Two-Jet Correlations in Multijet Events in the Regge Limit of QCD
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o-Jet Correlations in Multijet Events in the Regge Limit of QCD M. A. Nefedova, b, * and V. A. Saleevb, c, ** a
II Institute for Theoretical Physics, Hamburg University, Hamburg, 22761 Germany bSamara National Research University, Samara, 443086 Russia c Joint Institute for Nuclear Research, Dubna, 141980 Russia *e-mail: [email protected] **e-mail: [email protected] Received December 20, 2019; revised January 16, 2020; accepted January 29, 2020
Abstract—A new method for matching calculations in the leading approximation in the kT-factorization approach with the higher-order contributions of perturbation theory, which appear due to the emission of additional hard partons, is proposed. In the proposed method, azimuthal correlations between the leading and subleading jets in a multijet event are considered. The calculations are carried out within the parton Reggeization approach (PRA) that is based on kT-factorization of hard processes in multi-Regge kinematics, the Kimber–Martin–Ryskin model for nonintegrated parton distribution functions (nPDF), and the effective field theory of Reggeized gluons and quarks proposed by L.N. Lipatov. Theoretical predictions are compared with the CMS collaboration data collected at the Large Hadron Collider at energy S = 13 TeV. DOI: 10.1134/S1063779620040528
1. INTRODUCTION Inclusive processes of production of several hard jets with large transverse momenta (usually pT ≥ 100 GeV) are intensively explored in experiments carried out at the Large Hadron Collider by CMS [1, 2] and ATLAS [3] collaborations at energies 7 and 13 TeV. The studies of azimuthal correlations (distributions on the difference of azimuthal angles) between the two most energetic, the leading and the subleading jets, are of special interest in these experiments. The azimuthal correlations are very sensitive to higher-order perturbation quantum chromodynamics (QCD) theory contributions, and primarily to the emission of additional partons with large transverse momenta. A deviation from the basic configuration, when the leading jets are generated in opposite directions in the azimuthal plane ( Δφ = π) can be a sign of either an additional hard emission or effects depending on the transverse momentum and the QCD evolution of the PDF prior to the process of hard scattering. In the collinear parton model (CPM), in which initial partons are on the mass shell and have no transverse momentum, it is impossible to describe correlations over the difference of azimuthal angles of the leading jets Δφ within the fixed order of the QCD perturbation theory even in the range close to π. In order to describe the experimental data within the CPM, it is necessary to consider (nonfactorized) contributions of jets of parton showers in the initial state [4–6]. The parton showers generate transverse momenta of initial partons and the
radiation of additional hard partons, which induces the decorrelation over the azimuthal angle between the leading jets. The agreement with data on the distributions as a function of Δφ is obtained by using the
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