient granularity for reactions up to 197Au+197Au. Moreover, it will also improve the time resolution and henceforth the particle identification capability of the spectrometer. The RPC technology chosen has proven to provide robust detectors and very good performance at the same time. The mass production is in progress and final design iteration of the front-end electronics are about to finish. It turned out that the read-out board developed for the RPC detector read out is a very versatile device. We decided therefore to foresee this type of board also for other detector systems. This had some consequences for the work flow and task assignment in HADES-3.
- HADES-2 / task 9
The new detector system for forward angles is a result of recycling a detectors system used before at the KAOS spectrometer at GSI, which was shut down several years ago. The main activities here are the reconstruction of the read-out stage of the scintillators and the installation of a read-out system compatible with the HADES DAQ and trigger system. All detector elements are reassembled and currently the new support structure is under construction.
- HADES-3 / task 10
The major goal of the DAQ upgrade is to relevant parts of the by now more then 10 years old DAQ components. Rapid progress in the technology of microelectronics allows solution with much higher performance today. A good example is the flexibility of the read-out board developed for the RPC project. Based on this design replacements for the respective board used in the read-out chains of other detectors system in HADES can be effectively developed. Therefore, it became also possible to replace the old trigger distribution system and to introduce further detectors into the trigger decision process. Because of widening the scope of the HADES-3 project we now face some delays but in view of the improvement possible this is more then tolerable.
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