Time resolution of the ALICE Time-Of-Flight detector with the first Run 3 pp collisions at ${\bf \sqrt{\textit{s}} = 13.6}$ TeV

TL;DR

This paper reports the performance of the upgraded ALICE Time-Of-Flight detector (TOF) in Run 3 pp collisions at $\sqrt{s}=13.6$ TeV, focusing on achieving high-precision timing under continuous readout. It details the Run 3 TOF upgrades (electronics, continuous readout with an asynchronous trigger near $f_T\approx 33\ { m kHz}$, and offline calibration) and presents two independent methods to extract TOF timing resolution: a Delta-Delta $t_{TOF}$ approach and a FT0-event-time-based method, both incorporating an exponentially modified Gaussian model to describe non-Gaussian tails. The measurements yield TOF timing resolutions better than $80$ ps, with $\sigma_{TOF}=74.7\pm2.3$ ps from Delta-Delta and $72.8\pm0.5$ ps (and $77.9\pm0.8$ ps averaged over $|\eta|<0.9$) from the FT0 method in the momentum region $1.4<p<1.5$ GeV/$c$, confirming the Run 3 PID performance. These results demonstrate ALICE's continued capability to perform precise particle identification at high data-taking rates, enabling physics analyses in both Pb–Pb and pp collisions during Run 3 and beyond, with further improvements anticipated from ongoing commissioning and calibration efforts.

Abstract

Particle identification (PID) is a fundamental aspect of the ALICE detector system, central to its heavy-ion and proton-proton physics programs. Among the different PID strategies, ALICE uses the Time-Of-Flight (TOF) detector to identify particles at intermediate momenta ($0.5 < p_{\rm T} < 4$ GeV/$c$). The ALICE TOF detector performed successfully during the first ten years of LHC operations. During the Long Shutdown 2, many ALICE sub-detectors, including TOF, were upgraded to fully leverage the targeted 50 kHz interaction rate of Pb-Pb collisions, which required the implementation of a continuous readout scheme. The TOF detector electronics were upgraded and refurbished, while processing algorithms for data quality control, reconstruction, calibration, and analysis were rewritten. This paper presents the upgraded TOF detector operation and calibration procedures and its performance in terms of timing resolution, a key factor for particle separation in ALICE analyses. Using 2022 pp collision data at $\sqrt{s} = 13.6$ TeV from Run 3, the time resolution of the detector was estimated with two independent methods, both yielding consistent results, better than 80 ps. Despite the excellent performance already achieved, further improvements are expected after additional detector commissioning and refined calibration procedures, thus enhancing the ALICE PID capabilities for Run 3 and beyond.