Study of the performance of Micromegas detectors in magnetic field

Sampsonidis Dimitrios,S Dalla Torre,S Levorato,L Ropelewski,F Tessarotto,B Gobbo

doi:10.1051/epjconf/201817405003

Sampsonidis Dimitrios, S Dalla Torre + Show 4 more

Open Access

https://doi.org/10.1051/epjconf/201817405003

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Abstract

Resistive Micromegas (MICRO MEsh GAseous Structure) detectors have been chosen by the ATLAS collaboration at LHC for the high luminosity upgrade, due to their capability to maintain full efficiency and high spatial resolution at high occupancy, for tracking muons in the forward region of the detector. The Inner Muon Station, in the high-rapidity region, the so called New Small Wheel (NSW), will be composed of micromegas detectors that will have to maintain good performance in the presence of magnetic field of up to about 0.3 T. The response of micromegas detectors is affected by the magnetic field, where the deflection of the drift electrons is described by the Lorentz angle, resulting in a bias in the reconstructed track position. Several test-beam campaigns have been performed to test the behaviour of small size resistive micromegas prototypes (10×10 cm2) in magnetic fields up to 1 T, using high momentum muon and hadron beams at CERN. These studies are performed in order to validate the capability of the chambers to provide unbiased tracks in the NSW conditions. Measurements of the Lorentz angle and drift velocity as a function of the magnetic field are presented and both are compared to expectations based on Garfield-Magboltz simulations. Several methods to correct the position bias are applied, based on the chamber configuration or on the knowledge of the local value of the magnetic field. The results of these studies are presented together with an overall discussion of the Micromegas tracking capability in magnetic field.

Highlights

The New Small Wheel LayoutThe NSW, following the present structure of the Muon Spectrometer, is divided in sixteen sectors, eight large and eight small sectors
PT > 20 GeV) single muon trigger rate, will be kept at an acceptable level.The New Small Wheel (NSW), following the present structure of the Muon Spectrometer, is divided in sixteen sectors, eight large and eight small sectors
The principles of operation of the MM chambers chosen for the NSW are shown in Fig. 3, as well as the baseline parameters of the ATLAS-NSW chambers

Summary

The New Small Wheel Layout

The NSW, following the present structure of the Muon Spectrometer, is divided in sixteen sectors, eight large and eight small sectors. Each sector comprises sixteen layers of trigger and precision tracking detectors, namely sTGCs and MM covering a total area of 1200 m2. For both technologies, each module is a multiplet of four active layers each ( quadruplets) and is arranged in the following order: sTGC-MM-MM-sTGC. The readout strips are covered by a layer of resistive strips on top of a thin insulator. In such a way the MM is protected from the sparks and able to operate in high rate environment [6]. For the ATLAS NSW, the mesh has been grounded and positive HV was applied to the resistive strips

The Micromegas chambers

The Micromegas detector

Micromegas in a Magnetic Field

Test Beam

Conclusions