A brief history of Timing

Abstract

This review traces the evolution of precision timing in particle physics experiments, from the first large-scale applications of scintillator and photomultiplier tube (PMT) systems in the 1990s to the picosecond-precision detectors of future colliders. Four technological generations are identified: (i) the era of discrete electronics (NIM, CAMAC, VME) and PMTs, which established the three canonical uses of timing -- particle identification via time-of-flight, background and pile-up rejection, and directionality triggering; (ii) the silicon revolution enabled by Silicon Photomultipliers (SiPMs), Low-Gain Avalanche Diodes (LGADs), and Application-Specific Integrated Circuits (ASICs); (iii) the current transition to ubiquitous four-dimensional (4D) tracking, in which time is a coordinate measured at every point along a particle trajectory. Under-construction systems at the HL-LHC (CMS MTD, ATLAS HGTD, CMS HGCAL) demonstrate the maturity of 30--50\,ps silicon timing at the million-channel scale. The EIC, LHCb VELO Upgrade~II, and ALICE~3 push this technology into new regimes of radiation hardness, material budget, and granularity. (iv) The Far-future facilities such as the Muon Collider and FCC require a further leap to $\sim$10\,ps, setting the agenda for the next decade of detector R\&D.