//set event filters
bool useFilter=true;
if (useFilter)
{
      // Filters are:
      // -----------
      // Multiplicity filter: fastSim->SetMultFilter(type, min, max); 
      // requires min <= mult <= max
      
      // available types are:
      
      //  "+"   : positive charged particles
      //  "-"   : negative charged particles
      //  "gam" : gammas
      //  "pi0" : pi0 candidates ( -> 2 gammas); mass window 0.135 +- 0.03 GeV
      //  "eta" : eta candidates ( -> 2 gammas); mass window 0.547 +- 0.04 GeV 
      //  "ks"  : K_S candidates ( -> pi+ pi-);  mass window 0.497 +- 0.04 GeV
      
      fastSim->SetMultFilter("+",   2,1000);  // at least 2 trk+
      fastSim->SetMultFilter("-",   2,1000);  // at least 2 trk-
      fastSim->SetMultFilter("gam", 0,   4);  // at most 4 gammas

      // Invariant Mass filter: fastSim->SetInvMassFilter(comb, m_min, m_max, mult);
    
      // requires at least mult combined candidates with m_min < m < m_max
	      
      // comb is a TString describing the combinatoric
      // - particle codes are: e+ e- mu+ mu- pi+ pi- k+ k- p+ p- gam pi0 ks eta
      // - codes must be separated exactly with a single blank; no extra blank somewhere else!
      // - for charged final states only the mass is set; no pdg code selection is done! 
      // - optional a 'cc' added at the end also takes into account charge conjugation;
      //   not to be used with symmetric channels like pi+ pi- pi0, K+ K-, etc.!!
      
      // Examples: 
      // - ("k+ k-", 0.98, 1.1, 2)       : forms K+ K- candidate and requires >=2 in the given window
      // - ("ks k+ pi- cc", 2.8, 3.2,1 ) : forms ks k+ pi- / ks k- pi+ cands and req. at least one in window
     
      fastSim->SetInvMassFilter("e+ e-",2.8,3.3,1);  // look for J/psi -> e+ e- candidate
}