Hadronic dissipative effects on elliptic flow in ultrarelativistic heavy-ion collisions

Abstract

We study the elliptic flow coefficient v_2(eta,b) in Au+Au collisions at sqrt(s)=200 A GeV as a function of pseudorapidity eta and impact parameter b. Using a hybrid approach which combines early ideal fluid dynamical evolution with late hadronic rescattering, we demonstrate strong dissipative effects from the hadronic rescattering stage on the elliptic flow. With Glauber model initial conditions, hadronic dissipation is shown to be sufficient to fully explain the differences between measured v_2 values and ideal hydrodynamic predictions. Initial conditions based on the Color Glass Condensate model generate larger elliptic flow and seem to require additional dissipation during the early quark-gluon plasma stage in order to achieve agreement with experiment.

Figures (4)

• Figure 1: (Color online) Initial spatial eccentricity $\varepsilon{\,=\,}\frac{\langle y^2{-}x^2\rangle}{\langle y^2{+}x^2\rangle}$ at midrapidity as a function of impact parameter $b$, for 200 $A$ GeV Au+Au collisions with CGC (solid red) and BGK (dashed blue) initial conditions. For comparison we also show initial conditions where the initial parton density at midrapidity scales with the transverse density of wounded nucleons (dotted green) and of binary collisions (dash-dotted black) Kolb:2001qz.
• Figure 2: (Color online) $p_T$-integrated elliptic flow for charged hadrons at midrapidity ($\mid\eta\mid < 1$) from 200 $A$ GeV Au+Au collisions, as a function of the number $N_{\rm part}$ of participating nucleons. The thin lines show the prediction from ideal fluid dynamics with a freeze-out temperature $T_{\rm dec}{\,=\,}100$ MeV, for CGC (solid red) and BGK (dashed blue) initial conditions. The thick lines (solid red for CGC and dashed blue for BGK initial conditions) show the corresponding results from the hydro+cascade hybrid model. The data are from the PHOBOS Collaboration data.
• Figure 3: (Color online) The pseudorapidity dependence of $v_2$ for charged hadrons in (a) central (3-15%), (b) semicentral (15-25%), and (c) peripheral (25-50%) Au+Au collisions at $\sqrt{s}{\,=\,}200\,A$ GeV. The corresponding impact parameters are, respectively, $b=4.0, 6.3,$ and 8.5 fm. The hydrodynamic evolution is initialized with modified BGK initial conditions. The lines show the predictions from ideal fluid dynamics with $T_\mathrm{dec}{\,=\,}100$ MeV (solid blue) and $T_\mathrm{dec}{\,=\,}169$ MeV (dashed green). The red circles show the corresponding results from the hydro+cascade hybrid model. The black squares are measurements by the PHOBOS Collaboration data.
• Figure 4: (Color online) Same as Fig. \ref{['F3']}, except for using CGC instead of BGK initial conditions.