  We present ratios of the numbers of charged antiparticles to particles
(pions, kaons and protons) in Au + Au collisions at $\sqrt{s_{NN}}=200$ GeV as
a function of rapidity in the range $y$=0-3. While the particle ratios at
midrapidity are approaching unity, the $K^-/K^+$ and $\bar{p}/p$ ratios
decrease significantly at forward rapidities. An interpretation of the results
within the statistical model indicates a reduction of the baryon chemical
potential from $\mu_B \approx 130$MeV at $y$=3 to $\mu_B \approx 25$MeV at
$y$=0.

Nuclear Experiment