Login

FCC-FS EPOL group and FCCIS WP2.5 meeting 27

→ Europe/Zurich
Description

The FCC technical and financial feasibility study comprises a work package (EPOL) on precision determination of the centre of mass energy at FCCee. using resonant depolarisation of the beams, in conjunction with precise measurement of the energy spread and other parameters using physics events in the detectors, and other beam diagnostics in particular to control the collision parameters. Specific equipment involves polarimeters for both beams, polarisation wigglers, and depolarising RF kickers. The possible mono-chromatization of the beams in view of a measurement of the e+ e- —> H (125) process will also be studied and special requirements investigated. 

Short group meetings are foreseen at 16:30 on Thursday typically every three weeks. 

FCC-FS EPOL group meeting
Zoom Meeting ID
63437787216
Host
Alain Blondel
Alternative host
Jacqueline Keintzel
Useful links
Join via phone
Zoom URL
Hide

G. Wilkinson and J. Keintzel remind that the FCCIS final report should be finalized until about end of 2024. This includes monochromatization and lessons learnt from di-fermion events. 

Y. Wu presents the impact of misalignments on the polarization. In general, spread of the achievable polarization is increased with increasing misalignment errors. Sextupoles are off when long range misalingments are included.  J. Wenninger suggests to not correct the orbit to 0, but to the smooth alignment curve.  The spin tune is shifted up to +/- 0.003 for 100 um misalignment. A. Blondel suggests to think of translating this shift to a measurable quantity. E. Gianfelice comments that at ttbar the spin axis must be basically 0 to achieve polarization. 

Furthermore, she presents updates on harmonic spin matching, now performed in MAD-X (BMAD in the past). Using lattices with errors, resulting in low polarization, combined with HSM, have shown a significant increase in the achievable polarization. It is noted that HSM and orbit correction could counter-act one another. It is aimed that together with L. van Riesen-Haupt this cross talk will be evaluated and possibly improved. 

Additionally, machine learning could help for the optimization process, which is being investigated.

D. Barber explains about spin tune shifts due to closed orbit distortions. Starting from the 3x3 orthogonal matrix on the design orbit, its eigenvectors are observed. The first eigenvector (=1) represents the effective rotation of the one turn map. Using perturbation theory, the first order spin tune shift is given in Eq. 3.9 in the provided paper. The first order spin tune shift is 0 for purely vertical distortions. However, vertical CO distortions and solenoids can cause a second order spin tune shift. 

A. Blondel asks that if misalingments are introduced not only the spin tune is shifted but also the beam energy. D. Barber confirms that statement and suggests to evaluate the spin tune shift numerically. 

Z. Duan presents on updates on the imperfection spin resoanance in the high energy booster for 2 lattice options (FODO and HFD). DEPOL code is used to calculate the resonance spectrum. At Z about 90% polarization could be transportet, and 60% at W, and 15% for H and 0 for ttbar. Simulations do not show dependence on the rms vertical orbit. D. Barber comments that DEPOL can only be used with low coupling.

There are minutes attached to this event. Show them.