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SUMMARY:Longitudinal hydrodynamic response and pseudo-rapidity dependent h
armonic flow in relativistic heavy-ion collisions
DTSTART;VALUE=DATE-TIME:20191105T012000Z
DTEND;VALUE=DATE-TIME:20191105T014000Z
DTSTAMP;VALUE=DATE-TIME:20200221T073601Z
UID:indico-contribution-3535655@indico.cern.ch
DESCRIPTION:Speakers: Li Yan (Fudan University)\nIn heavy-ion collisions\,
it is well-established that geometrical shapes of the initial density dis
tribution in transverse plane are responsible for the observed harmonic fl
ow\, through the hydrodynamic response of a set of modes. In particular\,
elliptic flow $V_2$ is linearly proportional to initial eccentricity $\\ma
thcal{E}_2$. \n\nIn this work\, we generalize the framework to study hydro
dynamic response along the longitudinal direction. We propose a differenti
al hydrodynamic response relation\, $V_2(\\eta)=\\int d\\xi G(\\eta-\\xi)
\\mathcal{E}_2(\\xi)$\, to describe the formation of a pseudo-rapidity dep
endent elliptic flow\, in response to a 3D initial density profile. By ana
lyzing the medium expansion using event-by-event simulations of 3+1D MUSIC
\, with initial conditions generated via the AMPT model for the Pb-Pb coll
isions at $\\sqrt{s_{NN}}=2.76$ TeV\, the differential response relation i
s verified and expansion coefficients to very high orders are identified i
n the response function $G(\\eta-\\xi)$.\n\nOur investigations of the hydr
odynamic response function have yielded two important insights: 1. The two
-point auto-correlation of elliptic flow in pseudo-rapidity (an observable
in heavy-ion experiments)\, can be separated as medium response and two-p
oint correlation of initial $\\mathcal{E}_2$. Especially\, shear viscosity
of the medium reduces the correlation length systematically. 2. Higher or
der expansion coefficients increase exponentially\, which implies a finite
radius of convergence of the gradient expansion in the dispersion relatio
n of hydrodynamics. The radius of convergence in the response function res
ults in a minimal length scale that can be used to estimate the applicabil
ity of hydrodynamic modeling of heavy-ion collisions\, which provides a po
ssible solution to the question of fluidity in small systems.\n\nhttps://i
ndico.cern.ch/event/792436/contributions/3535655/
LOCATION:Wanda Reign Wuhan Hotel Ball Room 1
URL:https://indico.cern.ch/event/792436/contributions/3535655/
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