arXiv subjects

Maria Lucia Sambataro

Publications and source records attributed to Maria Lucia Sambataro.

10 recordsLinked to original sources

arXiv2026

Heavy Quark Recombination Across Collision Systems: Meson and Baryon production

Measurements of heavy-flavor baryons in nucleus--nucleus and proton--proton collisions have provided strong evidence that heavy-quark hadronization cannot be described solely in terms of vacuum fragmentation. In particular, the large enhancement of the $Λ_c/D^0$, $Ξ_c/D^0$ and $Ω_c/D^0$ ratios observed at RHIC and LHC energies has been successfully described within a coalescence plus fragmentation approach, supporting the relevance of recombination mechanisms in both large and small collision systems. Building on these results, we discuss recent developments in the coalescence hadronization framework. Particular emphasis is given to the production of multi-charmed baryons, namely $Ξ_{cc}$, and $Ω_{ccc}$, whose yields are predicted in a wide range of collision systems from PbPb to KrKr, ArAr and OO collisions. The strong sensitivity of these states, especially $Ω_{ccc}$, to the underlying charm-quark distribution makes them valuable probes of charm thermalization and non-equilibrium effects in the QGP. We also present recent extensions of the model to the beauty sector, including predictions for $Λ_b/B^0$, $Ξ_b/B^0$ and $Ω_b/B^0$ production. The results indicate sizeable recombination effects and a stronger baryon enhancement than in the charm sector, highlighting the increasing role of coalescence for heavier quarks. Finally, we briefly comment on ongoing developments toward a unified description of open and hidden heavy flavor through the application of the same framework to quarkonium production in small collision systems.

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arXiv2026

Directed flow of D and B mesons in an electrically and chirally conductive QGP at LHC energies

We investigate the directed flow of D and B mesons in the presence of electromagnetic fields incorporating finite electrical and chiral conductivities at LHC energies. The momentum evolution of heavy quarks in the quark-gluon plasma (QGP) is studied using Langevin dynamics, with their interactions with the medium described within the extended quasiparticle model (QPMp) framework. The electromagnetic fields are obtained from analytical solutions of Maxwell equations that account for both electrical and chiral conductivities. These conductivities modify the space-time evolution of the electromagnetic fields and influence the splitting of the directed flow between mesons and anti-mesons. However, the influence of chiral conductivity remains secondary to that of electrical conductivity and its impact on the directed flow is marginal. The results show that heavy mesons containing a charm quark develop a directed flow with a sign opposite to that of heavy mesons containing a bottom quark, with a smaller magnitude for the latter. The present study indicates that a simultaneous experimental measurement of v1 for heavy mesons containing both charm and bottom quarks would provide valuable insight into the electromagnetic field origin of v1 for heavy quarks.

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arXiv2026

Probing collective behaviour of Heavy Quarks through $p_T$-differential radial flow $v_0(p_T)$

We discuss the $p_T$-differential radial flow $v_0(p_T)$ of charmed hadrons within a Langevin dynamics coupled to relativistic Boltzmann transport approach in an event-by-event basis. We propose heavy flavour $v_0(p_T)$ as a novel observable to probe the strength of the interaction of heavy quarks with the expanding Quark-Gluon Plasma. By comparing different temperature dependence for the spatial diffusion coefficient $D_s(T)$ we show that the $v_0(p_T)$ keep a strong sensitivity to the heavy-quark transport coefficients at intermediate $p_T$. At low $p_T$, the observable is also sensitive to hadronization where we observe a larger $v_0(p_T)$ for $Λ_c$ baryons than for $D$ mesons.

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arXiv2026

Non-equilibrium Dynamical Attractors and Thermalisation of Charm Quarks in Nuclear Collisions at the LHC Energy

We study the non-equilibrium dynamics, thermalisation and attractor behaviour of charm quarks in a longitudinally expanding Quark-Gluon Plasma within the Relativistic Boltzmann Transport approach in 1+1D Bjorken expansion. Considering both a strong AdS/CFT coupling scenario with constant $2πT D_s=1$ and a temperature-dependent diffusion coefficient $D_s^\text{lQCD}(T)$ from the recent unquenched lattice QCD data, we analyse the evolution of effective temperature, momentum moments and distribution functions for different initial conditions, including FONLL and EPOS4HQ spectra. We find that charm quarks exhibit dynamical attractors; however, the temperature dependence of $D_s^\text{lQCD}(T)$ leads to significantly longer relaxation times compared to the strong coupling limit. While dynamical attractors occur within $\sim 1-1.5 \rm \,fm$ for $2πT D_s=1$, they are delayed to $\sim 5 \rm \,fm$ for $D_s^\text{lQCD}(T)$, becoming comparable to the lifetime of the Quark-Gluon Plasma phase in ultra-relativistic collisions. This indicates that charm quarks may not fully thermalise, especially in small systems such as peripheral or light-ion collisions. We further show that, for $D_s^\text{lQCD}(T)$, the deviation from equilibrium becomes as large as $δf_{HQ}/f_{eq} \sim p_T^β\sim \mathcal{O}(1)$ already at $p_T\simeq 3\rm\, GeV$, rising with $β\sim 4.5$, thus questioning the applicability of viscous hydrodynamics to charm dynamics.

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arXiv2025

Probing the QGP through $p_T$-differential radial flow of heavy quarks

We introduce the $p_T$-differential radial flow $v_0(p_T)$ in the heavy-quark sector. Within an event-by-event Langevin framework, we show that this observable exhibits a strong sensitivity to the heavy quark-bulk interaction. It provides a powerful and novel tool to constrain the transport coefficients of heavy quarks in the QGP and, more generally, to assess the strength of the interaction of a Brownian particle in an expanding bulk medium. The results further indicate that heavy quarks exhibit collective behavior driven by the isotropic expansion of the QGP in heavy-ion collisions and, at low $p_T$, it offers a marked signature of the heavy quark hadronization mechanism.

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arXiv2025

Assessing the lattice QCD space diffusion coefficient and the thermalization time of charm quark by mean of D meson observables at LHC

A central goal in the study of heavy-flavour production is to determine the interaction strength between Heavy Quarks (HQs) and the Quark-Gluon Plasma (QGP), quantified by the spatial diffusion coefficient $D_s(T)$. Recent lattice QCD (lQCD) results with dynamical fermions suggest a remarkably low value of $2πT D_s \approx 1$ at $T=T_c$ for charm quarks - significantly lower than both quenched QCD estimates and most phenomenological models - which typically yield $2πT D_s \approx 3.5 - 5$. This discrepancy raises the question of whether such a small $D_s(T)$, corresponding to a thermalization time $τ_{th} \approx 1 - 1.5$ fm/c, is compatible with experimental measurements of key observables like the nuclear modification factor $R_{AA}$, the elliptic and triangular flow coefficients $v_2$ and $v_3$ for D mesons. Using an event-by-event Langevin transport framework, we analyze several scenarios and highlight the pivotal role played by the momentum dependence of the drag coefficient $A(p) = τ_{th}^{-1}(p)$. Our findings show that a small $2πT D_s (p\rightarrow 0)\approx 1 - 2$ values can align with experimental data \emph{only} if a significant momentum dependence in $τ_{th}(p)=1/A(p)$ is included, as predicted by T-matrix approaches, or by the extended Quasi-Particle Model (QPMp). In contrast, assuming a momentum-independent $τ_{th} = M_c D_s^{\text{lQCD}} / T$, it fails to reproduce the observed phenomenology. Furthermore, a short thermalization time of $τ_{th} \approx 1.5$ fm/c implies a loss of sensitivity of the final-state observables to the initial charm-quark momentum distribution up $p_T \approx M_c$, suggesting a possible universal behavior driven by a dynamical attractor.

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arXiv2024

Quasi particle model vs lattice QCD thermodynamics: extension to $N_f=2+1+1$ flavors and momentum dependent quark masses

In the last decade a Quasi-Particle Model ($QPM$) has supplied the basis for the study of HQ production in ultra-relativistic AA collisions, allowing for a phenomenological estimate of the HQ diffusion coefficient $D_s(T)$. Taking advantage of the new lattice QCD results for the Equation of State (EoS) with 2+1+1 dynamical flavors, we extend our $QPM$ approach from $N_f=2+1$ to $N_f=2+1+1$, in which the charm quark is included. Given an effective coupling $g(T)$ fixed by a fit to the lQCD energy density $ε(T)$, we evaluate the impact of different temperature parametrizations of charm quark mass on EoS and susceptibilities $χ_q(T)$ of light, $χ_s(T)$ of strange and $χ_c(T)$ of charm quarks, the last favouring a charm quark mass increasing toward $T_c$. We also explore the extension of the $QPM$ approach to a more realistic approach, that we label $QPM_p$, in which quark and gluon masses explicitly depend on their momentum converging to the current quark mass at high momenta, as expected from asymptotic free dynamics. The $QPM_p$ is seen to allow for a simultaneous quantitative description not only of the EoS but also of the quark susceptibilities ($χ_q(T)$, $χ_s(T)$), which instead are underestimated in the simple $QPM$ model. Furthermore, evaluating the spatial diffusion coefficient $2πT D_s(T)$ in the $QPM_p$, we find it is also significantly closer than $QPM$ to the recent lQCD data performed including dynamical fermions. Finally, in a 1+1D expanding system, we evaluate the $R_{AA}(p_T)$ in the $QPM$ and $QPM_p$, finding a significant reduction at low momenta for $QPM_p$ which could lead in a realistic scenario to a better agreement to experimental data.

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arXiv2023

B meson production in Pb+Pb at 5.02 ATeV at LHC: estimating the diffusion coefficient in the infinite mass limit

In the last decade a Quasi-Particle Model (QPM) has been developed to study charm quark dynamics in ultra-relativistic heavy-ion collisions supplying a satisfactory description of the main observables for $D$ meson and providing an estimate of the space-diffusion coefficient $D_s(T)$ from the phenomenology. In this paper, we extend the approach to bottom quarks describing their propagation in the quark-gluon plasma within an event-by-event full Boltzmann transport approach followed by a coalescence plus fragmentation hadronization. We find that QPM approach is able to correctly predict the first available data on $R_{AA}(p_T)$ and $v_{2}(p_T)$ of single-electron from B decays without any parameter modification w.r.t. the charm. We show also predictions for centralities where data are not yet available for both $v_{2}(p_T)$ and $v_{3}(p_T)$. Moreover, we discuss the significant breaking of the expected scaling of the thermalization time $τ_{th}$ with $M_Q/T$, discussing the evolution with mass of $D_s(T)$ to better assess the comparison to lQCD calculations. We find that at $T=T_c$ charm quark $D_s(T)$ is about a factor of 2 larger than the asymptotic value for $M \rightarrow \infty$, while bottom $D_s(T)$ is only a $20-25\%$ higher. This implies a $D_{s}(T)$ which is consistent within the current uncertainty to the most recent lattice QCD calculations with dynamical quarks for $M \rightarrow \infty$.

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arXiv2022

Event shape Engineering analysis of D meson in ultrarelativistic heavy ion collisions

We describe the propagation of charm quarks in the quark-gluon plasma (QGP) by means of an event-by-event transport approach. In our calculations the non-perturbative interaction between heavy quarks and light quarks has been taken into account through a quasi-particle approach with thermal light quark masses tuned to reproduce lQCD thermodynamics. We found that the flow observables $v_2$ and $v_3$ of D mesons are comparable with the experimental measurements for Pb+Pb collisions at 5.02 ATeV in different ranges of centrality selections. The results are analyzed with Event-Shape Engineering technique. The comparison of the anisotropic flow coefficients $v_n$ with experimental data show a quite well agreement with experimental data for different flow vector $q_2$ selections, which confirms the strong coupling between charm quarks and light quarks in the QCD matter. Furthermore, we present here a novel study of the event-by-event correlations between flow harmonics of $D$ mesons and soft hadrons at LHC energy with the Event-Shape Engineering technique that can put further constraints on heavy quark transport coefficients toward a solid comparison between the phenomenological determination and the lattice QCD calculations.

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arXiv2020

Impact of off-shell dynamics on the transport properties and the dynamical evolution of Charm Quarks at RHIC and LHC temperatures

We evaluate drag and diffusion transport coefficients comparing a quasi-particle approximation with on-shell constituents of the QGP medium and a dynamical quasi-particles model with off-shell bulk medium at finite temperature T. We study the effects of the width $γ$ of the particles of the bulk medium on the charm quark transport properties exploring the range where $γ< M_{q,g}$. We find that off-shell effects are in general quite moderate and can induce a reduction of the drag coefficient at low momenta that disappear already at moderate momenta, $p \gtrsim 2-3\, \rm GeV$. We also observe a moderate reduction of the breaking of the Fluctuation-Dissipation theorem (FDT) at finite momenta. Moreover, we have performed a first study of the dynamical evolution of HQ elastic energy loss in a bulk medium at fixed temperature extending the Boltzmann (BM) collision integral to include off-shell dynamics. A comparison among the Langevin dynamics, the BM collisional integral with on-shell and the BM extension to off-shell dynamics shows that the evolution of charm energy when off-shell effects are included remain quite similar to the case of the on-shell BM collision integral.

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