Time evolution of ground motion-dependent depolarisation at linear colliders

TL;DR

This paper investigates how ground motion affects the depolarisation of polarized beams in future linear colliders, using spin tracking simulations to quantify the resulting uncertainties in polarization over time.

Contribution

It provides the first detailed simulation-based analysis of ground motion-induced depolarisation at the ILC and CLIC, including realistic misalignments and their impact.

Findings

Depolarisation exceeds 0.1% within a day at noisy sites.

Depolarisation at the IP surpasses 0.1% for both ILC and CLIC.

Simulations highlight the importance of ground motion effects on polarization stability.

Abstract

Future linear colliders plan to collide polarised beams and the planned physics reach requires knowledge of the state of polarisation as precisely as possible. The polarised beams can undergo depolarisation due to various mechanisms. In order to quantify the uncertainty due to depolarisation, spin tracking simulations in the International Linear Collider (ILC) Beam Delivery System (BDS) and at the Interaction Point (IP) have been performed. Spin tracking in the BDS was achieved using the BMAD subroutine library, and the CAIN program was used to do spin tracking through the beam-beam collision. Assuming initially aligned beamline elements in the BDS, a ground motion model was applied to obtain realistic random misalignments over various time scales. Depolarisation at the level of 0.1% occurs within a day of ground motion at a noisy site. Depolarisation at the IP also exceeds 0.1% for the nominal parameter sets for both the ILC and for the Compact Linear Collider (CLIC). Theoretical work is underway to include radiative corrections in the depolarisation processes and simulation of the depolarisation through the entire collider is envisaged.