Equation of state and speed of sound of ( 2+1 )-flavor QCD in strangeness-neutral matter at nonvanishing net baryon-number density

We update results on the QCD equation of state in ($2+1$)-flavor QCD with nonzero conserved charge chemical potentials obtained from an eighth-order Taylor series. To construct bulk thermodynamic observables, we use continuum extrapolated results for the second and fourth order expansion coefficients of pressure, while using spline interpolated result based on high statistics $N_{\tau }=8$ data for the sixth and eighth order expansion coefficients. We present results for basic bulk thermodynamic observables of strangeness-neutral strong-interaction matter, i.e., pressure, number densities, energy, and entropy density, and resum Taylor series results using Padé approximants. Furthermore, we calculate the speed of sound as well as the adiabatic compression factor of the strangeness-neutral matter on lines of constant entropy per net baryon number. We show that the equation of state [$P(n_B),\epsilon (n_B)$] is already well described by the 4th-order Taylor series in almost the entire range of temperatures accessible with the beam energy scan in collider mode at the Relativistic Heavy Ion Collider.