Ratios of collective flow observables in high-energy isobar collisions are insensitive to final-state interactions

The ratios of bulk observables, such as harmonic flow v(2) and v(3), between high-energy Ru-96 + Ru-96 and Zr-96 + Zr-96 collisions were recently argued to be a clean probe of the nuclear structure differences between Ru-96 and Zr-96. Using a transport model simulation of isobar collisions, we quantify this claim from the dependence of the ratios v(2,Ru)/v(2,Zr) and v(3,Ru)/v(3,Zr) on various final-state effects, such as the shear viscosity, hadronization, and hadronic cascade. Although the v(2) and v(3) change by more than 50% when varying the final-state effects, the ratios are unchanged. In addition, these ratios are independent of the transverse momentum p(T) and hadron species, despite of up to a factor of 2 change in v(n). The ratio of mean transverse momentum < p(T)> is found to be controlled by the nuclear skin and nuclear radius but is only slightly impacted by the final-state effects. Therefore, these isobar ratios serve as a clean probe of the initial condition of the quark-gluon plasma, which, in turn, is controlled by the collective structure of the colliding nuclei.

Automated summary

Research has shown that the ratios of v(2) and v(3) in isobar collisions remain unchanged despite variations in final-state effects, making them a clean probe of the initial conditions of the quark-gluon plasma.