ATLAS Forward Proton Time-of-Flight Detector: LHC Run2 performance and experiences

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 PhotoMulTipliers (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 cross-talk 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.

Overview of ATLAS forward proton detectors: status, performance, and new physics results

“…However, the train efficiency was < 7 % in both FAR stations for the majority of data-taking due to fast degradation of the PMTs in harsh operating conditions [16], rendering ToF information unusable in Run 2 physics analyses. New PMTs were installed and an out-of-vacuum solution was developed in an attempt to address ToF inefficiencies [17]. Performance…”

4D-tracking in the 10-ps range: A technological perspective

“…In high-density integrated electronics, the circuit design parameter space is limited by tough system constraints, as listed in Table 1 [11,12]. Similar demanding requirements are presently at different stages of discussion and definition in other LHC developments (CMS-PPS [13], ATLAS AFP [14], and CMS run-5 [15]). The same trend, with even hardened specifications, will continue in future hadron collider experiments in the longer term [16].…”

ATLAS Forward Proton Detectors – Special 2017 Low Pile-up Runs

“…The typical acceptance in and is illustrated in reconstruct the primary vertex position. The ToF detectors are based on Cherenkov radiation in quartz crystals, which leads to a timing resolution of around 25 ps, or equivalently a longitudinal vertex position resolution of about 5 mm [24,25].…”