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

Abstract

Deep-inelastic positron-proton scattering events at low photon virtuality, Q 2 , with a forward jet, produced at small angles with respect to the proton beam, are measured with the H1 detector at HERA. A subsample of events with an additional jet in the central region is also studied. For both samples, differential cross sections and normalised distributions are measured as a function of the aza e-mail: krueger@mail.desy.de b Also at Physics Department, National Technical University, Zografou Campus, GR-15773 Athens, Greece. imuthal angle difference, φ, between the forward jet and the scattered positron in bins of the rapidity distance, Y , between them. The data are compared to predictions of Monte Carlo generators based on different evolution approaches as well as to next-to-leading order calculations in order to test the sensitivity to QCD evolution mechanisms.

DIS with KaTie

“…The relevant observable sensitive to the final-state momentum inbalance, and therefore potentially to saturation, is the angle between the final-state electron and the two jets (this observable has been studied in other contexts in e.g. [22,23]). One can observe that different rates of saturation included in the Kutak-Sapeta gluon distributions [24] lead to distinguishable shapes for the angle distribution.…”

Estimation of saturation and coherence effects in the KGBJS equation — a non-linear CCFM equation

“…It is important to study especially the behaviour of the solution of the CCFM with the splitting function with only terms singular in z = 0 and z = 1 (7). The most interesting is the x distribution.…”

“…Let us do a careful analysis of what happens at z → 0 taking the splitting function (7). Let us calculate the Sudakov form factor with fixed p = |k| = Q0 = 1 GeV to see, that for fixed |q| it grows with z getting smaller:…”

“…The BFKL equation [3] seems to be the appropriate effective theory for describing high energy initial state radiation in the kinematic region where the Mandelstam invariants t of the momentum exchange and s of the total scattering momentum are strongly ordered: Λ 2 QCD ≪ |t| ≪ s. It is well known that the relevant phase space region is very important at the LHC, but signs of its importance were already observed at the HERA [7,8] and other colliders.…”

Forward-Central Jet Correlations

“…These MC generators usually use the DokshitzerGribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations [1][2][3][4] approximation. Alternative approaches like the Balitski-Fadin-Kuraev-Lipatov (BFKL) approximation [5][6][7] or the CiafaloniCatani-Fiorani-Marchesini (CCFM) approach [8][9][10][11] have since long been investigated, especially at HERA [12][13][14][15][16][17]. However, although in some cases significant discrepancies between data and DGLAP-based models have been observed, it has not been possible to pin down BFKL or CCFM effects in a convincing manner.…”