Quantum mechanics

Voltage

Relativistic Heavy Ion Collider

Nuclear physics

Eccentricity (behavior)

Atomic physics

Harmonics

Fourier series

Physics

Heavy ion

Mathematics

Astronomy

Quantum electrodynamics

Flow (mathematics)

Political science

Mathematical analysis

Elliptic flow

Azimuth

Mechanics

Thermalisation

Nuclear Physics A

The second and fourth Fourier harmonics of the azimuthal distribution of particles, $v_2$ and $v_4$, have been mesured in Au-Au collisions at the Relativistic Heavy Ion Collider (RHIC). The ratio $v_4/(v_2)^2$ is significantly larger than predicted by hydrodynamics. Effects of partial thermalization are estimated on the basis of a transport calculation, and are shown to increase the ratio by a small amount. We argue that the large value of $v_4/(v_2)^2$ seen experimentally is mostly due to elliptic flow fluctuations. However, the standard model of eccentricity fluctuations is unable to explain the large magnitude of $v_4/(v_2)^2$ in central collisions.

Why is larger than predicted by hydrodynamics?