Effect of transport processes on elliptic flow centrality dependence under different initial conditions in the AMPT model

Abstract Using the AMPT model, we study charged hadron elliptic flow ( $$v_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>v</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> ) centrality dependence in Au+Au collisions at $$\sqrt{s_{NN}}=200~\textrm{GeV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mrow> <mml:mi>NN</mml:mi> </mml:mrow> </mml:msub> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>200</mml:mn> <mml:mspace/> <mml:mtext>GeV</mml:mtext> </mml:mrow> </mml:math> . We find distinct centrality-dependent roles for partonic ( $$\sigma _{p}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mi>p</mml:mi> </mml:msub> </mml:math> ) and hadronic ( $$\sigma _{H}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mi>H</mml:mi> </mml:msub> </mml:math> ) transport processes. In central collisions, $$v_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>v</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> is dominantly amplified by larger $$\sigma _{p}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mi>p</mml:mi> </mml:msub> </mml:math> (reducing partonic viscosity) but insensitive to $$\sigma _{H}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mi>H</mml:mi> </mml:msub> </mml:math> . In peripheral collisions, larger $$\sigma _{H}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mi>H</mml:mi> </mml:msub> </mml:math> (reducing hadronic viscosity) significantly enhances $$v_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>v</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> , flattening its centrality dependence and improving agreement with STAR data. Initial pressure gradients (enhanced by Lund parameter $$a_{L}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>a</mml:mi> <mml:mi>L</mml:mi> </mml:msub> </mml:math> ) also increase $$v_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>v</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> , while $$b_{L}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>b</mml:mi> <mml:mi>L</mml:mi> </mml:msub> </mml:math> affects spectra but not flow. This centrality-differential sensitivity to $$\sigma _{p}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mi>p</mml:mi> </mml:msub> </mml:math> and $$\sigma _{H}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mi>H</mml:mi> </mml:msub> </mml:math> provides a novel strategy for extracting phase-specific shear viscosities.