//calculate Plab for given E in CM [GeV]

void Ecm_Plab(double Ecm=3.527){
  double mp = 0.938272;//proton mass, GeV
  double mp2 = TMath::Power(mp,2);
  double Ecm2 = TMath::Power(Ecm,2)/(2*mp);
  //  cout<<" Ecm2 = "<<Ecm2<<endl;
  double term = Ecm2-mp;
  double plab2 = TMath::Power(term,2)-mp2;
  double plab = TMath::Power(plab2,0.5);
  cout<<"For Ecm = "<<Ecm<<" Plab = "<<plab<<endl;
}