A high-precision polarimeter

Abstract

We have built a polarimeter in order to measure the electron beam polarization in hall C at JLAB. Using a superconducting solenoid to drive the pure-iron target foil into saturation, and a symmetrical setup to detect the Moller electrons in coincidence, we achieve an accuracy of <1%. This sets a new standard for Moller polarimeters.Comment: 17 pages, 9 figures, submitted to N.I.

Møller scattering polarimetry for high energy e+e− linear colliders

“…This precision, in fact, was obtained in the experiment which operated with an electron beam of few µA having the energies of 1-6 GeV at JLAB (see Ref. [7]). …”

“…In the experiments which operated during the last decade the targets used for the Møller polarimeters have been Fe alloy or pure Fe foils [5,7,8]. In these kind of materials the K-and L-shell electrons are unpolarised (with mean momentum of 90 keV and 30 keV) and the polarised ones reside in the M-and N-shells (with 10 keV and 2 keV average momenta).…”

“…At SLC the effect was found to be large due to the low emittance of the beam and the fine resolution of the detector. The solution to this problem, already adopted by E143 at SLC and JLAB [6,7] experiments, is given by adopting the coincidence measurement method using a double-arm polarimeter. These polarimeters have larger acceptance and poorer resolution so that the Levchuk effect was shown to be very small.…”

“…A novel approach has been recently developed and put to use [7,17]. This new target is made out of a thin pure iron foils polarised outof-plane in saturation with a 4 Tesla magnetic field parallel to the electron beam.…”

“…From the values given in Table 4 it is obvious that the local temperature will be above the melting point 8 if all the bunches within one pulse will hit the same 7 If the target is polarised in plane it has to be oriented at an angle ψ relative to the beam with the result that the longitudinal polarisation of the target electrons is reduced to P T L = P T ·cos ψ and its effective thickness is increased to d eff = d/ sin ψ. 8 The Iron melting point is T = 1808 K.…”