Timepix3 (TPX3) Luminosity Determination of 13 TeV Proton-Proton Collisions at the ATLAS Experiment

Medipix and Timepix devices, installed in the ATLAS cavern at LHC, have proved to provide valuable complementary luminosity information. Results are presented from a new measurement network, based on the latest Timepix3 chip. In contrast to previously employed frame-based data acquisition, the TPX3 detector remains active continuously, sending information on pixel hits as they occur. Hit- and cluster-counting methods were used for the luminosity determination of the LHC proton-proton collisions. By counting the number of clusters, instead of just pixel hits, the precision of the luminosity determination could be improved. The LHC luminosity versus time is determined using these two methods, and fitted to a simple model incorporating luminosity reduction from single bunch and beam-beam interactions. The internal precision and long-term time stability of the TPX3 luminosity measurement were determined. The TPX3, owing to its precise time resolution, is able to resolve the time structure of the luminosity due to the collisions of individual LHC proton bunches.