The importance of kinematic twists and genuine saturation effects in dijet production at the Electron-Ion Collider

Abstract

We compute the differential yield for quark anti-quark dijet production in high-energy electron-proton and electron-nucleus collisions at small x as a function of the relative momentum P⊥ and momentum imbalance k⊥ of the dijet system for different photon virtualities Q2, and study the elliptic and quadrangular anisotropies in the relative angle between P⊥ and k⊥. We review and extend the analysis in [1], which compared the results of the Color Glass Condensate (CGC) with those obtained using the transverse momentum dependent (TMD) framework. In particular, we include in our comparison the improved TMD (ITMD) framework, which resums kinematic power corrections of the ratio k⊥ over the hard scale Q⊥. By comparing ITMD and CGC results we are able to isolate genuine higher saturation contributions in the ratio Qs/Q⊥ which are resummed only in the CGC. These saturation contributions are in addition to those in the Weizsäcker-Williams gluon TMD that appear in powers of Qs/k⊥. We provide numerical estimates of these contributions for inclusive dijet production at the future Electron-Ion Collider, and identify kinematic windows where they can become relevant in the measurement of dijet and dihadron azimuthal correlations. We argue that such measurements will allow the detailed experimental study of both kinematic power corrections and genuine gluon saturation effects.

Dijet impact factor in DIS at next-to-leading order in the Color Glass Condensate

“…Recent numerical studies at leading order [55,[93][94][95][96] suggest the importance of kinematic power [97][98][99] and genuine saturation effects [100][101][102] at kinematics accessible at current and future colliders.…”

“…This DIS process off the proton, and in large nuclei, is of great phenomenological interest at the future EIC. The computation of the impact factor to NLO accuracy can provide novel information on the effects of gluon saturation in back-to-back dihadron/dijets [51], the JHEP11(2021)222 study of the Weizsäcker-Williams gluon distribution [52,53] and in the extraction of a fundamental building block of high energy QCD -the quadrupole correlator of Wilson lines at small x [54,55].…”

Azimuthal Angular Asymmetry of Soft Gluon Radiation in Jet Production

“…7) that the inclusion of power corrections in the soft emission kernel results in a better agreement with the CMS data in the large-q ⊥ region. The importance of power corrections in the hard part for the extraction of the linearly polarized gluon distribution has been discussed recently [108,109]. A combined analysis of re-summation and power-corrections seems to be necessary to correctly interpret the experimental data.…”

“…The gauge link L v is constructed in the adjoint representation and depends on the process [115]. For an unpolarized nucleon at leading twist, the above matrix element contains two independent TMD gluon distributions 1 Recent studies [108,109] show that power-corrections in the hard part can also affect the cos(2φ) asymmetry from the linearly polarized gluon distribution .…”

Small x Improved Transverse Momentum Dependent Factorization and some of its recent applications

“…While in the paper [18] the ITMD was generalized to account for masses of produced hadrons as well as longitudinally polarized gluons (see also [19] for discussion of the role of transverse gauge links). Furthermore in the papers [20,21] the ITMD was shown to agree very well with full CGS results (accounting on top of kinematical twist for genuine twist effects) in the region dominated by hard jets i.e. k T , p T > Q s While the original ITMD formula, as well as the works studying the jet correlation limit within CGC, include gluon saturation effects, they do not account for all contributions proportional to logarithms of the hard scale set by the large transverse momenta of jets -the so-called Sudakov logarithms.…”