4.6.1 SUBROUTINE ZAUVF1(FRCREJ, ERROR) : Vertex Fit 1

This routine fits the main vertex in several steps :

• decide roughly which tracks to consider
• fit with this set by calling ZAUVF2 with beamspot-constraint on, prob cut at 0.01, significance scaling at 2.
• Call ZAURST to reject strange particles, gamma conversions etc.
• Call ZAUVF2 again, with strange particles rejected.

It is possible to call ZAUVF2 directly form the user-code, but as this call is rather complicated, and needs setting up of several control-variables, ZAUVF1 is supplied as an easy interface. If the user wants to use her own vertex-fitting procedure, ZAUVF1 can be useful as an example.

ARGUMENTS:

INPUT :

    FRCREJ : bitted word. If bit i is set, then all tracks
            with true history code i are rejected from the vertex fit.
            The special value -1 means that all non-vertex tracks are
            rejected. The value 0 means that the routine ZAURST will
            try, using the meassured momenta, to find tracks from K_O
            and Lambda decays as well as from photon conversions and
            nuclear interactions in the detector material.

OUTPUT :

       ERROR : error-flag
                 0  : OK
                 -1 : Not possible to get vertex with requested
                      probability. Beam-spot returned in XYZ, and
                      beam-spot covariance matrix in VCOV.
                 <-1: OK, but measured covariance matrix not calculated,
                      VCOVM = VCOV, SFACT = 1.0
                Hence, testing ERROR .LE. 0 would be OK, but if ERROR = -1
                errors are larger than otherwise. They are statistically
                correct, however.

IMPLICIT INPUTS:

    From /ZAEVT/ : SFACT, error scale factor; NSGINI, # of sigmas for
                   sfact definition; PCUT, prob-cut to accept vertex;
                   MTRK, total # of seen tracks.
    From /ZASTE/ : DOWNUP, vertex-fit method : include tracks until Xi^2
                   becomes bad (.TRUE.), or exclude tracks until it becomes
                   good (.FALSE.).
    From /ZATRS/ : PAR and WGT, perigee parameters with weight-matrix;
                   INVTX, the track is in the main vertex;
                   INSV, the track is in a sec. vertex (initialised here);

IMPLICIT OUTPUTS:

    To /ZAEVT/ : XYZ, fitted vertex pos; VCOV, calculated vertex cov mat;
                 VCOVM,  measured vertex cov mat;
                 CHI2VX, chi^2 of vertex; NVTRK, # of track in vertex;

CALLED BY :

ZAUSER, USER code (see 4.5.10).

CALLED ROUTINE(S):

ZAUVF2 (see 4.6.2)

(To do Vertex Fit 2.)

ZAURST (see 4.6.3)

(To Reject STrange particle decay prods.)

SIDE EFFECTS:

none.

AUTHORS:

M. Berggren, UFRJ

CREATION DATE:

11-APR-1995