Mode-coupling effects in anisotropic flow in heavy-ion collisions

Abstract

Higher-order anisotropic flows in heavy-ion collisions are affected by nonlinear mode coupling effects. It has been suggested that the associated nonlinear hydrodynamic response coefficients probe the transport properties and are largely insensitive to the spectrum of initial density fluctuations of the medium created in these collisions. To test this suggestion, we explore nonlinear mode coupling effects in event-by-event viscous fluid dynamics, using two different models for the fluctuating initial density profiles, and compare the nonlinear coupling coefficients between the initial eccentricity vectors before hydrodynamic expansion and the final flow vectors after the expansion. For several mode coupling coefficients we find significant sensitivity to the initial fluctuation spectrum. They all exhibit strong sensitivity to the specific shear viscosity at freeze-out, but only weak dependence on the shear viscosity during hydrodynamic evolution.

Azimuthal Correlations and Mixed Higher Order Flow Harmonics from CMS at the LHC

“…In the former the results are compared with predictions from AMPT and hydrodynamics with a deformed symmetric Gaussian density profile with the initial condition using η/s = 0.08 in Ref. [3], and from iEBE-VISHNU hydrodynamics with Glauber and KLN initial conditions using the same η/s [16]. Predictions from AMPT are favored by the data.…”

Latest results on anisotropy flow of light and heavy flavors in PbPb collisions at CMS

“…The AMPT model describes the experimental results for all harmonics well. Comparisons to hydrodynamic model with a deformed symmetric Gaussian density profile [2] and with iEBE-VISHNU hydrodynamic [3], where both calculations have been performed with η/s = 0.08, show a strong sensitivity of the non-linear response coefficients to the initial-state conditions. It also shows that the sensitivity increases with an increase of the harmonic order n. The comparison to the hydrodynamic model [3] calculated with the same KLN initial-state condition but with different η/s values which is performed in [9] shows that the non-linear response coefficients are sensitive to the η/s values too, especially for the odd harmonics.…”

“…[2,3] provide the definitions of the mixed higher order harmonics v 4 {Ψ 22 }, v 5 {Ψ 23 }, v 6 {Ψ 222 }, v 6 {Ψ 33 } and v 7 {Ψ 223 }, and the corresponding non-linear response coefficients, χ mkl . The sensitivity of the v n {Ψ mkl } and the χ mkl to the initial-state conditions and transport properties of the formed medium could be used to test theoretical models.…”

“…The influence of the initial-state fluctuations on the hydrodynamic flow can be studied by the correlations between v n {Ψ n } harmonics measured with respect to their own plane, and mixed harmonics v n {Ψ mkl } (m, k, l < n) measured with respect to the direction of multiple lower order harmonics. The following relations [2,3] decompose higher order harmonics into their linear (V nL ) and non-linear contributions…”

Studies of three-particle correlations and reaction-plane correlators from STAR

“…The observable C m,n,m+n can be approximated as correlations of flow harmonics, v n s, and corresponding event plane angles, Ψ n s, as v m v n v m+n cos(mΨ m + nΨ n − (m + n)Ψ m+n ) . Theoretical studies show that such an observable can probe non-linear hydrodynamic response and therefore become more sensitive to viscosity than individual flow harmonics v n [1][2][3][4][5][6][7][8][9][10]. Better sensitivity to viscous effects can be very useful towards more precise extraction of different transport parameters and possibly their temperature dependence by comparison to hydrodynamic simulations [11,12].…”