$A$ dependence of $\frac{J}{\psi }$ production in ${\pi }^{-}$-nucleus collisions at 530 GeV/c

The $A$ dependence of the cross section for $\frac{J}{\psi }$ production was measured in the Feynman-$x$ region $0.1\le x_F\le 0.8$ with a 530-GeV/c ${\pi }^{-}$ beam. Thick targets of C, Al, Cu, and Pb were employed. Using the cross-section parametrization $\sigma ={\sigma }_0{A}^{\alpha }$, we find $\alpha =0.85\mathrm{}\pm 0.06$. No statistically significant dependence of $\alpha$ on either $x_F$ or transverse momentum $p_t$ is observed.