{
h=new TH1D("h","rapidity",500,-500,500);
Double_t m,px,py,pz,pt,p,E
m=200.45626;
for(Int_t i=0;i<10000;i++)
{
gRandom->Rannor(px,py);
gRandom->Rannor(pz,pt);
p=-(px*px+py*py+pz*pz)+(pt*pt);
E=sqrt((p*p)+(m*m));
y=.5*log((E+pz)/(E-pz));
h->Fill(y);
}
h->Draw();
}