Speaker
Description
Parton Reggeization Approach (PRA) is a generalized scheme of kT-factorization which uses the formalism of Reggeized quarks and gluons to define gauge-invariant hard-scattering matrix elements with off-shell partons in the initial state (See Ref. [1] for more detailed discussion). The calculations in PRA are performed in the framework of Lipatov's gauge invariant effective theory for Multi-Regge processes in QCD. LO calculations in PRA combine this matrix elements with unintegrated PDFs, defined in the Kimber-Martin-Ryskin (KMR) scheme, which resum leading doubly-logarithmic corrections ~log^2(t/mu^2), where t is the virtuality of the parton and mu^2 is the hard scale.
The aim of PRA is to improve order-by-order stability of the predictions for multi-scale observables which are sensitive to the radiation of additional hard partons, such as azimuthal decorrelations of pairs of jets and vector bosons or polarization observables in the Drell-Yan process. Some of these observables can be successfully described already in the LO of PRA, while in the conventional Collinear Parton Model (CPM), the NLO and even NNLO corrections to this observables are found to be significant. See Refs. [1-4] for examples.
While the results of LO calculations in PRA seems promising for a certain class of observables, the calculation of full NLO corrections is required to achieve the level of precision, required by the modern experiments and to show, that the order-by-order stability of the predictions is indeed improved. The necessary first step in this program is to compute NLO corrections to a certain set of benchmark single-scale observables, such as DIS structure functions or spectra of inclusive jets or prompt photons, differential in rapidity and pT. For this observables, the validity of the CPM and a good convergence rate of perturbative expansion is established. Since in the PRA the unintegrated PDFs are derived from the ordinary PDFs of CPM using the KMR formula, the results of calculation of single-scale observables should simply reproduce known results at the NLO of CPM. On the other hand, calculation of single-scale observables will allow us to fix the scheme of NLO calculations in the PRA.
The calculation of real and virtual NLO corrections in PRA significantly differs form the similar calculations in CPM. Concerning real NLO corrections, one needs to perform a certain subtraction of the double counting of contributions of additional real partons which are highly separated in rapidity from the central region, which arises between the NLO corrections to the hard scattering matrix element and unintegrated PDFs (See Ref. [1] for the further details). Computing the virtual corrections in the Lipatov's theory, one encounters the new type of divergences of loop integrals -- so called rapidity divergences, which are related with Reggeization of the parton in the t-channel. See Ref. [5] and references therein for the basic discussion of rapidity divergences in PRA. The techniques and results of calculations of NLO corrections to the F_2 and F_L structure functions in the PRA, and comparison with the corresponding CPM results will be presented in the talk.
References:
[1] M. Nefedov and V. Saleev, "Diphoton production at the Tevatron and the LHC in the NLO* approximation of the parton Reggeization approach", Phys. Rev. D 92, no. 9, 094033 (2015) [arXiv:1505.01718 [hep-ph]].
[2] M.A.Nefedov, V.A.Saleev and A.V.Shipilova, "Dijet azimuthal decorrelations at the LHC in the parton Reggeization approach", Phys. Rev. D 87, no. 9, 094030 (2013) [arXiv:1304.3549 [hep-ph]].
[3] M.A.Nefedov, N.N.Nikolaev and V.A.Saleev, "Drell-Yan lepton pair production at high energies in the Parton Reggeization Approach", Phys. Rev. D 87, no. 1, 014022 (2013) [arXiv:1211.5539 [hep-ph]].
[4] B.A.Kniehl, M.A.Nefedov and V.A.Saleev, "Prompt-photon plus jet associated photoproduction at HERA in the parton Reggeization approach", Phys. Rev. D 89, no. 11, 114016 (2014) [arXiv:1404.3513 [hep-ph]].
[5] M. Nefedov and V.~Saleev, "Towards NLO calculations in the parton Reggeization approach", arXiv:1608.04201 [hep-ph].