Studies of the gas volume current density in the ATLAS Resistive Plate Chamber detector during the 2018 data-taking at the LHC

D Krasnopevtsev

doi:10.1088/1748-0221/15/10/c10024

D Krasnopevtsev

Open Access

https://doi.org/10.1088/1748-0221/15/10/c10024

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Abstract

The ATLAS Resistive Plate Chamber (RPC) detector is a tracking detector, used to primarily trigger muons in the ATLAS barrel region (which corresponds to a pseudorapidity range of |η|<1.05) at the 40 MHz collision rate, and to provide η and ϕ coordinates. The RPC system consists of about 3700 gas volumes covering a sensitive surface of about 4000 m2. It is arranged in three concentric doublet layers at radius 7 m, 8 m and 10 m, and operating in an approximately 0.5–1 T toroidal magnetic field. RPCs provide up to 6 space points along the muon track with a space-time resolution of about 1 cm2 × 1 ns. This document studies systematically the gas volume current as a function of the electric field applied across the gas volume and of temperature both with and without the Large Hadron Collider (LHC) beam induced background and up to an instantaneous luminosity Linst = 2×1034 cm−2 s−1 (twice larger than the design LHC luminosity). These measurements have been used to study the RPC working conditions and to extrapolate the detector response to the High-Luminosity LHC regime with Linst = 7.5×1034 cm−2 s−1.

Highlights

Currents in gas volumes measured at the working Resistive Plate Chamber (RPC) voltage but without proton-proton collisions are subtracted to show the net effect of the luminosity
The RPCs disconnected from the high voltage (HV) or those exhibiting low efficiencies are excluded from the analysis
Mean of the gas volume current density distribution without beam induced background increases by 15% from V=9.2 kV to V=9.6 kV, where a 5% increase comes from the ohmic contribution, while the other 10% are from the avalanche growth

Summary

Results with LHC beam induced background

The current is obtained individually for each gas volume, by measuring the voltage across a 100 kΩ resister in serial connection with the gas volume and ground. Densities over gas volumes for various RPC chambers in the η station 1 as a function of Linst, shown separately for the middle (BMx) and outer (BOx) layers, and large (L) and small (S) chamber types. This plot shows that the gas volume current density decreases with increasing distance from the proton-proton collision point. This effect is explained by the particle flux reduction at larger radii.

12 ATLAS Muon Operations

Results without LHC beam induced background

Conclusion