Abstract:A precise measurement of the inclusive deep-inelastic e + p scattering cross section is reported in the kinematic range 1.5 ≤ Q 2 ≤ 150 GeV 2 and 3 · 10 −5 ≤ x ≤ 0.2. The data were recorded with the H1 detector at HERA in 1996 and 1997, and correspond to an integrated luminosity of 20 pb −1 . The double differential cross section, from which the proton structure function F 2 (x, Q 2 ) and the longitudinal structure function F L (x, Q 2 ) are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured derivative (∂F 2 (x, Q 2 )/∂ ln Q 2 ) x is observed to rise continuously towards small x for fixed Q 2 . The cross section data are combined with published H1 measurements at high Q 2 for a next-to-leading order DGLAP QCD analysis. The H1 data determine the gluon momentum distribution in the range 3 · 10 −4 ≤ x ≤ 0.1 to within an experimental accuracy of about 3% for Q 2 = 20 GeV 2 . A fit of the H1 measurements and the µp data of the BCDMS collaboration allows the strong coupling constant α s and the gluon distribution to be simultaneously determined. A value of α s (M To be submitted to Eur. Phys. J. C

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A measurement is presented of dijet and 3-jet cross sections in low-|t| diffractive deepinelastic scattering interactions of the type ep → eXY , where the system X is separated by a large rapidity gap from a low-mass baryonic system Y . Data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 18.0 pb −1 , are used to measure hadron level single and double differential cross sections for 4 < Q 2 < 80 GeV 2 , x IP < 0.05 and p T,jet > 4 GeV. The energy flow not attributed to jets is also investigated. The measurements are consistent with a factorising diffractive exchange with trajectory intercept close to 1.2 and tightly constrain the dominating diffractive gluon distribution. Viewed in terms of the diffractive scattering of partonic fluctuations of the photon, the data require the dominance of qqg over qq states. Soft colour neutralisation models in their present form cannot simultaneously reproduce the shapes and the normalisations of the differential cross sections. Models based on 2-gluon exchange are able to reproduce the shapes of the cross sections at low x IP values.