Spin transport and polarimetry in the beam delivery system of the international linear collider

Abstract

Polarised electron and positron beams are key ingredients to the physics programme of future linear colliders. Due to the chiral nature of weak interactions in the Standard Model -and possibly beyond -the knowledge of the luminosity-weighted average beam polarisation at the e + e − interaction point is of similar importance as the knowledge of the luminosity and has to be controlled to permille-level precision in order to fully exploit the physics potential. The current concept to reach this challenging goal combines measurements from Laser-Compton polarimeters before and after the interaction point with measurements at the interaction point. A key element for this enterprise is the understanding of spin-transport effects between the polarimeters and the interaction point as well as collision effects. We show that without collisions, the polarimeters can be cross-calibrated to 0.1 %, and we discuss in detail the impact of collision effects and beam parameters on the polarisation value relevant for the interpretation of the e + e − collision data.

CP-violating top quark couplings at future linear $$e^+e^-$$ e + e - colliders

“…The detailed study of the ILC case in Ref. [72] envisages a determination to the 10 −3 level. The study of (single) W -boson production is expected to provide per-mille level precision at high energy.…”

Prospects for Electroweak Precision Measurements and Triple Gauge Couplings at a Staged ILC

“…Thereby, for each beam, the upstream polarimeter is located 1.65 km before the IP, while the downstream polarimeter is located 150 m after the IP. In order to determine the polarization at the IP, the result of the polarimeter measurement is extrapolated to the IP via spin tracking [5]. For the absolute scale calibration, the luminosity-weighed averaged polarization is additionally calculated from collision data providing the information directly at the IP.…”

Beam Polarization at the ILC: Physics Case and Realization

“…A dedicated software framework for such spin-tracking studies has been developed, showing that it is possible to cross-calibrate the polarimeters to 0.1%, and that both the upstream and the downstream measurements can be individually extrapolated to the e + e − IP if the spent beam properties are monitored on a level of 10%. 30 As absolute scale calibration for the polarization measurement, the long-term average of the polarization can be extracted from e + e − collision data by studying any abundant and well-known physics process that is sensitive to the polarization. Several approaches have been studied, e.g.…”