E ds/dp^3=           ds                ds
              E -----------  = E  ---------------------
		2piPtdPtdPz      Pzmax 2piPtdPt dPz/Pzmax

                   E          ds
              =  -------------------------
	          Pzmax  2piPtdPt dXf


              =    E                      ds
	        ------ Sinel ------------------
		 Pzmax        2piPtdPt  Sinel dXf


              =        E                  dN
	        Sinel------    -------------------
		      Pzmax    2piPtdPt Nev dXf

 E/Pzmax = sqrt(  Pz^2 + Pt^2) /Pzmax  = sqrt(Xf^2 +(Pt/Pzmax)^2)

  if Pzmax~ 100GeV and Pt=1 GeV,  Pt/Pzmax~0.01
             Xf>0.1  ==>  E/Pzmax = Xf


Plab   A   Sinel mb
100   207   1716
100    64   768
100    27   414
100    12   230
100    1    31.4

