4.6.2 SUBROUTINE ZAUVF2(TYPE, MTRK, PAR, WGT, INVTX, PCUT, XYZ, VCOV, VCOVS, TRWT, SFACT, NSIGM, CHI2VX, NVTRK, ERROR) : Vertex FIT 2

This routine fits the primary vertex by calling PXFVTX and checking the $\chi^2$ probability of the fit. If it is bellow PCUT, the worst track is removed from the fit and a new attempt is done. The routine returns the $\chi^2$ of the fit, the position of the vertex with covariance matrix, and a list of tracks used in the fit.

ARGUMENTS:

INPUT :

    TYPE : CHARACTER type of fit :
             'BSPOT' : Just return the beamspot (cov-mat is diagonal,
                        with beamspot uncertainties)
             'BSCONSTR' : Full fit with beam-spot constraint
             anything else : Full fit without beam-spot constraint
    MTRK : total number of tracks
    PAR & WGT : TKR parameters with weight matrix at the perigee
                 for each track
    INVTX : LOGICAL array flagging which tracks should initially
              be considered in the fit
    PCUT : Xi^2 probability when track rejection should stop
    NSIGM : SFACT, the scale factor for observed errors (rather
            than calculated) is such that the probability contents
            inside +-SFACT*NSIGM is the same as that inside +-NSIGM
            if the errors would have been gaussian.

OUTPUT :

    XYZ    : position of primary vertex.
    VCOV   : Covariance matrix of XYZ calculated from track errors.
    VCOVS  :    "         "    "   "       "     from observed spread
             of tracks around XYZ.
    TRWT   : Contribution of each track to the fit (makes 'de-fitting'
             possible.
    SFACT : number to scale the diagonal elements of VCOVS with so
            that the probability contents inside
            W +- SFACT*NSIGN*sqrt(VCOVS_w,w) ( where w is x,y, or z)
            the same as within +-NSIGN for a standardized Gaussian
    CHI2VX : Xi^2 of the fit.
    INVTX : LOGICAL array flagging which tracks were used in the fit
    NVTRK : Number of tracks used in the fit
    ERROR : error flag.

IMPLICIT INPUTS:

     From  /PXCPRO/ : BEAMOY average beam position, and SIGBE beam-spread

IMPLICIT OUTPUTS:

    none

CALLED BY :

ZAUVF1, Vertex Fit 1 (or directly by ZAUSER) (see 4.6.1).

CALLED ROUTINE(S):

PXFVX2

(To call a slightly hacked version of DELPHI PXDST routine PXFVT for vertex fitting.

FKMI5

(To do matrix invert.)

UCOPY,VZERO,LVMAX,PROB,VADD,STUDIN,TRQSQ

(CERNLIB routines)

SIDE EFFECTS:

none

AUTHORS:

M. Berggren, LAL

CREATION DATE:

27-jul-1992