Fast Vertexing Code

We present a new fast vertexing algorithm for the determination of primary vertices, relying on linear extrapolation of tracks near the beamline, as the curvature of the track for such short distances is negligible. The method treats tracks as infinitely elongated ellipsoids, thereby transforming the vertex-finding problem into a proximity one—between points with ellipsoidal error matrices. We have implemented this approach in C++ using our proprietary NXV4 package for vector and matrix operations. We have tested the resolution and speed performance on SpdRoot simulated data, for the SPD experiment at JINR.