Azimuthal Harmonics in Small and Large Collision Systems at RHIC Top Energies

Area of Science:

• Nuclear and High-Energy Physics
• Quantum Chromodynamics (QCD) Phase Diagram
• Heavy-Ion Collisions

Background:

• Understanding the properties of the quark-gluon plasma (QGP) is crucial for mapping the QCD phase diagram.
• Azimuthal anisotropy coefficients (v_n) probe the QGP's initial conditions and transport properties.
• Previous studies have focused on specific collision systems and energy ranges.

Purpose of the Study:

• To systematically study the first (v_{1}^{fluc}), second (v_{2}), and third (v_{3}) harmonic coefficients of azimuthal particle distribution.
• To investigate the system size and multiplicity dependence of these coefficients across various collision systems.
• To provide insights into initial-state geometry fluctuations and the effects of viscous hydrodynamics.

Main Methods:

• Extraction of v_{1}^{fluc}, v_{2}, and v_{3} coefficients for charged hadrons at midrapidity.
• Analysis as a function of transverse momentum (p_{T}) and mean charged particle multiplicity density (⟨N_{ch}⟩).
• Measurements performed in U+U, Au+Au, Cu+Au, Cu+Cu, d+Au, and p+Au collisions at STAR.

Main Results:

• v_{1}^{fluc} and v_{3} are independent of the collision system for a given ⟨N_{ch}⟩.
• v_{2} shows system independence only when normalized by the initial-state eccentricity (ϵ_{2}).
• A linear scaling of ln(v_{2}/ϵ_{2}) with ⟨N_{ch}⟩^{-1/3} is observed.

Conclusions:

• The findings suggest a universal behavior of certain anisotropy coefficients, independent of system size, under specific conditions.
• The observed scaling provides crucial information about initial-state geometry fluctuations in heavy-ion collisions.
• These results contribute to a deeper understanding of the interplay between initial conditions, system evolution, and final-state observables in small to large collision systems.