Deep-inelastic inclusive ep scattering at low x and a determination of αs

A precise measurement of the inclusive deep-inelastic ep scattering cross section is reported in the kinematic range 1.5 ≤ Q ≤ 150GeV 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 F2(x,Q) and the longitudinal structure function FL(x,Q) are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured derivative (∂F2(x,Q)/∂ lnQ)x is observed to rise continuously towards small x for fixedQ. The cross section data are combined with published H1 measurements at high Q 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 = 20GeV. A fit of the H1 measurements and the μp data of the BCDMS collaboration allows the strong coupling constant αs and the gluon distribution to be simultaneously determined. A value of αs(M Z) = 0.1150±0.0017(exp) −0.0005 (model) is The H1 Collaboration: Deep-inelastic inclusive ep scattering at low x and a determination of αs 35 obtained in NLO, with an additional theoretical uncertainty of about ±0.005, mainly due to the uncertainty of the renormalisation scale.