4.4.3 SUBROUTINE ZTFOLN(IGEOM, PP, VERT, LAYLIS) : FOLlow Neutral particle

This routine tracks a neutral particle with momentum PP at position VERT through the detector , and returns a list of transversed layers.

ARGUMENTS:

INPUT :

    IGEOM : Index of the detector description to be used.
    PP     : Momentum of particle
    VERT   : Position where PP is given

OUTPUT :

    LAYLIS : List of detector layers hit by particle :
              LAYLIS(1,i) = number of the i:th hit layer.
                            LAYLIS(2,i) tells if it is a  plane
                            or a cylinder, if it measures or not,
                            and if it is the reference layer.
              LAYLIS(2,i) = 0  : mathematical layer : no material,
                                 no measurement. Ignored in all
                                 calculations
                            1  : seen by a cylinder
                            2  : seen by a plane
                            -1 : particle went through a cylinder, but
                                 was not seen by the detector.
                            -2 : particle went through a plane, but
                                 was not seen by the detector.
                            10 : the layer is a reference cylinder
                            20 : the layer is a reference plane
              LAYLIS(3,i) = No. of radiation lengths in layer.
              LAYLIS(1,i) = -1 -> end of list.
    ERROR  : Error flag. 0 -> no error
                         1 -> P = 0

IMPLICIT INPUTS:

    from /ZTGPT/ : LOCYL and HICYL : index of the first and last cylinder
                    of this geometry; LOPLA and HIPLA : index of the first
                    and last plane of this geometry; ROFF : radial offset.
    from /ZTBAR/ : RAD,ZMX,ZMN : radius and z-extent of cylinders; NCYL :
                   number of cylinders; MEASB : measurement flag;
                   PH1B,PH2B,PH3B,PHTY1B,PHTY2B, and PHTY3B,
                   phi-segmentation; DENSB : No. of rad. lengths of
                   cylinders.
    from /ZTFWD/ : ZED,RMX,RMN : z position and radial extent of planes;
                   NPLA :number of planes ; MEASF : measurement flag;
                   PH1F,PH2F,PH3F,PHTY1F,PHTY2F, and PHTY3F,
                   phi-segmentation; DENSF : No. of rad. lengths of planes.

    From /ZTTRJ/ : IREF : type of reference surface.

    From /ZTSEL/ : RREF and ZREF : radius of reference surface (for
                 cylinder) or Z-coordinate ( for plane).

IMPLICIT OUTPUTS:

    to /ZTTRJ/ : R,Z,PHI,BETA : track parameters at intersection of each
                detector element; NPT : number of intersected elements;
                IORD : pointer into R etc ordered in increasing track-
                length; DIST : track-length to each intersection;
                ITYP : cylinder/plane (1/2) and measurement/no measurement
                (+ve/-ve); ICYPL : number of the intersected element for
                each intersection point; JREF : the position of the
                reference surface intersection in rack-length ordering.

CALLED BY :

ZDETSI, DETector SImulation (see 4.3.1).

CALLED ROUTINE(S):

ZUI2PI (see 4.7.2)

(To bring angle In the range 0 to 2PI.)

VSCALE,VADD,VMOD,VDIST

(CERNLIB routines.)

SIDE EFFECTS:

none.

AUTHORS:

M. Berggren, UFRJ, M. A. Do Vale, UFRJ

CREATION DATE:

06-APR-1995