The circular electron–positron collider beam energy measurement with Compton scattering and beam tracking method

Abstract

The beam energy of the circular electron–positron collider should be measured precisely to the order of 1 MeV, in order to decrease the uncertainty of the Higgs/W/Z bosons’ mass measurement. For this purpose, a lepton bunch is extracted from the collider and collides with an Yttrium–Aluminum–Garnet laser pulse. After the inverse Compton scattering, the main beam and the scattered beam pass through an analytical magnetic field and are deflected to different angles. At the end of the drift beam pipes, the deflecting distances are detected with the spatial resolution of several microns. The systematic uncertainties caused by the detector arrangement, the magnetic field, the angle between the detector plane and the incident beam, and the synchrotron radiation are discussed in detail. The simulations of the statistical errors are given with a toy Monte Carlo sample. With some proper corrections, the beam energy uncertainty of the Higgs mode is around 2 MeV. Our method is applicable to different operating modes of the collider.

A Low Noise Readout System for Diamond Microstrip Detectors

“…Diamond detectors are widely adopted in physics experiments [1][2][3][4] owing to its good radiation hardness, fast pulse response and short waveform edges, etc. In the pre-research of Circular Electron Positron Collider (CEPC) beam energy calibration, a measurement method based on Compton Backscatter is proposed, in which a diamond microstrip detector with high position resolution is employed to measure the angle information of the scattered gammas [5,6]. However, due to the larger band gap and lower atomic number of diamond, the amount of generated charges is much smaller compared with other traditional semiconductor detectors.…”

A new method for high energy beam energy measurement with microwave-beam Compton backscattering

“…Considering the head-to-head collision between the laser and the electron beam, the beam energy is measured by measuring the positions of scattered electrons, scattered photons, and un-scattered beams downstream of the magnetic system. In the Higgs mode of CEPC, the uncertainty of the beam energy measurement is 2MeV [5]. The precision can meet the physical requirements, but this method has high requirements for the system design and detectors in the future.…”

“…To generate the scattered photon energy within 10MeV, the collision angle between the laser and the beam is required to be about 0.04rad. If the accuracy of beam energy measurement is required to be 1MeV, the uncertainty of the angle is 0.5µrad [5]. A small collision angle will reduce the interaction luminosity of Compton backscattering and the number of scattered photons.…”