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L. M. Abreu

Publications and source records attributed to L. M. Abreu.

At least 37 records · Page 2Linked to original sources
arXiv2021

Understanding the $K^*/K$ ratio in heavy ion collisions

We study the $K^*$ meson dissociation in heavy ion collisions during the hadron gas phase. We use the production and absorption cross sections of the $K^*$ and $K$ mesons in a hadron gas, which were calculated in a previous work. We compute the time evolution of the $K^*$ abundance and the $K^* /K$ ratio during the hadron gas phase. Assuming a Bjorken type cooling and using an empirical relation between the freeze-out temperature and the central multiplicity density, we are able to write $K^* /K$ as a function of ($ dN /d η(η=0)$). The obtained function is in very good agreement with recent experimental data.

hep-ph↗
arXiv2020

The bottom-charmed meson spectrum from a QCD approach based on Tamm--Dancoff approximation

The bottom-charmed meson spectrum is studied in this work via an effective version of the Coulomb gauge QCD Hamiltonian. The Tamm-Dancoff approximation is employed to estimate the energies of the low-lying and radial-excited $B_c$ states with quantum numbers $J^P = 0^{-}, 0^{+}, 1^{-}, 1^{+}, 2^{+}, 2^{-}$. In particular, we analyze the effects of incorporating an effective transverse hyperfine interaction and spin mixing. The Regge trajectories and hyperfine splitting of both $S$- and $P$-wave states are also examined. The numerical results are compared with available experimental data and theoretical predictions of other models.

hep-ph↗
arXiv2020

Revisiting the tensor $J^{PC} = 2^{--}$ meson spectrum

This work is devoted to the discussion and characterization of the tensor $2^{-(-)}$ meson spectrum, by making use of the Coulomb gauge Hamiltonian approach to QCD, with the interactions being given by an improved confining potential and a transverse hyperfine interaction, whose kernel is a Yukawa-type potential. Our aim is to study the basic features of $2^{-(-)}$ mesons within an unified framework through the whole range of quark masses. We concentrate our investigation on predictions of expected but yet-unobserved ground states of unflavored light mesons and on charmonium and bottomonium states. The numerical results are compared with existing literature.

hep-ph↗
arXiv2020

An effective field theory approach to monopolium

In this work we investigate the interaction between spin-zero and spin-one monopoles by making use of an effective field theory based on two-body and four-body interaction parts. In particular, we analyze the formation of bound state of monopole-antimonopole (i.e. monopolium). The magnetic-charge conjugation symmetry is studied in analogy to the usual charge conjugation to define a particle basis, for which we find bound-state solutions with relatively small binding energies and which allows us to identify the bounds on the parameters in the effective Lagrangians. Estimations of their masses, binding energies and scattering lengths are performed as functions of monopole masses and interaction strength in a specific renormalization scheme. We also examine the general validity of the approach and the feasibility of detecting the monopolium.

hep-th↗
arXiv2019

Critical behaviour of an effective relativistic mean field model in the presence of magnetic background and boundaries

In the present work we investigate the combined influence of magnetic background and boundaries on the thermodynamic properties of effective relativistic mean field models, like the so-called Walecka model. This is done by making use of generalized zeta-function approach and mean-field approximation at effective chemical equilibrium, focusing on the dependence with the size of compactified spatial dimension, the temperature and the magnetic field strength. The findings suggest a rich phase structure in the parameter space. The maintenance of long-range correlations is strongly affected under the change of these parameters, with the symmetric phase being favoured due to both inverse magnetic catalysis effect and the reduction of size of compactified dimension.

hep-th↗
arXiv2019

Finite-volume and magnetic effects on the phase structure of the three-flavor Nambu--Jona-Lasinio model

In this work we analyze the finite-volume and magnetic effects on the phase structure of a generalized version of Nambu--Jona-Lasinio model with three quark flavors. By making use of mean-field approximation and Schwinger's proper-time method in a toroidal topology with antiperiodic conditions, we investigate the gap equation solutions under the change of the size of compactified coordinates, strength of magnetic field, temperature and chemical potential. The 't Hooft interaction contributions are also evaluated. The thermodynamic behavior is strongly affected by the combined effects of relevant variables. The findings suggest that the broken phase is disfavored due to both increasing of temperature and chemical potential, and the drop of the cubic volume of size $L$, whereas it is stimulated with the augmentation of magnetic field. In particular, the reduction of $L$ (remarkably at $L\approx 0.5 - 3 $~fm) engenders a reduction of the constituent masses for $u,d,s$-quarks through a crossover phase transition to the their corresponding current quark masses. On the other hand, the presence of a magnetic background generates greater values constituent quark masses, inducing smaller sizes and greater temperatures at which the constituent quark masses drop to the respective current ones.

hep-ph↗
arXiv2018

Impact of unitarization on the $J/ψ$-light meson cross section

Hidden charm mesons continue playing an essential role as relevant probes to understand the evolution of partonic matter. It is expected that the charmonia that survived the quark-gluon plasma phase suffer collisions with other particles composing the hadronic matter. In this work, we intend to contribute on this subject by presenting an updated study about the interactions of $J/ψ$ with surrounding hadronic medium. The meson-meson interactions are described with a $SU(4)$ effective Lagrangian, and within the framework of unitarized coupled channel amplitudes projected onto s-wave. The symmetry is explicitly broken to $SU(3)$ by suppression of the interactions driven by charmed mesons. We calculate the cross sections for $J/ψ$ scattering by light pseudoscalar mesons ($π, K, η$) and vector mesons ($ρ, K^\ast, ω$), as well as their inverse processes. Keeping the validity of this present approach in the low CM energy range, the most relevant channels are evaluated and a comparison of the findings with existing literature is performed.

hep-ph↗
arXiv2018

$Υ$ suppression in a hadron gas

In this work we study the interactions of bottom mesons which lead to $Υ$ production and absorption in hot hadronic matter. We use effective Lagrangians to calculate the $Υ$ production cross section in processes such as $ \bar{B}^{(*)} + B^{(*)} \to Υ+ (π, ρ)$ and also the $Υ$ absorption cross section in the corresponding inverse processes. We update and extend previous calculations by Lin and Ko, introducing anomalous interactions. The obtained cross sections are used as input to solve the rate equation which allows us to follow the time evolution of the $Υ$ multiplicity. In contrast to previous conjectures, our results suggest that the interactions in the hadron gas phase strongly reduce the $Υ$ abundance.

nucl-th↗
arXiv2018

New charm resonances and $J/ψ$ interactions in a hadron gas

In relativistic heavy ion collisions, after the quark gluon plasma (QGP) phase there is a hadron gas (HG) phase. In both phases $J/ψ$ may be formed and destroyed. In this note we study the $J/ψ$ interactions with other mesons in the hadron gas phase. Making use of effective field Lagrangians we obtain the cross sections for the production and absorption processes. With respect to the existing calculations, the improvements introduced here are the inclusion of $K$ and $K^*$'s in the effective Lagrangian approach and the inclusion of processes involving the new exotic charmonium states $Z_c(3900)$ and $Z_c(4025)$. We conclude that the interactions between $J/ψ$ and all the considered mesons reduce the original $J/ψ$ abundance ( determined at the end of the quark gluon plasma phase ) by 20 \% and 24 \% in RHIC and LHC collisions respectively. Consequently, any really significant change in the $J/ψ$ abundance comes from dissociation and regeneration processes in the QGP phase.

nucl-th↗
arXiv2017

$J/ψ$ regeneration in a hadron gas: an update

In heavy ion collisions after the quark-gluon plasma there is a hadronic gas phase. Using effective Lagrangians we study the interactions of charmed mesons which lead to $J/ψ$ production and absorption in this gas. We update and extend previous calculations introducing strange meson interactions and also including the interactions mediated by the recently measured exotic charmonium resonances $Z(3900)$ and $Z(4025)$. These resonances open new reaction channels for the $J/ψ$, which could potentially lead to changes in its multiplicity. We compute the $J/ψ$ production cross section in processes such as $D_{(s)}^{(*)} + \bar{D}^{(*)} \to J/ψ+ (π, ρ, K, K^{\ast})$ and also the $J/ψ$ absorption cross section in the corresponding inverse processes. Using the obtained cross sections as input to solve the rate equation, we conclude that the interactions in the hadron gas phase do not significantly affect the $J/Ψ$ abundance. In other words, there is neither a charmonium suppression nor charmonium regeneration from light mesons in the hadronic phase.

hep-ph↗
arXiv2017

Finite-size effects on the Phase Structure of the Walecka Model

In this work we investigate the finite-size effects on the phase structure of Walecka model within the framework of generalized Zeta-function, focusing on the influence of temperature as well as the number and length of compactified spatial dimensions. Here we concentrate on the situation of larger values of the coupling between the scalar and fermion fields, in which a phase transition of first order takes place. The phase transitions are analyzed and compared with the system in the situations of one, two and three compactified spatial dimensions. Our findings suggest that the thermodynamic behavior of the system depends on the length and number of spatial dimensions, with the symmetric phase being favored as the size of the system diminishes.

nucl-th↗
arXiv2017

$Z_b(10610)$ in a hadronic medium

In this work we investigate the $Z_b (10610)$ (called simply $Z_b$) abundance in the hot hadron gas produced in the late stage of heavy ion collisions. We use effective Lagrangians to calculate the thermally averaged cross sections of $Z_b $ production in processes such as $B^{(*)} + \bar{B}^{(*)} \to π+ Z_b (10610)$ and also of its absorption in the corresponding inverse processes. We then solve the rate equation to follow the time evolution of the $Z_b$ multiplicity, and the results remarkably suggest that this quantity is not significantly affected by the considered reactions. The number of $Z_b$'s produced at the end of the quark-gluon plasma phase remains constant during the hadron phase.

hep-ph↗
arXiv2017

On the absorption and production cross sections of $K$ and $K^*$

We have computed the isospin and spin averaged cross sections of the processes $πK^*\to ρK$ and $ρK^*\to πK$, which are crucial in the determination of the abundances of $K^*$ and $K$ in heavy ion collisions. Improving previous calculations, we have considered several mechanisms which were missing, such as the exchange of axial and vector resonances ($K_1(1270)$, $K^*_2(1430)$, $h_1(1170)$, etc...) and also other processes such as $πK^*\to ωK, ϕK$ and $ωK^*,\,ϕK^*\to πK$. We find that some of these mechanisms give important contributions to the cross section. Our results also suggest that, in a hadron gas, $K^*$ production might be more important than its absorption.

hep-ph↗
arXiv2017

Production and absorption of exotic bottomonium-like states in high energy heavy ion collisions

We investigate the production and absorption of $Z_b (10610)$ and $Z_b ^{\prime}(10650)$ states in a hadronic medium, via the processes $\bar{B}^{(*)} B^{(*)} \rightarrow πZ_b ^{(\prime)} $ and the corresponding inverses reactions. We use effective field Lagrangians based on an $SU(4)$-extension of the hidden gauge formalism to account for the couplings between light and heavy mesons, and a phenomenological Lagrangian involving the $ B^{\ast} B^{(\ast)} Z_b ^{(\prime)}$ vertices. The absorption cross sections are found to be much larger than the production ones.

hep-ph↗
arXiv2016

Analysis of $X(3872)$ production via Heavy-Meson Effective Theory

We analyze the $X(3872)$ production in the processes $ \bar{D} D \rightarrow πX $, $\bar{D}^* D \rightarrow πX $ and $\bar{D}^* D^* \rightarrow πX $, making use of the Heavy-Meson Effective Theory, with an effective Lagrangian built based on chiral $SU(3)_{L} \times SU(3)_{R}$ and heavy quark symmetries. In this scenario, we consider $X$ as a bound state of $D^{*} \bar{D} + c.c.$, including neutral and charged components, and obtain the cross sections the mentioned reactions as function of collision energy.

hep-ph↗
arXiv2016

$X(3872)$ production and absorption in a hot hadron gas

We calculate the time evolution of the $X(3872)$ abundance in the hot hadron gas produced in the late stage of heavy ion collisions. We use effective field Lagrangians to obtain the production and dissociation cross sections of $X(3872)$. In this evaluation we include diagrams involving the anomalous couplings $πD^*\bar{D}^*$ and $X \bar{D}^{\ast} D^{\ast}$ and also the couplings of the $X(3872)$ with charged $D$ and $D^*$ mesons. With these new terms the $X(3872)$ interaction cross sections are much larger than those found in previous works. Using these cross sections as input in rate equations, we conclude that during the expansion and cooling of the hadronic gas, the number of $X(3872)$, originally produced at the end of the mixed QGP/hadron gas phase, is reduced by a factor of 4.

hep-ph↗
arXiv2015

Hadronic states with both open charm and bottom in effective field theory

We perform a field-theoretical study of possible deuteron-like molecules with both open charm and bottom, using the Heavy-Meson Effective Theory. In this approach, we analyze the parameter space of the coupling constants and discuss the formation of loosely-bound $D^{(*)} B^{(*)} $-states. We estimate their masses and other properties.

hep-ph↗