Hit reconstruction in the CBM silicon tracking system

Abstract

The Silicon Tracking System (STS) is the main tracking appliance of the future Compressed Baryonic Matter (CBM) experiment @FAIR. The STS employs double-sided silicon micro-strip sensors with double metal layers. An accurate detector model is a prerequisite for proper design and correct reconstruction of physical signals. In this report, we describe the hit reconstruction in the STS. Our detector response model includes creation of the charge carriers, their drift, collection, the cross-talk, and the signal digitization. The unbiased cluster position finding algorithm simplifies the hit error estimation and yields a spatial resolution close to that obtained with the Centre-Of-Gravity algorithm. We have developed a method to estimate the hit position error, which includes the non-uniformity of an incident particle energy loss, the detector noise, the signal discretisation, and the error introduced by the cluster position finding algorithm. A reliable estimate of the hit position error is required to obtain a valid χ2 of the track, which is further used to discard ghost track candidates. This improves the signal-to-background ratio of the reconstructed physical signals. Both the hit pull (residual/error) and the track χ2 distributions verify the viability of the method: the pull width is about 1, its shape reproduce the shape of the residual distribution, mean of the χ2 distribution is unity.