Claudia Ratti - INFN, Turin & Turin University

Claudia Ratti
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Claudia Ratti
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INFN, Turin & Turin University
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High Energy Physics - Phenomenology (26)
 
High Energy Physics - Lattice (16)
 
Nuclear Theory (15)
 
Nuclear Experiment (4)
 
High Energy Physics - Theory (1)

Publications Authored By Claudia Ratti

We employ an Einstein-Maxwell-Dilaton (EMD) holographic model, which is known to be in good agreement with lattice results for the QCD equation of state with $(2+1)$ flavors and physical quark masses, to investigate the temperature and baryon chemical potential dependence of the susceptibilities, conductivities, and diffusion coefficients associated with baryon, electric, and strangeness conserved charges. We also determine how the bulk and shear viscosities of the plasma vary with increasing baryon density. The diffusion of conserved charges and the hydrodynamic viscosities in a baryon rich quark-gluon plasma are found to be suppressed with respect to the zero net baryon case. Read More

Fluctuations of conserved charges allow to study the chemical composition of hadronic matter. A comparison between lattice simulations and the Hadron Resonance Gas (HRG) model suggested the existence of missing strange resonances. To clarify this issue we calculate the partial pressures of mesons and baryons with different strangeness quantum numbers using lattice simulations in the confined phase of QCD. Read More

The precision reached by recent lattice QCD results allows for the first time to investigate whether the measured hadronic spectrum is missing some additional strange states, which are predicted by the Quark Model but have not yet been detected. This can be done by comparing some sensitive thermodynamic observables from lattice QCD to the predictions of the Hadron Resonance Gas model (with the inclusion of decays [3]). We propose a set of specific observables, defined as linear combinations of conserved charge fluctuations, which allow to investigate this issue for baryons containing one or more strange quarks separately. Read More

Event-by-event fluctuations caused by quantum mechanical fluctuations in the wave function of colliding nuclei in ultrarelativistic heavy ion collisions were recently shown to be necessary for the simultaneous description of $R_{AA}$ as well as the elliptic and triangular flow harmonics at high $p_T$ in PbPb collisions at the Large Hadron Collider. In fact, the presence of a finite triangular flow as well as cumulants of the flow harmonic distribution that differ from the mean are only possible when these event-by-event fluctuations are considered. In this paper we combine event-by-event viscous hydrodynamics and jet quenching to make predictions for high $p_T$ $R_{AA}$, $v_2\{2\}$, $v_3\{2\}$, and $v_2\{4\}$ in PbPb collisions at $\sqrt{s_{NN}}=5. Read More

We show that it is possible to isolate a set of kaon fluctuations in lattice QCD. By means of the Hadron Resonance Gas (HRG) model, we calculate the actual kaon second-to-first fluctuation ratio, which receives contribution from primordial kaons and resonance decays, and show that it is very close to the one obtained for primordial kaons in the Boltzmann approximation. The latter only involves the strangeness and electric charge chemical potentials, which are functions of $T$ and $\mu_B$ due to the experimental constraint on strangeness and electric charge, and can therefore be calculated on the lattice. Read More

We present an overview of the most recent results on bulk and transport properties of QCD matter inferred from lattice QCD simulations. Read More

By analyzing preliminary experimental measurements of charge-balance functions from the STAR Collaboration at the Relativistic-Heavy-Ion Collider (RHIC), it is found that pictures where balancing charges are produced in a single surge, and therefore separated by a single length scale, are inconsistent with data. In contrast, a model that assumes two surges, one associated with the formation of a thermalized quark-gluon plasma and a second associated with hadronization, provides a far superior reproduction of the data. A statistical analysis of the model comparison finds that the two-surge model best reproduces the data if the charge production from the first surge is similar to expectations for equilibrated matter taken from lattice gauge theory. Read More

We study the sensitivity of the higher-order moments of produced particle multiplicity distributions to the chemical freeze-out parameters in relativistic heavy ion collisions using the Hadron Resonance Gas (HRG) model. We compare the obtained sensitivity level to the one extracted from the ratios of particle yields. We find that, for certain final state hadrons, the fluctuation measurements add significant information to the determination of the hadro-chemical freeze-out properties of the deconfined phase of matter obtained at RHIC and the LHC. Read More

We report on a continuum extrapolated result (arXiv:1309.5258) for the equation of state (EoS) of QCD with $N_f=2+1$ dynamical quark flavors and discuss preliminary results obtained with an additional dynamical charm quark ($N_f=2+1+1$). For all our final results, the systematics are controlled, quark masses are set to their physical values, and the continuum limit is taken using at least three lattice spacings corresponding to temporal extents up to $N_t=16$. Read More

Preliminary charge balance functions from the STAR Collaboration at the Relativistic Heavy Ion Collider (RHIC) are compared to a model where quarks are produced in two waves. If a chemically equilibrated quark-gluon plasma (QGP) is created the strength and diffusive spread of the first wave should be governed by the chemical composition of the QGP, while the second wave should be determined by the increased number of quarks required to make the observed final-state hadrons. A simple model parameterizes the chemistry of the super-hadronic matter and the two correlation lengths for the two waves. Read More

2014Aug
Affiliations: 1NCSU, Raleigh, 2INFN, Turin & Turin U., 3INFN, Turin & Turin U., 4Houston U., 5INFN, Turin & Turin U., 6Duke U., 7INFN, Turin & Turin U.

We extract chemical freeze-out conditions via a thermal model approach from fluctuation observables measured at RHIC and compare with results from lattice QCD and statistical hadronization model fits. The possible influence of additional critical and non-critical fluctuation sources not accounted for in our analysis is discussed. Read More

We calculate ratios of higher-order susceptibilities quantifying fluctuations in the number of net protons and in the net-electric charge using the Hadron Resonance Gas (HRG) model. We take into account the effect of resonance decays, the kinematic acceptance cuts in rapidity, pseudo-rapidity and transverse momentum used in the experimental analysis, as well as a randomization of the isospin of nucleons in the hadronic phase. By comparing these results to the latest experimental data from the STAR collaboration, we determine the freeze-out conditions from net-electric charge and net-proton distributions and discuss their consistency. Read More

We present a quasiparticle model for the pure gauge sector of QCD, in which transverse quasigluons propagate in a Polyakov loop background field. By incorporating thermodynamic self-consistency in the approach, we show that our Polyakov loop extended quasiparticle model allows an accurate description of recent lattice results for all the thermodynamic quantities, including the Polyakov loop expectation value, in the deconfined phase. The related quasigluon mass exhibits a distinct temperature dependence, which is connected with the non-perturbative behavior seen in the scaled interaction measure of the pure gauge theory. Read More

We investigate net-proton fluctuations as important observables measured in heavy-ion collisions within the hadron resonance gas (HRG) model. Special emphasis is given to effects which are a priori not inherent in a thermally and chemically equilibrated HRG approach. In particular, we point out the importance of taking into account the successive regeneration and decay of resonances below the chemical freeze-out, which lead to a randomization of the isospin of nucleons and thus to additional fluctuations in the net-proton number. Read More

We present possible indications for flavor separation during the QCD crossover transition based on continuum extrapolated lattice QCD calculations of higher order susceptibilities. We base our findings on flavor specific quantities in the light and strange quark sector. We propose a possible experimental verification of our prediction, based on the measurement of higher order moments of identified particle multiplicities. Read More

In this talk we review, the quasiparticle description of the hot Yang-Mills theories, in which the quasiparticles propagate in (and interact with) a background field related to Z(N)-lines. We compare the present description with a more common one in which the effects of the Z(N)-lines are neglected. We show that it is possible to take into account the nonperturbative effects at the confinement transition temperature even without a divergent quasiparticle mass. Read More

We present an update on the QCD equation of state of the Wuppertal-Budapest Collaboration, extending our previous studies [JHEP 0601 (2006) 089, JHEP 1011 (2010) 077]. A Symanzik improved gauge and a stout-link improved staggered fermion action is utilized. We discuss partial quenching and present preliminary results for the fully dynamical charmed equation of state. Read More

We present the full results of the Wuppertal-Budapest lattice QCD collaboration on flavor diagonal and non-diagonal quark number susceptibilities with 2+1 staggered quark flavors, in a temperature range between 125 and 400 MeV. The light and strange quark masses are set to their physical values. Lattices with Nt=6, 8, 10, 12, 16 are used. Read More

Recent lattice QCD calculations, at physical pion masses and small lattice spacings that approach the continuum limit, have revealed that non-diagonal quark correlators above the critical temperature are finite up to about 2 $T_c$. Since the transition from hadronic to free partonic degrees of freedom is merely an analytic cross-over, it is likely that, in the temperature regime between 1-2 $T_c$, quark and gluon quasiparticles and pre-hadronic bound states can coexist. The correlator values, in comparison to PNJL model calculations beyond mean-field, indicate that at least part of the mixed phase resides in color-neutral bound states. Read More

2011Sep
Affiliations: 1Wuppertal-Budapest Collaboration, 2Wuppertal-Budapest Collaboration, 3Wuppertal-Budapest Collaboration, 4Wuppertal-Budapest Collaboration, 5Wuppertal-Budapest Collaboration, 6Wuppertal-Budapest Collaboration

We present the new results of the Wuppertal-Budapest lattice QCD collaboration on flavor diagonal and non-diagonal quark number susceptibilities with 2+1 staggered quark flavors, in a temperature regime between 120 and 400 MeV. A Symanzik improved gauge and a stout-link improved staggered fermion action is utilized; the light and strange quark masses are set to their physical values. Lattices with $N_t=6, 8, 10, 12$ are used. Read More

2011Sep
Affiliations: 1Wuppertal-Budapest Collaboration, 2Wuppertal-Budapest Collaboration, 3Wuppertal-Budapest Collaboration, 4Wuppertal-Budapest Collaboration, 5Wuppertal-Budapest Collaboration, 6Wuppertal-Budapest Collaboration, 7Wuppertal-Budapest Collaboration, 8Wuppertal-Budapest Collaboration

The QCD transition is studied on lattices up to $N_t=16$. The chiral condensate is presented as a function of the temperature, and the corresponding transition temperature is extracted. The equation of state is determined on lattices with $N_t=6,8,10$ and at some temperature values with $N_t=12$. Read More

The thermodynamic behavior of QCD matter at high temperature is currently studied by lattice QCD theory. The main features are the fast rise of the energy density $\epsilon$ around the critical temperature $T_c$ and the large trace anomaly of the energy momentum tensor $< \Theta_\mu^\mu >=\epsilon - 3 P$ which hints at a strongly interacting system. Such features can be accounted for by employing a massive quasi-particle model with a temperature-dependent bag constant. Read More

2010Dec
Affiliations: 1Wuppertal-Budapest Collaboration, 2Wuppertal-Budapest Collaboration, 3Wuppertal-Budapest Collaboration, 4Wuppertal-Budapest Collaboration, 5Wuppertal-Budapest Collaboration, 6Wuppertal-Budapest Collaboration, 7Wuppertal-Budapest Collaboration

We present our most recent investigations on the QCD cross-over transition temperatures with 2+1 staggered flavours and one-link stout improvement [JHEP 1009:073, 2010]. We extend our previous two studies [Phys. Lett. Read More

We conclude our investigation on the QCD equation of state (EoS) with 2+1 staggered flavors and one-link stout improvement. We extend our previous study [JHEP 0601:089 (2006)] by choosing even finer lattices. These new results [for details see arXiv:1007. Read More

We conclude our investigations on the QCD cross-over transition temperatures with 2+1 staggered flavours and one-link stout improvement. We extend our previous two studies [Phys. Lett. Read More

The present paper concludes our investigation on the QCD equation of state with 2+1 staggered flavors and one-link stout improvement. We extend our previous study [JHEP 0601:089 (2006)] by choosing even finer lattices. Lattices with $N_t=6,8$ and 10 are used, and the continuum limit is approached by checking the results at $N_t=12$. Read More

2010May
Affiliations: 1Wuppertal-Budapest Collaboration, 2Wuppertal-Budapest Collaboration, 3Wuppertal-Budapest Collaboration, 4Wuppertal-Budapest Collaboration, 5Wuppertal-Budapest Collaboration, 6Wuppertal-Budapest Collaboration, 7Wuppertal-Budapest Collaboration

The present paper concludes our investigations on the QCD cross-over transition temperatures with 2+1 staggered flavours and one-link stout improvement. We extend our previous two studies [Phys. Lett. Read More

We consider the radiation of photons from quarks scattering on color-magnetic monopoles in the Quark-Gluon Plasma. We consider a temperature regime $T\gsim2T_c$, where monopoles can be considered as static, rare objects embedded into matter consisting mostly of the usual "electric" quasiparticles, quarks and gluons. The calculation is performed in the classical, non-relativistic approximation and results are compared to photon emission from Coulomb scattering of quarks, known to provide a significant contribution to the photon emission rates from QGP. Read More

The role of color-magnetic monopoles in a pure gauge plasma at high temperature $T>2T_c$ is considered. In this temperature regime, monopoles can be considered heavy, rare objects embedded into matter consisting mostly of the usual "electric" quasiparticles, quarks and gluons. The gluon-monopole scattering is found to hardly influence thermodynamic quantities, yet it produces a large transport cross section, significantly exceeding that for pQCD gluon-gluon scattering up to quite high $T$. Read More

The possibility of describing the behavior of a $Q\overline{Q}$ pair in a hot plasma in terms of an effective potential is investigated. It is shown that as long as medium effects can be embodied in a gaussian action, like in the QED case, the $Q\overline{Q}$ propagator obeys a closed temporal evolution equation whose large-time behavior is governed by an effective potential. The latter, beside screening, displays also an imaginary part related to collisions. Read More

We study the role of magnetic monopoles at high enough temperature $T>2T_c$, when they can be considered heavy, rare objects embedded into matter consisting mostly of the usual "electric" quasiparticles, quarks and gluons. We review available lattice results on monopoles at finite temperatures. Then we proceed to classical and quantum charge-monopole scattering, solving the problem of gluon-monopole scattering for the first time. Read More

The Polyakov loop extended Nambu and Jona-Lasinio model (PNJL model) in a mean field framework shows astonishingly good agreement with lattice QCD calculations which needs to be better understood. The present work reports on further developments concerning both Polyakov loop and mesonic fluctuations beyond mean field approximation. Corrections beyond mean field are of special interest for the thermal expectation values of the Polyakov loop $\Phi$ and its conjugate $\Phi^*$, which differ once the quark chemical potential is non-zero. Read More

QCD thermodynamics is studied using a model which combines Polyakov loop dynamics with spontaneous chiral symmetry breaking and its restoration (the PNJL model). The input is fixed entirely by pure-gauge lattice QCD results and by pion properties in vacuum. Successful comparisons with results from thermal lattice QCD are achieved, including extrapolations to finite quark chemical potential. Read More

Quark number susceptibilities at finite quark chemical potential are investigated in the framework of the Polyakov-loop-extended Nambu Jona-Lasinio (PNJL) model. A detailed comparison is performed between the available lattice data, extrapolated using a Taylor expansion around vanishing chemical potential, and PNJL results consistently obtained from a Taylor series truncated at the same order. The validity of the Taylor expansion is then examined through a comparison between the full and truncated PNJL model calculations. Read More

An updated version of the PNJL model is used to study the thermodynamics of N_f = 2 quark flavors interacting through chiral four-point couplings and propagating in a homogeneous Polyakov loop background. Previous PNJL calculations are extended by introducing explicit diquark degrees of freedom and an improved effective potential for the Polyakov loop field. The input is fixed exclusively by selected pure-gauge lattice QCD results and by pion properties in vacuum. Read More

QCD-based thermodynamics at zero and finite quark chemical potential is studied using an extended Nambu and Jona-Lasinio approach in which quarks couple simultaneously to the chiral condensate and to a background temporal gauge field representing Polyakov loop dynamics. This so-called PNJL model thus includes features of both deconfinement and chiral symmetry restoration. We discuss the phase diagram as it emerges from this approach in close comparison with results from lattice QCD thermodynamics. Read More

2001Dec
Affiliations: 1Ferrara Univ. and INFN Ferrara, 2ECT Trento, 3Ferrara Univ. and INFN Ferrara

We interpret lattice data for the equation of state of pure gauge $SU(3)_c$ by an evaporation model. At low temperatures gluons are frozen inside the gluon condensate, whose dynamics is described in terms of a dilaton lagrangian. Above the critical temperature quasi-free gluons evaporate from the condensate: a first order transition is obtained by minimizing the thermodynamical potential of the system. Read More