Performances of anode-resistive Micromegas for HL-LHC

Micromegas technology is a promising candidate to replace Atlas forward muon chambers -tracking and trigger- for future HL-LHC upgrade of the experiment. The LHC accelerator luminosity will be ten times the nominal one, increasing background and pile-up event probability in the same proportion. This requires detector performances which are currently under studies in intensive RD activities. We studied performances of four different resistive Micromegas detectors and with different read-out strip pitches. These chambers were tested using similar to 120 GeV momentum pions with rates from 25 up to 250 kHz/cm(2), at H6 CERN-SPS beam line in autumn 2010. We found that the resolution is degraded, if the strip pitch is too wide with respect to the charge distribution at the readout plane. To reduce the systematic effects of the charge sharing we propose a cluster reconstruction algorithm. For narrow strip pitch 500 m m we measure a resolution of similar to 90 mu m and a efficiency of similar to 98%. The track angle effect on the efficiency was also studied. Our results show that resistive techniques induce no degradation on the efficiency or resolution, with respect to the standard Micromegas. In some configuration the resistive coating is able to reduce the discharge currents at least by a factor of 100 and no HV breakdown was observed.