Sudakov effects in central-forward dijet production in high energy factorization

TL;DR

The paper addresses central-forward dijet production at the LHC, where both small-$x$ dynamics and Sudakov soft-gluon resummation are important. It adopts high energy factorization with off-shell matrix elements and two primary gluon TMDs, incorporating BK evolution with a kinematic constraint and a first-principles Sudakov factor for the dominant channels $qg\to qg$ and $gg\to gg$. The authors compute differential cross sections and azimuthal decorrelations, compare to CMS data, and demonstrate improved agreement over previous simplistic Sudakov models while providing publicly available KS gluon distributions. They find that Sudakov effects mostly influence the decorrelation shape and have a moderate impact on $p_T$ spectra, with saturation playing a smaller role in central-forward $p$-$p$ collisions. The work offers a theoretically robust framework for unifying Sudakov resummation with small-$x$ dynamics in HEF, with potential applications to forward-forward dijets and DIS at future facilities like the EIC.

Abstract

We discuss central-forward dijet production at LHC energies within the framework of high energy factorization. In our study, we profit from the recent progress on consistent merging of Sudakov resummation with small-$x$ effects, which allows us to compute two different gluon distributions which depend on longitudinal momentum, transverse momentum and the hard scale of the process: one for the quark channel and one for the gluon channel. The small-$x$ resummation is included by means of the BK equation supplemented with a kinematic constraint and subleading corrections. We test the new gluon distributions against existing CMS data for transverse momentum spectra in forward-central dijet production. We obtain results which are largely consistent with our earlier predictions based on model implementation of Sudakov form factors. In addition, we study dijet azimuthal decorrelations for the forward-central jets, which are known to be sensitive to the modeling of soft radiation.

Figures (5)

• Figure 1: KS gluon distribution, Eq. (\ref{['eq:gluon-dff']}) without and with the Sudakov form factors. The second row corresponds to the simple model-Sudakov given in Eq. (\ref{['eq:survival']}), while the third and the fourth rows show results obtained with the Sudakov factors derived from QCD and given in Eqs. (\ref{['eq:sudpertqg']}), (\ref{['eq:sudnpqg']}), and (\ref{['eq:sudpertgg']}), (\ref{['eq:sudnpgg']}), respectively.
• Figure 2: Distributions of the longitudinal momentum fractions, $x_A$, $x_B$, defined in Eq. (\ref{['eq:xAxB']}) from calculations with various version of the KS gluon distribution discussed in the article.
• Figure 3: The transverse momentum spectra of the central (left) and the forward (right) jets obtained with the KS gluon distribution, with and without Sudakov effects, computed for the central value of the factorization and renormalization scale, compared to CMS data Chatrchyan:2012gwa.
• Figure 4: As Fig. \ref{['fig:ptdist1']} but we only show predictions obtained with the original KS gluon distribution and the predictions with the KS gluon distribution with Sudakov from this work. The bands correspond to varying the renormalization and factorization scale by factors $2^{\pm 1}$.
• Figure 5: Differential cross sections as functions of the azimuthal distance between the jets $\Delta\phi$ (left) and jet rapidities (right) obtained with the KS gluon distribution with and without Sudakov effects.