Forward jet production in deep inelastic ep scattering and low-x parton dynamics at HERA

Abstract

Differential inclusive jet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector using an integrated luminosity of 38.7 pb(-1). The jets have been identified Using the k(T) cluster algorithm in the longitudinally invariant inclusive mode in the laboratory frame; they have been selected with jet transverse energy, E(T)(Jet) above 6 GeV and jet pseudorapidity, eta(jet), between -1 and 3. Measurements of cross sections as functions of E(T)(jet), Bjorken x and the photon virtuality, Q(2), are presented. Three phase-space regions have been selected in order to study parton dynamics from the most global to the most restrictive region of forward-going (close to the proton-beam direction) jets at low x, where the effects of BFKL evolution might be present. The measurements have been compared to the predictions of leading-logarithm parton-shower Monte Carlo models and fixed-order perturbative QCD calculations. In the forward region, O(alpha(1)(s)) QCD calculations underestimate the data up to an order of magnitude at low x. An improved description of the data in this region is obtained by including O(Ce2) QCD corrections, which account for the lowest-order t-channel gluon-exchange diagrams, highlighting the importance of such terms in the parton dynamics at low x. s (c) 2005 Elsevier B.V. All rights reserved

Low-x QCD with CMS at the LHC

“…(3), of enhanced parton saturation effects in the nuclear wave functions accelerated at ultra-relativistic energies has been one of the primary physics motivations for the heavy-ion programme at RHIC 4) [9]. Further, the properties of the high-density matter produced in the final-state of AA interactions cannot be properly interpreted without having determined the influence of initial state modifications of the nuclear 4) The saturation scale at y =0 in Au at RHIC is Q 2 s ∼ 2 GeV, much larger than that of protons probed at HERA, Q 2 s ∼ 0.5 GeV. PDFs.…”

“…Thus, their appropriate description is in terms of k T -unintegrated PDFs, xg(x, k T ), described by the Balitski-Fadin-Kuraev-Lipatov (BFKL) equation which governs parton evolution in x at fixed Q 2 [3]. Hints of extra BFKL radiation have been recently found in the enhanced production of forward jets at HERA compared to DGLAP expectations [4,5]. …”

Azimuthal decorrelation of forward jets in deep inelastic scattering

“…For a future comparison with the experimental results in this work we implement the same kinematical cuts and constraints as those used at HERA. The ZEUS [12] and H1 [13] collaborations have imposed upper and lower cuts in the transverse momentum of the forward jet taking into account the photon virtuality Q 2 . They performed these cuts in order to ensure that both ends of the gluon ladder have a similar characteristic transverse scale.…”

Measurement of the azimuthal correlation between the most forward jet and the scattered positron in deep-inelastic scattering at HERA

“…In these measurements as well as in the present one, the requirements on the forward jet and the phase space were chosen in such a way that the standard DGLAP evolution is suppressed and the effects of BFKL dynamics are enhanced. Preference for models which employ QCD evolution non-ordered in transverse momentum was observed [10][11][12][13][14][15][16].…”