F. Grancagnolo

New results on ATLAS RPC's aging at CERN's GIF

In order to ensure that the resistive plate chambers used in the ATLAS experiment will not show, during their operation, any abnormal aging effect which could degrade their performances, an aging test is being performed at X5-GIF, CERNs gamma irradiation facility. In this paper, the latest results are presented, together with an example of successful damage recovery technique.

Slice Test Results of the ATLAS Barrel Muon Level-1 Trigger

The muon spectrometer of the ATLAS experiment makes use of the Resistive Plate Chambers detectors for particle tracking in the barrel region. The level-1 muon trigger system has to measure and discriminate muon transverse momentum, perform a fast and coarse tracking of the muon candidates, associate them to the bunch crossing corresponding to the event of interest, measure the second coordinate in the nonbending projection. The on-detector electronics first collects front-end signals coming from the two inner RPC stations on the low-pT PAD boards, each one covering a region of ∆η×∆φ=0.2×0.2, and hosting four Coincidence Matrix ASICs. Each CMA performs the low-pT trigger algorithm and data readout on a region of ∆η×∆φ=0.2×0.1. Data coming from the four CMAs are assembled by the low-pT PAD logic. Each low-pT PAD board sends data to the corresponding high-pT PAD boards, located on the outer RPC station. Four CMA on each board make use of the low-pT trigger result and of the front-end signals coming from the outer RPC stations to perform the high-pT algorithm. The overall results are assembled by the high-pT PAD logic and sent via optical fibre to the off-detector electronics. Each optical receiver board collects data from six or seven fibres, covering a region of ∆η×∆φ=1.0×0.1. Trigger data are sent to the local Sector Logic, which elaborates trigger data and sends them to the Muon Central Trigger Processor Interface via dedicated copper links. Readout data are sent to the Read-Out Drivers Boards. Laboratory and muon beam test on the readout and trigger chains are presented.

Test beam results and integration of the ATLAS level-1 muon barrel trigger

The ATLAS level-1 muon trigger will be crucial for the online selection of events with high transverse momentum muons and for its correct association to the bunch-crossing corresponding to the detected events. This system uses dedicated coarse granularity and fast detectors capable of providing measurements in two orthogonal projections. The resistive plate chambers (RPCs) are used in the barrel region (|/spl eta/| < 1). The associated trigger electronics is based on a custom chip, the coincidence matrix, that performs space coincidences within programmable roads and time gates. The system is highly redundant and communicates with the ATLAS level-1 trigger processor with the MUCTPI interface. The trigger electronics provides also the readout of the RPCs. Preliminary results achieved with a full trigger tower with production detectors in the H8 test beam at CERN will be shown, in particular preliminary results on the integration of the barrel muon trigger electronics with the MUCTPI interface and with the ATLAS DAQ system will be discussed.

The RPC LVL1 trigger system of the muon spectrometer of the ATLAS experiment at LHC

The Atlas Trigger System has been designed to reduce the LHC interaction rate of about 1 GHz to the foreseen storage rate of about 100 Hz. Three trigger levels are applied in order to fulfill such a requirement. A detailed simulation of the ATLAS experiment including the hardware components and the logic of the Level-1 Muon trigger in the barrel of the muon spectrometer has been performed. This simulation has been used not only to evaluate the performances of the system but also to optimize the trigger logic design. In the barrel of the muon spectrometer the trigger will be given by means of resistive plate chambers (RPCs) working in avalanche mode. Before being mounted on the experiment, accurate quality tests with cosmic rays are carried out on each RPC chamber using the test station facility of the INFN and University laboratory of Napoli. All working parameters are measured and the uniformity of the efficiency on the whole RPC surface is required. A summary of the Napoli cosmic rays tests, together with a brief description of the Atlas Trigger, in particular of the Level-1 Muon Trigger in the barrel, and the results of the trigger simulation will be given.

Test beam results from the ATLAS LVL1 muon barrel trigger and RPC readout slice

The ATLAS barrel level-1 muon trigger system has the following main requirements: coarse measurement and discrimination of the muon transverse momentum PT; bunch crossing identification; fast and coarse tracking to identify tracks in the precision chambers that are related to the muon candidate; 2nd-coordinate measurement with a required resolution of 5-10 mm. Integration tests have been carried out between the various components of the system and in conjuction with the detector, front-end and other general sub-systems of the experiment. Results from test beam measurements have been performed in the CERN H8 test beam area, where production detectors from one full trigger tower have been installed.

Ageing test of ATLAS RPCs at CERN's Gamma Irradiation Facility

An ageing test of three ATLAS production RPC stations is in progress at X5 GIF, the CERN irradiation facility. The chamber efficiency as a function of the operating voltage is measured at different source intensities, up to a maximum counting rate of about 700 Hz/cm/sup 2/. All along the test, plate resistivity has been monitored using two different methods: by measuring the I-V characteristics in pure Ar, and by comparing the efficiency vs high voltage curves at different source intensities. The increase in plate resistivity, which is one of the dominant ageing effects for RPCs with phenolic-melaminic electrodes, has been shown to be strongly dependent on environmental relative humidity. Indeed, after setting to values between 40% and 50% the relative humidity of both the operating gas and the air surrounding the chambers, a significant decrease of the plate resistivity has been observed.