The dilepton production at forward rapidities in hadronic collisions at the LHC energies is considered and the helicity density matrix elements of gauge bosons that enter the Drell-Yan angular coefficients associated with the gauge boson decay ($\textit{G}$ = $\textit{γ}$ , $\textit{Z}$ , $\textit{W}$) are derived using the color-dipole $\textit{S}$-matrix framework. We show results for $\textit{pp}$ collisions at $$ \sqrt{s} $$ = 14 TeV for the nonvanishing helicity density matrix elements in the rapidity range of 2.0 ≤ $\textit{y}$ ≤ 4.0 of the gauge boson. We consider different models for the proton unintegrated gluon distributions, among others a solution of the Balitsky-Kovchegov equation. We compare the associated predictions with those obtained disregarding the non-linear term in the evolution equation. In addition, the Lam-Tung relation is discussed.

Brazil

Poland

Yan Bandeira

Victor Gonçalves

Wolfgang Schäfer

Dilepton angular distributions in the color-dipole $\textit{S}$-matrix framework

We discuss inclusive electromagnetic dissociation processes in proton–proton ( <math altimg='si13.svg'><mrow><mi>p</mi><mi>p</mi></mrow></math>) and proton&#8211;nucleus ( <math altimg='si14.svg'><mrow><mi>p</mi><mi>A</mi></mrow></math>) scattering at the LHC where one or both of the protons dissociate. These processes which involve the exchange of a virtual photon in the <math altimg='si15.svg'><mi>t</mi></math>&#8211;channel are calculable in terms of deep inelastic structure functions (virtual photoabsorption cross sections). For the <math altimg='si16.svg'><mrow><mi>p</mi><mi>A</mi><mo>&#8594;</mo><mi>X</mi><mi>A</mi></mrow></math> reaction there emerges the possibility of measuring the total photoabsorption cross section on the proton at very high energies.

Robert Gȩbarowski

Agnieszka Łuszczak

Marta Łuszczak

Photoinduced inclusive cross sections in hadronic collisions at the LHC

The inclusive <math altimg='si1.svg'><msup><mi>D</mi><mn>0</mn></msup></math> photoproduction in <math altimg='si2.svg'><mrow><mi>P</mi><mi>b</mi><mi>P</mi><mi>b</mi></mrow></math> collisions at the center - of - mass energies of the Large Hadron Collider (LHC) is investigated considering the color dipole <math altimg='si5.svg'><mi>S</mi></math> - matrix approach. The analytical expressions for the differential distributions are derived in the impact parameter and transverse momentum spaces and predictions for the rapidity and transverse momentum distributions are presented considering three distinct models for the unintegrated gluon distribution of the nuclear target. In particular, we compare the predictions derived assuming a linear dynamics, with and without the inclusion of nuclear effects, with those obtained by solving the running coupling Balitsky - Kovchegov equation. A comparison of these predictions with the recent (preliminary) CMS data is also performed. Our results indicate that a detailed analysis of this observable will be very useful to improve our understanding of the strong interaction theory at high energies and in a nuclear medium.

Victor P. Gonçalves

Luana Santana

Investigating the inclusive <math altimg='si1.svg'><msup><mi>D</mi><mn>0</mn></msup></math> photoproduction in ultraperipheral <math altimg='si2.svg'><mrow><mi>P</mi><mi>b</mi><mi>P</mi><mi>b</mi></mrow></math> collisions at the Large Hadron Collider

<p>The cross section for the associated production of a jet with an electroweak gauge boson (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>G</mi><mo>=</mo><msup><mrow><mi>W</mi></mrow><mrow><mo>±</mo></mrow></msup><mo>,</mo><msup><mrow><mi>Z</mi></mrow><mrow><mn>0</mn></mrow></msup><mo>,</mo><mi>γ</mi></mrow></math>) at forward rapidities in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>A</mi></math> collisions is derived within the color-dipole <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math>-matrix framework. We present the full expressions for the differential cross section of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>q</mi><mi>p</mi><mo stretchy="false">→</mo><mi>G</mi><mi>q</mi><mi>X</mi></math> process in the transverse momentum space, considering the longitudinal and transverse polarizations of the gauge boson. We demonstrate that the final formulas can be expressed in terms of the unintegrated gluon distribution and reproduce previous results for the associated <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>jet</mi><mo>+</mo><mi>γ</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>jet</mi><mo>+</mo><msup><mrow><mi>Z</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> production, derived using other frameworks. Moreover, we derive the back-to-back correlation limit of the spectra and show that it can be expressed in terms of the unpolarized and linearly polarized transverse momentum gluon distributions. Our results improve the description of the inclusive jet plus color neutral particle production at forward rapidities, not far from the proton fragmentation region, in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>A</mi></math> collisions, and are the main ingredient to study the impact of nonlinear QCD effects in two-particle correlations.</p>

Yan B. Bandeira

Associated <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>jet</mi><mo>+</mo><mtext>electroweak</mtext></mrow></math> gauge boson production in hadronic collisions at forward rapidities in the color-dipole <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math>-matrix framework

We calculate several differential distributions for diffractive dijets production in <math><mrow><mi>e</mi><mi>p</mi><mo>→</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>′</mo></mrow></msup><mi>jet</mi></mrow></math> <math><mrow><mi>jet</mi><mi>p</mi></mrow></math> in the perturbative QCD dipole approach using off diagonal unintegrated gluon distributions (generalized transverse momentum dependent distributions, GTMDs). Different models from the literature are used. We concentrate on the contribution from exclusive <math><mi>q</mi><mover><mi>q</mi><mo>¯</mo></mover></math> dijets. Results of our calculations are compared to H1 and ZEUS data, including specific experimental cuts in our calculations. In general, except for one GTMD, our results are below the HERA data. The considered mechanism is expected to gives a sizeable contribution to the ZEUS data, while it is negligible in the kinematics of the H1 measurement. This is in contrast to recent results from the literature where the normalization was adjusted to some selected distributions of the H1 collaboration and no agreement with other observables was checked. The ZEUS data provide stricter limitations on the GTMDs than the H1 data. We conclude, based on comparison to different observables, that the calculated cross sections are only a small fraction of the measured ones which contain probably also processes with pomeron remnant. Alternatively one could try to explain the experimental data by inclusion of <math><mi>q</mi><mover><mi>q</mi><mo>¯</mo></mover><mi>g</mi></math> component of the photon wave function. We present also azimuthal correlations between the sum and the difference of dijet transverse momenta. The cuts on transverse momenta of jets generate corresponding azimuthal correlations that can be misidentified as due to elliptic gluon distributions.

Barbara Linek

Antoni Szczurek

Probing gluon GTMDs of the proton in deep inelastic diffractive dijet production at HERA

In this brief note, we confront our results on diffractive photoproduction of <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> mesons with the putative gluon shadowing ratio defined as <math><msub><mrow><mi>R</mi></mrow><mrow><mi>g</mi></mrow></msub><mo>=</mo><msqrt><mrow><mi>σ</mi><mo>(</mo><mi>γ</mi><mi>A</mi><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><mi>A</mi><mo>)</mo><mo>/</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>IA</mi><mo>.</mo></mrow></msub></mrow></msqrt></math>, where <math><msub><mrow><mi>σ</mi></mrow><mrow><mi>IA</mi></mrow></msub></math> is the result in impulse approximation. Building on our earlier description of the process in the color-dipole approach, where we took into account the rescattering of <math><mi>c</mi><mover><mrow><mi>c</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> states only, we demonstrate that the inclusion of <math><mi>c</mi><mover><mrow><mi>c</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>g</mi></math>-Fock states improves the description at small x commonly associated with gluon shadowing.

Gluon shadowing in nuclei and the role of the State in the Coherent Photoproduction of / In Nucleus-nucleus Collisions

The cross-section for the production of an electroweak gauge boson (G = W  ± , Z 0, γ) at forward rapidities in pp collisions is derived within the color-dipole S-matrix framework. We present the full expressions for the differential cross-section of the qp → GX process in the impact parameter and transverse momentum spaces, considering the longitudinal and transverse polarizations of the gauge boson. The particular cases associated with the Drell-Yan process and real photon production are discussed. We demonstrate that the final formulae are expressed in terms of the dipole-proton cross-section or the unintegrated gluon distribution, and can be used to estimate the impact of the saturation effects in the gauge boson production at the LHC and future colliders.

China

Production of electroweak gauge bosons at forward rapidities in the color-dipole S-matrix framework

We continue our work on the light-front formulation of quarkonium γ ∗ γ transition form factors, extending the formalism to J  PC  = 2++ tensor meson states. We present an analysis of γ ∗ γ → χ  c2 transition amplitude and the pertinent helicity form factors. Our relativistic formalism is based on the light-front quark-antiquark wave function of the quarkonium. We calculate the two-photon decay width as well as three independent γ ∗ γ transition form factors for J  z  = 0, 1, 2 as a function of photon virtuality Q 2. We compare our results for the two-photon decay width to the recently measured ones by the Belle and BES III collaborations. Even when including relativistic corrections, a very small Γ(λ = 0)/Γ(λ = 2) ~ 10 −3 ratio is found which is beyond present experimental precision. We also present the form factors as a function of photon virtuality and compare them to the sparse experimental data on the so-called off-shell width. The formalism presented here can be used for other 2++ mesons, excited charmonia or bottomonia or even light   <math> <mi>q</mi> <mover> <mi>q</mi> <mo>¯</mo> </mover> </math>  $$ q\overline{q} $$ -mesons.

Izabela Babiarz

Sweden

Roman Pasechnik

χ  c2 tensor meson transition form factors in the light front approach

One of the main goals of future electron-ion colliders is to improve our understanding of the structure of hadrons. In this letter, we study the exclusive <math><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub></math> production by <math><msup><mrow><mi>γ</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mi>γ</mi></math> interactions in eA collisions and demonstrate that future experimental analysis of this process can be used to improve the description of the <math><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub></math> transition form factor. The rapidity, transverse momentum and photon virtuality distributions are estimated considering the energy and target configurations expected to be present at the EIC, EicC and LHeC and assuming different predictions for the light-front wave function of the <math><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub></math> meson. Our results indicate that the electron-ion colliders can be considered an alternative to providing supplementary data to those obtained in <math><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup></math> colliders.

Germany

Victor P. Goncalves

Exclusive Production by Interactions in Electron-ion Collisions

We study the exclusive diffractive   <math> <mi>c</mi> <mover> <mi>c</mi> <mo>¯</mo> </mover> </math>  $$ c\overline{c} $$  photoproduction in ultraperipheral pA collisions. The formalism makes use of off-diagonal generalizations of the unintegrated gluon distribution, the so-called generalized transverse momentum dependent distributions (GTMDs). We present two different formulations. The first one is based directly on gluon GTMD parametrizations in momentum space. Another option is the calculation of the GTMD as a Fourier transform of the dipole-nucleon scattering amplitude N(Y,   <math> <mover> <mi>r</mi> <mo>→</mo> </mover> </math>  $$ \overrightarrow{r} $$  ⊥,   <math> <mover> <mi>b</mi> <mo>→</mo> </mover> </math>  $$ \overrightarrow{b} $$  ⊥). The latter approach requires some extra regularization discussed in the paper. Different dipole amplitudes from the literature are used. Compared to previous calculations in the literature, we integrate over the full phase space and therefore cross sections for realistic conditions are obtained. We present distributions in rapidity of c or   <math> <mover> <mi>c</mi> <mo>¯</mo> </mover> </math>  $$ \overline{c} $$ , transverse momentum of the   <math> <mi>c</mi> <mover> <mi>c</mi> <mo>¯</mo> </mover> </math>  $$ c\overline{c} $$  pair, four-momentum transfer squared as well as the azimuthal correlation between a sum and a difference of the c and   <math> <mover> <mi>c</mi> <mo>¯</mo> </mover> </math>  $$ \overline{c} $$  transverse momenta. The azimuthal correlations are partially due to the so-called elliptic gluon Wigner distribution. Different models lead to different modulations in the azimuthal angle. The modulations are generally smaller than 5%. They depend on the range of transverse momentum selected for the calculation.

Probing proton structure with   <math> <mi>c</mi> <mover> <mi>c</mi> <mo>¯</mo> </mover> </math>  $$ \textrm{c}\overline{\textrm{c}} $$  correlations in ultraperipheral pA collisions