M. Alfonsi

The triple-GEM detector for the M1R1 muon station at LHCb

Twenty-four triple-GEM detectors with 20times24 cm2 active area will equip the inner region of the first station of the muon detector at the LHCb experiment. After three years of R&D to prove that this detector, operated with a CF4 based gas mixture, satisfies the stringent requirements in terms of time performance and radiation hardness, the project is entering in the construction phase. The final design of the detector, the selected materials and the construction procedure and tools will be described in details. The quality control of components, such as planarity measurements on the PCB-panels and the HV test of the GEM foil, as well as the leak test and the X-ray tomography of constructed chambers will be discussed. The chamber equipped with front end electronics, Faraday cage and HV divider is finally tested with cosmics. The construction of the detector, shared between the two production sites of Cagliari-INFN and Laboratori Nazionali di Frascati-INFN, should be completed in spring 2006. The installation is foreseen by the end of the 2006

The LHCb triple-GEM detector for the inner region of the first station of the muon system: construction and module-0 performance

A triple-gas electron multiplier (GEM) detector, operated with the gas mixture Ar/CO2/CF4 (45/15/40), is going to equip station M1, region R1 of the LHCb muon system. A Module-0 of this detector, with full area (20 cmtimes24 cm) GEM foils, was recently built and tested. In this paper, new measurements of efficiency and pad multiplicity are presented. These new measurements were very important to select of the final pad board configuration. The sensitivity to discharges is a very important issue in this type of detector; we discuss here new measurements of the maximum number of discharges that a triple-GEM detector can stand before breakdown, and we show that detector operation in LHCb is safe from this point of view. We also discuss new measurements of the time performance of the detector in the presence of background radiation, indicating that no significant deterioration of the performances is expected in the LHCb environment

Aging measurements on triple-GEM detectors operated with CF/sub 4/-based gas mixtures

We present the results of a global irradiation test of full size triple-GEM detectors operated with CF/sub 4/-based gas mixtures. This study has been performed in the framework of an R&D activity on detectors for the innermost region of the first muon station of the LHCb experiment. The prototypes have been irradiated at the Calliope facility of the ENEA-Casaccia with a high intensity 1.25 MeV /spl gamma/ from a /sup 60/Co source. After the irradiation test the detectors performances have been measured with X-rays and with a 3 GeV pion beam at CERN. A SEM analysis on several samples of the detectors has been performed to complete the understanding of the physical processes occurring in the GEM detector during the strong irradiation.

Advances in fast multi-GEM-based detector operation for high-rate charged-particle triggering

In this paper we summarize the results obtained in an R&D work performed in the period 2000-2003 within the LHCb Collaboration to develop a triple-GEM based detector for the inner region of the first muon station. Since the information coming from this detector will he used at the L0 trigger level, many studies were performed in order to optimize its time resolution. By using CF/sub 4/-based gas-mixtures a time resolution of 4.5 ns RMS was obtained, which translates in efficiencies higher than 96 % in a 20 ns time window for a large operating region. Moreover, measurements of discharge probability per incident charged particle with a high intensity pion/proton beam for these gas mixture are also reported. All these results show that triple-GEM detectors can he used for triggering in the LHCb Muon Detector. Preliminary results on a global aging test performed with a 25 kCi /sup 60/Co source are also reported and compared to other aging tests performed with X-rays and hadron beams.

The commissioning of the GEM detector for the muon apparatus of the LHCb experiment

The 24 triple-GEM detectors for the innermost region of the first muon station (M1R1) of the LHCb experiment are ready to be installed. The major challenges have been the improvement of the time performance in terms of efficiency of the bunch crossing identification and a high radiation hardness in the harsh environment typical of LHC experiments. During the R&D phase we demonstrated, with several laboratory and beam tests, that GEMs operated with an Ar/CO2/CF4 (45/15/40) gas mixture can achieve a time resolution below 3 ns r.m.s, giving an efficiency better than 96% in 25 ns time window. A rate capability better than 50 MHz/cm2 and a robustness against discharges (tests with alpha and low momentum particles at PSI ) have been measured. A severe global irradiation test of the final detector has been required to study the compatibility of the construction materials with the gas mixture, showing that the detector survives, without permanent damages and serious performance losses, after an integrated charge of 2.2 C/cm2, corresponding to 12 years of LHCb. The construction of chambers, based on an innovative stretching technique of the GEM foils, has been realized in a class 1000 clean room. Quality control of components and the HV test of GEM foil, as well as the gas leak test and X-ray tomography of the detectors have been performed. The performances of the final GEM detector, integrated with the front-end electronics based on the CARIOCA-GEM chip, have been measured with the LHCb DAQ electronic chain in a recent beam test at the SPS operated with a 25 ns time structure, similar to the LHC running condition. The results demonstrate that the GEMs fulfill the experiment requirements with a safe working range of 90 V corresponding to a factor of 4 in gain.