Measurement of dijet cross-sections in low Q2 ep collisions and the extraction of an effective parton density for the virtual photon

The triple-differential dijet cross-section, d(3)sigma(ep)/dQ(2)d (E) over bar(t)(2) dx(gamma)(jets), is measured with the H1 detector at HERA as a function of the photon virtuality the fraction of the photon's momentum carried by the parton entering the hard scattering, x(gamma)(jets), and the square of the mean transverse energy, (E) over bar(t)(2), of the two highest E-t jets. Jets are found using a longitudinal boost-invariant k(T) clustering algorithm in the gamma*p center of mass frame. The measurements cover the ranges 1.6 < Q(2) < 80 GeV2 in 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 a:, and probing scale dependences of the parton density show characteristic features of photon structure, and a suppression of this structure with increasing Q(2) is seen.