Abstract
Linear collider designs foresee some bends of about 5-10 mrad. The spin precession angle of one TeV electrons on 10 mrad bend is 23.2 rad and it changes proportional to the energy. Measurement of the spin direction using Compton scattering of laser light on electrons before and after the bend allows determining the beam energy with an accuracy about of 10^{-5}. In this paper the principle of the method, the procedure of the measurement and possible errors are discussed. Some remarks about importance of plasma focusing effects in the method of beam energy measurement using Moller scattering are given.
Highlights
Linear colliders (LC) are machines for the precision measurement of particle properties, good knowledge of the beam energy is of great importance
The required knowledge of the beam energy for the t-quark mass measurement is of the order of, for the WW-boson pair threshold measurement it is 3, and ultimate energy resolution, down to, is needed for a new improved Z-mass measurement
In this paper a new method of the beam energy measurement is considered based on the precession of the electron spin in big-bend regions at linear colliders
Summary
Linear colliders (LC) are machines for the precision measurement of particle properties, good knowledge of the beam energy is of great importance. In this paper a new method of the beam energy measurement is considered based on the precession of the electron spin in big-bend regions at linear colliders. The bending angle b is measured using geodesics methods and BPM, s can be measured using the Compton polarimeter which is sensitive to the longitudinal electron polarization, i.e., to the projection of the spin vector to the direction of motion. In the considered method the electron polarization vector should be oriented in the bending plane with high accuracy. Two Compton polarimeters measure the angle of the polarization vectors (before and after the bend). This allows one to find the beam energy. The expected absolute accuracy of polarimeters is O1% , but the relative variation of the polarization can be measured much more precisely
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