Effect of bulk viscosity on interferometry correlations in ultrarelativistic heavy-ion collisions

A temperature-dependent bulk viscosity coefficient is used in $3+1$-dimensional hydrodynamic simulations. I study the effect of the increase of bulk viscosity around the critical temperature on the system dynamics in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=2760$ GeV. With increasing bulk viscosity the lifetime of the system increases slightly. Also the shape of the freeze-out hypersurface changes; the outer layers of the fireball live longer. This effect causes a small reduction of the ratio of two interferometry radii, $R_{\mathrm{out}}/R_{\mathrm{side}}$, improving the agreement with experimental data.

Figure 1

The temperature dependence of the ratio of the bulk viscosity coefficient to entropy density $\zeta /s$ for the two scenarios considered, with the bulk viscosity in the low temperature region only (solid line) and with an additional peak of the bulk viscosity around the critical temperature (dotted line).

Figure 2

The shape of the freeze-out hypersurface from hydrodynamic simulations with two scenarios for the bulk viscosity coefficient, with and without a bulk viscosity peak (dotted and solid lines, respectively).

Figure 3

The HBT radii $R_{\mathrm{out}}$ (a), $R_{\mathrm{side}}$ (b), and $R_{\mathrm{long}}$ (panel c) for central Pb-Pb collisions at 2760 GeV. ALICE Collaboration data (squares) compared to hydrodynamic calculations with smooth initial conditions, with (dotted lines) and without (solid lines) a peak in the temperature dependence of the bulk viscosity.

Figure 4

The ratio of HBT radii $R_{\mathrm{out}}/R_{\mathrm{side}}$ for central Pb-Pb collisions at 2760 GeV. ALICE Collaboration data (squares) are compared to hydrodynamic calculations using smooth initial conditions with (dotted line) and without (solid line) a peak in the temperature dependence of the bulk viscosity.

Figure 5

Same as Fig. 2 but starting the evolution with one particular initial condition from a Glauber–Monte Carlo model.

Figure 6

The harmonic flow coefficients $v_2$ (a) and $v_3$ (b) calculated with (dotted line) and without (solid line) a bulk viscosity peak at the critical temperature. Data are from the ALICE Collaboration [22].

Figure 7

Same as Fig. 3 but for a calculation using an ensemble of fluctuating initial conditions from a Glauber–Monte Carlo model.

Figure 8

Same as Fig. 4 but for a calculation using an ensemble of fluctuating initial conditions from a Glauber–Monte Carlo model.