Probing double parton scattering via associated open charm and bottom production in ultraperipheral pApA collisions

In this article, we propose a novel channel for phenomenological studies of the double-parton scattering (DPS) based upon associated production of charm $c\bar{c}$ and bottom $b\bar{b}$ quark pairs in well-separated rapidity intervals in ultra-peripheral high-energy proton-nucleus collisions. This process provides a direct access to the double-gluon distribution in the proton at small-$x$ and enables one to test the factorised DPS pocket formula. We have made the corresponding theoretical predictions for the DPS contribution to this process at typical LHC energies and beyond and we compute the energy-independent (but photon momentum fraction dependent) effective cross section.Comment: 15 pages, 7 figs., 1 table. One fig. added. Version accepted for publication at EPJ

Exclusive heavy quark-pair production in ultraperipheral collisions

In this article, we study the fully differential observables of exclusive production of heavy (charm and bottom) quark pairs in high-energy ultraperipheral $pA$ and $AA$ collisions. In these processes, the nucleus $A$ serves as an efficient source of the photon flux, while the QCD interaction of the produced heavy-quark pair with the target ($p$ or $A$) proceeds via an exchange of gluons in a color singlet state, described by the gluon Wigner distribution. The corresponding predictions for differential cross sections were obtained by using the dipole $S$-matrix in the McLerran--Venugopalan saturation model with impact parameter dependence for the nucleus target, and its recent generalization, for the proton target. Prospects of experimental constraints on the gluon Wigner distribution in this class of reactions are discussed.Comment: 21 pages, 18 figures, improved conclusio

Luminosity indicators in dusty photoionized environments

The luminosity of the central source in ionizing radiation is an essential parameter in a photoionized environment, and one of the most fundamental physical quantities one can measure. We outline a method of determining luminosity for any emission-line region using only infrared data. In dusty environments, grains compete with hydrogen in absorbing continuum radiation. Grains produce infrared emission, and hydrogen produces recombination lines. We have computed a very large variety of photoionization models, using ranges of abundances, grain mixtures, ionizing continua, densities, and ionization parameters. The conditions were appropriate for such diverse objects as H II regions, planetary nebulae, starburst galaxies, and the narrow and broad line regions of active nuclei. The ratio of the total thermal grain emission relative to H$\beta$ (IR/H$\beta$) is the primary indicator of whether the cloud behaves as a classical Str\"{o}mgren sphere (a hydrogen-bounded nebula) or whether grains absorb most of the incident continuum (a dust-bounded nebula). We find two global limits: when $IR/H\beta<100$ infrared recombination lines determine the source luminosity in ionizing photons; when $IR/H\beta\gg100$ the grains act as a bolometer to measure the luminosity.Comment: 12 pages 3 figures. Accepted ASP Sept.9

Exclusive photoproduction of excited quarkonia in ultraperipheral collisions

In this paper, we discuss the exclusive photoproduction of ground and excited states of $\psi(1S,2S)$ and $\Upsilon(1S,2S)$ in ultraperipheral collisions (UPCs). Using the potential model in order to obtain the vector meson wave function, we find a good agreement of our calculations with data from the LHC and HERA colliders for $J/\psi (1S,2S)$ and $\Upsilon(1S)$ in $\gamma p$ collisions. We extend the calculations to the nuclear target case applying them to $AA$ UPCs with the use of the shadowing and finite coherence length effects fitted to the data. Our results are compared to the recent LHC data, in both incoherent ($J/\Psi(1S)$ at 2.76 TeV) and coherent ($J/\Psi(1S)$ at 2.76 and 5.02 TeV) processes. We also show the corresponding predictions for the excited states, in the hope that future measurements could provide more detailed information about the vector meson wave functions and nuclear effects.Comment: 21 pages, 7 figs, revised versio

Exclusive photo- and electroproduction of excited light vector mesons via holographic model

In this paper, we study total and differential observables of electro- and photoproduction of light $\rho$, $\omega$ and $\phi$ mesons as functions of the center-of-mass energy of the $\gamma p$ collision and momentum transfer squared $|t|$. The corresponding vector mesons wave functions have been computed in the framework of relativistic AdS/QCD holographic approach. A satisfactory description of all available data on ground-state $\rho(1S)$, $\omega(1S)$ and $\phi(1S)$ mesons production cross sections has been achieved in the color dipole picture. Finally, the key observables of excited $\rho(2S)$, $\omega(2S)$ and $\phi(2S)$ states production in $\gamma^{(*)} p$ collisions have been presented here using a common wave function formalism. This study reveals a large theoretical uncertainty coming from the modeling of the partial dipole amplitude in the nonperturbative kinematical domain. Hence, the latter could benefit from future measurements of photoproduction of the excited states