arXiv subjects

Claudia Ratti

Publications and source records attributed to Claudia Ratti.

At least 73 records · Page 4Linked to original sources

arXiv2022

Thermal-model-based characterization of heavy-ion-collision systems at chemical freeze-out

We investigate the chemical freeze-out in heavy-ion collisions (HICs) and the impact of the hadronic spectrum on thermal model analyses. Detailed knowledge of the hadronic spectrum is still an open question, which has phenomenological consequences on the study of HICs. By varying the number of resonances included in Hadron Resonance Gas (HRG) Model calculations, we can shed light on which particles may be produced. Furthermore, we study the influence of the number of states on the so-called two flavor freeze-out scenario, in which strange and light particles can freeze-out separately. We consider results for the chemical freeze-out parameters obtained from thermal model fits and from calculating net-particle fluctuations. We will show the effect of using one global temperature to fit all particles and alternatively, allowing particles with and without strange quarks to freeze-out separately.

hep-ph↗

arXiv2021

Quantifying corrections to the hadron resonance gas with lattice QCD

The hadron resonance gas (HRG) model and its extensions are often used to describe the hadronic phase of strongly interacting matter. In our work we use lattice-QCD simulations with temporal extents of $N_τ=8,10$ and $12$ to quantify corrections to the ideal HRG. Firstly, we determine a number of subleading fugacity expansion coefficients of the QCD free energy via a two-dimensional scan on the imaginary baryon number chemical potential ($μ_B$) - strangeness chemical potential ($μ_S$) plane. Using the aforementioned coefficients, we also extrapolate ratios of baryon number and strangeness fluctuations and correlations to finite chemical potentials via a truncated fugacity expansion. Our results extrapolated along the crossover line $T_\mathrm{c}(μ_B)$ at strangeness neutrality are able to reproduce trends of experimental net-proton fluctuations measured by the STAR Collaboration.

hep-lat↗

arXiv2021

Equation of state of QCD at finite chemical potential from an alternative expansion scheme

The equation of state of Quantum Chromodynamics (QCD) at finite density is currently known only in a limited range in the baryon chemical potential $μ_B$. This is due to fundamental shortcomings of traditional methods such as Taylor expansion around $μ_B=0$. In this contribution, we present an alternative scheme that displays substantially improved convergence over the Taylor expansion method. We calculate the alternative expansion coefficients in the continuum, and show our results for the thermodynamic observables up to $μ_B/T\le3.5$.

hep-lat↗

arXiv2021

The BEST framework for the search for the QCD critical point and the chiral magnetic effect

The Beam Energy Scan Theory (BEST) Collaboration was formed with the goal of providing a theoretical framework for analyzing data from the Beam Energy Scan (BES) program at the relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory. The physics goal of the BES program is the search for a conjectured QCD critical point as well as for manifestations of the chiral magnetic effect. We describe progress that has been made over the previous five years. This includes studies of the equation of state and equilibrium susceptibilities, the development of suitable initial state models, progress in constructing a hydrodynamic framework that includes fluctuations and anomalous transport effects, as well as the development of freezeout prescriptions and hadronic transport models. Finally, we address the challenge of integrating these components into a complete analysis framework. This document describes the collective effort of the BEST Collaboration and its collaborators around the world.

nucl-th↗

arXiv2021

Constraining the hadronic spectrum and repulsive interactions in a hadron resonance gas via fluctuations of conserved charges

We simultaneously incorporate two common extensions of the hadron resonance gas model, namely the addition of extra, unconfirmed resonances to the particle list and the excluded volume repulsive interactions. We emphasize the complementary nature of these two extensions and identify combinations of conserved charge susceptibilities that allow to constrain them separately. In particular, ratios of second-order susceptibilities like $χ_{11}^{BQ}/χ_2^B$ and $χ_{11}^{BS}/χ_2^B$ are sensitive only to the baryon spectrum, while fourth-to-second order ratios like $χ_4^B/χ_2^B$, $χ_{31}^{BS}/χ_{11}^{BS}$, or $χ_{31}^{BQ}/χ_{11}^{BQ}$ are mainly determined by repulsive interactions. Analysis of the available lattice results suggests the presence of both the extra states in the baryon-strangeness sector and the repulsive baryonic interaction, with indications that hyperons have a smaller repulsive core than non-strange baryons. The modified hadron resonance gas model presented here significantly improves the description of lattice QCD susceptibilities at chemical freeze-out and can be used for the analysis of event-by-event fluctuations in heavy-ion collisions.

nucl-th↗

arXiv2021

Strangeness neutral equation of state with a critical point

We formulate a family of equations of state for Quantum Chromodynamics that exhibit critical features and obey the charge conservation conditions present in heavy-ion collisions (HICs). This construction utilizes the first-principle Lattice QCD (LQCD) results up to $\mathcal{O}(μ_B^4)$ by matching the Taylor coefficients at each order. The criticality of the equation of state (EoS) is implemented based on the well-established principle of universal scaling behavior, where QCD belongs to the 3D Ising Model universality class. The critical point can be placed in a range of temperature and baryonic chemical potential relevant for the Beam Energy Scan II at RHIC. Furthermore, the strength of the critical features can be varied as well. This flexibility is embedded in four free parameters, that could potentially be constrained by the experimental data. We will discuss the features and versatility of our EoS, as well as present the relevant thermodynamic quantities which are important for hydrodynamical simulations of HICs.

nucl-th↗

arXiv2021

Off-of-equilibrium effects on Kurtosis Along Strangeness-Neutral Trajectories

The Beam Energy Scan program at the Relativistic Heavy Ion Collider (RHIC) is searching for the QCD critical point. The main signal for the critical point is the kurtosis of the distribution of proton yields obtained on an event-by-event basis where one expects a peak at the critical point. However, its exact behavior is still an open question due to out-of-equilibrium effects and uncertainty in the equation of state. Here we use a simplistic hydrodynamic model that enforces strangeness-neutrality, selecting trajectories that pass close to the critical point. We vary the initial conditions to estimate the effect of out-of-equilibrium hydrodynamics on the kurtosis signal.

nucl-th↗

arXiv2021

Shear viscosity at finite baryon densities

We use the excluded volume Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate $ηT/w$ at low temperatures and at finite baryon densities $ρ_B$. This $ηT/w$ is then matched to a QCD-based shear viscosity calculation of the QGP for different profiles of $ηT/w$ across {T,$μ_{B}$} including cross-over and critical point transitions. When compared to ideal hydrodynamic trajectories across {T,$μ_{B}$}, we find that the $ηT/w(T,μ_B)$ profiles would require initial conditions at much larger baryon density to reach the same freeze-out point.

hep-ph↗

arXiv2021

Hot and dense quark-gluon plasma thermodynamics from holographic black holes

We present new results on the equation of state and transition line of hot and dense strongly interacting QCD matter, obtained from a bottom-up Einstein-Maxwell-Dilaton holographic model. We considerably expand the previous coverage in baryon densities in this model by implementing new numerical methods to map the holographic black hole solutions onto the QCD phase diagram. We are also able to obtain, for the first time, the first-order phase transition line in a wide region of the phase diagram. Comparisons with the most recent lattice results for the QCD thermodynamics are also presented.

nucl-th↗

arXiv2021

Smooth matching of $\hat{q}$ from hadronic to quark and gluon degrees of freedom

One of the key signatures of the Quark Gluon Plasma (QGP) is the energy loss of high momentum particles as they traverse the strongly interacting medium. The energy loss of these particles is governed by the jet transport coefficient $\hat{q}/T^3$, wherein it has been thought that there is a large jump as the system transitions between the hadron gas and Quark Gluon Plasma phases. Here we calculate $\hat{q}/T^3$ within the Hadron Resonance Gas (HRG) model with the particle list PDG16+ and find that, if one incorporates the experimental error in the hadronic calculation of $\hat{q}/T^3$ and assumes a higher pseudo-critical temperature, then a smooth transition from the hadron gas phase into the Quark Gluon Plasma phase is possible. We also find a significant enhancement in $\hat{q}/T^3$ at finite baryon chemical potential and find issues with the relationship between the shear viscosity and the jet transport coefficient within a hadron gas phase.

nucl-th↗

arXiv2021

Building a testable shear viscosity across the QCD phase diagram

Current experiments at the Relativistic Heavy Ion Collider (RHIC) are probing finite baryon densities where the shear viscosity to enthalpy ratio $ηT/w$ of the Quark Gluon Plasma remains unknown. We use the Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate $ηT/w$ at low temperatures and at finite baryon densities $ρ_B$. We then match $ηT/w$ to a QCD-based shear viscosity calculation within the deconfined phase to create a table across $\left\{T,μ_B\right\}$ for different cross-over and critical point scenarios at a specified location. We find that these new $ηT/w(T,μ_B)$ values would require initial conditions at significantly larger $ρ_B$, compared to ideal hydrodynamic trajectories, in order to reach the same freeze-out point.

nucl-th↗

arXiv2021

Corrections to the hadron resonance gas from lattice QCD and their effect on fluctuation-ratios at finite density

The hadron resonance gas (HRG) model is often believed to correctly describe the confined phase of QCD. This assumption is the basis of many phenomenological works on QCD thermodynamics and of the analysis of hadron yields in relativistic heavy ion collisions. We use first-principle lattice simulations to calculate corrections to the ideal HRG. Namely, we determine the sub-leading fugacity expansion coefficients of the grand canonical free energy, receiving contributions from processes like kaon-kaon or baryon-baryon scattering. We achieve this goal by performing a two dimensional scan on the imaginary baryon number chemical potential ($μ_B$) - strangeness chemical potential ($μ_S$) plane, where the fugacity expansion coefficients become Fourier coefficients. We carry out a continuum limit estimation of these coefficients by performing lattice simulations with temporal extents of $N_τ=8,10,12$ using the 4stout-improved staggered action. We then use the truncated fugacity expansion to extrapolate ratios of baryon number and strangeness fluctuations and correlations to finite chemical potentials. Evaluating the fugacity expansion along the crossover line, we reproduce the trend seen in the experimental data on net-proton fluctuations by the STAR collaboration.

hep-lat↗

arXiv2020

Future Physics Perspectives on the Equation of State from Heavy Ion Collisions to Neutron Stars

With the computational power and algorithmic improvements available today, the ongoing STAR/RHIC and HADES/GSI experiments, the future FAIR and NICA facilities becoming operational, and the new precise measurements from NICER and LIGO/VIRGO, the high-energy nuclear physics and astrophysics communities are in the unique position to set very stringent constraints on the equation of state of strongly interacting matter. We review the state-of-the-art of different approaches used in the description of hot and ultradense baryonic matter in and out of equilibrium, and discuss the regions in the phase diagram where heavy-ion collisions and neutron star mergers can overlap. Future perspectives are discussed to help define a comprehensive, multi-disciplinary strategy to map out the phase diagram of strongly interacting matter from heavy ion collisions to neutron stars.

nucl-th↗

arXiv2020

QCD equation of state matched to lattice data and exhibiting a critical point singularity

We construct a family of equations of state for QCD in the temperature range 30 MeV $\leq T\leq$ 800 MeV and in the chemical potential range $0\leq μ_B \leq$ 450 MeV. These equations of state match available lattice QCD results up to $\mathcal{O}(μ_B^4)$ and in each of them we place a critical point in the 3D Ising model universality class. The position of this critical point can be chosen in the range of chemical potentials covered by the second Beam Energy Scan at RHIC. We discuss possible choices for the free parameters, which arise from mapping the Ising model onto QCD. Our results for the pressure, entropy density, baryon density, energy density and speed of sound can be used as inputs in the hydrodynamical simulations of the fireball created in heavy ion collisions. We also show our result for the second cumulant of the baryon number in thermal equilibrium, displaying its divergence at the critical point. In the future, comparisons between RHIC data and the output of the hydrodynamic simulations, including calculations of fluctuation observables, built upon the model equations of state that we have constructed may be used to locate the critical point in the QCD phase diagram, if there is one to be found.

hep-ph↗

arXiv2020

Chemical freeze-out parameters of net-kaons in heavy-ion collisions

We study chemical freeze-out parameters for heavy-ion collisions by performing two different thermal analyses. We analyze results from thermal fits for particle yields, as well as, net-charge fluctuations in order to characterize the chemical freeze-out. The Hadron Resonance Gas (HRG) model is employed for both methods. By separating the light hadrons from the strange hadrons in thermal fits, we study the proposed flavor hierarchy. For the net-charge fluctuations, we calculate the mean-over-variance ratio of the net-kaon fluctuations in the HRG model at the five highest energies of the RHIC Beam Energy Scan (BES) for different particle data lists. We compare these results with recent experimental data from the STAR collaboration in order to extract sets of chemical freeze-out parameters for each list. We focused on particle lists which differ largely in the number of resonant states. By doing so, our analysis determines the effect of the amount of resonances included in the HRG model on the freeze-out conditions. Our findings have potential impact on various other models in the field of relativistic heavy-ion collisions.

hep-ph↗

arXiv2020

Off-diagonal correlators of conserved charges from lattice QCD and how to relate them to experiment

Like fluctuations, non-diagonal correlators of conserved charges provide a tool for the study of chemical freeze-out in heavy ion collisions. They can be calculated in thermal equilibrium using lattice simulations, and be connected to moments of event-by-event net-particle multiplicity distributions. We calculate them from continuum extrapolated lattice simulations at $μ_B=0$, and present a finite-$μ_B$ extrapolation, comparing two different methods. In order to relate the grand canonical observables to the experimentally available net-particle fluctuations and correlations, we perform a Hadron Resonance Gas (HRG) model analysis, which allows us to completely break down the contributions from different hadrons. We then construct suitable hadronic proxies for fluctuations ratios, and study their behavior at finite chemical potentials. We also study the effect of introducing acceptance cuts, and argue that the small dependence of certain ratios on the latter allows for a direct comparison with lattice QCD results, provided that the same cuts are applied to all hadronic species. Finally, we perform a comparison for the constructed quantities for experimentally available measurements from the STAR Collaboration. Thus, we estimate the chemical freeze-out temperature to 165 MeV using a strangeness-related proxy. This is a rather high temperature for the use of the Hadron Resonance Gas, thus, further lattice studies are necessary to provide first principle results at intermediate $μ_B$.

hep-lat↗

arXiv2020

The QCD crossover at finite chemical potential from lattice simulations

We provide the most accurate results for the QCD transition line so far. We optimize the definition of the crossover temperature $T_c$, allowing for its very precise determination, and extrapolate from imaginary chemical potential up to real $μ_B \approx 300$ MeV. The definition of $T_c$ adopted in this work is based on the observation that the chiral susceptibility as a function of the condensate is an almost universal curve at zero and imaganiary $μ_B$. We obtain the parameters $κ_2=0.0153(18)$ and $κ_4=0.00032(67)$ as a continuum extrapolation based on $N_t=10,12$ and $16$ lattices with physical quark masses. We also extrapolate the peak value of the chiral susceptibility and the width of the chiral transition along the crossover line. In fact, both of these are consistent with a constant function of $μ_B$. We see no sign of criticality in the explored range.

hep-lat↗

arXiv2019

Determination of Chemical Freeze-out Parameters from Net-kaon Fluctuations at RHIC

We calculate the mean-over-variance ratio of the net-kaon fluctuations in the Hadron Resonance Gas (HRG) Model for the five highest energies of the RHIC Beam Energy Scan (BES) for different particle data lists. We compare these results with the latest experimental data from the STAR collaboration in order to extract sets of chemical freeze-out parameters for each list. We focused on the PDG2012 and PDG2016+ particle lists, which differ largely in the number of resonant states. Our analysis determines the effect of the amount of resonances included in the HRG on the freeze-out conditions.

hep-ph↗