2022 Impact factor 4.4
Particles and Fields

Eur. Phys. J. C 21, 33-61 (2001)
DOI: 10.1007/s100520100720

Deep-inelastic inclusive ep scattering at low x and a determination of $\alpha_s$

The H1 Collaboration C. Adloff and et al.

Fachbereich Physik, Bergische Universität Gesamthochschule Wuppertal, Wuppertal, Germany

(Received: 21 December 2000 / Revised version: 10 May 2001 / Published online: 6 July 2001 -© Springer-Verlag / Società Italiana di Fisica 2001 )

A precise measurement of the inclusive deep-inelastic e+ p scattering cross section is reported in the kinematic range $1.5
\le Q^2 \le 150$ GeV2GeV2and $ 3 \cdot 10^{-5} \le x \le 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,Q2)and the longitudinal structure function FL(x,Q2)are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured derivative $(\partial
F_2(x,Q^2) / \partial \ln Q^2)_x $ is observed to rise continuously towards small x for fixed Q2. The cross section data are combined with published H1 measurements at high Q2 for a next-to-leading order DGLAP QCD analysis. The H1 data determine the gluon momentum distribution in the range $3 \cdot 10^{-4} \le x \le
0.1$ to within an experimental accuracy of about 3% for Q2 =20 GeV2GeV2. A fit of the H1 measurements and the $\mu p $ data of the BCDMS collaboration allows the strong coupling constant $\alpha_s$ and the gluon distribution to be simultaneously determined. A value of $\alpha _s (M_Z^2) =0.1150 \pm 0.0017 (exp)
^{+0.0009}_{-0.0005} (model)$ is obtained in NLO, with an additional theoretical uncertainty of about $\pm 0.005$, mainly due to the uncertainty of the renormalisation scale.

© Società Italiana di Fisica, Springer-Verlag 2001