Self-polarization for energy calibration at FCC-ee Z and WW energies · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Self-polarization for energy calibration at FCC-ee Z and WW energies
Plain
Measuring a collider's beam energy to a part per million uses spins that line up by themselves through synchrotron radiation; at higher energies this alignment is weak and easily destroyed.
Precise · changed · core
Revision 1: Resonant depolarization gives the beam energy to below 1e-6 relative precision if a transverse polarization of about 5-10 percent builds up by the Sokolov-Ternov effect. For a $\sim 9e6\, \mathrm{cm}$ circumference ring at $E = 45.6\, \mathrm{GeV}$ and $E \sim 80\, \mathrm{GeV}$, determine the equilibrium polarization and build-up time with polarization wigglers, including depolarization from energy spread $\sigma_E/E \sim 4e-4 \text{ to } 1e-3$ and lattice errors, and whether calibration at the WW threshold is feasible.
Revision 2: Resonant depolarization gives the beam energy to below $10^{-6}$ relative precision if a transverse polarization of about 5-10 percent builds up by the Sokolov-Ternov effect. For a $\sim 9 \times 10^{6}\, \mathrm{cm}$ circumference ring at $E = 45.6\, \mathrm{GeV}$ and $E \sim 80\, \mathrm{GeV}$, determine the equilibrium polarization and build-up time with polarization wigglers, including depolarization from energy spread $\sigma_E/E \sim 4 \times 10^{-4} \text{ to } 10^{-3}$ and lattice errors, and whether calibration at the WW threshold is feasible.
Settled by
Spin-diffusion calculations with realistic errors and wiggler settings, validated against LEP polarization data.
Kind
well-posed
Answer type
value
References
(empty)
Literature status
open
Status note
(empty)
Posed since
(empty)

Decisions