Asymmetries in Silicon Microstrip Response Function and Lorentz Angle

Abstract: An experimental set up, dedicated to isolate an error present in the $\eta$-algorithm, gave an unexpected result. The average of a center of gravity algorithm at orthogonal particle incidence turns out to be non zero. This non zero average signals an asymmetry in the response function of the strips, and introduces a further parameter in the corrections: the shift of the strip response center of gravity respect its geometrical position. A strategy to extract this parameter from a standard data set is discussed. Some simulations with various asymmetric response functions are explored for this test. The method is able to detect easily the asymmetry parameters introduced in the simulations. Its robustness is tested against angular rotations, and we see an almost linear variation with the angle. This simple property is used to simulate a determination of a Lorentz angle with and without the asymmetry of the response function.