Save a track

To save track ITK means to copy it into a new track ISAVE and to assign a particle name to the track copy. This particle name can be used later for direct access to this particle (see 7.4). Note that the mass is NOT changed in KVSAVE (see KIDSAV, 9.2.11).

The class (KRECO / KMONTE / Lorentz frame; see 7.4.1) of a saved track is given by its history (in the example below, the class of JPSI is set equal to that of ITK1 and ITK). A dedicated routine KVSAVC (see 9.2.12) makes it possible to copy a track into a different or new class. KVSAVC must be used instead of KVSAVE if the track class cannot be deduced from the track history (see example in 9.2.12).

If `part-name' is equal to ` ', KVSAVE only performs a copy, and the track copy has no particle name. In contrast to QVCOPY (see 9.2.4), KVSAVE never overwrites a track.

In a decay chain, the daughter-mother relation is established by KVSAVE. The inverse relation (mother-daughter) is established in routines like QVADDx.

Example: $\psi$ $\rightarrow$ e⁺e^-:

     ISUM = KVNEW (DUMMY)
     ITK1 = KPDIR ('E+', KRECO)
  10 IF (ITK1 .NE. 0)  THEN
       ITK2 = KPDIR ('E-', KRECO)
  20   IF (ITK2 .NE. 0)  THEN
C ... all e+ e- combinations:
         CALL QVADD2 (ISUM, ITK1, ITK2)
C ... cut on invariant mass and save J/psi candidates:
         IF (ABS (QM(ISUM) - QPMASS ('JPSI')) .LT. (your cut))
    &      ITKPSI = KVSAVE (ISUM, 'JPSI')
         ITK2 = KFOLLO (ITK2)
         GO TO 20
       ENDIF
       ITK1 = KFOLLO (ITK1)
       GO TO 10
     ENDIF

The daughter-mother relation is established only for the accepted (i.e., saved) $\psi$s. In subsequent loops, the $\psi$(s) is (are) directly accessible by their name and can be used, for example, to analyze $\psi{^\prime}$ $\rightarrow$ $\psi$$\pi^{+}_{}$$\pi^{-}_{}$ in the same way as $\psi$ $\rightarrow$ e⁺e^-.