Probing the parton evolution in DIS at low xBJ using jet observables

The advent of the ep collider HERA at the DESY research center has opened a wide kinematical window for the study of the Deep Inelastic Scattering (DIS) processes e+p→ e+X. Recent measurements of the structure function F2 of the proton have confirmed the fact that the Bjorken scaling which arises from the naive Quark-Parton Model is broken in the limit where the scaling variable, x-Bjorken, is small. It also revealed that F2 grows exponentially with x-Bjorken, at low x. The standard picture of parton evolution, based on the DGLAP equations, reproduces this steep rise if it is used with an appropriate set of F2 parametrizations. However these parametrizations include "ad-hoc" assumptions on the non-perturbative behaviour of the structure functions and depend on a large set of phenomenological parameters.The steep rise can also be reproduced by using a different perturbative treatment for the parton evolution. This treatment, based on the BFKL evolution equations, differs from the standard DGLAP picture by the lack of ordering in the transverse energy of the emitted partons. Unlike DGLAP, the BFKL picture reproduces the steep rise of F2 without assuming any particular shape of the structure function in the non-perturbative domain.In order to gain an insight on parton dynamics in DIS at low x and discriminate between these two pictures, jet observables are used as they are expected to be closely related to the hard scattering and depend only slightly on the hadronization effects. Two jet observables are studied here in more details: the azimuthal correlation between the two leading-order jets and the cross section of the forward jet production. The measured cross sections are corrected for detector effects and compared to several DIS Monte Carlo models and next-to-leading order simulations over a wide kinematic range. The results are evaluated in the light of the BFKL and the DGLAP pictures. The experimental results are compared to other models of parton evolution as well, like the Colour Dipole Model (CDM), the Linked Dipole Chain (LDC) and the resolved photon model in DIS