Transverse Momentum Dependent Quark Research Articles

Unpolarized transverse-momentum-dependent sea quark asymmetries of light nuclei in nonperturbative QCD

We investigate the transverse-momentum dependence of sea quark asymmetries in helium and deuteron nuclei. Accordingly, we calculate the nuclear sea quark distributions, in the first step, based on the modified chiral quark exchange formalism at the low Q 2 scale (Q 2 = 0.35 GeV2) in the nonperturbative region of quantum chromodynamics. In this formalism, the sea quark distributions are not symmetric because of chiral symmetry breaking. In the next step, we compute the transverse-momentum dependence of sea quark distributions using the covariant parton model, in which the unpolarized transverse-momentum-dependent (TMD) quark distribution functions are related to corresponding integrated ones. Finally, we obtain TMD quark–antiquark asymmetry of the strange sea for 3 He and deuteron, and also asymmetry for 3 He. To study the European Muon Collaboration (EMC) effect in the 3 He nucleus, we determine the ratio of the TMD strange sea asymmetries of 3 He and deuteron.

T-odd quark-gluon-quark correlation function in the light-front quark-diquark model

We have scrutinized the transverse momentum dependent quark–gluon–quark correlation function. We have utilized the light-front quark-diquark model to study the time-reversal-odd interaction-dependent twist-3 gluon distributions which we have obtained from the disintegration of the transverse momentum dependent quark–gluon–quark correlator. Specifically, we have studied the behavior of \tilde{e}_{L}ẽL and \tilde{e}_{T}ẽT while considering our diquark to be an axial-vector.

Lepton-Jet Correlations in Deep Inelastic Scattering at the Electron-Ion Collider.

We propose the lepton-jet correlation in deep inelastic scattering as a unique tool for the tomography of nucleons and nuclei at the electron-ion collider (EIC). The azimuthal angular correlation between the final state lepton and jet depends on the transverse momentum dependent quark distributions. We take the example of single transverse spin asymmetries to show the sensitivity to the quark Sivers function. When the correlation is studied in lepton-nucleus collisions, transverse momentum broadening effects can be used to explore cold nuclear matter effects. These features make lepton-jet correlations an important new hard probe at the EIC.

Employing RHIC and LHC data to determine the transverse momentum dependent gluon density in a proton

Transverse momentum dependent (TMD) parton distributions in a proton are important in high energy physics from both theoretical and phenomenological points of view. Using the latest RHIC and LHC data on the inclusive soft hadron production in $pp$ and $AA$ collisions at small transverse momenta, we determine the parameters of the initial TMD gluon density, derived in the framework of quark-gluon string model at the low scale $\mu_0 \sim 1 - 2$ GeV and refine its large-$x$ behaviour using the LHC data on the $t \bar t$ production at $\sqrt s = 13$ TeV. Then, we apply the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation to extend the obtained TMD gluon density to the whole kinematical region. In addition, the complementary TMD valence and sea quark distributions are generated. The latter are evaluated in the approximation where the gluon-to-quark splitting occurs at the last evolution step using the TMD gluon-to-quark splitting function. Several phenomenological applications of the proposed TMD quark and gluon densities to the LHC processes are discussed.

Nonperturbative functions for SIDIS and Drell–Yan processes

We update the well-known BLNY fit to the low transverse momentum Drell–Yan lepton pair productions in hadronic collisions, by considering the constraints from the semi-inclusive hadron production in deep inelastic scattering (SIDIS) from HERMES and COMPASS experiments. We follow the Collins–Soper–Sterman (CSS) formalism with the [Formula: see text]-prescription. A nonperturbative form factor associated with the transverse momentum dependent quark distributions is found in the analysis with a new functional form different from that of BLNY. This releases the tension between the BLNY fit to the Drell–Yan data with the SIDIS data from HERMES/COMPASS in the CSS resummation formalism.

Collinear and TMD quark and gluon densities from parton branching solution of QCD evolution equations

We study parton-branching solutions of QCD evolution equations and present a method to construct both collinear and transverse momentum dependent (TMD) parton densities from this approach. We work with next-to-leading-order (NLO) accuracy in the strong coupling. Using the unitarity picture in terms of resolvable and non-resolvable branchings, we analyze the role of the soft-gluon resolution scale in the evolution equations. For longitudinal momentum distributions, we find agreement of our numerical calculations with existing evolution programs at the level of better than 1% over a range of five orders of magnitude both in evolution scale and in longitudinal momentum fraction. We make predictions for the evolution of transverse momentum distributions. We perform fits to the high-precision deep inelastic scattering (DIS) structure function measurements, and we present a set of NLO TMD distributions based on the parton branching approach.

Transverse momentum dependent quark and gluon distributions of light nuclei

We investigate the unpolarized transverse momentum dependent (TMD) structure of light nuclei in the modified chiral quark exchange model (QEM), for the first time. To this end, we calculate the TMD quark and gluon distributions inside the bound state nucleons of the light nuclei based on the modified chiral quark model in which the TMD bare quark distributions of the bounded nucleons are needed. In order to compute these bare distributions, we first obtain the bare quark momentum densities using the QEM and then calculate the TMD bare distributions applying a theoretical method in which the light-cone variables are used. Finally, considering the nucleon structure of helium, tritium and deuteron nuclei, we obtain their TMD quark and gluon densities at low Q2 scale. It is shown that our results have appropriate properties that are expected for the TMD distribution functions.

Impact of gluon polarization on Higgs boson plus jet production at the LHC

In this paper we consider Higgs boson plus jet production as a process that is sensitive to the linear polarization of gluons inside the unpolarized protons of the LHC. The leading order expressions for the transverse momentum distribution of the Higgs boson plus jet pair are provided in terms of transverse momentum dependent quark and gluon distributions. This includes both angular independent and azimuthal angular dependent contributions, presented directly in the laboratory frame. Lacking experimental constraints on the linearly polarized gluon distribution, we study its effects on Higgs boson plus jet production using two different models to illustrate the generic features and maximal effects. It is found that the $\mathrm{cos}2\ensuremath{\phi}$ distribution may be the most promising observable, as it is driven by only one initial linearly polarized gluon. The potential advantages of the Higgs boson plus jet process compared to other processes sensitive to the linear polarization of gluons are discussed.

Unpolarized transverse momentum-dependent densities based on the modified chiral quark model

We investigate the transverse momentum-dependent (TMD) quark and gluon distribution functions in the modified chiral quark model (χQM). Calculations of the TMD quark and gluon densities, using the modified χQM, are carried out for the first time in this article. For this propose, we first formulate the TMD interactions that occur in the χQM at low Q 2 scale (Q 2 = 0.35 GeV2) and then obtain the TMD parton distributions inside the proton, considering these interactions. To this end, we need to compute the TMD bare quark distributions. These TMD bare densities are calculated using the solution of the Dirac equation with a squared radial symmetry potential. It is shown that our results present appropriate behavior, which is expected for the TMD parton distributions.

Drell-Yan lepton pair production at the LHC and transverse momentum dependent quark densities of the proton

We consider the transverse momentum dependent (TMD) quark densities of the proton which are very important ingredients for unpolarized Drell-Yan lepton pair production in proton-proton collisions at the LHC energies. We investigate the case where the gluon-to-quark splitting occurs at the last evolution step and calculate the TMD sea quark density as a convolution of the Catani-Ciafaloni-Fiorani-Marchesini-evolved gluon distribution and the TMD gluon-to-quark splitting function. This splitting function contains all single logarithmic small-$x$ corrections to the sea quark evolution for any order of perturbation theory. Based on the $\mathcal{O}(\ensuremath{\alpha})$ production amplitude ${q}^{*}+{\overline{q}}^{*}\ensuremath{\rightarrow}Z/{\ensuremath{\gamma}}^{*}\ensuremath{\rightarrow}{l}^{+}+{l}^{\ensuremath{-}}$, calculated by taking into account the effective ${q}^{*}{\overline{q}}^{*}Z/{\ensuremath{\gamma}}^{*}$ vertex, we analyze the distributions on the dilepton invariant mass, transverse momentum and rapidity and specific angular correlations between the produced leptons as measured by the CMS, ATLAS and LHCb collaborations. We show that our predictions are sensitive to the TMD quark distributions of the proton.

T-odd quark–gluon–quark correlation function in the diquark model

We study the transverse momentum dependent quark–gluon–quark correlation function. Using a spectator diquark model, we calculate the eight time-reversal-odd interaction-dependent twist-3 quark distributions appearing in the decomposition of the transverse momentum dependent quark–gluon–quark correlator. In order to obtain finite results, we assume a dipole form factor for the nucleon–quark–diquark coupling, instead of a point-like coupling. The results are compared with the time-reversal-odd interaction-independent twist-3 TMDs calculated in the same model.

Recent results from the HERMES experiment

Results are presented from the Hermes experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon. Data have been accumulated for pion and kaon double spin asymmetries, single-spin azimuthal asymmetries for meson electroproduction, deep virtual Compton scattering (DVCS), and meson multiplicities. These results provide information on the properties of the strange sea in the proton, constraints on transverse momentum dependent quark parton distributions, and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton.

Nuclear dependence of azimuthal asymmetry in semi-inclusive deep inelastic scattering

Within the framework of a generalized factorization, semi-inclusive deeply inelastic scattering (SIDIS) cross sections can be expressed as a series of products of collinear hard parts and transverse-momentum-dependent (TMD) parton distributions and correlations. The azimuthal asymmetry <cos\phi>$ of unpolarized SIDIS in the small transverse momentum region will depend on both twist-2 and 3 TMD quark distributions in target nucleons or nuclei. Nuclear broadening of these twist-2 and 3 quark distributions due to final-state multiple scattering in nuclei is investigated and the nuclear dependence of the azimuthal asymmetry $<\cos\phi>$ is studied. It is shown that the azimuthal asymmetry is suppressed by multiple parton scattering and the transverse momentum dependence of the suppression depends on the relative shape of the twist-2 and 3 quark distributions in the nucleon. A Gaussian ansatz for TMD twist-2 and 3 quark distributions in nucleon is used to demonstrate the nuclear dependence of the azimuthal asymmetry and to estimate the smearing effect due to fragmentation.