real function gj(t)
*
* Angle between gottfried-jackson and 
* helicity frames as function of t
* and vector meson mass
* ref: Gilman et al, PL B31, 387 (1970)
*
* JAC 10 feb 98
*
      vector vmmass(1)
*
      vm2=vmmass(1)**2.
*
      cc=(vm2-t)/(vm2+t)
*
*
      gj=sqrt(1.-cc**2)
*
*
*      print *,t,gj
*
      end