  The ratios of charged antiparticles to particles have been obtained for
pions, kaons and protons near midrapidity in central Au+Au collisions at
sqrt(s_NN) = 200 GeV. Ratios of <pi->/<pi+> = 1.025 +/- 0.006 (stat.) +/- 0.018
(syst.), <K->/<K+> = 0.95 +/- 0.03 (stat.) +/- 0.03 (syst.) and <pbar>/<p> =
0.73 +/- 0.02 (stat.) +/- 0.03 (syst.) have been observed. The <K->/<K+> and
<pbar>/<p> ratios are consistent with a baryochemical potential mu_B of 27 MeV,
roughly a factor of 2 smaller than in sqrt(s_NN) = 130 GeV collisions. The data
are compared to results from lower energies and model calculations. Our
accurate measurements of the particle ratios impose stringent constraints on
current and future models dealing with baryon production and transport.
