Abstract
In position-sensitive detectors with segmented readout (pixels or strips), charged particles activate in general several adjacent read-out channels. The first step in the reconstruction of the hit position is thus to identify clusters of active channels associated to one particle crossing the detector. In conventionally triggered systems, where the association of raw data to events is given by a hardware trigger, this is an easy-to-solve problem. It, however, becomes more involved in untriggered, free-streaming read-out systems like the one employed by the CBM experiment. Here, the time coordinate of the single-channel measurement must be taken into account to decider whether neighbouring active channels belong to a cluster. A simple extension of well-known cluster finding algorithms is not satisfactory because of involving increasing combinatorics, which are prohibitive for reconstruction in real-time. In this article, a cluster-finding solution for the Silicon Tracking System of the CBM experiment is presented which avoids any combinatorics or loops over detector channels. Its execution time is thus independent on the size of the data packages (time slices) delivered by the data acquisition, making it suitable for being used in online reconstruction.
Highlights
Position-sensitive detectors reconstruct the intersection point of a particle from the charge distribution generated by the particle during its passage through the active detector material
The time coordinate of the single-channel measurement must be taken into account to decider whether neighbouring active channels belong to a cluster
The algorithm does not require the association of measurements to events by an event trigger
Summary
Position-sensitive detectors reconstruct the intersection point of a particle from the charge distribution generated by the particle during its passage through the active detector material. Several readout segments (channels) are activated by a single particle, allowing to determine the coordinate by an analysis of the charge measurements in those channels. The first step in the reconstruction of the hit coordinate is the identification of a cluster of active channels associated to one particle crossing the detector. In a conventionally triggered readout system, this is a rather trivial problem, since the trigger defines a set of measurements corresponding to a single (or a limited number of) event, in which clusters can be searched for. The data set in which to search for neighbouring active channels is well defined. The complexity of the problem increases, which is of particular importance if the cluster finding algorithm should be suitable for application in real-time as part of online reconstruction. The cluster-finding algorithm developed for that system is described
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