Construction and operation of large scale Micromegas detectors for the ATLAS Muon upgrade

After the forthcoming upgrade of the LHC accelerator at CERN, its luminosity will increase up to 7.5 × 1034 cm−2s−1. That will raise the readout rates and the background data to unmanageable levels for the existing ATLAS muon spectrometer. The ATLAS collaboration has proposed to replace the present small wheel muon detector with the New Small Wheel (NSW) to surpass those limitations. The new wheels consist of Micromegas (MM) and small-strip Thin Gap Chambers (sTGC). The first technology aims for precision tracking, and the last one for trigger purposes. Each wheel will be equipped with eight small and eight large sectors, while each sector will have a double MM wedge surrounded by sTGC wedges. The MM detectors for the NSW will be the largest developed Micro Pattern Gaseous Detector (MPGD) as they will cover an area up to 1280 m2. During detectors’ manufacture have been used various custom materials (PCBs, mesh) and innovative construction techniques. This paper describes the MM drift panels production at Aristotle University of Thessaloniki laboratory. Then will be presented resolution results of the MM detectors with cosmic-ray tests at CERN facilities.

MuCap: Muon Capture on the Proton

The singlet muon capture rate \Lambda_SΛS on the proton \mu^-\ p \to \nu_\mu~nμ−p→νμn is determined in a high precision lifetime measurement. The main apparatus consists of a new hydrogen time projection chamber as muon detector, developed by PSI, surrounded by cylindrical wire chambers and a plastic scintillator hodoscope as electron detectors. The parameter \Lambda_SΛS is evaluated as the difference between the inverse \mu\,pμp lifetime and that of the free \mu^+μ+. The result \Lambda_S^\text{MuCap} = (715.6 \pm 5.4^\text{stat} \pm 5.1^\text{sys})\,\text{s}^{-1}ΛSMuCap=(715.6±5.4stat±5.1sys)s−1 is in excellent agreement with the prediction of chiral perturbation theory \Lambda_S^{\chi\text{PT}} = (715.4 \pm 6.9)\,\text{s}^{-1}ΛSχPT=(715.4±6.9)s−1. From \Lambda_S^\text{MuCap}ΛSMuCap a recent analysis derives for the induced pseudoscalar coupling g^\text{MuCap}_p = 8.23 \pm 0.83gpMuCap=8.23±0.83 whereas \bar{g}^{\chi\text{PT}}_p = 8.25 \pm 0.25g‾pχPT=8.25±0.25.

Muon reconstruction and identification efficiency in ATLAS using the full Run 2 pp collision data set at $$\sqrt{s}=13$$ TeV

This article documents the muon reconstruction and identification efficiency obtained by the ATLAS experiment for 139 $$\hbox {fb}^{-1}$$ fb - 1 of pp collision data at $$\sqrt{s}=13$$ s = 13 TeV collected between 2015 and 2018 during Run 2 of the LHC. The increased instantaneous luminosity delivered by the LHC over this period required a reoptimisation of the criteria for the identification of prompt muons. Improved and newly developed algorithms were deployed to preserve high muon identification efficiency with a low misidentification rate and good momentum resolution. The availability of large samples of $$Z\rightarrow \mu \mu $$ Z → μ μ and $$J/\psi \rightarrow \mu \mu $$ J / ψ → μ μ decays, and the minimisation of systematic uncertainties, allows the efficiencies of criteria for muon identification, primary vertex association, and isolation to be measured with an accuracy at the per-mille level in the bulk of the phase space, and up to the percent level in complex kinematic configurations. Excellent performance is achieved over a range of transverse momenta from 3 GeV to several hundred GeV, and across the full muon detector acceptance of $$|\eta |<2.7$$ | η | < 2.7 .