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© The Author(s) 2011. First measurements are presented of the diffrac-tive cross section σ<inf>ep→e</inf>XY at centre-of-mass energies √s of 225 and 252 GeV, together with a precise new measurement at √s of 319 GeV, using data taken with the H1 detector in the years 2006 and 2007. Together with previous H1 data at √s of 301 GeV, the measurements are used to extract the diffractive longitudinal structure function FD in the range of photon virtualities 4.0 < Q<sup>2</sup> < 44.0 GeV<sup>2</sup> and fractional proton longitudinal momentum loss 5 x 10-<sup>4</sup>≤xp ≤ 3×10<sup>−3</sup>. The measured F<sup>D</sup> <inf>L</inf> is compared with leading twist predictions based on diffractive parton densities extracted in NLO QCD fits to previous measurements of diffractive Deep-Inelastic Scattering and with a model which additionally includes a higher twist contribution derived from a colour dipole approach. The ratio of the diffractive cross section induced by longitudinally polarised photons to that for transversely polarised photons is extracted and compared with the analogous quantity for inclusive Deep-Inelastic Scattering.

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Journal article


European Physical Journal C

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