Speaker
Li Yan
(CNRS)
Description
Higher-order harmonics of anisotropic flow ($v_n$ with $n\ge 4$) can
be measured with the direction of lower-order harmonics, e.g., $v_4$
with respect to the $v_2$ plane.
We show that one can scale these measurements by quantities involving
lower-order harmonics in such a way that the
ratio is independent of initial conditions, and solely involves the
medium nonlinear response.
The resulting ratios allow to directly confront hydrodynamics with
experimental data [1].
We construct four independent such ratios involving $v_4$, $v_5$ and
$v_6$ and extract their values from LHC data on Pb+Pb collisions, as a
function of centrality.
We then calculate these ratios using single-shot hydrodynamics and
using the transport model AMPT [2].
Model calculations are in very good agreement with data.
We point out that hydrodynamics predicts simple scaling relations
between these response coefficients, which can be read off directly from
data.
A substantial response ratio in the seventh harmonic is found
in theoretical calculations (both in AMPT and in hydrodynamics), from
which we argue that a nonzero $v_7$ signal should be seen when
measured with respect to elliptic and triangular flow. We present
predictions for $v_7$ versus centrality in Pb+Pb collisions at the
LHC.
Finally, we point out that combined measurements of higher-order
harmonics with their own plane and with respect to lower-order planes
can be quantitatively related to
event-plane correlations. As an illustration, we show that CMS data on
$v_4$ and $v_6$ are compatible with ATLAS data on event-plane correlations.
[1] L. Yan and J. Y. Ollitrault,
Phys.Lett. B ${\bf 744}$, 82 (2015)
[arXiv:1502.02502 [nucl-th]].
[2] L. Yan, S. Pal and J. Y. Ollitrault, in preparation
| On behalf of collaboration: | NONE |
|---|
Primary author
Li Yan
(CNRS)
Co-authors
Jean-Yves Ollitrault
(CNRS)
Subrata Pal
(Tata Institute of Fundamental Research, Mumbai, India)
