Deep-inelastic inclusive ep scattering at low cursive Greek chi and a determination of αs

A precise measurement of the inclusive deep-inelastic e+p scattering cross section is reported in the kinematic range 1.5 ≤ Q2 ≤ 150 GeV2 and 3 · 10-5 ≤ cursive Greek chi ≤ 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(cursive Greek chi, Q2) and the longitudinal structure function FL(cursive Greek chi, Q2) are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured derivative (∂F2 (cursive Greek chi, Q2)/∂ln Q2)cursive Greek chi, is observed to rise continuously towards small cursive Greek chi for fixed Q2. The cross section data are combined with published H1 measurements at high Q2 for a next-to-leading order DGLAP QGD analysis. The H1 data determine the gluon momentum distribution in the range 3 · 10-4 ≤ cursive Greek chi ≤ 0.1 to within an experimental accuracy of about 3% for Q2 = 20 GeV2. 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(M2Z) = 0.1150±0.0017(exp)+0.0009-0.0005(model) is obtained in NLO, with an additional theoretical uncertainty of about ±0.005, mainly due to the uncertainty of the renormalisation scale.0SCOPUS: ar.j