Photoproduction of three jets in the CGC: gluon TMDs and dilute limit

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For studying small-x gluon saturation in forward dijet production in high-energy dilute-dense collisions, the improved TMD (ITMD) factorization formula was recently proposed. In the Color Glass Condensate (CGC) framework, it represents the leading term of an expansion in inverse powers of the hard scale. It contains the leading-twist TMD factorization formula relevant for small gluon’s transverse momentum kt, but also incorporates an all-order resummation of kinematical twists, resulting in a proper matching to high-energy factorization at large kt. In this paper, we evaluate the accuracy of the ITMD formula quantitatively, for the case of quark dijet production in high-energy proton-proton(p+p) and proton-nucleus (p+A) collisions at LHC energies. We do so by comparing the quark-antiquark azimuthal angle ∆ϕ distribution to that obtained with the CGC formula. For a dijet with each quark momentum pt much larger than the target saturation scale, Qs, the ITMD formula is a good approximation to the CGC formula in a wide range of azimuthal angle. It becomes less accurate as the jet pt’s are lowered, as expected, due to the presence of genuine higher-twists contributions in the CGC framework, which represent multi-body scattering effects absent in the ITMD formula. We find that, as the hard jet momenta are lowered, the accuracy of ITMD start by deteriorating at small angles, in the high-energy-factorization regime, while in the TMD regime near ∆ϕ = π, very low values of pt are needed to see differences between the CGC and the ITMD formula. In addition, the genuine twists corrections to ITMD become visible for higher values of pt in p + A collisions, compared to p+p collisions, signaling that they are enhanced by the target saturation scale.

Section: Jhep12(2020)181mentioning

confidence: 99%

Comparison of improved TMD and CGC frameworks in forward quark dijet production

Fujii¹,

Marquet²,

Watanabe³

2020

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“…In the end, let us note that at present, the ITMD formalism does not account for the linearly-polarized gluons in unpolarized target. In CGC theory, such a contribution is absent for massless two-particle production, but appears in heavy quark production [44] and will appear in higher multiplicity processes as it has been already observed in the correlation limit for three-parton final state [45] basing on the quark-initiated three-jet production formulae in CGC [46].…”

Section: Introductionmentioning

confidence: 71%

Forward trijet production in p-p and p-Pb collisions at LHC

Bury

Hameren

Kotko

et al. 2020

We calculate various azimuthal angle distributions for three jets produced in the forward rapidity region with transverse momenta pT> 20 GeV in proton-proton (p-p) and proton-lead (p-Pb) collisions at center of mass energy 5.02 TeV. We use the multiparton extension of the so-called small-x Improved Transverse Momentum Dependent factorization (ITMD). We study effects related to change from the standard kT -factorization to ITMD factorization as well as changes as one goes from p-p collision to p-Pb. We observe rather large differences in the distribution when we change the factorization approach, which allows to both improve the small-x TMD gluon distributions as well as validate and improve the factorization approach. We also see significant depletion of the nuclear modification ratio, indicating a possibility of searches for saturation effects using trijet final states in a more exclusive way than for dijets.

“…The many unpolarized gluon TMDs involved in that process were obtained in [41], and the associated H ns (c) matrix elements were computed numerically in [20]. From studies of the TMD limit of other three-particle processes [42][43][44], it is known that the missing H h (c) 's are nonzero, and we would like to assess how important they are, in processes where we do know them.…”

Section: Numerical Comparison Between the Itmd* And Itmd Frameworkmentioning

confidence: 99%

Low-x improved TMD approach to the lepto- and hadroproduction of a heavy-quark pair

Altinoluk

Marquet

Taels

2021

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We study the lepto- and hadroproduction of a heavy-quark pair in the ITMD factorization framework for dilute-dense collisions. Due to the presence of a nonzero quark mass and/or nonzero photon virtuality, new contributions appear compared to the cases of photo- and hadroproduction of dijets, for which the ITMD framework was originally derived. These extra terms are sensitive to gluons that are not fully linearly polarized. At small x, those gluons emerge only when all saturation effects are carefully taken into account. Therefore, the resulting contributions are absent in linear small-x frameworks, where gluons are fully linearly polarized. We show, however, that even for large gluon transverse momentum, these contributions are not always negligible, due to the behavior of the off-shell hard factors.