Abstract
The performance of the ATLAS Forward Proton Time-of-Flight (ToF) Cherenkov detector is studied using the ATLAS data collected in 2017 during the LHC Run2. The detailed analysis of the results, including detector efficiency and time resolution of the ToF detector, is discussed.
The detector construction and its expected performance based on beam test results are briefly summarized first. Operational experiences are presented.
They include problems due to attempts to operate Micro-Channel Plate Photomultiplier Tubes (MCP-PMTS) in the vacuum, leading to changes in the detector construction. In addition, a new MCP-PMT design was needed, as a result of the observed gain drop for high rates and its non-recoverability.
Also, other hardware changes are presented - the effect of the replacement of glued crystal bars by monolithic ones, as well as the change of the MCP-PMT back-end electronics, based on simulation to reduce signal crosstalk resulting in further detector time resolution improvement. The second part of the document is devoted to the achieved time resolutions, 20 +/- 4 ps and 26 +/- 5 ps, of two installed ToF detectors.
Despite their very low efficiencies (below 10%) in major parts of the analyzed data, this represents a superb time resolution for detectors operating a few millimeters from the LHC beams. Based on the time resolution, this result characterizes the best ToF detector among those operated by the different LHC experiments in the forward regions during the LHC Run2.
Finally, the possibility of reconstructing the z-coordinate of the ATLAS interaction region using the ToF detectors is shown.