Micromegas detectors for the muon spectrometer upgrade of the ATLAS experiment

M Bianco

doi:10.1016/j.nima.2015.11.076

Abstract

Large area Micromegas (MM) detectors will be employed for the Muon Spectrometer upgrade of the ATLAS experiment at the LHC. A total surface of about 150m2of the forward regions of the Muon Spectrometer will be equipped with 8 layers of MM modules. Each module covers a surface area of approximately 2–3m2 for a total active area of 1200m2. Together with the small-strips Thin Gap Chambers, they will compose the two New Small Wheels, which will replace the innermost stations of the ATLAS Endcap Muon tracking system in the planned 2018/2019 shutdown. This upgrade will maintain a low pT threshold for single muons and provide excellent tracking capabilities for the HL-LHC phase. The New Small Wheel (NSW) project requires fully efficient MM chambers with spatial resolution down to 100μm, at rate capability up to about 15kHz/cm2 and operation in a moderate (highly inhomogeneous) magnetic field up to B=0.3T. The required tracking capability is provided by the intrinsic spatial resolution combined with a challenging mechanical precision. The design, recent progress in the construction and results from the substantial R& D phase (with a focus on novel technical solutions) is presented. In the R& D phase, small and medium size single layer prototypes have been built, along with, more recently, the first two MM quadruplets in a configuration very close to the final one chosen for the NSW. Several tests have been performed on these prototypes at a high-energy test-beam at CERN, to demonstrate that the achieved performances fulfil the requirements. Recent tests applying various configuration and operating conditions are presented.

Highlights

In 2018/2019 the Large Hadron Collider [1] instantaneous luminosity will be increased to 2 À 3 Â 1034 cm À 2 s À 1 and eventually will reach up to 7 Â 1034 cm À 2 s À 1 after the long shutdown in 2023, exceeding the design value of 1 Â 1034 cm À 2 s À 1 and considerably extending the physics program at LHC
The electrons, produced by the ionization, drift towards the mesh and the amplification region, where the signal is created by means of an electric field of about 40–50 kV/cm; the mesh is kept in position by a grid of 128 μm high pillars built on the readout board
The results presented here correspond to chambers operated with Ar=CO2 93=7% gas mixture, the drift plane was set to 300 V while the resistive strips were set at entroid method : the position is given by the calculation of the strips centroid weighted by the signal amplitude of each strip which belongs to a cluster;

Summary

Introduction

In 2018/2019 the Large Hadron Collider [1] instantaneous luminosity will be increased to 2 À 3 Â 1034 cm À 2 s À 1 and eventually will reach up to 7 Â 1034 cm À 2 s À 1 after the long shutdown in 2023, exceeding the design value of 1 Â 1034 cm À 2 s À 1 and considerably extending the physics program at LHC. In order to take advantage of the improved LHC operation the ATLAS detector [2], and in particular the forward region of the Muon Spectrometer, must be upgraded to have better performance at the expected high luminosity. The detector will be composed of eight active layers covering a total area of 1200 m2. It is subdivided into 128 modules each with

The Micromegas chambers

Layout and construction of Micromegas for the New Small Wheel

Conclusion