From LO to NLO in the parton Reggeization approach

Maxim Nefedov,Vladimir Saleev,V.E Volkova,Y.V Zhezher,D.G Levkov,V.A Rubakov,V.A Matveev

doi:10.1051/epjconf/201819104007

Maxim Nefedov, Vladimir Saleev + Show 5 more

Open Access

https://doi.org/10.1051/epjconf/201819104007

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Abstract

We present recent developments of the parton Reggeization approach (PRA), which is based on high-energy factorization of hard processes in the multi-Regge kinematics and Lipatov’s effective theory of Reggeized gluons and Reggeized quarks. The scheme of calculations in the leading order (LO) of the PRA is discussed. We present important examples of LO PRA applications for cross section calculations of multi-scale hard processes, such as pair production ofBB¯-mesons, pair production of photons, and pair production of jets. Also the problem of matching of NLO calculations in PRA with NLO results in the Collinear Parton Model is discussed.

Highlights

To describe high-energy hadron-hadron or lepton-hadron collisions in Quantum Chromodynamics (QCD), one usually have to introduce some kind of factorization, which separates the effects of long and short distances [1, 2]
The fully-unintegrated factorization, which takes into account all four components of momentum of initial-state parton is needed to describe such processes [2, 8], at present there is no systematic theory of such factorization and it is not clear neither how to calculate the gauge-invariant hard scattering coefficient (HSC)
The main difference of parton Reggeization approach (PRA) from the multitude of studies in the transverse momentum depended (TMD)-factorization and kT -factorization is the application of matrix elements with off-shell initial-state partons (Reggeized quarks and gluons) from Lipatov’s Effective Field Theory (EFT) [12, 13], which allows one to study the arbitrary processes involving non-Abelian structure of QCD without violation of gaugeinvariance due to the nonzero virtuality of initial-state partons

Summary

Introduction

To describe high-energy hadron-hadron or lepton-hadron collisions in Quantum Chromodynamics (QCD), one usually have to introduce some kind of factorization, which separates the effects of long and short distances [1, 2]. Q,g where fq,g(x, μ) are collinear parton distribution functions (PDFs), μ is the scale of hard process, σ CPM is the cross section of quark-gluon interaction, and Λ2 is the typical energy scale of non-perturbative phenomena in QCD. The object of our special concern are the azimuthal decorrelation observables in the whole range of 0 ≤ ∆φ ≤ π, which can be studied in the pair production of jets, photons, mesons e.t.c. In principle, the fully-unintegrated factorization, which takes into account all four components of momentum of initial-state parton is needed to describe such processes [2, 8], at present there is no systematic theory of such factorization and it is not clear neither how to calculate the gauge-invariant hard scattering coefficient (HSC). Parton Reggeization Approach is an attempt to extend the formalism of High-Energy factorization to deal with above-mentioned multi-scale observables without introduction of fully-unintegrated PDF. More details can be found in [9], the development of PRA in the NLO approximation is further discussed in [10, 11]

The LO framework of PRA

Towards NLO calculations in PRA