基于微波-电子康普顿背散射的环形正负电子对撞机束流能量测量方案

Circular electron-positron collider beam energy measurement scheme based on microwave-electronic Compton backscattering

环形正负电子对撞机(CEPC)束流能量的精确标定是希格斯粒子质量宽度、W/Z玻色子质量的精确测量,从而精确检验标准模型的基本实验依据.基于此,束流能量的误差控制要求在10-5水平.康普顿背散射方法是适用于百GeV高能电子对撞机束流能量高精度标定的测量方法.本文拟采用微波电子康普顿背散射后对散射光子能量的精确测量,来反推CEPC束流能量,理论预计精度可达到3 MeV左右.首先根据设计需求选定圆波导传输TM_(01)模微波,并求解该条件下的电磁场分布情况及坡印廷矢量.根据波导内光子分布传输情况提出设计思路简化计算的复杂程度,结合高纯锗探测器灵敏度、同步辐射本底等限制条件联立方程求解符合设计要求的参数.使用最优的一组波导内径、微波波长、电子入射角数据求得微波功率为100 W时的微分散射截面对能量的导数及对撞亮度,进一步求得15 MeV能量的散射光子数密度,根据该能量下同步辐射光子数密度的大小分析了信噪比.理论上论证了该方案的可行性并讨论了该方案有待进一步研究的技术难点与问题.

The accurate calibration of the beam energy of the circular electron-positron collider(CEPC)is performed to accurately measure the mass width of Higgs particle and the mass of W/Z boson,thus providing the basic experimental basis for the accurate test of the standard model.Based on this,the error control of beam energy is required to be at a level of 10-5.Compton backscattering method is suitable for high precision calibration of beam energy in the Hundred GeV high energy electron collider.In this work,the CEPC beam energy is predicted to reach a theoretical accuracy of about 3 MeV by using the accurate measurement of the scattered photon energy after microwave electron Compton backscattering.Firstly,TM_(01) mode microwave transmission in circular waveguide is selected according to the design requirements,and the electromagnetic field distribution and Poynting vector under this condition are solved.According to the photon distribution and transmission in the waveguide,the design idea is proposed to simplify the complexity of calculation,and the parameters conforming to the design requirements are solved by combining the simultaneous equations of the high purity germanium detector sensitivity and the background of synchrotron radiation.Using the optimal set of waveguide inner diameter,microwave wavelength and electron incident angle data,the derivative of the differential scattering cross section with respect to energy and the collision brightness are obtained when the microwave power is 100 W.The scattered photon density of 15 MeV energy is further obtained,and the signal-to-noise ratio is analyzed according to the photon density of synchrotron radiation under this energy.The feasibility of the scheme is demonstrated theoretically and the technical difficulties and problems to be further studied are discussed.