R&D of Muon Trigger Chamber for the Use in Proton-proton Collider Experiment

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R&D study has been performed for the Thin Gap Chambers (TGC), which will be used for the muon trigger chamber in the ATLAS experiment of Large Hadron Collider (LHC). Based on the results in 1995, it turned out that the gas mixture of CO_2n+n-pentane was suitable from the viewpoint of detection efficiency. So that the aging tests for this gas mixture were carried out in 1996. The chamber was exposed to the beta rays whose radiation amount corresponded to the expected one for 10 years in the ATLAS experiment, and the deterioration of the chamber performance was examined. No significant deterioration was observed during the irradiation for the amplification factor and for the time resolution. The detection efficiency was found to be nearly 100% up the radiation rate of 100kHz/cm^2, and this gas mixture will be safely used in the ATLAS experiment since the expected radiation rate is at maximum 1kHz/^2The time resolution of CO_2+n-pentane is slightly worse than that of CF_4+iso-butane due to its slower electron drift velocity. In order to improve this time resolution, the chamber with smaller wire spacing was constructed and tested. The time resolution was improved so that we can identify successive crossing bunches in the ATLAS experiment.In is known that the muons emerging from the interaction point enter the TGC with the incident angle of 5-40 degrees. The dependence of the time resolution on this incident angle was measured and and found to be consistent with the expectation from the Monte Carlo simulation.In summary, the various properties of Thin Gap Chambers with the gas mixture of CO_2+n-pentane were examined in detail, and we found that they satisfy the requirements of ATLAS experiment.