arXiv subjects

V. P. Goncalves

Publications and source records attributed to V. P. Goncalves.

At least 19 recordsLinked to original sources

arXiv2026

Effect of sub-nucleon fluctuations on the DVCS process in proton and nuclear targets at the EIC

The impact of the sub - nucleon fluctuations on the Deeply Virtual Compton Scattering (DVCS) process at the Electron - Ion Collider (EIC) is investigated considering proton and nuclear targets. Assuming the hot - spot model, we estimate the energy dependence of the coherent and incoherent cross - sections for different values of the photon virtuality and atomic number. Predictions for the $t$ - distributions are also presented. We demonstrate that the sub - nucleon fluctuations in the proton, as described by the hot - spot model, implies a turn - over in the energy dependence of the incoherent cross - section, with the position of the maximum being dependent of the photon virtuality. Our results indicate that the ratio between the coherent and incoherent cross - sections increases with energy, atomic numbers and for smaller values of $Q^2$. Moreover, we predict a maximum in the $t$ - distribution of the nuclear incoherent cross - section at a fixed center - of - mass energy, which is dependent on the atomic number and $Q^2$.

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arXiv2023

Production of fully-heavy tetraquark states through the double parton scattering mechanism in $pp$ and $pA$ collisions

The production of fully-heavy tetraquark states in proton-proton ($pp$) and proton-nucleus ($pA$) collisions at the center-of-mass energies of the Large Hadron Collider (LHC) and at the Future Circular Collider (FCC) is investigated considering that these states are produced through the double parton scattering mechanism. We estimate the cross sections for the $T_{4c}$, $T_{4b}$ and $T_{2b2c}$ states and present predictions for $pp$, $pCa$ and $pPb$ collisions considering the rapidity ranges covered by central and forward detectors. We demonstrate that the cross sections for $pA$ collisions are enhanced in comparison to the $pp$ predictions scaled by the atomic number. Moreover, our results indicate that a search of these exotic states is, in principle, feasible in the future runs of the LHC and FCC.

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arXiv2023

Timelike Compton scattering in ultraperipheral $pPb$ collisions

The study of exclusive processes in photon - induced interactions allow us to probe the generalized parton distributions (GPDs), which provide information about the 3 dimensional description of the quark and gluon content of hadrons. In this paper we investigate the timelike Compton scattering (TCS) in ultraperipheral $pPb$ collisions at the LHC. Such process is characterized by the exclusive dilepton production through the subprocess $γp \rightarrow γ^*p \rightarrow l^+ l^- p$, with the real photon in the initial state being emitted by the nucleus. Assuming a given model for the GPDs, the TCS differential cross section is estimated as well the contribution associated to the interference between the TCS and Bethe - Heitler (BH) amplitudes. Predictions for the TCS, BH and interference contributions are presented considering the kinematical range covered by the LHC detectors.

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arXiv2022

Electrically charged supermassive twin stars

By assuming that ultra dense hybrid neutron stars are endowed with a distribution of electric charge, we study the corresponding twin star solutions and their properties resulting from a sharp first order transition from confined hadronic to a deconfined quark phase. Two distinct quark matter equations of state with increasing stiffness are considered and the values for the maximum gravitational masses of the hadronic and hybrid twin configurations are obtained for different values of the total electric charge. Interestingly, our calculations indicate that sharp transitions make charged twin hybrid stars more massive than their neutral counterparts, and that the {$\SI{2}{M_{\odot}}$ constraint from PSR J0740+6620} is surpassed for standard values of electric charge and can be considered stable only satisfying $\partial M/\partial ε_0 > 0$. In particular, our charged stellar models reach masses even higher than the unknown compact object measured in the GW190814 event.

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arXiv2021

Photoproduction of relativistic QED bound states in hadronic collisions

In this paper we investigate the photoproduction of QED bound states in proton -- proton, proton -- nucleus and nucleus -- nucleus collisions at RHIC, LHC and FCC energies considering an accurate treatment of the absorptive corrections and for the nuclear form factor. The total cross sections for the production of singlet and triplet $(l^+ l^-)$ states, with $l = e,\, μ, \, τ$, are estimated and a detailed analysis of the photoproduction of singlet QED bound states is performed considering the rapidity ranges covered by central and forward detectors. The impact of the Coulomb corrections on the parapositronium production in heavy ion collisions is estimated. We predict a large number of events associated to the production of ($e^+ e^-$) and ($μ^+ μ^-$) states in hadronic collisions.

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arXiv2021

Searching for axionlike particles with low masses in $pPb$ and $PbPb$ collisions

The production of axionlike particles (ALPs) with small masses in ultraperipheral $Pb - p$ and $Pb - Pb$ collisions at the LHC is investigated. The cross section and kinematical distributions associated to the diphoton final state produced in the $γγ\rightarrow a \rightarrow γγ$ subprocesses are estimated considering a realistic set of kinematical cuts. A detailed analysis of the backgrounds is performed and the expected sensitivity to the ALP production is derived. Our results demonstrate that a future experimental analysis of the exclusive diphoton production for the forward rapidities probed by the LHCb detector can improve the existing exclusion limits on the ALP - photon coupling in the mass range 2 GeV $\le m_a \le$ 5 GeV.

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arXiv2021

Non-exclusive particle production by $γγ$ interactions in $pp$ collisions at the LHC

Particle production in two-photon interactions at hadronic collisions is becoming increasingly relevant in the LHC physics programme as a way to improve our understanding of the Standard Model and search for signals of New Physics. A key ingredient for the study of these interactions in $pp$ collisions is the description of the photon content of the proton, which allow us to derive predictions for the cross sections associated to events where occur the proton dissociation (non - exclusive processes) and for those where both incident protons remain intact (exclusive processes). In this paper, a detailed comparison of the different models for the elastic and inelastic photon distributions found in the literature is presented and the current theoretical uncertainty is estimated. The impact on the invariant mass distribution for the dimuon production is analyzed. Moreover, the relative contribution of non - exclusive events is estimated and its dependence on the invariant mass of the pair is presented. We demonstrate that the predictions for production of pairs with large invariant mass is strongly dependent on the model assumed to describe the elastic and inelastic photon distributions and that the ratio between non - exclusive and exclusive cross sections present a mild energy dependence. Finally, our results indicate that a future experimental analysis of the non - exclusive events will be useful to constrain the photon content of proton.

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arXiv2020

Exclusive axionlike particle production by gluon -- induced interactions in hadronic collisions

The exclusive production of axionlike particles (ALPs) by gluon -- induced interactions is investigated in this exploratory study considering $pp$ and $PbPb$ collisions for the energies of the next run of the Large Hadron Collider (LHC). Assuming the Duhram model, we estimate the associated cross sections for the rapidity ranges probed by central and forward detectors. A comparison with the predictions for the exclusive ALP production by photon -- induced interactions is presented. Our results indicate that the contribution of gluon -- induced interactions is nonnegligible and can become dominant in $pp$ collisions for small values of the ALP mass.

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arXiv2020

Diffractive deeply inelastic scattering in future electron-ion colliders

The impact of nonlinear effects in the diffractive observables that will be measured in future electron-ion collisions is investigated. We present, for the first time, the predictions for the diffractive structure function and reduced cross sections derived using the solution to the Balitsky--Kovchegov equation with the collinearly-improved kernel and including the impact-parameter dependence. We demonstrate that the contribution of the diffractive events is enhanced in nuclear collisions and that the study of the ratio between the nuclear and proton predictions will be useful to discriminate among different models of the dipole-target scattering amplitude and, consequently, will allow us to constrain the description of QCD dynamics in parton densities.

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arXiv2020

Diffractive $γγ$ production in $pp$ collisions at the LHC

In this letter we estimate the contribution of the double diffractive processes for the diphoton production in $pp$ collisions at the Large Hadron Collider (LHC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity and, transverse momentum distributions are presented. A comparison with the predictions for the Light -- by -- Light (LbL) scattering and exclusive diphoton production is performed. We demonstrate that the events associated to double diffractive processes can be separated and its study can be used to constrain the behavior of the diffractive parton distribution functions.

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arXiv2020

Electrically charged strange stars with an interacting quark matter equation of state

The properties of electrically charged strange quark stars predicted by an interacting quark matter equation of state (EoS) based on cold and dense perturbative quantum chromodynamics (pQCD) are investigated. The stability of strange stars is analyzed considering different models for the electric charge distribution inside the star as well as for distinct values for the total electric charge. A comparison with the predictions derived using the MIT bag model is also presented. We show that the presence of a net electric charge inside strange stars implies in a larger maximum mass in comparison to their neutral counterparts. Moreover, we demonstrate that the pQCD EoS implies larger values for the maximum mass of charged strange stars, with very heavy charged stars being stable systems against radial oscillations. For an electric charge distribution given by $q(r) = βr^3$, the pQCD EoS implies unstable configurations for large values of the renormalization scale as well as for large values of $β$, in contrast to the MIT bag model predictions.

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arXiv2020

Thermal radiation and inclusive production in the running coupling $k_T$ -- factorization approach

The characteristics of the thermal radiation are investigated using a two - component model, with the hard component being described by the Color Glass Condensate formalism. The inclusive transverse momentum spectra of charged hadrons produced in proton - proton and proton - nucleus collisions at LHC energies and large - $p_T$ are estimated using the running coupling $k_T$ - factorization formula and the solution of the Balitsky - Kovchegov equation. Our results indicate that the thermal term is necessary to describe the experimental data and that the effective thermal temperature has an energy dependence similar to the saturation scale. We demonstrate that the enhancement of the thermal temperature in $pPb$ collisions is consistent with that predicted by the saturation scale.

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arXiv2020

Dark photons from pions produced in ultraperipheral $PbPb$ collisions

In this letter we propose the search of dark photons in the decay of pions produced by $γγ$ interactions in ultraperipheral $PbPb$ collisions. The cross section is estimated considering an accurate treatment for the absorptive corrections and for the nuclear form factor. Predictions for the event rates are presented considering the expected luminosities for the LHC, High -- Luminosity LHC and High -- Energy LHC as well as for the Future Circular Collider. Our results indicate that a future experimental analysis of the pion production in ultraperipheral heavy ion collisions can be useful to probe the dark photon production and constrain its properties.

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arXiv2020

An introduction to strange stars

The description of the heaviest neutron stars observed in Nature depends on the understanding of the physical concepts present in General Relativity and Quantum Chromodynamics. In this work, we review the basic concepts need to describe strange stars, constituted by up, down and strange quarks, which is one of the possible alternatives to describe the general properties of the most dense neutron stars. We will review the Bodmer-Witten-Terazawa hypothesis, which states that strange matter is absolutely stable in relation to ordinary nuclear matter, and discuss the basic properties that characterize strange stars. Our goal is to present the necessary concepts to understand this important theme of Astroparticles.

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arXiv2020

Charged charm stars

The study of the general properties and stability of charm stars with a net electric charge is performed within the MIT bag model framework. We consider two different models for the electric charge distribution and demostrate that both imply stellar configurations with larger masses and that satisfy the equilibrium condition. The dynamical stability against radial oscillations is investigated. Our results demonstrate that the eigenfrequencies are modified by the presence of a net electric charge, but the instability, previously demonstrated for the electrically neutral case, is also present in charged charm stars.

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arXiv2020

Exclusive heavy quark photoproduction in $pp$, $pPb$ and $PbPb$ collisions at the LHC and FCC energies

In this paper we present a comprehensive analysis of the exclusive heavy quark photoproduction in $pp$, $pPb$ and $PbPb$ collisions at LHC and FCC energies using the color dipole formalism and taking into account of nonlinear corrections to the QCD dynamics. We estimate the rapidity distributions and cross sections for the charm and bottom production considering three phenomenological models for the dipole-proton scattering amplitude that are able to describe the $ep$ HERA data. Our results indicate that a future experimental analysis of this process is feasible, which will allow us to improve our understanding of the QCD dynamics.

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arXiv2020

Photoproduction of pentaquarks states at the LHC

In this paper we investigate the production of pentaquark states in the photon -- proton interactions present in hadronic collisions at the RHIC and LHC. We consider two phenomenological models for the $J/Ψ$ photoproduction that consider the presence of the $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ resonances in the $s$ -- channel of the $γp \rightarrow J/Ψp$ reaction. The rapidity distribution is estimated for $pA$ collisions at the RHIC and LHC. Predictions for $pPb$, $Pb \, Ar$ and $Pb \,He$ fixed -- target collisions at the LHC are also presented. We demonstrate that the experimental analysis of the $J/Ψ$ photoproduction in fixed -- target collisions can provide complementary and independent checks on these states, and help to understand their underlying nature.

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arXiv2020

True muonium production in ultraperipheral $PbPb$ collisions

In this paper we investigate the production of a true muonium state, which is an atom consisting of a $μ^+ μ^-$ bound state, by $γγ$ interactions in ultraperipheral $PbPb$ collisions considering an accurate treatment of the absorptive corrections and for the nuclear form factor. The rapidity distributions and cross sections are estimated considering the RHIC, LHC and FCC energies. Our results indicate that the experimental analysis can be useful to observe, for the first time, the true muonium state.

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