The track finding algorithm of the Belle II vertex detectors

Abstract

Abstract. The Belle II experiment is a high energy multi purpose particle detector operated at the asymmetric e + e − -collider SuperKEKB in Tsukuba (Japan). In this work we describe the algorithm performing the pattern recognition for inner tracking detector which consists of two layers of pixel detectors and four layers of double sided silicon strip detectors arranged around the interaction region. The track finding algorithm will be used both during the High Level Trigger on-line track reconstruction and during the off-line full reconstruction. It must provide good efficiency down to momenta as low as 50 MeV/c where material effects are sizeable even in an extremely thin detector as the VXD. In addition it has to be able to cope with the high occupancy of the Belle II detectors due to the background. The underlying concept of the track finding algorithm, as well as details of the implementation are outlined. The algorithm is proven to run with good performance on simulated Υ(4S ) → BB events with an efficiency for reconstructing tracks of above 90% over a wide range of momentum.

The design, construction, operation and performance of the Belle II silicon vertex detector

“…A stand-alone track finder Vertex Detector Track Finding (VXDTF2) [68,69] had been developed to improve the overall track finding efficiency as well as to have a track finder orthogonal to the CDC finder for cross-checks and for the study of systematic effects. The SVD together with the VXDTF2 brings the track finding and fitting efficiency above 87% for 𝑝 𝑡 ∼ 0.1 GeV/𝑐 for all particles in 𝐵𝐵 events (see figure 149).…”

“…The VXDTF2 [68] gradually builds up the track candidates starting from the SpacePoints whose reconstruction is described in section 8.2.2. Pairs of SpacePoints, whose positions are sufficiently close to the trajectory of a charged particle from the IP, are combined in a segment.…”

Track Finding

“…5.3. In tracking detectors with few layers and little redundancy [25], the CA can be complemented by prior information stored in a sector map [26,27]. In this concept, the sensors are partitioned into sectors.…”