Abstract

Since start of data taking the ATLAS muon spectrometer performs according to specification. End of this decade after the luminosity upgrade of LHC by a factor of ten the increasing background rates require the replacement of the detectors in the most forward part of the muon spectrometer to ensure high quality muon triggering and tracking. Square meter sized micromegas detectors together with improved thin gap trigger detectors are suggested as replacement. Micromegas detectors are intrinsically high rate capable. A single hit spatial resolution below 40mm has been shown for 250mm anode strip pitch and perpendicular incidence of high energy muons or pions. The development of large micromegas structures and their investigation under non-perpendicular incidence or in high background environments is ongoing. Micromegas using resistive strip technology do not show ageing under large fluxes of low-energy neutrons. They have been successfully operated under HL-LHC equivalent fluences of 11 MeV neutrons. In ATLAS most of the 30 mm diameter high-pressure drift-tubes will remain in place. They may be operated using a considerably faster and more linear drift-gas mixture. Such gas mixtures have been shown to be marginally sensitive to high photon fluences and not to age due to ionizing radiation.

Highlights

  • IntroductionThe ATLAS muon spectrometer [1] performs according to the specifications of efficiency, occupancy and spatial resolution at present

  • The ATLAS muon spectrometer [1] performs according to the specifications of efficiency, occupancy and spatial resolution at present peak-luminosities of

  • Using 20 MeV protons, we have shown that track reconstruction efficiency and spatial resolution of 15 mm drift-tube detectors is robust against up to 20 kHz/cm2 highly ionizing background hits

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Summary

Introduction

The ATLAS muon spectrometer [1] performs according to the specifications of efficiency, occupancy and spatial resolution at present. By end of this decade about ten times higher peak-luminosities are envisaged after the high luminosity upgrade of LHC to HL-LHC. The currently used detectors in the forward part of the muon spectrometer, the Small Wheel, need to be replaced [2]. The present Small Wheel, see figure 1, is made up of cathode strip chambers (CSC) in its inner part and 30 mm high-pressure drift tube detectors (MDT) in the outer region. 2. Square meter sized micromegas detectors [6] and improved thin gap trigger chambers are under discussion as replacement in the Small Wheel. Online angular track reconstruction within 1 mrad and a few mm position resolution is required

Investigation of a large size micromegas detector with floating strip anode
A Linear and fast driftgas for 30 mm monitored drift-tube chambers
Irradiation studies
Findings
Summary
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