Arrays for Particles

All the particles (photons, electrons, positrons) carry the following variables.

TXYS(i)

(i=0,1,2,3) Particle coordinates in meter.
   Note that, in contrast to ABEL, the time and the s-coordinates are also defined for each particle. During tracking by PUSH-ENDPUSH command all the particles have basically the same time coordinate (an exception is the particles just created), whereas in some cases (e.g., after defined by BEAM command, after DRIFT S= command, etc.) they have different t but same s.
Also note that, in contrast to ABEL, s-coordinate does not simply change as but changes according to the instantaneous longitudinal velocity so that longitudinal mixing may occur for low energy or large angle particles.

EP(i)

(i=0,1,2,3) Energy-momentum in units of (eV,eV/c).

SPIN(i)

(i=1,2,3) The polarization component   for electrons/positrons, and the Stokes parameter   for photons.
is defined, as usual, in particle's rest frame. Therefore, it aquires the Thomas precession  under Lorentz transformation by LORENTZ command.
to 2em For defining the Stokes parameter, one needs a set of orthonormal basis vectors with the third vector parallel to the momentum. In CAIN, the first vector is taken to be the unit vector along and . This is ill-defined when the momentum is exactly parallel to the x-axis but this possibility is simply ignored. Except for large angle photons, is almost equal to for right-going photons, and for left-going photons.
to 2em See the next subsection for more detail on the polarization.

GEN

Generation.  When a particle is generated by BEAM command by Twiss parameters, etc, GEN=1. Created particles such as beamstrahlung photons have GEN larger by one than that of the parent particle. (This is also true for the `spent' parents.) GEN of the secondary particles due to particle-particle interaction (such as incoherent pairs) is the sum of GENs of the parents. In this case GENs of the parents do not change.

WGT

Weight. Number of real particles represented by the macro-particle.

NAME

4-byte character string. Normally blanks. The test particles have Tnnn where nnn is a three-digit number. NAME of the particles created by incoherent (particle-particle) interactions starts with `I'. For example, `IBW ', `IBH ', `ILL ' for the pairs created by incoherent Breit-Wheeler, Bethe-Heitler, Landau-Lifshitz processes, respectively.