2020 Impact factor 4.590
Particles and Fields
Eur. Phys. J. C 13, 397-414
DOI 10.1007/s100520000144

Measurement of dijet cross-sections in low ${\rm {\bf Q^2}}$ ep collisions and the extraction of an effective parton density for the virtual photon

The H1 Collaboration

C. Adloff34 - et al.

34 Fachbereich Physik, Bergische Universität Gesamthochschule Wuppertal, Wuppertal, Germany

Received: 18 December 1998 / Published online: 25 February 2000 - © Springer-Verlag 2000

The triple-differential dijet cross-section, $\ensuremath{{\rm d}^3\sigma_{ep}/{\rm d}\ensuremath{Q^2} {\rm d}\ensuremath{\overline{E_t}^2} {\rm d}\ensuremath{x^{jets}_{\gamma}} } $, is measured with the H1 detector at HERA as a function of the photon virtuality Q2, the fraction of the photon's momentum carried by the parton entering the hard scattering, $\ensuremath{x^{jets}_{\gamma}} $, and the square of the mean transverse energy, $\ensuremath{\overline{E_t}^2} $, of the two highest Et jets. Jets are found using a longitudinal boost-invariant kT clustering algorithm in the $\gamma^* p$ center of mass frame. The measurements cover the ranges 1.6 < Q2 < 80 GeV2in virtuality and 0.1 < y < 0.7 in inelasticity y. The results are well described by leading order QCD models which include the effects of a resolved component to the virtual photon. Models which treat the photon as point-like fail to describe the data. An effective leading order parton density for the virtual photon is extracted as a function of the photon virtuality, the probing scale and the parton momentum fraction. The $x_{\gamma}$ and probing scale dependences of the parton density show characteristic features of photon structure, and a suppression of this structure with increasing Q2 is seen.

Copyright Società Italiana di Fisica, Springer-Verlag 2000