This picture illustrates the distribution of the average angular velocity along the y-axis wy in the rapidity-transverse momentum plane in ¹²C + ¹⁹⁷Au collision at \sqrt{s_NN}= 200 GeV. The impact parameter is b = 4.5 fm for the mid-central collision. The left to right panels correspond to the freeze-out partons, the hadrons without hadronic rescattering, and the fi nal-state hadrons, respectively. While from top to bottom are the three different nuclear structure confi gurations listed as the Woods–Saxon structure, the chain α – clustering structure, and the triangle α – clustering structure. It implied that most participants carried a small angular velocity of the order of magnitude of approximately10^-2. NUCL SCI TECH (2018)29:186, page 5, Figure 4.