Beam-beam interaction-induced bias to precision luminosity measurement

The mutual electromagnetic interaction between counter-rotating bunches crossing at the interaction points (IPs) of a particle collider has been studied since the dawn of the storage-ring era. It can result in a significant bias to absolute-luminosity calibrations determined by the van der Meer (vdM) method. Numerical models developed to study such beam—beam-induced biases at a single IP of the Large Hadron Collider (LHC) have been recently extended to better account for actual operating conditions, such as head-on collisions at non-scanning IPs during vdM scans, or scans performed during physics data-taking using higher-brightness beams than used during vdM-calibration sessions. As part of a long-term effort aimed at quantifying the beam-beam bias to luminosity-related observables in hadron colliders, in this paper we compare results from a dedicated beam-beam experiment performed at the LHC in 2022 to the predictions of the numerical model. We also report some preliminary observations about the impact of the beam-beam interaction on the instantaneous luminosity during physics operation, and investigate beam-beam contributions to the apparent non-linearity and overall stability of experimental luminometers during physics data taking.