Upgrade of the ATLAS liquid argon calorimeters for the high-luminosity LHC

Abstract

The increased particle flux at the high luminosity phase of the Large Hadron Collider (HL-LHC), with instantaneous luminosities of up to 7.5 times the original design value, will have an impact on many sub-systems of the ATLAS detector. This contribution highlights the particular impacts on the ATLAS liquid argon calorimeter system, together with an overview of the various upgrade plans leading up to the HL-LHC. The higher luminosities are of particular importance for the forward calorimeters (FCal), where the expected increase in the ionization load poses a number of problems that can degrade the FCal performance such as beam heating and space-charge effects in the liquid argon gaps and high-voltage drop due to increased current drawn over the current-limiting resistors. A proposed FCal replacement as a way to counter some of these problems is weighed against the risks associated with the replacement. To further mitigate the effects of increased pile-up, the installation of a high-granularity timing detector at the front face of each end-cap cryostat is also currently under consideration. Several different sensor technologies and layouts are being investigated.

Study of silicon sensors for precise timing measurement

“…LGADs are silicon sensors with the internal amplification mechanism, which have already been proved to realize the timing resolution down to 30 ps [5]. However, normal reach-through LGADs have an issue that the amplification factor heavily depends on the position of the hit, because the amplification region is not uniformly formed due to the surface structure.…”