Elliptic flow
Encyclopedia
The elliptic flow is described as one of the most important observations measured at the Relativistic Heavy Ion Collider
(RHIC). It is one of the strongest evidences for the Quark-gluon plasma
discovery. It describes the azimuthal momentum space anisotropy of particle emission
from non-central heavy-ion collisions in the plane transverse to the beam direction. Elliptic flow is characterized by the second harmonic coefficient of an azimuthal Fourier decomposition of the momentum distribution.
Elliptic flow is a fundamental observable since it directly reflects the initial spatial anisotropy
, of the nuclear overlap region in the transverse plane, directly translated into to the observed momentum
distribution of identified particles. Since the spatial anisotropy is largest at the beginning of the evolution, elliptic flow is especially sensitive to the early stages of system evolution. A measurement of elliptic flow thus provides access to the fundamental thermalization time scale and many more things in the early stages of a relativistic
heavy-ion collision.
Relativistic Heavy Ion Collider
The Relativistic Heavy Ion Collider is one of two existing heavy-ion colliders, and the only spin-polarized proton collider in the world. It is located at Brookhaven National Laboratory in Upton, New York and operated by an international team of researchers...
(RHIC). It is one of the strongest evidences for the Quark-gluon plasma
Quark-gluon plasma
A quark–gluon plasma or quark soup is a phase of quantum chromodynamics which exists at extremely high temperature and/or density. This phase consists of asymptotically free quarks and gluons, which are several of the basic building blocks of matter...
discovery. It describes the azimuthal momentum space anisotropy of particle emission
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
from non-central heavy-ion collisions in the plane transverse to the beam direction. Elliptic flow is characterized by the second harmonic coefficient of an azimuthal Fourier decomposition of the momentum distribution.
Elliptic flow is a fundamental observable since it directly reflects the initial spatial anisotropy
Anisotropy
Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
, of the nuclear overlap region in the transverse plane, directly translated into to the observed momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
distribution of identified particles. Since the spatial anisotropy is largest at the beginning of the evolution, elliptic flow is especially sensitive to the early stages of system evolution. A measurement of elliptic flow thus provides access to the fundamental thermalization time scale and many more things in the early stages of a relativistic
Theory of relativity
The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word relativity is sometimes used in reference to Galilean invariance....
heavy-ion collision.