Collision-geometry fluctuations and triangular flow in heavy-ion collisions

By Burak Han Alver, G. Roland. 2010

643 citations recorded by the source corpus.

We introduce the concepts of participant triangularity and triangular flow in heavy-ion collisions, analogous to the definitions of participant eccentricity and elliptic flow. The participant triangularity characterizes the triangular anisotropy of the initial nuclear overlap geometry and arises from event-by-event fluctuations in the participant-nucleon collision points. In studies using a multiphase transport model (AMPT), a triangular flow signal is observed that is proportional to the participant triangularity and corresponds to a large third Fourier coefficient in two-particle azimuthal correlation functions. Using two-particle azimuthal correlations at large pseudorapidity separations measured by the PHOBOS and STAR experiments, we show that this Fourier component is also present in data. Ratios of the second and third Fourier coefficients in data exhibit similar trends as a function of centrality and transverse momentum as in AMPT calculations. These findings suggest a significant contribution of triangular flow to the ridge and broad away-side features observed in data. Triangular flow provides a new handle on the initial collision geometry and collective expansion dynamics in heavy-ion collisions.

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Citations in the corpus

Strongly correlated quantum fluids: ultracold quantum gases, quantum chromodynamic plasmas and holographic duality (2012, background): “Odd Fourier moments such as v1 and v3 arise mainly from fluctuations in the initial state [260, 261].”
Improved Monte Carlo Glauber predictions at present and future nuclear colliders (2017, unknown): “The second moment, also called eccentricity [20], the third moment, also called triangularity [21], and higher moments [22] of the collision region at impact parameter b, which are used to characterize the initial geometrical shape, are given by”
Relativistic Hydrodynamics in Heavy-Ion Collisions: General Aspects and Recent Developments (2016, background): “The first numerical demonstration of the role of lumpy initial energy density (or event-by-event fluctuation) in the transverse plane (plane defined by the impact parameter vector and one of the perpendicular axis to the beam direction) to the experimentally observed non-zero odd flow harmonics (par”
Schwinger mechanism revisited (2015, background): “In contrast, the azimuthal correlations can be produced at any time, and are easily explainable by the hydrodynamical flow that develops in the later stages of the collision process [44, 45].”
Evidence for collectivity in pp collisions at the LHC (2016, background): “reflect the medium response to, respectively, the initial collision geometry and its fluctuations [23], providing insight into fundamental transport properties of the medium [24–26].”
Small System Collectivity in Relativistic Hadronic and Nuclear Collisions (2018, background): “To date, nearly all observations in A+A collisions that provided strong evidence for the heavy ion standard model “quark–gluon plasma as near-perfect fluid” have now been measured in p+Pb and d+Au collisions (see Reference (60) for an excellent review).”
Non linearities in the harmonic spectrum of heavy ion collisions with ideal and viscous hydrodynamics (2012, background): “For example, the experimental ratio 〈〈v(2) 3〉〉 / 〈〈v(2) 2〉〉 closely follows the geometric deformations 〈〈 (2)3〉〉 / 〈〈 (2)2〉〉 as a function of centrality [7].”
Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV (2012, background): “The vn coefficients are sensitive to the geometry of the initial state of the colliding nuclei [16, 17] and can be related to the transport properties of the strongly-interacting de-confined matter via hydrodynamic models [18–20].”
Properties of hot and dense matter from relativistic heavy ion collisions (2015, background): “More recently, it was realized that fluctuations in the initial energy density generate substantial higher harmonics, including odd Fourier moments such as v3 [184], as well as fluctuations of the flow angles relative to the impact parameter plane [185].”
Conformal hydrodynamics in Minkowski and de Sitter spacetimes (2010, methodology): “3 Parameterizing anisotropies Recently, the authors of [3] have provided an explanation of certain features of two-particle correlations at RHIC which relies on the propagation of fluctuating initial conditions.”