Near-side one-dimensional $\Delta\eta$ correlation function in pp collisions at $\sqrt{s}=$ 13 TeV obtained using Eq. \eqref{eq:etaproj}. The correlation is fitted with a generalised Gaussian distribution parameterised by Eq. \eqref{eq:gaus}. The projected correlation function is presented after the baseline subtraction (see text for details). The statistical uncertainties are smaller than the marker size, and the systematic uncertainties are not shown.