Beam-induced backgrounds in CLICdet

To ensure the optimal exploitation of the physics potential of a future electron–positron collider detector, a careful study of the beam-induced backgrounds is essential. In this note, the beam conditions and the beam-induced background processes at the CLIC energy stages of 380 GeV and 3 TeV are considered. To study the occupancies, the electron–positron beams are transported through the Beam Delivery System (BDS) using PLACET and brought to collisions with Guinea-Pig, which simulates the creation of the beam-induced backgrounds. Synrad+ is used to generate the synchrotron radiation photons and simulate their transport through the BDS geometry, taking into account the effects of photon reflections from the vacuum chamber walls. Full detector simulations are performed with the CLICdet model, in which the unwanted particles are simulated. It is found that the cell occupancies in the tracking detectors are below an acceptable limit of 3% per bunch train. High occupancies are found in the HCal endcap and MuonID endcap, for which mitigations are proposed through addition of shielding and modification of granularity. It is also observed that the reflection of synchrotron radiation leads to a large flux of energy in the detector acceptance. Taking considerations from transverse wakefields, beam dynamics and the impact on the detector into account, an optimised beam pipe for the BDS and Final Focus System is proposed.