arXiv subjects

Victor P. Goncalves

Publications and source records attributed to Victor P. Goncalves.

At least 73 records · Page 4Linked to original sources

arXiv2022

Challenging exclusive top quark pair production at low and high luminosity LHC

The elastic production of top quark pairs in $pp$ collisions at low and high luminosity regimes is investigated in detail. We extend the study performed in Phys. Rev. D102, 074014 (2020) which has demonstrated that the sum of two semi-exclusive $t\bar{t}$ production modes, namely in photon-Pomeron and Pomeron-Pomeron interactions, can be experimentally measured when the $t\bar{t}$ system decays semi-leptonically, $t\bar{t}\rightarrow jjblν_l\bar{b}$, both forward protons are tagged and a low amount of pile-up is present. In this study we focus on separating individual channels and a special attention is paid to the situation at high-luminosity LHC environment. We observe that the separation of the pomeron-pomeron and photon-photon events is a challenging task, especially at high amounts of pile-up even with an optimistic 10~ps resolution of timing detectors. In contrast, the photon-Pomeron signal is relatively well separable from all backgrounds at low levels of pile-up, allowing us to discover the elastic $t\bar{t}$ production and probe, for the first time, the production of a top quark pair in the photon-Pomeron interactions. The diffractive photoproduction of such a complex system as the $t\bar{t}$ pair hence can be used not only to study diffractive properties of the scattering amplitude but also to search for new physics beyond the Standard Model, and consequently to be a solid part of the physics programme of forward proton detectors at LHC.

hep-ph↗

arXiv2022

Exclusive processes in $ep$ collisions at the EIC and LHeC: A closer look on the predictions of saturation models

The exclusive production of vector mesons and photons in $ep$ collisions is investigated considering three phenomenological saturation models based on distinct assumptions for the treatment of the dipole - hadron scattering amplitude. The latest high precision HERA data for the reduced and vector meson cross sections are used to update the saturation model proposed by Marquet - Peschanski - Soyez (MPS), which predicts that the saturation model is dependent of the squared momentum transfer $t$. The MPS predictions for the photon virtuality, energy and $t$ - dependencies of the exclusive $ρ$, $J/Ψ$ and DVCS cross sections are presented and a detailed comparison with the results derived using the impact parameter saturation models is performed. Our results indicate that a future experimental analysis of the $t$ - distribution $dσ/dt$ for exclusive processes in the kinematical range that will covered by the EIC and LHeC, considering the distinct photon polarizations and large values of $t$, will be able to discriminate between the distinct approaches for the QCD dynamics at high energies.

hep-ph↗

arXiv2021

Near threshold heavy vector meson photoproduction at LHC and EicC

The exclusive $J/Ψ$ and $Υ$ photoproduction in fixed - target collisions at the LHC and $ep(A)$ collisions at the Electron ion collider in China (EicC) is investigated considering different models for the treatment of the vector meson production at low energies, close to the threshold. Results for the total cross sections and associated distributions are presented. We predict a large number of $J/Ψ$ events at the LHC in the rapidity range covered by the LHCb detector. For the EicC, our predictions point out that a detailed analysis of the near threshold $J/Ψ$ and $Υ$ photoproduction is feasible. Moreover, our results indicate that the modeling of the near threshold vector meson production can be constrained by future experimental analyzes at the LHC and EicC.

hep-ph↗

arXiv2021

Intrinsic charm in the nucleon and forward production of charm: a new constrain from IceCube Neutrino Observatory

The predictions for the atmospheric neutrino flux at high energies strongly depend on the contribution of prompt neutrinos, which are determined by the production of charmed meson in the atmosphere at very forward rapidities. Here we estimate the related cross sections taking into account the presence of an intrinsic charm (IC) component in the proton wave function. The impact on the predictions for the prompt neutrino flux is investigated assuming different values for the probability to find the IC in the nucleon.

hep-ph↗

arXiv2021

Impact of intrinsic charm amount in the nucleon and saturation effects on the prompt atmospheric $ν_μ$ flux for IceCube

The predictions for the atmospheric neutrino flux at high energies strongly depend on the contribution of prompt neutrinos, which are determined by the production of charmed meson in the atmosphere at very forward rapidities. In this paper we estimate the related cross sections taking into account the presence of an intrinsic charm (IC) component in the proton wave function and the QCD dynamics modified by the onset of saturation effects. The impact on the predictions for the prompt neutrino flux is investigated assuming different values for the probability to find the IC in the nucleon. Comparison with the IceCube data is performed and conclusions are drawn.

hep-ph↗

arXiv2021

Fully-heavy tetraquark production by $γγ$ interactions in hadronic collisions at the LHC

We investigate the production of the fully - heavy tetraquark states $T_{4Q}$ in the $γγ$ interactions present in proton-proton, proton-nucleus and nucleus-nucleus collisions at the CERN Large Hadron Collider (LHC). We focus on the $γγ\rightarrow {\cal{Q}}{\cal{Q}}$ (${\cal{Q}} = J/ψ,\, Υ$) subprocess, mediated by the $T_{4Q}$ resonance in the $s$ - channel, and present predictions for the hadronic cross sections considering the kinematical ranges probed by the ALICE and LHCb Collaborations. Our results demonstrate that the experimental study of this process is feasible and can be used to investigate the existence and properties of the $T_{4c}(6900)$ and $T_{4b}(19000)$ states.

hep-ph↗

arXiv2020

Exclusive dilepton production at forward rapidities in $PbPb$ collisions

The dilepton production in diffractive and exclusive processes at forward rapidities considering ultraperipheral $PbPb$ collisions at the LHC is investigated. Predictions for the $e^+ e^-$, $μ^+ μ^-$ and $τ^+ τ^-$ cross sections are presented taking into account of realistic cuts that can be implemented by the LHCb Collaboration in a future experimental analysis. Our results indicate that the background associated with the diffractive production can be strongly suppressed and the exclusive processes can be cleanly separated. For the $τ^+ τ^-$ production, the semi and purely leptonic decay channels are considered. Our results indicate that a future experimental analysis of the dilepton production at the LHCb is feasible and can be useful to search for BSM physics.

hep-ph↗

arXiv2020

Probing hidden-bottom pentaquarks in fixed-target collisions at the LHC

In this paper we investigate the possibility of searching for the hidden-bottom pentaquark states in photon-induced interactions at the LHC. We consider the presence of the $P_b$ resonance in the $s$-channel of the $γp \rightarrow Υp$ reaction and estimate its contribution for the exclusive $Υ$ photoproduction in the fixed-target mode of the LHC. Predictions for the total cross sections, rapidity and transverse momentum distributions are derived using the STARlight Monte Carlo considering $Pb-p$, $Pb-He$ and $Pb-Ar$ fixed-target collisions at the LHC. Our results indicate that the presence of the $P_b$ resonance implies an enhancement in the rapidity distribution in the kinematical range covered by the LHCb detector. We demonstrate that the $P_b$ contribution for the $Υ$ photoproduction becomes dominant if kinematical cuts are imposed on the rapidity and transverse momentum of the final state. These results indicate that an experimental analysis of the $Υ$ photoproduction in fixed-target collisions can provide complementary and independent checks of the existence of these states, and help to understand their underlying nature.

hep-ph↗

arXiv2020

Top quark pair production in the exclusive processes at LHC

We analyze the LHC prospects for measurements of the $t\bar{t}$ pair produced exclusively in photon-photon or semi-exclusively in photon-Pomeron and Pomeron-Pomeron processes using protons tagged in forward proton detectors on both sides of the interaction point. These processes are interesting from the point of view of a possible measurement of the top quark mass and constraining models used in Beyond Standard Model physics. Focusing on the semi-leptonic channel, $t\bar{t}\rightarrow jjblν_l\bar{b}$, making use of the exclusive nature of the final state, together with the use of timing information provided by forward proton detectors, relevant exclusive and inclusive backgrounds are studied in detail for different luminosity (or pile-up) scenarios and found to be important for further considerations. While good prospects are found for observing the signal, the top quark mass measurement turns out not to be competitive with measurements in inclusive channels.

hep-ph↗

arXiv2020

An introduction to the time evolution of model universes

In this paper we describe the evolution of the Universe in terms of the Friedmann equation, which takes into account of the composition and geometry of the Universe. The dependence of the solution on the geometry and composition for different combinations of the basic constituents are discussed. The distinct behaviors for the temporal evolution of the Universe are determined and the scenario predicted by the Standard Cosmology is presented.

physics.pop-ph↗

arXiv2020

New opportunities at the photon energy frontier

Ultra-peripheral collisions (UPCs) involving heavy ions and protons are the energy frontier for photon-mediated interactions. UPC photons can be used for many purposes, including probing low-$x$ gluons via photoproduction of dijets and vector mesons, probes of beyond-standard-model processes, such as those enabled by light-by-light scattering, and studies of two-photon production of the Higgs.

hep-ph↗

arXiv2020

Exclusive vector meson production in electron-ion collisions at the EIC, LHeC and FCC-$eh$

The exclusive vector meson production in electron-ion collisions for the energies of the future colliders is investigated. We present predictions for the coherent and incoherent $ϕ$ and $J/ψ$ production in $eAu$ collisions considering the possible states of nucleon configurations in the nuclear wave function and taking into account of the non-linear corrections to the QCD dynamics. The cross sections and transverse momentum distributions are estimated assuming the energies of the Electron-Ion Collider (EIC), Large Hadron Electron Collider (LHeC) and Future Circular Collider (FCC-$eh$). Our results indicate that a future experimental analysis of these processes can shed light on the modeling of the gluon saturation effects and constrain the description of the QCD dynamics at high energies.

hep-ph↗

arXiv2020

Coherent and incoherent $J/Ψ$ photoproduction in $PbPb$ collisions at the LHC, HE -- LHC and FCC

The coherent and incoherent $J/Ψ$ photoproduction in $PbPb$ collisions are investigated considering the possible states of nucleon configurations in the nuclear wave function and taking into account of the non - linear corrections to the QCD dynamics. The cross sections and the rapidity and transverse momentum distributions are estimated for the energies of the next run of the LHC, High -- Energy LHC and Future Circular Collider. Our results indicate that a future experimental analysis of these processes will be useful to discriminate between different approaches for the QCD dynamics as well to improve our description of the gluon saturation effects.

hep-ph↗

arXiv2020

Isolated photon production and pion-photon correlations in high-energy $pp$ and $pA$ collisions

A phenomenological study of the isolated photon production in high energy $pp$ and $pA$ collisions at RHIC and LHC energies is performed. Using the color dipole approach we investigate the production cross section differential in the transverse momentum of the photon considering three different phenomenological models for the universal dipole cross section. We also present the predictions for the rapidity dependence of the ratio of $pA$ to $pp$ cross sections. As a further test of the formalism, for different energies and photon rapidites we analyse the correlation function in azimuthal angle $Δϕ$ between the photon and a forward pion. The characteristic double-peak structure of the correlation function around $Δϕ\simeq π$ observed previously for Drell-Yan pair production is found for isolated photon emitted into the forward rapidity region which can be tested by future experiments.

hep-ph↗

arXiv2019

The ${γ^* γ^* \to η_c (1S,2S)}$ transition form factors for spacelike photons

We derive the light-front wave function (LFWF) representation of the $γ^* γ^* \to η_c(1S)\,,η_c(2S)$ transition form factor $F(Q_1^2, Q_2^2)$ for two virtual photons in the initial state. For the LFWF, we use different models obtained from the solution of the Schrödinger equation for a variety of $c \bar c$ potentials. We compare our results to the BaBar experimental data for the $η_c(1S)$ transition form factor, for one real and one virtual photon. We observe that the onset of the asymptotic behaviour is strongly delayed and discuss applicability of the collinear and/or massless limit. We present some examples of two-dimensional distributions for $F (Q_1^2,Q_2^2)$. A factorization breaking measure is proposed and factorization breaking effects are quantified and shown to be almost model independent. Factorization is shown to be strongly broken, and a scaling of the form factor as a function of $\bar Q^2 = (Q_1^2 + Q_2^2)/2$ is obtained.

hep-ph↗

arXiv2018

From $D_{s}^{\pm}$ production asymmetry at the LHC to prompt $ν_τ$ at IceCube

The description of the heavy meson production at large energies and forward rapidities at the LHC is fundamental to derive realistic predictions of the prompt atmospheric neutrino flux at the IceCube Observatory. In particular, the prompt tau neutrino flux is determined by the decay of $D_s$ mesons produced in cosmic ray - air interactions at high energies and large values of the Feynman - $x_F$ variable. Recent data from the LHCb Collaboration indicate a production asymmetry for $D_s^+$ and $D_s^-$ mesons, which cannot be explained in terms of the standard modelling of the hadronization process. In this paper we demonstrate that this asymmetry can be described assuming an asymmetric strange sea ($s(x) \ne \bar s(x)$) in the proton wave function and taking into account of the charm and strange fragmentation into $D_s$ mesons. Moreover, we show that the strange quark fragmentation contribution is dominant at large - $x_F$ ($\ge 0.3$). The prompt $ν_τ$ flux is calculated and the enhancement associated to the strange quark fragmentation contribution, disregarded in previous calculations, is estimated.

hep-ph↗

arXiv2017

Mapping the dominant regions of the phase space associated with $c \bar c$ production relevant for the Prompt Atmospheric Neutrino Flux

We present a detailed mapping of the dominant kinematical domains contributing to the prompt atmospheric neutrino flux at high neutrino energies by studying its sensitivity to the cuts on several kinematical variables crucial for charm production in cosmic ray scattering in the atmosphere. This includes the maximal center-of-mass energy for proton-proton scattering, the longitudinal momentum fractions of partons in the projectile (cosmic ray) and target (nucleus of the atmosphere), the Feynman $x_F$ variable and the transverse momentum of charm quark/antiquark. We find that the production of neutrinos with energies larger than $E_ν >$ 10$^7$ GeV is particularly sensitive to the center-of-mass energies larger than the ones at the LHC and to the longitudinal momentum fractions in the projectile 10$^{-8}$ $< x <$ 10$^{-5}$. Clearly, these are regions where we do not control the parton, in particular gluon, densities. We also analyse the characteristic theoretical uncertainties in the charm production cross section coming from its QCD modelling. The precision data on the prompt atmospheric neutrino flux can efficiently constrain the mechanism of heavy quark production and underlying QCD dynamics in kinematical ranges beyond the reach of the current collider measurements.

hep-ph↗

arXiv2017

Heavy flavor production in high-energy $pp$ collisions: color dipole description

We present a detailed study of open heavy flavor production in high-energy $pp$ collisions at the LHC in the color dipole framework. The transverse momentum distributions of produced $b$-jets, accounting for the jet energy loss, as well as produced open charm $D$ and bottom $B$ mesons in distinct rapidity intervals relevant for LHC measurements are computed. The dipole model results for the differential $b$-jet production cross section are compared to the recent ATLAS and CMS data while the results for $D$ and $B$ mesons production cross sections -- to the corresponding LHCb data. Several models for the phenomenological dipole cross section have been employed to estimate theoretical uncertainties of the dipole model predictions. We demonstrate that the primordial transverse momentum distribution of the projectile gluon significantly affects the meson spectra at low transverse momenta and contributes to the largest uncertainty of the dipole model predictions.

hep-ph↗