4.4.1 SUBROUTINE ZTTRAK( FIRST, PIN, XIN, CFIRST, CLAST, ZLAST, RPROD, ZPROD, IGEOM, PAR, TRIPRP, TIPZ, PHIIP, LAYLIS, ERROR) : TRAcK a particle through the detector

This routine tracks a charged particle with momentum PIN at position XIN through the detector , and returns a list of transversed layers. It also returns the track parameters at the perigee and the true impact-parameters (Geometrical sign).

ARGUMENTS:

INPUT :

    FIRST : TRUE if first call for this track
    PIN : Momentum of particle
    XIN  : Position where PIN is given
    CFIRST  : Radius or z of where to start including measurements, going
              outwards. NB. if CFIRST is exactly equal to a detector
              position, that detector if NOT used. If CFIRST=0,
              then there is no inner limitation. NB
    CLAST : Radius of where to stop including measurements, going
              outwards. NB. if CLAST is exactly equal to a detector
              position, that detector if NOT used. If CLAST=0,
              then there is no outer limitation.
    ZLAST : z-position of end of track (=0. if no end)
    RPROD : radius of production point of track. No material or measurements
            inside this distance will be used.
    ZPROD : z of production point of track. No material or measurements
            inside this distance will be used.
    IGEOM : Index of the detector description to be used.

OUTPUT :

    WGTINT : Internal weight-matrix.
    PAR  : TKR parameters
    TRIPRP,TIPZ : True values of Impact parameters in RPhi and z
    PHIIP : True phi-angle to perigee.
    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
             3 - other error, no parameters returned

IMPLICIT INPUTS:

    from /ZTTRJ/ : NPT, number of detector elements intersected;
                   ICYPL, list of ditto; ITYP, status of ditto.

IMPLICIT OUTPUTS:

    none

CALLED BY :

ZDETSI, DETector SImulation (see 4.3.1).

CALLED ROUTINE(S):

ZTREFL (see 4.4.12)

(To REFLect track in x-y plane.)

ZTTCYL (see 4.4.6)

(To get Track intersection with CYLinder.)

ZTFOLL (see 4.4.56)

(To FOLLow the track through the detector.)

VMOD,VZERO,UCOPY

(CERNLIB routines)

SIDE EFFECTS:

none

AUTHORS:

M. Berggren, LAL

CREATION DATE:

27-jul-1992