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Maxim Nefedov

Publications and source records attributed to Maxim Nefedov.

At least 19 recordsLinked to original sources
arXiv2026

Relativistic corrections and high-energy resummation for exclusive heavy quarkonium photoproduction

The $O(v^2)$ correction to the high-energy resummed coefficient function for the exclusive photoproduction of vector ($1^{--}$) heavy quarkonia off hadrons is computed, thereby taking into account corrections of $O(v^2 \alpha_s^n \ln^{n-1}(x/\xi))$. When expressed in terms of the physical vector-meson mass ($M_V$) and the relative heavy-quark velocity ($\langle v^2 \rangle$) using the Gremm-Kapustin relation, the computed correction turns out to be negligible at the scale $\mu_F=M_V$. However, it partially cancels the $\mu_F$ dependence of the $O(v^2)$ correction to the LO coefficient function in $\alpha_s$, thereby improving the robustness of the predictions.

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arXiv2026

Running coupling effects in the anti-collinear resummation in high energy evolution

We study the effects of the running of the QCD coupling on the anti-collinear resummation in JIMWLK evolution in the linear (BFKL) regime. We determine the appropriate scale choice for the coupling entering the JIMWLK kernel, and derive the anti-collinearly resummed BFKL kernel, which includes running-coupling effects both in the resummation equation (i.e. DGLAP) and in the JIMWLK kernel proper. We find that the running of the coupling generally further slows down BFKL evolution, as expected. Surprisingly however the value of the generalized characteristic function at $\gamma=1$ is unaffected by the running coupling owing to subtle cancellations. We develop an approximation that allows us to use the generalized characteristic function to study the BFKL Green's function. Within this approximation we find that the Pomeron intercept in the anti-collinear regime is significantly reduced by both, the resummation and the running of the coupling.

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arXiv2026

Complete NLO BFKL impact factors for quarkonium hadroproduction in NRQCD: the case of ${}^1S_0^{[1]}$, ${}^1S_0^{[8]}$, and ${}^3S_1^{[8]}$ states

We present the first complete next-to-leading-order calculation of the impact factors for hadroproduction of the ${}^1S_0^{[1]}$, ${}^1S_0^{[8]}$, and ${}^3S_1^{[8]}$ NRQCD states within the BFKL formalism. We complete the recent virtual-correction computation presented in JHEP 12 (2024) 129 by that of the real-emission contributions. We observe the cancellation of the soft divergences between these real- and virtual-emission contributions and we note that the surviving collinear singularities are compatible with factorisation up to one loop for a novel class of processes where BFKL resummation can be applied. Our work indeed represents the first complete NLO quarkonium impact factor in the BFKL framework and paves the way to first next-to-leading-logarithmic-precision studies for hadroproduction of forward-backward quarkonium associated production at hadron colliders.

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arXiv2026

Anti-collinear resummation in JIMWLK evolution in the linear regime

The recently-proposed resummation procedure for anti-collinear logarithms in the JIMWLK kernel~\cite{Kovner:2023vsy} is studied in the linear (BFKL) regime in the fixed-coupling approximation. Simple closed form expressions for the resummed momentum space kernel and characteristic function $\chi(n,\gamma)$ are found. We find that the anti-collinear pole in the leading order characteristic function at $\gamma=1$ disappears, and instead $\chi(\gamma=1)=\frac{12}{11}\frac{\pi}{\alpha_sN_c}$ for $n_F=0$. Comparison with the known NLO BFKL eigenvalue, with the target-Bjorken limit ($Q_T\gg Q_P$) of the $\gamma^*(Q_P)+\gamma^*(Q_T)$-scattering amplitude and with the ``all-poles'' resummation prescription are presented.

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arXiv2025

Hybrid high-energy factorization and evolution at NLO from the high-energy limit of collinear factorization

We derive the scheme of NLO computations of generic observables in high-energy hadron-hadron collisions within the framework of high-energy factorization (HEF) with one off-shell initial-state parton, by taking a high-energy limit of the NLO computation in collinear factorization (CF). The NLO terms belonging to the projectile and target are identified and the ambiguity of projectile-target separation is related with the Collins-Soper scale ($\mu_Y$). The NLO unintegrated PDF(UPDF) is constructed in terms of the usual PDFs, and its $\mu_Y$-evolution reproduces the Collins-Soper-Sterman equation in the TMD limit ($|k_\perp|\ll \mu_Y$). The resummation of high-energy logarithms is taken care of by the BFKL-Collins-Ellis evolution of the Green's function in the UPDF.

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arXiv2024

Prospective report of the French QCD community to the ESPPU 2025 with respect to the program of the LHC Run 5 and beyond and future colliders at CERN

This document summarizes the prospective physics plans of the French QCD and Heavy-Ion community, including the experimental programs at the LHC Run 5 and beyond and future colliders at CERN, within the context of the French contribution to the update of the European Strategy in Particle Physics (ESPPU 2025), as discussed in the workshop on European Strategy for Particle Physics Update 2025 organised by the QCD GdR in Oct. 2024.

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arXiv2024

Complete 1-loop study of exclusive $ J/\psi $ and $ \Upsilon $ photoproduction with full GPD evolution

We discuss the exclusive photoproduction of a heavy vector quarkonium, namely $J/\psi$ and $\Upsilon$ at 1-loop in $\alpha_s$. In collinear factorisation (CF), the amplitude for such a process is obtained by the convolution of a hard partonic sub-amplitude, with a universal generalised parton distribution (GPD). For the first time, we perform a complete calculation at 1-loop including full leading-log (LL) GPD evolution. We first demonstrate the huge instability of the cross section at high energies when the factorisation scale $\mu_F$ is varied. This instability has been reported previously in the literature, and occurs due to the large logarithms generated by the huge difference between the hard scale of the process, which is the mass of the heavy quarkonium here, and the centre-of-mass energy of the process. This problem was also reported in inclusive heavy vector quarkonium photoproduction. We show that this issue can be resolved by resumming these large logarithms using high-energy factorisation (HEF), by performing a matching with the result in CF using the doubly logarithmic approximation (DLA) in order to be consistent with the fixed order evolution of GPDs. Finally, we show that the cross sections obtained from such a matching, besides being free from the previously mentioned factorisation scale variation instabilities, are consistent with the H1 data for $J/\psi$ production and with the ZEUS data for $\Upsilon$ production.

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arXiv2024

Forward $\eta_Q$ production impact factor at NLO

The High-Energy Factorisation (HEF) coefficient function or impact factor for the hadroproduction of the state ${}^1S_0^{[1]}$ of a heavy quark-antiquark pair ($Q\bar{Q}$) at forward rapidities is computed at NLO in $\alpha_s$. This impact factor is an integral part of the resummation procedure for higher-order QCD corrections to the hadroproduction cross sections of $\eta_c$ or $\eta_b$ mesons at forward rapidities in collinear factorisation (CF), enhanced by logarithms of partonic center of mass energy. The NLO computation results of which are presented in this contribution, is an important step towards an extension of aforementioned resummation beyond the Leading Logarithmic Approximation(LLA).

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arXiv2024

One-loop impact factors for heavy quarkonium production: $S$-wave case

With the aim to extend the study of inclusive heavy quarkonium production at forward rapidities with the resummation of high partonic center-of-momentum-energy logarithms beyond Leading Logarithmic Approximation (LLA), the explicit analytic results for one-loop corrections to the following impact factors had been obtained: $\gamma R \to Q\bar{Q}\left[^1S_0^{[8]} \right]$, $g R \to Q\bar{Q}\left[^1S_0^{[1]} \right]$, $gR\to Q\bar{Q}\left[ ^1S_0^{[8]} \right]$ and $gR\to Q\bar{Q}\left[ ^3S_1^{[8]}\right]$, with $R$ being the Reggeized gluon and $Q$ is the heavy quark. The computation is done in the framework of Lipatov's gauge-invariant EFT for Multi-Regge processes in QCD with the tilted-Wilson-line regularisation for rapidity divergences. As expected, only single-logarithmic rapidity divergence proportional to the one-loop Regge trajectory of a gluon remains in the final result for impact-factors. Numerical comparison with Regge limits ($s/(-t) \gg 1$) of one-loop QCD amplitudes, described in the paper, provides a strong cross-check of obtained results. The relations of obtained results with other regularisation schemes for rapidity divergences used in low-$x$ physics, such as BFKL scheme, High-Energy Factorisation (HEF) scheme and shockwave scheme, are given.

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arXiv2023

Revisiting inclusive production of J/psi and Upsilon in high-energy gamma-gamma collisions

The impact of Next-to-Leading Order (NLO) QCD corrections to the differential distributions of J/psi and Upsilon mesons produced inclusively in gamma-gamma collisions is discussed for the kinematical conditions of LEP II for DELPHI and at the future Circular Electron-Positron Collider (CEPC). We take into account all sizeable contributions at LO in v^2 in NRQCD factorisation: 1) pure QED process gamma + gamma -> J/psi(3S^1_1) + \gamma up to alpha^3 alpha_s, 2) single-resolved-photon contributions up to alpha_s^4, 3) gamma+gamma -> J/psi + c c-bar up to alpha^2 alpha_s and 4) gamma+gamma -> J/psi + ggg up to alpha^2 alpha_s^3. We will also discuss the pure QED process as a contribution to the exclusive production in ultra-peripheral heavy-ion collisions (UPC) at the LHC.

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arXiv2023

On the high-energy instability of quarkonium production

The perturbative instability of NLO collinear factorisation (CF) computations of $p_T$-integrated cross sections of heavy quarkonium production at high hadronic or photon-hadron collision energy is discussed. We resolve this problem via the matching of NLO CF computation with the resummation of higher-order corrections $\propto \alpha_s^n \ln^{n-1}(\hat{s}/M^2)$ at high partonic center of mass energies $\hat{s}\gg M^2$. The resummation is performed in the Doubly-Logarithmic Approximation(DLA) of High-Energy Factorisation(HEF) formalism. We also report the results of the first computation of one-loop corrections to impact-factors involving heavy quark-antiquark pair in the intermediate states considered in the Non-Relativistic QCD (NRQCD) factorisation formalism for quarkonium production: $Q\bar{Q}\left[{}^1S_0^{[8]} \right]$ and $Q\bar{Q}\left[{}^1S_0^{[1]} \right]$. These results are necessary for the extension of our resummation formalism beyond DLA.

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arXiv2023

Curing the high-energy perturbative instability of vector-quarkonium-photoproduction cross sections at order $\alpha \alpha_s^3$ with high-energy factorisation

We cure the perturbative instability of the total-inclusive-photoproduction cross sections of vector $S$-wave quarkonia observed at high photon-proton-collision energies ($\sqrt{s_{\gamma p}}$) in Next-to-Leading Order (NLO) Collinear-Factorisation (CF) computations. This is achieved using High-Energy Factorisation (HEF) in the Doubly-Logarithmic Approximation (DLA), which is a subset of the Leading-Logarithmic Approximation (LLA) of HEF which resums higher-order QCD corrections proportional to $\alpha_s^n \ln^{n-1} (\hat{s}/M^2)$ in the Regge limit $\hat{s}\gg M^2$ with $M^2$ being the quarkonium mass and $\hat{s}$ is the squared partonic-center-of-mass energy. Such a DLA is strictly consistent with the NLO and NNLO DGLAP evolutions of the Parton Distribution Functions. By improving the treatment of the large-$\hat{s}$ asymptotics of the CF coefficient function, the resummation cures the unphysical results of the NLO CF calculation. The matching is directly performed in $\hat{s}$ space using the Inverse-Error Weighting matching procedure which avoids any possible double counting. The obtained cross sections are in good agreement with data. In addition, the scale-variation uncertainty of the matched result is significantly reduced compared to the LO results. Our calculations also yield closed-form analytic limits for $\hat{s}\gg M^2$ of the NLO partonic CF and numerical limits for contributions to those at NNLO scaling like $\alpha_s^2 \ln(\hat{s}/M^2)$.

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arXiv2022

White Paper on Forward Physics, BFKL, Saturation Physics and Diffraction

The goal of this whitepaper is to give a comprehensive overview of the rich field of forward physics. We discuss the occurrences of BFKL resummation effects in special final states, such as Mueller-Navelet jets, jet gap jets, and heavy quarkonium production. It further addresses TMD factorization at low x and the manifestation of a semi-hard saturation scale in (generalized) TMD PDFs. More theoretical aspects of low x physics, probes of the quark gluon plasma, as well as the possibility to use photon-hadron collisions at the LHC to constrain hadronic structure at low x, and the resulting complementarity between LHC and the EIC are also presented. We also briefly discuss diffraction at colliders as well as the possibility to explore further the electroweak theory in central exclusive events using the LHC as a photon-photon collider.

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arXiv2021

Matching next-to-leading-order and high-energy-resummed calculations of heavy-quarkonium-hadroproduction cross sections

The energy dependence of the total hadroproduction cross section of pseudo-scalar quarkonia is computed via matching Next-to-Leading Order (NLO) Collinear-Factorisation (CF) results with resummed higher-order corrections, proportional to $\alpha_s^{n}\ln^{n-1}(1/z)$, to the CF hard-scattering coefficient, where $z=M^2/\hat{s}$ with $M$ and $\hat{s}$ being the quarkonium mass and the partonic center-of-mass energy squared. The resummation is performed using High-Energy Factorisation (HEF) in the Doubly-Logarithmic (DL) approximation, which is a subset of the leading logarithmic $\ln (1/z)$ approximation. Doing so, one remains strictly consistent with the NLO and NNLO DGLAP evolution of the PDFs. By improving the treatment of the small-$z$ asymptotics of the CF coefficient function, the resummation cures the unphysical results of the NLO CF calculation. The matching is directly performed in the $z$-space and, for the first time, by using the Inverse-Error Weighting (InEW) matching procedure. As a by-product of the calculation, the NNLO term of the CF hard-scattering coefficient proportional to $\alpha_s^2\ln(1/z)$ is predicted from HEF.

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arXiv2021

Sudakov resummation from the BFKL evolution

The Leding-Logarithmic (LL) gluon Sudakov formfactor is derived from rapidity-ordered BFKL evolution with longitudinal-momentum conservation. This derivation further clarifies the relation between High-Energy and TMD-factorizations and can be extended beyond LL-approximation as well.

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arXiv2020

Estimates for the single-spin asymmetries in $p^{\uparrow}p \to J/\psi X$ process at PHENIX RHIC and SPD NICA

We study the transverse single-spin asymmetry (TSSA) in $p^{\uparrow}p \to J/\psi X$ reaction, incorporating both transverse-momentum and spin effects. To predict production cross section of prompt $J/\psi$ we use two different approaches, the non-relativistic QCD (NRQCD) factorization approach and the Improved Color Evaporation Model (ICEM), and show how the predicted results for TSSAs depend on choice of hadronization model. For initial-state factorization we consider two models: the standard Generalized Parton Model (GPM) and the Colour Gauge-Invariant version of it (CGI-GPM). We demonstrate that PHENIX collaboration data on TSSA in the process $p^{\uparrow}p \to J/\psi X$ constrain the gluon Sivers function of the proton and rule-out one of existing parameterizations. Estimates for the TSSAs in $p^{\uparrow}p \to J/\psi X$ process for the conditions of the future SPD NICA experiment are presented for the first time.

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arXiv2020

Towards stability of NLO corrections in High-Energy Factorization via Modified Multi-Regge Kinematics approximation

The perturbatively-stable scheme of Next-to-Leading order (NLO) calculations of cross-sections for multi-scale hard-processes in DIS-like kinematics is developed in the framework of High-Energy Factorization. The evolution equation for unintegrated PDF, which resums $\log 1/z$-corrections to the coefficient function in the Leading Logarithmic approximation together with a certain subset of Next-to-Leading Logarithmic and Next-to-Leading Power corrections, necessary for the perturbative stability of the formalism, is formulated and solved in the Doubly-Logarithmic approximation. An example of DIS-like process, induced by the operator ${\rm tr}\left[G_{\mu\nu}G^{\mu\nu}\right]$, which is sensitive to gluon PDF already in the LO, is studied. Moderate ($O(20\%)$) NLO corrections to the inclusive structure function are found at small $x_B<10^{-4}$, while for the $p_T$-spectrum of a leading jet in the considered process, NLO corrections are small ($<O(20\%)$) and LO of $k_T$-factorization is a good approximation. The approach can be straightforwardly extended to the case of multi-scale hard processes in $pp$-collisions at high energies.

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