1,729 research outputs found
Effect of initial-state nucleon-nucleon correlations on collective flow in ultra-central heavy-ion collisions
We investigate the effect of nucleon-nucleon correlations on the initial
condition of ultra-central heavy ion collisions at LHC energies. We calculate
the eccentricities of the MC-Glauber and IP-Glasma models in the 0--1%
centrality class and show that they are considerably affected by the inclusion
of such type of correlations. For an IP-Glasma initial condition, we further
demonstrate that this effect survives the fluid-dynamical evolution of the
system and can be observed in its final state azimuthal momentum anisotropy.Comment: 6 pages, 4 figure
Thermal photon radiation in high multiplicity p+Pb collisions at the Large Hadron Collider
The collective behaviour of hadronic particles has been observed in high
multiplicity proton-lead collisions at the Large Hadron Collider (LHC), as well
as in deuteron-gold collisions at the Relativistic Heavy-Ion Collider (RHIC).
In this work we present the first calculation, in the hydrodynamic framework,
of thermal photon radiation from such small collision systems. Owing to their
compact size, these systems can reach temperatures comparable to those in
central nucleus-nucleus collisions. The thermal photons can thus shine over the
prompt background, and increase the low direct photon spectrum by a
factor of 2-3 in 0-1% p+Pb collisions at 5.02 TeV. This thermal photon
enhancement can therefore serve as a clean signature of the existence of a hot
quark-gluon plasma during the evolution of these small collision systems, as
well as validate hydrodynamic behavior in small systems.Comment: 6 pages, 4 figure
The importance of the bulk viscosity of QCD in ultrarelativistic heavy-ion collisions
We investigate the consequences of a nonzero bulk viscosity coefficient on
the transverse momentum spectra, azimuthal momentum anisotropy, and
multiplicity of charged hadrons produced in heavy ion collisions at LHC
energies. The agreement between a realistic 3D hybrid simulation and the
experimentally measured data considerably improves with the addition of a bulk
viscosity coefficient for strongly interacting matter. This paves the way for
an eventual quantitative determination of several QCD transport coefficients
from the experimental heavy ion and hadron-nucleus collision programs.Comment: 5 pages, 3 figures. Light modifications to text and figures. To be
published in PR
Direct photon production and jet energy-loss in small systems
Two types of penetrating probes, direct photon and QCD jets, are investigated
in the background of a small and rapidly expanding droplet of quark-gluon
plasma. The additional thermal electromagnetic radiation results in a
50\% enhancement of the direct photons. In high multiplicity p+Pb
collisions, jets can lose a sizeable fraction of their initial energy, leading
to a charged hadron of 0.8 at a transverse momentum
around 10\,GeV. Those two proposed measurements can help understand the
apparent collective behaviour observed in small collision systems.Comment: 4 pages. Contribution to the Proceedings of Quark Matter 2015, Kobe,
Japa
Electromagnetic radiation as a probe of the initial state and of viscous dynamics in relativistic nuclear collisions
The penetrating nature of electromagnetic signals makes them suitable probes
to explore the properties of the strongly-interacting medium created in
relativistic nuclear collisions. We examine the effects of the initial
conditions and shear relaxation time on the spectra and flow coefficients of
electromagnetic probes, using an event-by-event 3+1D viscous hydrodynamic
simulation (MUSIC).Comment: 14 pages, 14 figures; v2: minor improvements to tex
Extracting the bulk viscosity of the quark-gluon plasma
We investigate the implications of a nonzero bulk viscosity coefficient on
the azimuthal momentum anisotropy of ultracentral relativistic heavy ion
collisions at the Large Hadron Collider. We find that, with IP-Glasma initial
conditions, a finite bulk viscosity coefficient leads to a better description
of the flow harmonics in ultracentral collisions. We then extract optimal
values of bulk and shear viscosity coefficients that provide the best agreement
with flow harmonic coefficients data in this centrality class.Comment: 4 pages, 5 figures, proceedings of the XXIV Quark Matter conference,
May 19-24 2014, Darmstadt (Germany
Probing the non-equilibrium dynamics of hot and dense QCD with dileptons
It is argued that, in heavy ion collisions, thermal dileptons are good probes
of the transport properties of the medium created in such events, and also of
its early-time dynamics, usually inaccessible to hadronic observables. In this
work we show that electromagnetic azimuthal momentum anisotropies do not only
display a sensitivity to the shear relaxation time and to the initial
shear-stress tensor profile, but also to the temperature dependence of the
shear viscosity coefficient.Comment: 4 pages, 6 figures, Proceedings for Quark Matter 2014, Darmstadt,
Germany, May 19-24, 201
Dilepton radiation and bulk viscosity in heavy-ion collisions
Starting from IP-Glasma initial conditions, we investigate the effects of
bulk pressure on thermal dilepton production at the Relativistic Heavy Ion
Collider (RHIC) and the Large Hadron Collider (LHC) energies. Though results of
the thermal dilepton under the influence of both bulk and shear viscosity
is presented for top RHIC energy, more emphasis is put on LHC energy where such
a calculation is computed for the first time. The effects of the bulk pressure
on thermal dilepton at the LHC are explored through bulk-induced
modifications on the dilepton yield.Comment: Talk given at the 8th International Conference on Hard and
Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2016),
September 23-27 2016, Wuhan, China; 4 pages, LaTeX, 2 PDF figure
Probing the early-time dynamics of relativistic heavy-ion collisions with electromagnetic radiation
Using 3+1D viscous relativistic fluid dynamics, we show that electromagnetic
probes are sensitive to the initial conditions and to the out-of-equilibrium
features of relativistic heavy-ion collisions. Within the same approach, we
find that hadronic observables show a much lesser sensitivity to these aspects.
We conclude that electromagnetic observables allow access to dynamical regions
that are beyond the reach of soft hadronic probes.Comment: Talk given at the 6th International Conference on Hard and
Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2013),
Nov 4-8, 2013, Stellenbosch, South Afric
The production of photons in relativistic heavy-ion collisions
In this work it is shown that the use of a hydrodynamical model of heavy ion
collisions which incorporates recent developments, together with updated photon
emission rates greatly improves agreement with both ALICE and PHENIX
measurements of direct photons, supporting the idea that thermal photons are
the dominant source of direct photon momentum anisotropy. The event-by-event
hydrodynamical model uses IP-Glasma initial states and includes, for the first
time, both shear and bulk viscosities, along with second order couplings
between the two viscosities. The effect of both shear and bulk viscosities on
the photon rates is studied, and those transport coefficients are shown to have
measurable consequences on the photon momentum anisotropy.Comment: 17 pages, 13 figures. Augmented discussion; now also includes STAR
photon data. Some typos corrected; agrees with published versio
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