arXiv subjects

Gabriele Coci

Publications and source records attributed to Gabriele Coci.

15 recordsLinked to original sources

arXiv2026

Quantum decoherence: a study applied to quarkonium-like bound states in strongly interacting matter

We study the quantum decoherence of a bound state interacting with a reservoir of strongly interacting matter within the framework of open quantum systems. The bound state is modeled as a quantum harmonic oscillator whose parameters are tuned to reproduce the root-mean-square radius of $J/\Psi$ particle. The surrounding medium, representing the many degrees of freedom of strongly interacting matter, acts as an environment that induces dissipation and decoherence through system-reservoir coupling. By analyzing the time evolution of the reduced density matrix, we quantify the loss of quantum coherence and its dependence on medium properties. Subsequently, we extend the model by introducing a time dependence in the system-thermal bath coupling, thereby simulating a temperature evolution similar to that occurring during the expansion of a fireball in the central region of heavy-ion collisions. We find that a temperature evolution has a relevant impact on the way the system loses coherence through the coupling with the expanding medium. Finally, we estimate the impact of the time-dependent temperature on the decoherence process, also analyzing a scenario that includes viscous effects without finding a significant change with respect to ideal hydrodynamical evolution.

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arXiv2025

Entropy from decoherence: a case study using glasma-based occupation numbers

We compute the entropy-per-particle, $S/N$, produced by the decoherence of a coherent state interacting with an environment, using an analytical open quantum system approach. The coherent state considered is characterized by occupation numbers borrowed from the glasma fields produced in the early stages of high-energy nuclear collisions. The environment is modeled as the vacuum, and decoherence arises from the interaction of the state with vacuum fluctuations. We describe the system-environment interaction via a phase-damping model, which represents continuous measurements on the system without altering its energy or particle number. Starting from the occupation numbers typical of the Glasma in high-energy proton-nucleus and nucleus-nucleus collisions, we find that the final $S/N$ after decoherence is lower than that of a two-dimensional thermal bath of ultrarelativistic gluons, except for proton-nucleus collisions at small values of $g\mu$. Our results indicate that quantum decoherence alone does not generate sufficient entropy to transform the initial coherent state into a thermalized gluon bath.

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arXiv2024

Systematic study of flow of protons and light clusters in intermediate-energy heavy-ion collisions with momentum-dependent potentials

We study the influence of the nuclear equation-of-state (EoS) on collective observables -- the directed ($v_1$) and elliptic flow ($v_2$) of nucleons and light clusters -- in heavy-ion collisions at GeV energies using the Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) approach. A novel development in this work is the inclusion of a momentum-dependent nucleon potential in the PHQMD in addition to the static, density-dependent Skyrme interaction. This enables three distinct EoS scenarios: two static ("soft" and "hard", differing in compressibility) and a soft, momentum-dependent EoS calibrated to $pA$ elastic scattering data. We find a strong EoS sensitivity in proton and cluster rapidity and $p_T$ distributions: soft and soft momentum-dependent EoS yield similar results, markedly different from the hard EoS. Softening the EoS reduces proton yields at midrapidity while enhancing light-cluster production. The EoS also affects flow observables differently for nucleons and clusters. For protons, a soft momentum-dependent potential increases slightly the magnitude of $v_1$ and $v_2$ relative to the hard EoS, whereas cluster flows are nearly similar. The soft momentum-dependent EoS provides an overall good agreement with experimental data from HADES and FOPI Collaborations while the soft EOS is not in line with the data. A scaling of $v_2$ with cluster mass number $A$ is observed at midrapidity for low $p_T$, which breaks at higher $p_T$. Finally, we examine the sensitivity of flow observables to deuteron production mechanisms. Deuterons formed via MST clustering exhibit different flow patterns from those produced by coalescence at freeze-out, indicating that flow harmonics may help discriminate between cluster formation scenarios.

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arXiv2024

Cluster and anti-cluster production in heavy-ion collisions and pA reactions

We investigate light cluster and anti-cluster production in heavy-ion collisions from SIS to RHIC energies within the Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) microscopic transport approach which propagates (anti-)baryons using n-body QMD dynamics. In PHQMD the clusters are formed dynamically by potential interactions between baryons - and recognized by the Minimum Spanning Tree (MST) algorithm - as well as by kinetic reactions in case of deuterons. We present the novel PHQMD results for different observables such as excitation functions of the multiplicity of deuterons, anti-deuterons and tritons, as well as their transverse momentum spectra. Moreover, we investigate the system size dependence of proton and deuteron production in p+A collisions and show the PHQMD results for p+A collisions (A = Be, Al, Cu, Au) at 14 AGeV/c, as well as for asymmetric Au+A collisions (A = Al, Cu, Pb) at a bombarding energy of about 10 AGeV.

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arXiv2023

Dynamical mechanisms for deuteron production at mid-rapidity in relativistic heavy-ion collisions from SIS to RHIC energies

The understanding of the mechanisms for the production of weakly bound clusters, such as a deuteron $d$, in heavy-ion reactions at mid-rapidity is presently one of the challenging problems which is also known as the "ice in a fire" puzzle. In this study we investigate the dynamical formation of deuterons within the Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) microscopic transport approach and advance two microscopic production mechanisms to describe deuterons in heavy-ion collisions from SIS to RHIC energies: kinetic production by hadronic reactions and potential production by the attractive potential between nucleons. Differently to other studies, for the "kinetic" deuterons we employ the full isospin decomposition of the various $\pi NN\leftrightarrow \pi d$, $NNN\leftrightarrow N d$ channels and take into account the finite size properties of the deuteron by means of an excluded volume condition in coordinate space and by the projection onto the deuteron wave function in momentum space. We find that considering the quantum nature of the deuteron in coordinate and momentum space reduces substantially the kinetic deuteron production in a dense medium as encountered in heavy-ion collisions. If we add the "potential" deuterons by applying an advanced Minimum Spanning Tree (aMST) procedure, we obtain good agreement with the available experimental data from SIS energies up to the top RHIC energy.

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arXiv2022

Midrapidity cluster formation in heavy-ion collisions

We study the production of clusters and hypernuclei at midrapidity employing the Parton-Hadron-Quantum-Molecular-Dynamics (PHQMD) approach, a microscopic n-body transport model based on the QMD propagation of the baryonic degrees of freedom with density dependent 2-body potential interactions. In PHQMD the cluster formation occurs dynamically, caused by the interactions. The clusters are recognized by the Minimum Spanning Tree (MST) algorithm. We present the PHQMD results for cluster and hypernuclei formation in comparison with the available experimental data at relativistic energies. PHQMD allows to study the time evolution of formed clusters and the origin of their production, which helps to understand how such weakly bound objects are formed and survive in the rather dense and hot environment created in heavy-ion collisions. It offers therefore an explanation of the 'ice in the fire' puzzle. To investigate whether this explanation of the 'ice in the fire' puzzle applies only to the MST results we study also the deuterons production by coalescence. We embed MST and coalescence in the PHQMD and UrQMD transport approaches in order to obtain model independent results. We find that both clustering procedures give very similar results for the deuteron observables in the UrQMD as well as in the PHQMD environment. This confirms that our solution for the 'ice in the fire' puzzle is common to MST and coalescence and independent of the transport approach.

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arXiv2021

Cluster and hyper-cluster production in relativistic heavy-ion collisions within the Parton-Hadron-Quantum-Molecular-Dynamics approach

We study cluster and hypernuclei production in heavy-ion collisions at relativistic energies employing the Parton-Hadron-Quantum-Molecular-Dynamics (PHQMD) approach, a microscopic n-body transport model based on the QMD propagation of the baryonic degrees of freedom with density dependent 2-body potential interactions. All other ingredients of PHQMD, including the collision integral and the treatment of the quark-gluon plasma (QGP) phase, are adopted from the Parton-Hadron-String Dynamics (PHSD) approach. In PHQMD the cluster formation occurs dynamically, caused by the interactions. The clusters are recognized by the Minimum Spanning Tree (MST) algorithm. We present the PHQMD results for cluster and hypernuclei formation in comparison with the available experimental data at AGS, SPS, RHIC-BES and RHIC fixed target energies. We also provide predictions on cluster production for the upcoming FAIR and NICA experiments. PHQMD allows to study the time evolution of formed clusters and the origin of their production, which helps to understand how such weakly bound objects are formed and survive in the rather dense and hot environment created in heavy-ion collisions. It offers therefore an explanation of the 'ice in the fire' puzzle.

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arXiv2021

Comparison of heavy ion transport simulations: Ag+Ag collisions at Elab = 1.58 AGeV

We compare the microscopic transport models UrQMD, PHSD, PHQMD, and SMASH to make predictions for the upcoming Ag+Ag data at $E_\mathrm{lab}=1.58$~$A$GeV ($\sqrt{s_\mathrm{NN}}=2.55$~GeV) by the HADES collaboration. We study multiplicities, spectra and effective source temperatures of protons, $\pi^{\pm,0}$, $K^\pm$, the $\eta$, $\Lambda+\Sigma^0$ and the $\Xi^-$ within these models. Despite variations in the detailed implementation of the dynamics in the different models, the employed transport approaches all show consistent multiplicities of the bulk of investigated hadrons. The main differences are in the $\Xi^-$ production, which is treated differently between UrQMD/SMASH on one side employing high mass resonance states with explicit decays to $\mathrm{Resonance}\rightarrow \Xi+K+K$ in contrast to PHSD/PHQMD which account only non-resonant $\Xi$ production channels. A comparison of the spectra, summarized by effective source temperatures, shows that all models provide similar source temperatures around $T_\mathrm{source}=80-95$~MeV, and show substantial radial flow on the order of $\langle v_T\rangle=0.22c-0.3c$ even for such a small system.

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arXiv2021

Prerequisites for heavy quark coalescence in heavy-ion collisions

The coalescence model assumes instant formation of a bound state from unbound particles based on the overlapping of two states in spatial and momentum spaces and quantum numbers. Therefore, applied to the hadronization of partons, it provides a snapshot of a Quark-Gluon Plasma (QGP) just before hadronization. We use the coalescence model for the formation of the ground state of open heavy flavor and the statistical model for heavier states. Assuming that all heavy flavors in thermal equilibrium hadronize through the coalescence, we find that the QGP just before hadronization is not composed of completely randomized partons but must have strong correlations in color charges as well as in momentum and/or coordinate spaces between heavy quark and light (anti-)quark.

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arXiv2019

Heavy-light flavour correlations of anisotropic flows at LHC energies within event-by-event transport approach

The heavy quarks (HQs) are unique probe of the hot QCD matter properties and their dynamics is coupled to the locally thermalized expanding quark gluon plasma. We present here a novel study of the event by event correlations between light and heavy flavour flow harmonics at LHC energy within a transport approach. Interaction between heavy quarks and light quarks have been taken into account exploring the impact of different temperature dependence of the transport coefficients $D_s$ and $Γ$. Our study indicates that $v^{heavy}_n-v^{light}_n$ correlation and the relative fluctuations of anisotropic flows, $σ_{v_{n}}/\langle v_n \rangle$, are novel observables to understand the heavy quark-bulk interaction and are sensitive to the temperature dependence even to moderate differences of $D_s(T)$, or $Γ(T)$. Hence a comparison of such new observables for HQ to upcoming experimental data at both RHIC and LHC can put further constraints on heavy quark transport coefficients and in particular on its temperature dependence toward a solid comparison between the phenomenological determination and the lattice QCD calculations.

hep-ph↗

arXiv2019

Impact of Glasma on heavy quark observables in nucleus-nucleus collisions at LHC

In the pre-thermal equilibrium stage of relativistic heavy-ion collisions, a strong quasi-classical transverse gluon field emerges at about $τ_0 \simeq 0.1 \, \rm fm/c$ and evolves together with their longitudinal counterparts according to the classical Yang-Mills (CYM) equations. Recently it has been shown that these fields induce a diffusion of charm quarks in momentum space resulting in a tilt of their spectrum without a significant drag. We find that in nucleus-nucleus collisions at LHC such a novel dynamics of charm quarks leads to an initial enhancement of the nuclear modification factor ($R_{AA}$) at $p_T$ larger than 2 GeV$/c$ contrary to the standard lore. Moreover, the same dynamics leads to a larger final elliptic flow ($v_2$) inducing a relation between $R_{AA}$ and $v_2$ that is quite close to the experimental measurements. Our study also shows that such an initial pre-thermal stage is unlikely to be described in terms of a standard drag and diffusion dynamics, because even if one tune such coefficients to reproduce the same $R_{AA}(p_T)$ this would imply a significantly smaller $v_2$.

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arXiv2019

Towards the determination of heavy-quark transport coefficients in quark-gluon plasma

Several transport models have been employed in recent years to analyze heavy-flavor meson spectra in high-energy heavy-ion collisions. Heavy-quark transport coefficients extracted from these models with their default parameters vary, however, by up to a factor of 5 at high momenta. To investigate the origin of this large theoretical uncertainty, a systematic comparison of heavy-quark transport coefficients is carried out between various transport models. Within a common scheme devised for the nuclear modification factor of charm quarks in a brick medium of a quark-gluon plasma, the systematic uncertainty of the extracted drag coefficient among these models is shown to be reduced to a factor of 2, which can be viewed as the smallest intrinsic systematical error band achievable at present time. This indicates the importance of a realistic hydrodynamic evolution constrained by bulk hadron spectra and of heavy-quark hadronization for understanding the final heavy-flavor hadron spectra and extracting heavy-quark drag coefficient. The transverse transport coefficient is less constrained due to the influence of the underlying mechanism for heavy-quark medium interaction. Additional constraints on transport models such as energy loss fluctuation and transverse-momentum broadening can further reduce theoretical uncertainties in the extracted transport coefficients.

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arXiv2019

Direct flow of heavy mesons as unique probe of the initial Electro-Magnetic fields in Ultra-Relativistic Heavy Ion collisions

In Ultra-relativistic Heavy-Ion Collisions (HICs) very strong initial electro-magnetic (E.M.) fields are created: the order of magnitude of the magnetic field is about $10^{19} \, Gauss$, the most intense field in the Universe, even larger than that of a magnetar. These fields rapidly decrease in time, inducing a drift of particles in the reaction plane. The resulting flow is odd under charge exchange and this allows to distinguish it from the large vorticity of the bulk matter due to the initial angular momentum conservation. Conjointly charm quarks, thanks to their large mass $M_{c}>>Λ_{QCD}$, are produced in hard partonic processes at formation time $τ_f \approx 1\,/\,( 2M_{HQ} )$ which is comparable with the time scale when the E.M. field attains its maximum value. Moreover, with a mass of $M_c \approx 1.3 \,$ GeV there should be no mixing with the chiral magnetic dynamics and the condition $M_c \gg T$ allows charm quarks to have sufficiently large thermalization time, so that they can probe the entire phase-space evolution of the QGP retaining the initial kick given by the E.M. field. We show that such E.M. field entails a transverse motion of charm quarks resulting in a splitting of directed flow $v_1$ of $ D$ and $\bar{D}$ mesons of few percent, i.e. much larger compared to the measured pion one.

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arXiv2018

Cracking the difference of estimating heavy quark transport coefficients in a Quark-Gluon Plasma

Heavy flavor observables provide valuable information on the properties of the hot and dense Quark-Gluon Plasma (QGP) created in ultra-relativistic nucleus-nucleus collisions. Various microscopic models have successfully described many of the observables associated with its formation. Their transport coefficients differ, however, due to different assumptions about the underlying interaction of the heavy quarks with the plasma constituents, different initial geometries and formation times, different hadronization processes and a different time evolution of the QGP. In this study we present the transport coefficients of all these models and investigate systematically how some of these assumptions influence the heavy quark properties at the end of the QGP expansion. For this purpose we impose on these models the same initial condition and the same model for the QGP expansion and show that both have considerable influence on $R_{AA}$ and $v_2$.

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arXiv2018

Charmed Hadrons from Coalescence plus Fragmentation in relativistic nucleus-nucleus collisions at RHIC and LHC

In a coalescence plus fragmentation approach we calculate the heavy baryon/meson ratio and the $p_T$ spectra of charmed hadrons $D^{0}$, $D_{s}$ and $Λ_{c}^{+}$ in a wide range of transverse momentum from low $p_T$ up to about 10 GeV and discuss their ratios from RHIC to LHC energies without any change of the coalescence parameters. We have included the contribution from decays of heavy hadron resonances and also the one due to fragmentation of heavy quarks which do not undergo the coalescence process. The coalescence process is tuned to have all charm quarks hadronizing in the $p_T\rightarrow 0$ limit and at finite $p_T$ charm quarks not undergoing coalescence are hadronized by independent fragmentation. The $p_T$ dependence of the baryon/meson ratios are found to be sensitive to the masses of coalescing quarks, in particular the $Λ_{c}/D^{0}$ can reach values of about $\rm 1÷1.5 $ at $p_T \approx \, 3$ \mbox{GeV}, or larger, similarly to the light baryon/meson ratio like $p/π$ and $Λ/K$, however a marked difference is a quite weak $p_T$ dependence with respect to the light case, such that a larger value at intermediate $p_T$ implies a relatively large value also for the integrated yields. A comparison with other coalescence model and with the prediction of thermal model is discussed.

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