arXiv subjects

L. M. Abreu

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

At least 19 recordsLinked to original sources

arXiv2026

Interactions of the deuteron with a hadronic medium

We investigate the interactions of the deuteron with light mesons during the hadronic phase in heavy-ion collisions. We treat the deuteron as a weakly bound state and employ the quasi-free approximation to describe the $dπ$ interaction. The underlying elementary $Nπ$ amplitudes are described by a hybrid effective model, combining the non-resonant background from chiral perturbation theory with resonant contributions via Breit-Wigner parameterizations. These amplitudes are used to calculate the vacuum and thermally-averaged cross-sections for deuteron dissociation and production, namely, $d + π\rightarrow N + N' + π$ and the corresponding inverse reaction. We then use these cross sections in a rate equation to estimate the time evolution of the deuteron multiplicity. For the initial conditions we consider two models: the statistical hadronization model and the coalescence model, where the deuteron is treated as a hadronic molecule. Our findings suggest that the final deuteron yield does not retain a memory of its initial production mechanism.

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arXiv2024

Hadronic scattering effects on $ψ(2S)$ suppression in relativistic heavy-ion collisions

In this work we estimate the $N_{ψ(2S)} / N_{J/ψ}$ yield ratio in heavy-ion collisions, considering the interactions of the $ψ(2S) $ and $J/ψ$ states with light mesons in the hadron gas formed at the late stages of these collisions. Starting from the appropriate effective Lagrangians, we first compute the thermally-averaged cross sections for the production and absorption of the mentioned states, and then use them as input in the rate equations to determine the time evolution of $N_{ψ(2S)}$, $N_{J/ψ}$ and $N_{ψ(2S)} / N_{J/ψ}$. The main conclusion of our study is that the $ψ(2S) $ and $J/ψ$ multiplicities do not change much in the hadron gas phase and that the $ψ(2S)$ is more absorbed than the $J/ψ$. The obtained final ratio is in qualitative agreement with experimental data.

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arXiv2024

Novel aspects of particle production in ultra-peripheral collisions

One of the hot topics in hadron physics is the study of the new exotic charmonium states and the determination of their internal structure. Another important topic is the search for effects of the magnetic field created in high energy nuclear collisions. In this note we show that we can use ultra-peripheral collisions to address both issues. We compute the cross section for the production of the $D^+ D^-$ molecular bound state in $γ-γ$ collisions. We also show how the magnetic field of the projectile can induce pion production in the target. Both processes have sizeable cross sections and their measurement would be very useful in the study of the topics mentioned above.

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arXiv2024

Production of meson molecules in ultra-peripheral heavy ion collisons

In this work we present a calculation of exotic charmonium production in ultra-peripheral collisions, in which the exotic state is explicitly treated as a meson molecule. Our formalism is general but we focus on the lightest possible exotic charmonium state: a $D^+ D^-$ molecular bound state. It was proposed some time ago and it has been object of experimental searches. Here we study the production of the open charm pair in the process $γγ\to D^+ D^-$. Then we use a prescription to project the free pair $ |D^+ D^- \rangle$ onto a bound state at the amplitude level and compute the cross section of the process $γγ\to B$ (where $B$ is the bound state). Finally, we convolute this last cross section with the equivalent photon distributions coming from the projectile and target in an ultra-peripheral collision and find the $A A \to A A B$ cross section, which, for $Pb-Pb$ collisions at $\sqrt{s_{NN}} = 5.02$ TeV, is of the order of $3 \, μ\mbox{b}$.

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arXiv2024

The $X(3872)$ to $ψ(2S)$ yield ratio in heavy-ion collisions

In this work we evaluate the $X(3872)$ to $ ψ(2S) $ yield ratio ($N_X/N_{ψ(2S)}$) in Pb Pb collisions, taking into account the interactions of the $ψ(2S) $ and $ X(3872)$ states with light mesons in the hadron gas formed at the late stages of these collisions. We employ an effective Lagrangian approach to estimate the thermally-averaged cross sections for the production and absorption of the $ψ(2S)$ and use them in the rate equation to determine the time evolution of $N_{ψ(2S)}$. The multiplicity of these states at the end of mixed phase is obtained from the coalescence model. The multiplicity of $X(3872)$, treated as a bound state of $(D\bar D^{*} + c.c.)$ and also as a compact tetraquark, was already calculated in previous works. Knowing these yields, we derive predictions for the ratio ($N_X/N_{ψ(2S)}$) as a function of the centrality, of the center-of-mass energy and of the charged hadron multiplicity measured at midrapidity $[dN_{ch}/dη\,(η<0.5)]$. Finally, we make predictions for this ratio in Pb Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV to be measured by the ALICE Collaboration in the Run 3.

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arXiv2023

Correlation function for the $T_{bb}$ state: Determination of the binding, scattering lengths, effective ranges and molecular probabilities

We perform a study of the $B^{*+}B^0,B^{*0}B^+$ correlation functions using an extension of the local hidden gauge approach which provides the interaction from the exchange of light vector mesons and gives rise to a bound state of these components in $I=0$ with a binding energy of about $21$~MeV. After that, we face the inverse problem of determining the low energy observables, scattering length and effective range for each channel, the possible existence of a bound state, and, if found, the couplings of such a state to each $B^{*+}B^0,B^{*0}B^+$ component as well as the molecular probabilities of each of the channels. We use the bootstrap method to determine these magnitudes and find that, with errors in the correlation function typical of present experiments, we can determine all these magnitudes with acceptable precision. In addition, the size of the source function of the experiment from where the correlation functions are measured can be also determined with a high precision.

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arXiv2023

Interaction of exotic states in a hadronic medium: the $Z_c(3900)$ case

We investigate the interactions of the charged exotic state $Z_c(3900)$ in a hadronic medium composed of light mesons. We study processes such as $Z_c π\to D\bar{D}$, $Z_c π\to D^*\bar{D}^*$, $Z_c π\to D\bar{D}^*$ and the inverse ones. Using effective Lagrangians and form factors calculated with QCD sum rules (treating the $Z_c(3900)$ as a tetraquark) we estimate the vacuum and thermally-averaged cross-sections of these reactions. We find that the $Z_c(3900)$ has relatively large interaction cross sections with the constituent particles of the hadronic medium. After that, we use the production and suppression cross sections in a rate equation to estimate the time evolution of the $Z_c$ multiplicity. We include the $Z_c$ decay and regeneration terms. The coalescence model is employed to compute the initial $Z_c$ multiplicity for the compact tetraquark configuration. Our results indicate that the combined effects of hadronic interactions, hydrodynamical expansion, decay and regeneration affect the final yield, which is bigger than the initial value. Besides, the dependence of the $Z_c$ final yield with the centrality, center-of-mass energy and the charged hadron multiplicity measured at midrapidity $[dN_{ch}/dη\,(η<0.5)]$ is also investigated.

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arXiv2023

The $χ_{c1}(4274)$ multiplicity in heavy-ion collisions

In a previous work we computed the thermally-averaged cross sections for the production and absorption of the $χ_{c1}(4274)$ state in the hot hadron gas formed in heavy ion collisions. In the present work we estimate the final yield of this exotic state in these collisions. We use the coalescence model to fix the initial multiplicities. The state is is treated as a $P-$wave bound state of $D_s\bar D_{s0}$ and also as a compact tetraquark. The Bjorken picture is used to model the hydrodynamic expansion and cooling. Then, the kinetic equation is solved to evaluate the time evolution of the $χ_{c1}(4274)$ yield during the hot hadron gas phase. Since the $χ_{c1}(4274)$ decay width is large it might decay inside the hadron gas. Therefore we also include the $chi_{c1}(4274)$ decay and regeneration terms by means of an effective coupling, estimated from the available data. The combined effects of hadronic interactions and the $χ_{c1}(4274)$ decay have a strong impact on the final yield. Also, predictions of the $χ_{c1}(4274)$ multiplicity as a function of centrality and of the charged hadron multiplicity (measured at midrapidity) are presented. Finally, we calculate the yield of a proposed $P-$wave molecular state of $D_s \bar{D_{s0}}$, $Y^{\prime}(4274)$, characterized by a smaller width and smaller coupling constant obtained from the Weinberg compositeness condition.

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arXiv2023

The isospin and compositeness of the $T_{cc}(3875)$ state

We perform a fit to the LHCb data on the $T_{cc}(3875)$ state in order to determine its nature. We use a general framework that allows to have the $D^0 D^{*+}$, $D^+ D^{*0}$ components forming a molecular state, as well as a possible nonmolecular state or contributions from missing coupled channels. From the fits to the data we conclude that the state observed is clearly of molecular nature from the $D^0 D^{*+}$, $D^+ D^{*0}$ components and the possible contribution of a nonmolecular state or missing channels is smaller than 3\%, compatible with zero. We also determine that the state has isospin $I=0$ with a minor isospin breaking from the different masses of the channels involved, and the probabilities of the $D^0 D^{*+}$, $D^+ D^{*0}$ channels are of the order of 69\% and 29\% with uncertainties of 1\%. The differences between these probabilities should not be interpreted as a measure of the isospin violation. Due to the short range of the strong interaction where the isospin is manifested, the isospin nature is provided by the couplings of the state found to the $D^0 D^{*+}$, $D^+ D^{*0}$ components, and our results for these couplings indicate that we have an $I=0$ state with a very small isospin breaking. We also find that the potential obtained provides a repulsive interaction in $I=1$, preventing the formation of an $I=1$ state, in agreement with what is observed in the experiment.

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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

Interactions of the $χ_{c1}(4274)$ state with light mesons

We investigate the interactions of the $χ_{c1}(4274)$ state with light mesons in the hot hadron gas formed in heavy ion collisions. The vacuum and thermally-averaged cross sections of production of $χ_{c1}(4274)$ accompanied by light pseudoscalar and light vector mesons as well as the corresponding inverse processes are estimated within the context of an effective Lagrangian approach. The results suggest non-negligible thermal cross-sections, with larger magnitudes for most of the suppression reactions than those for production. This might be a relevant feature to be considered in the analysis of future data collected in heavy ion collisions.

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arXiv2023

Multiplicity of $Z_{cs}(3985)$ in heavy ion collisions

Using the coalescence model we compute the multiplicity of $Z_{cs} (3985)^-$ (treated as a compact tetraquark) at the end of the quark gluon plasma phase in heavy ion collisions. Then we study the time evolution of this state in the hot hadron gas phase. We calculate the thermal cross sections for the collisions of the $Z_{cs} (3985)^-$ with light mesons using effective Lagrangians and form factors derived from QCD sum rules for the vertices $Z_{cs}\bar{D}_{s }^* D $ and $Z_{cs} \bar{D}_{s} D^{*}$. We solve the kinetic equation and find how the $Z_{cs} (3985)^-$ multiplicity is affected by the considered reactions during the expansion of the hadronic matter. A comparison with the statistical hadronization model predictions is presented. Our results show that the tetraquark yield increases by a factor of about $2-3$ from the hadronization to the kinetic freeze-out. We also make predictions for the dependence of the $Z_{cs} (3985)^-$ yield on the centrality, the center-of-mass energy and the charged hadron multiplicity measured at midrapidity $ \left[ d N_{ch} / d η(η< 0.5)\right]$.

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arXiv2023

Shedding light on the $ X(3930) $ and $ X(3960) $ states with the $B^- \to K^- J/ψω$ reaction

We have studied the contribution of the state $X(3930)$, coming from the interaction of the $D \overline{D}$ and $D^{+}_s D^{-}_s$ channels, to the $B^- \to K^- J/ψω$ decay. The purpose of this work is to offer a complementary tool to see if the $X(3930)$ state observed in the $D^+ D^-$ channel is the same or not as the $X(3960)$ resonance claimed by the LHCb collaboration from a peak in the $D^{+}_s D^{-}_s$ mass distribution around threshold. We present results for what we expect in the $J/ψω$ mass distribution in the $B^- \to K^- J/ψω$ decay and conclude that a clear signal should be seen around $3930\,\rm MeV$. At the same time, finding no extra resonance signal at $3960\,\rm MeV$ would be a clear indication that there is not a new state at $3960\,\rm MeV$, supporting the hypothesis that the near-threshold peaking structure peak in the $D^{+}_s D^{-}_s$ mass distribution is only a manifestation of a resonance below threshold.

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arXiv2022

Hadronic medium effects on $Z_{cs} (3985)^-$ production in heavy-ion collisions

In this work we study the interactions of the multiquark state $Z_{cs} (3985)^-$ with light mesons in a hot hadron gas. Using an Effective Lagrangian framework, we estimate the vacuum cross sections as well as the thermal cross sections of the production processes $ \bar{D}_{s}^{(*)} D_{s}^{(*)} \rightarrow Z_{cs}^- X \, (X=π, K, η) $ and the corresponding inverse reactions. The results indicate that the considered processes have sizeable cross sections. Most importantly, the thermal cross sections for $Z_{cs}$ annihilation are much larger than those for production. This feature might produce relevant effects on some observables, such as the final $Z_{cs}$ multiplicity, measured in heavy ion collisions.

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arXiv2022

Production of $T^+_{cc}$ in heavy ion collisions

We study the production of heavy multiquark states in the heavy ion collisions performed at the LHC. We assume that they are produced at the end of the quark-gluon plasma phase and then interact with light hadrons during the hadron gas phase. We use the coalescence model to compute the initial multiplicities and effective Lagrangians to describe the interactions. We find that the initial multiplicity of molecules is two orders of magnitude larger than that of tetraquarks. The interactions in the hadron gas reduce the number of molecules and increase the number of tetraquarks by a factor two in each case. At kinetic freeze-out, the difference is still very large.

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arXiv2022

The $D^*/D$ ratio in heavy ion collisions

In this work we study the $D^*$ and $D$ multiplicities and how they change during the hadron gas phase of heavy ion collisions. With the help of an effective Lagrangian formalism, we calculate the production and absorption cross sections of the $D^*$ and $D$ mesons in a hadronic medium. We compute the time evolution of the abundances and the ratio $D^* /D$. They are approximately constant in time. Also, assuming a Bjorken type cooling and using an empirical relation between the freeze-out temperature and the central multiplicity density, we estimate $D^* /D$ as a function of $ dN /d η(η=0)$, which represents the system size. We find that, while the number of $D^*$'s and $D$'s grows significantly with the system size, their ratio remains approximately constant. This prediction can be compared with future experimental data. Our results suggest that the charm meson interactions in the hadron gas do not change their multiplicities and consequently these mesons are close to chemical equilibrium.

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arXiv2022

Interactions of the doubly charmed state $T_{cc} ^+$ with a hadronic medium

We investigate the absorption and production processes of this new state in a hadronic medium, considering the reactions $T_{cc}^+ π, T_{cc}^+ ρ\rightarrow D^{(*)} D^{(*)} $ and the corresponding inverse reactions. We use effective field Lagrangians to account for the couplings between light and heavy mesons, and give special attention to the form factors in the vertices. We calculate here for the first time the $ T_{cc}^+ - D - D^*$ form factor derived from QCD sum rules. The results are also obtained by testing widely utilized empirical form factors. The absorption cross sections are found to be larger than the production ones. We compare our results with the only existing estimate of these quantities, presented in a work of J.~Hong, S.~Cho, T.~Song and S.~H.~Lee, in which the authors employed the quasi-free approximation. We find cross sections which are one order of magnitude smaller.

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arXiv2021

Boundary effects on constituent quark masses and on chiral susceptibility in a four-fermion interaction model

In this work we investigate the finite-size effects on the phase structure of a two-flavor four-fermion interaction model with a flavor-mixing four-body interaction and in the presence of a magnetic background, taking into account different boundary conditions. We employ mean-field approximation and Schwinger's proper-time method in a toroidal topology with antiperiodic and periodic boundary conditions. The chiral susceptibility and constituent quark masses are studied under the change of the relevant parameters: size of compactified coordinates, temperature, chemical potential and magnetic field strength, within the different scenarios of boundary conditions and the value of flavor-mixing parameter. The findings suggest that the thermodynamic behavior of this system is strongly affected by the combined effects of relevant variables, depending on the range of their change, the value of flavor-mixing parameter and the choice of boundary conditions.

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