Double_t e=TMath::Sqrt(p2 + mass*mass);
if ( TMath::Abs(dE) > 0.3*e ) return kFALSE; //30% energy loss is too much!
//cP4 = (1.- e/p2*dE);
+ if ( (1.+ dE/p2*(dE + 2*e)) < 0. ) return kFALSE;
cP4 = 1./TMath::Sqrt(1.+ dE/p2*(dE + 2*e)); //A precise formula by Ruben !
if (TMath::Abs(fP4*cP4)>100.) return kFALSE; //Do not track below 10 MeV/c