4D Tracking: design, technologies and impact on physics

Starting from August 2026, CERN's Large Hadron Collider (LHC) will be upgraded to become the HL-LHC, a particle accelerator capable of more than doubling its current luminosity. The HL-LHC will start the high-intensity phase of high-energy physics, enabling the collection of a huge amount of statistics, which will enable precision physics and the potential discovery of new physics. Many challenges arise due to the increasing luminosity, mainly due to the increased pile-up of primary collisions and to the high radiation damage the detectors will have to sustain. The solution adopted to mitigate the pile-up is 4D-tracking, that is, measuring both the position and the time of arrival (ToA) of the particles through the detector layers, in order to perform a precise temporal segmentation of each bunch crossing and correctly associate each track with the corresponding primary collisions. INFN, in Italy, is committed to providing new sensor and ASIC technologies capable not only of performing 4D-tracking, but also of maintaining high performance such as a spatial resolution of the order of 10 μm (per hit) and a temporal resolution of the order of 50 ps (per hit), up to a fluence of ϕ = 1×1017 1MeV neq/cm2, and beyond. INFN TimeSPOT and IGNITE projects achieved relevant results, confirming 3D-trench sensors and 28nm CMOS ASIC as good candidates to fit next generation tracker detectors. Possible detectors where this technology could be installed are the LHCb U2 VELO and the beam and muon spectrometers suggested by the NuScope proto-collaboration. Those detectors require similar specifications, i.e. less than 50 ps (per hit) in temporal resolution and radiation hardness up to ϕ = 5×1016 1MeV neq/cm2. Further details on the recent results of the INFN TimeSPOT and IGNITE collaboration, as well as an overview of LHCb VELO UII and NuScope, will be presented in the paper.