ALPHA ``Tracks'' and ``Vertices''

Before QUEVNT is called for each event, ALPHA fills its own data structure with information from the event. Each ``tracklike'' object (eg., tracks, calorimeter objects, energy flow objects, etc.) is assigned a unique number. (A ``tracklike'' object is any object which can be described with a 4 vector.) This ALPHA ``track'' number is equal to the JULIA ``track'' number + a constant. Unique ALPHA numbers are also assigned to vertices (reconstructed vertices and Monte Carlo vertices). The constant is introduced in order to obtain a unique numbering scheme for all species of ``tracks'' or vertices (in JULIA and GALEPH, different species start with the number 1). In the description below, ITK always refers to an ALPHA ``track'' number and IVX to an ALPHA vertex number.

The properties of the tracks and vertices are found using functions which refer to the ALPHA ``track'' and vertex numbers. For example, the energy of ALPHA ``track'' ITK is QE(ITK). The properties available for each tracklike object and each vertex are described in sections 8.1 and 8.4, respectively.

In the following sections, several methods for determining ALPHA track and vertex numbers are described. All of these methods can be nested. Functions which give simple access to relationships between different types of objects are also described.