The LHCb RICH detectors will introduce timing information O ( 100 ps ) for each detected photon during LHC Run 4. Using the RICH time information, the primary vertex time (PV t 0 ) can be estimated for the first time in LHCb, which is a key input parameter for exploiting fast-timing techniques in the experiment. In the RICH reconstruction algorithm, a photon object (PO) is created for each combination of a detector hit and particle track that passes a set of initial spatial constraints. Using the LHCb tracking systems, tracks can be associated with different PVs. On average, hundreds of photons are detected per PV, generating a multitude of POs which allows the PV t 0 to be determined with high precision. The key challenge is to identify, among all generated photon objects and in the presence of pile-up and background hits, those that are correctly associated with the PV. Simulation studies show that approximately 20% of the initial POs have a correct association to the PV. Therefore, new techniques in the reconstruction algorithm have been explored to identify a subset of POs with the highest probability to have a correct PV association. New results, generated using the LHCb experiment simulation framework, have been presented. The proposed techniques provide a PV t 0 resolution of 85 ± 3 ps (FWHM) for 94% of the PVs, starting from an initial PV time spread of 330 ps (FWHM) at the simulated bunch crossings. The use of additional information from a first iteration of the RICH reconstruction likelihood-maximisation algorithm has also been explored. The resulting PV t 0 resolutions obtained with the two approaches are compared in this work.
Keizer et al. (Wed,) studied this question.