A toy Monte Carlo simulation for the transverse polarization of high-energy electron beams

Abstract

Transversely-polarized beams are heuristic to the mechanism of CP violation and explore new physics. Besides, the transverse-polarization monitoring is a key point for the beam energy calibration by the resonant depolarization technique. In the article, the transverse polarization measurement of a high-energy electron beam is performed by Monte Carlo simulation on the circular electron-positron collider. The principle based on the Compton back-scattering combining a deflection magnetic field is discussed in detail. The physical presentation of the analyzing power is used to fit the asymmetric distribution of scattered electrons, which is proportional to the transverse polarization. Furthermore, we develop an efficient algorithm that obtain this analyzing power function and use different strategies to measure the transverse polarization for cross-check. Our measurement method is theoretically suitable with a statistical error 1% within few tens of seconds in Z pole on the circular electron-positron collider. The total systematic uncertainties are controlled to be about 0.6% related to the magnetic field, the drift distance, the laser polarization, the beam energy spread and the related uncertainties of a position sensitive detector.

A quantitative study of systematic uncertainties due to QED corrections in accurate Compton polarimetry experiments

“…[20]. It is similar in concept as those proposed for CEPC [18] and previously at ILC [19]. Placed after a dipolar magnetic field, this detector mainly acts as a spectrometer in the horizontal dimension.…”

“…the phase space, and accordingly the bias on the extraction of polarization gets large and depends on detector configuration, see Figure 2, different results when performing fits of the spectrum as a whole are expected. This is what has been made or proposed for some projects [18,20,36]. One thus introduces a global 𝜒 2 obtained by considering the measured distribution as a whole, (1) 𝑖,𝑢 + 𝑃𝜎 (1) 𝑖, 𝑝 − 𝛿𝑃𝜎 (0) 𝑖, 𝑝 ] 2 𝜎 𝑖,𝑢 + 𝑃𝜎 𝑖, 𝑝 ,…”

“…The statistical precision will be of 1% in four seconds for each bunch, or 0.1% in one second averaged over all bunches. More recently, a preliminary concept for a transverse Compton polarimeter at the CEPC has been proposed [18], improving on a proposal that was proposed several years ago for ILC [19]. In the past years, a totally new proposal of three-dimensional (3D) polarimeter [20] has been introduced in the context of precise electron and positron beam polarimetry for the accurate calibration of beam energies by resonant depolarization [9] at FCC-ee.…”

Conceptual study of a Compton polarimeter for the upgrade of the SuperKEKB collider with a polarized electron beam

“…This can be done either by directly measuring photons' energies or by measuring position of scattered electrons after a bending magnet. Spatial distributions of electrons can thus be measured with pixel detectors to quantify the longitudinal and also the transverse component of the electron beam polarization [21,23]. It is foreseen to implement High Voltage-Monolithic Active Pixel Sensors (HVMAPS) for the detection of electrons [6].…”

“…It will also allow to identify bunches or runs with degraded polarization performance, and thus be used as an important data quality tool. This polarimeter must thus meet new constraints with respect to those implemented in the past [9][10][11][12][13][14][15][16][17][18][19] or in other projects [20][21][22][23]. In particular, its insertion in the ring must consist in a minor modification, and in particular we investigate the possibility to insert the laser system in the SuperKEKB ring itself, without the need for additional excavation.…”