One-dimensional Gaussian HBT radius in \pp collisions at $\sqrt{s}$ = 900 GeV as a function of transverse momentum $\kt$ (full dots) The mean charged-particle multiplicity density was $\langle$d$N_{\rm ch}$/d$\eta$$\rangle$ = 3.6 PHOJET simulation was used to determine the baseline of the correlations Using PYTHIA and a flat baseline leads to systematic deviations up and down,respectively; the related systematic errors as indicated by the shaded area Stars and filled boxes represent the radii measured at RHIC [14] and Tevatron [25], respectively.