Net-Baryon Number Fluctuations in (2+1)-Flavor QCD (original) (raw)
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Net-baryon Number Fluctuations
Acta Physica Polonica B Proceedings Supplement, 2021
The appearance of large, none-Gaussian cumulants of the baryon number distribution is commonly discussed as a signal for the QCD critical point. We review the status of the Taylor expansion of cumulant ratios of baryon number fluctuations along the freeze-out line and also compare QCD results with the corresponding proton number fluctuations as measured by the STAR Collaboration at RHIC. To further constrain the location of a possible QCD critical point we discuss poles of the baryon number fluctuations in the complex plane. Here we use not only the Taylor coefficients obtained at zero chemical potential but perform also calculations of Taylor expansion coefficients of the pressure at purely imaginary chemical potentials.
Fluctuations in the vicinity of the phase transition line for two flavor QCD
Nuclear Physics B - Proceedings Supplements, 2005
We study the susceptibilities of quark number, isospin number and electric charge in numerical simulations of lattice QCD at high temperature and density. We discuss the equation of state for 2 flavor QCD at non-zero temperature and density. Derivatives of ln Z with respect to quark chemical potential (µq) are calculated up to sixth order. From this Taylor series, the susceptibilities are estimated as functions of temperature and µq. Moreover, we comment on the hadron resonance gas model, which explains well our simulation results below Tc.
Physical Review D, 2012
We calculate the quadratic fluctuations of net baryon number, electric charge and strangeness as well as correlations among these conserved charges in (2+1)-flavor lattice QCD at zero chemical potential. Results are obtained using calculations with tree level improved gauge and the highly improved staggered quark (HISQ) actions with almost physical light and strange quark masses at three different values of the lattice cut-off. Our choice of parameters corresponds to a value of 160 MeV for the lightest pseudo scalar Goldstone mass and a physical value of the kaon mass. The three diagonal charge susceptibilities and the correlations among conserved charges have been extrapolated to the continuum limit in the temperature interval 150 MeV ≤ T ≤ 250 MeV. We compare our results with the hadron resonance gas (HRG) model calculations and find agreement with HRG model results only for temperatures T < ∼ 150 MeV. We observe significant deviations in the temperature range 160 MeV < ∼ T < ∼ 170 MeV and qualitative differences in the behavior of the three conserved charge sectors. At T ≃ 160 MeV quadratic net baryon number fluctuations in QCD agree with HRG model calculations while, the net electric charge fluctuations in QCD are about 10% smaller and net strangeness fluctuations are about 20% larger. These findings are relevant to the discussion of freeze-out conditions in relativistic heavy ion collisions. 2
Baryon number and charge fluctuations from lattice QCD
Nuclear Physics A, 2013
We calculate electric and baryonic charge fluctuations on the lattice. Results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with spacial extent of N τ = 6, 8, 12. Higher order cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which is arising due to a critical point of QCD in the chiral limit. Considering cumulants up to the sixth order, we observe that they generically behave as expected from universal scaling laws, which is quite different from the cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be compared to the experimental measurements. Such a comparison will unambiguously relate the QCD transition temperature that has been determined on the lattice with the freeze out temperature of heavy ion collision at LHC and RHIC.
Critical line of 2+1 flavor QCD: Toward the continuum limit
2016
We determine the continuum limit of the curvature of the pseudocritical line of QCD with n_f=2+1 staggered fermions at nonzero temperature and quark density. We perform Monte Carlo simulations at imaginary baryon chemical potentials, adopting the HISQ/tree action discretization, as implemented in the code by the MILC collaboration. Couplings are adjusted so as to move on a line of constant physics, as determined in Ref. Bazavov:2011nk, with the strange quark mass m_s fixed at its physical value and a light-to-strange mass ratio m_l/m_s=1/20. The chemical potential is set at the same value for the three quark species, μ_l=μ_s≡μ. We attempt an extrapolation to the continuum using the results on lattices with temporal size up to L_t=12. Our estimate for the continuum value of the curvature κ at zero baryon density, κ=0.020(4), is compared with recent lattice results and with experimental determinations of the freeze-out curve.
Conserved charge fluctuations at vanishing net-baryon density from Lattice QCD
EPJ Web of Conferences, 2022
We present here continuum extrapolated results for all 2nd order cumulants using the most resent results obtained by the HotQCD collaboration in (2+1)-flavor QCD. We constrain the applicability of various HRG models by presenting a detailed comparison of our results based on different sets of hadron spectra as well as with virial expansion based model calculations. A comparison with our lattice QCD results for 2nd order cumulants with models that parametrize repulsive interactions among baryons and anti-baryons in a hadron resonance gas through a single excluded volume parameter (EVHRG) is also shown.
oS(LATTICE 2007)175 Bulk thermodynamics and charge fluctuations at non-vanishing baryon density
2007
We present results on bulk thermodynamic quantities as well as net baryon number, strangeness and electric charge fluctuations in QCD at non-zero density and temperature obtained from lattice calculations with almost physical quark masses for two values of the lattice cut-off aT = 1/4 and 1/6. We show that with our improved p4fa3-action the cut-off effects are under control when using lattices with a temporal extent of 6 or larger and that the contribution to the equation of state, which is due to a finite chemical potential is small for μq/T < 1. Moreover, at vanishing chemical potential, i.e. under conditions almost realized at RHIC and the LHC, quartic fluctuations of net baryon number and strangeness are large in a narrow temperature interval characterizing the transition region from the low to high temperature phase. At non-zero baryon number density, strangeness fluctuations are enhanced and correlated to fluctuations of the net baryon number. If strangeness is furthermore ...
On the critical line of 2+1 flavor QCD
2014
We determine the curvature of the (pseudo)critical line of QCD with n_f=2+1 staggered fermions at nonzero temperature and quark density, by analytic continuation from imaginary chemical potentials. Monte Carlo simulations are performed adopting the HISQ/tree action discretization, as implemented in the code by the MILC collaboration, suitably modified to include a nonzero imaginary baryon chemical potential. We work on a line of constant physics, as determined in Ref.Bazavov:2011nk, adjusting the couplings so as to keep the strange quark mass m_s fixed at its physical value, with a light to strange mass ratio m_l/m_s=1/20. In the present investigation we set the chemical potential at the same value for the three quark species, μ_l=μ_s≡μ. We explore lattices of different spatial extensions, 16^3× 6 and 24^3× 6, to check for finite size effects, and present results on a 32^3 × 8 lattice, to check for finite cut-off effects. We discuss our results for the curvature κ of the critical li...
Numerical Study of the Equation of State for Two Flavor QCD at Non-Zero Baryon Density
Strong and Electroweak Matter 2004, 2005
We discuss the equation of state (EoS) for two flavor QCD at non-zero temperature and density. Derivatives of ln Z with respect to quark chemical potential µq are calculated up to sixth order. From this Taylor series, the pressure, quark number density and associated susceptibilities are estimated as functions of temperature and µq. It is found that the fluctuations in the quark number density increase in the vicinity of the phase transition temperature and the susceptibilities start to develop a pronounced peak as µq is increased. This suggests the presence of a critical endpoint in the (µq, T) plane. Moreover, we comment on the hadron resonance gas model, which explains well our simulation results below Tc.
Baryonic thermal fluctuations in finite temperature QCD
Physics Letters B, 1998
We show how, contrary to physical intuition, thermal fluctuations of physical states having a non-vanishing baryonic number can be fully neglected in the thermodynamics of QCD at any physical temperature. We also discuss on the consistency between our results and the CP T theorem. The last part of this article is devoted to comment some interesting physical features which follow from this result.