E781 V0 package Description

  1.1 The main object of V0 package is 2 prong vertex. The simplest
      objects are lambda in proton and pion decay and K short in two
      charged pion decay mode (vee objects). The kink (e.g. sigma plus
      in proton and pi0 decay mode) are disabled in current version.
      Once vee was found, a possibility to have a parent decay into vee
      and charged track is checked (e.g. ksi(1321) -> lambda, pi-).
            
  1.2 The system names for the objects of the V0 package are as follows:
            
   lam  : lambda
   k0s  : K short
   xla  : lambda without production vertex (x0 -> lam, pi0 candidate)
   ome  : o- identified by lam  K- and vertex segment of ome itself
   ksi  : x- identified by lam  i- and vertex segment of ksi itself
   csk  : o- identified by lam  K- (s channel)
   csi  : x- identified by lam  i-
   ctk  : o- identified by lam  and vertex segment (t channel)
   cti  : x- identified by lam  and vertex segment (t channel)
   si0  : s0 identified by lam  and gamma
   xl0  : x0 identified by xla  and i0
           
     All anti-particles have leading 'a' in their names.
           
  1.3 All the reconstructions may be classified into
      vx_recn and not_vx_recn. For example, lambda with 2 vx tracks
      is vx_recn, ome is vx_recn, csk is not_vx_recn for ome decay etc.
      All the reconstructions may be classified into 2p and 1p objects.
      For example, lambda with 2 measured momenta (proton & pion) is
      2p object, csk with measured kaon momentum is 2p object, even if
      pion momentum of lambda was not measured.

      All such V0 objects do have different momentum spectrum, momentum
      resolution, reconstruction/detection efficiency and background. 
            
  1.4 Soap commands.
      Switch on V0 reconstruction :           exe V0;
      Switch on V0 dump:                      set on V0 dump;
      Setup soft cut mode:                    set on v0 soft;
      Save info in vbk file:                  set on v0 save
      Setup v0 cuts:                          set cut v0 zmin -20.0;
      See default.cmd and v0_par.inc for all v0 parameters.
      vbk file is created with the name of hbk file except the extention.
      In addition one can setup specific version of vbk stuff.      
      The optimal rate over background you will have in soft cut mode.
            
  1.5 Several subroutines allow you to use V0 objects in Recon package:

    a) recon_v0 - produces reconstructions from system v0 objects;
    b) recon_tv - makes a reconstruction from v0 object and not primary
       track (dca - distance of closest approach cut etc);
    c) recon_gr - adds 1 gamma on existing reconstruction;
    d) recon_2g - adds 2 gammas to get a certain mass (e.g. pi0);
    e) recon_0v - adds 2 gamma mass on existing reconstruction

 (to be continued...)