  With the experimental data from STAR and PHENIX on the centrality dependence
of the $p_T$ spectra of protons and anti-protons produced at mid-rapidity in
Au+Au collisions at 200 GeV, we show that for protons and anti-protons there
exists a scaling distribution independent of the colliding centrality. The
scaling functions can also describe data from BRAHMS for both proton and
anti-proton spectra at $y=2.2$ and 3.2. The scaling behaviors are shown to be
incompatible with the usual string fragmentation scenario for particle
production.
