Vertex reconstruction using a single layer silicon detector

Abstract

Typical vertex finding algorithms use reconstructed tracks, registered in a multilayer detector, which directly point to the common point of origin. A detector with a single layer of silicon sensors registers the passage of primary particles only in one place. Nevertheless, the information available from these hits can also be used to estimate the vertex position, when the geometrical properties of silicon sensors and the measured ionization energy losses of the particles are fully exploited. In this paper the algorithm used for this purpose in the PHOBOS experiment is described. The vertex reconstruction performance is studied using simulations and compared with results obtained from real data. The very large acceptance of a single-layered multiplicity detector permits vertex reconstruction for low multiplicity events where other methods, using small acceptance subdetectors, fail because of insufficient number of registered primary tracks.

Scaling properties in bulk andpT-dependent particle production near midrapidity in relativistic heavy ion collisions

“…To maximize the usability of this dataset, two new vertex reconstruction techniques were designed to allow for the analysis of the more peripheral events. The first method finds the vertex position from hits in the single-layer Octagon detector (|η| < 3.2) using a probabilistic approach applied to the energy deposited at each hit [8]. The overall vertex resolution attained by this technique is found to be σ ≈ 0.6-1.0 cm, dependent on the multiplicity of a given event.…”