The Micromegas chambers for the ATLAS New Small Wheel upgrade

The ATLAS collaboration at LHC has chosen the resistive Micromegas technology, along with the small-strip Thin Gap Chambers (sTGC), for the high luminosity upgrade of the first muon station in the high-rapidity region, the so called New Small Wheel (NSW) project. After the R&D, design and prototyping phase, the series production Micromegas quadruplets are being constructed at the involved construction sites in France, Germany, Italy, Russia and Greece. At CERN, the final validation and the integration of the modules in Sectors are in progress. The installation of the first NSW, the NSW-A is foreseen for the LHC long shutdown in 2020. The construction of the four types of large size quadruplets, all having trapezoidal shapes with surface areas between 2 and 3 m2 , will be reviewed. The achievement of the requirements for these detectors revealed to be even more challenging than expected, when scaling from the small prototypes to the large dimensions. The encountered problems will be described, to a large extent common to other micro-pattern gaseous detectors, along with the adopted solutions. Final quality assessment and validation results on the achieved mechanical precision, on the High-Voltage stability during operation with and without irradiation will be reviewed together with the most relevant steps and results of the modules integration into sectors

Gas and irradiation studies for the Micromegas detectors of the ATLAS New Small Wheel

The ATLAS collaboration has chosen the resistive Micromegas technology for the high luminosity upgrade of the first forward muon station, the New Small Wheel (NSW). One of the main features being studied is the HV stability of the detectors, mainly related to the resistivity pattern of the strips. Among the several approaches to enhance the stability of the detectors, the use of different gas mixtures are being studied. A ternary argon-CO2-isobutane mixture has shown to be effective in dumping discharges and dark currents. The presence of isobutane in the mixture required a set of ageing studies, ongoing at the GIF++ radiation facility at CERN. A summary of the results obtained up to now will be shown, as well as the upcoming test plans, mainly focused on O(1 year equivalent) time scale ageing effects

Gas and irradiation studies for the Micromegas detectors of the ATLAS New Small Wheel

The ATLAS collaboration has chosen the resistive Micromegas technology for the high luminosity upgrade of the first forward muon station, the New Small Wheel (NSW). One of the main features being studied is the HV stability of the detectors, mainly related to the resistivity pattern of the strips. Among the several approaches to enhance the stability of the detectors, the use of different gas mixtures are being studied. A ternary argon-CO2-isobutane mixture has shown to be effective in dumping discharges and dark currents. The presence of isobutane in the mixture required a set of ageing studies, ongoing at the GIF++ radiation facility at CERN. A summary of the results obtained up to now will be shown, as well as the upcoming test plans, mainly focused on O(1 year equivalent) time scale ageing effects

Flow and transverse momentum fluctuations in Pb+Pb and Xe+Xe collisions with ATLAS: assessing the initial condition of the QGP

Constraining the initial condition of the QGP using experimental observables is one of the most important challenges in our field. Recent studies show that the Pearson Correlation Coefficient (PCC) between vn and event-wise mean transverse momentum [pT], ρn(vn, [pT]), and [pT] fluctuations can probe several ingredients of the initial state. This talk presents precision measurements of vn − [pT] correlation for n=2,3 and 4 and high order [pT] fluctuations in 129Xe+129Xe and 208Pb+208Pb collisions, and they are found to be small in the mid-central and central collisions in these systems. The ρn and variance and skewness of [pT] fluctuations show non-monotonic dependence on centrality, pT and η. It was also found that the result depends on the centrality estimator used in the analysis, indicating a strong influence of volume fluctuations. In central collisions, where models generally show good agreement, the v2–[pT] correlations are sensitive to the triaxiality of the quadrupole deformation. A comparison of the model with the Pb+Pb and Xe+Xe data confirms that the 129Xe nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the 129Xe nucleus from high-energy heavy-ion collisions

The Micromegas chambers for the ATLAS New Small Wheel upgrade

The ATLAS collaboration at LHC has chosenthe resistive Micromegas technology, along withthe small-strip Thin Gap Chambers (sTGC), for the high luminosity upgrade of the first muonstation in the high-rapidity region, the so called New Small Wheel (NSW) project. After theR&D, design and prototyping phase, the series production Micromegas quadruplets are beingconstructed at the involved construction sites in France, Germany, Italy, Russia and Greece.AtCERN, the final validation and the integration of the modules in Sectors are in progress.Theseare big steps forward for the installation of the first NSW, the NSW-A foreseen for the LHClong shutdown in 2020. The construction of the four types of large size quadruplets, all havingtrapezoidal shapes with surface areas between 2 and 3 m2, will be reviewed. The achievement ofthe requirements for these detectors revealed to be even more challenging than expected, whenscaling from the small prototypes to the large dimensions. We will describe the encounteredproblems, to a large extent common to other micro-pattern gaseous detectors, and the adoptedsolutions. Final quality assessment and validation results on the achieved mechanical precision,on the High-Voltage stability during operation with and without irradiation will be presentedtogether with the most relevant steps and results of the modules integration into sectors