Machine-induced Background Simulation Studies for LHC Run 1, Run 2 and HL-LHC

The study of machine-induced background to the experiments is vital for several reasons. Too much background can be an issue for operation and the difficult part is to judge when exactly “too much” is attained. It is a complex topic as experiments are directly or indirectly affected by conditions all around the LHC ring e.g. collimation settings and vacuum quality. A detailed study of background can also help understanding the machine better to identify potential issues and complemented by dedicated machine tests. Finally such a study is relevant for the experiments to analyse the characteristics of machine background to make sure not to count it into a new physics signal. This report summarises simulation results of three background sources, local beam-gas, beam-halo from the betatron collimation in IR7 and for the first time beam-halo from momentum collimation in IR3. Two of the most dominant sources, local beam-gas and betatron halo, have been systematically studied for LHC Run 1 and Run 2 cases, and several HL–LHC scenarios. We analyse the evolution of background of these scenarios and discuss rates expected for HL-LHC. Impacts on the tertiary collimators upstream of ATLAS and CMS are analysed, while particle distributions streaming into the experimental area were estimated for ATLAS only in detailed shower simulations in all of these scenarios.