Abstract
A combination of the inclusive diffractive cross section measurements made by the H1 and ZEUS Collaborations at HERA is presented. The analysis uses samples of diffractive deep inelastic ep scattering data at a centre-of-mass energy $\sqrt{s}=318~\mathrm{GeV}$ where leading protons are detected by dedicated spectrometers. Correlations of systematic uncertainties are taken into account, resulting in an improved precision of the cross section measurement which reaches 6 % for the most precise points. The combined data cover the range 2.5<Q 2<200 GeV2 in photon virtuality, $0.00035 < \mbox{$x_{\mathbb{P}}$}< 0.09$ in proton fractional momentum loss, 0.09<|t|<0.55 GeV2 in squared four-momentum transfer at the proton vertex and 0.0018<β<0.816 in $\beta=x/\mbox{$x_{\mathbb{P}}$}$ , where x is the Bjorken scaling variable.