Speaker
Description
The Roman Pot detector geometry of the CMS Precision Proton Spectrometer, PPS, was designed to cover the leading proton hit distribution for horizontal beam crossing in the CMS interaction point, IP5. This default beam crossing scheme was used throughout Runs 1 - 3 until 2024. In 2025, however, the beam crossing plane in IP5 was changed to vertical, which led to a vertically shifted and wider proton hit distribution, only very insufficiently covered by the detectors, in particular, the diamond timing detectors having a vertical extent of only 4 mm.
To mitigate the almost total acceptance loss, an extensive hardware modification and beamline intervention campaign has been carried out during the winter Technical Stop 2024/2025, rotating all previously horizontal Roman Pots by 27 degrees around the beam axis. This optimal rotation angle was calculated on the basis of the beam optics to maximise the acceptance. Operationally, the insertion of movable devices at a skew angle represented an unprecedented challenge, not foreseen in the collimation hierarchy offering protective shadows in the horizontal and vertical directions.
This presentation shows the adapted Roman Pot insertion scheme and beam-based alignment strategy, optimised with analytical calculations. The proton acceptance in terms of the kinematic variables of the scattering processes is derived for the new Roman Pot insertion positions.