M. Schulc

Anisotropic flow of the fireball fed by hard partons

In nuclear collisions at highest accessible LHC energies, often more than one dijet pairs deposit momentum into the deconfined expanding medium. With the help of 3+1 dimensional relativistic hydrodynamic simulation we show that this leads to measurable contribution to the anisotropy of collective transverse expansion. Hard partons generate streams in plasma which merge if they come close to each other. This mechanism correlates the resulting contribution to flow anisotropy with the fireball geometry and causes an increase of the elliptic flow in non-central collisions.

Rapidity correlations of protons from a fragmented fireball

Abstract.We investigate proton rapidity correlations for a fireball that fragments due to non-equilibrium effects at the phase transition from the deconfined to the hadronic phase. Such effects include spinodal fragmentation in the case of a first-order phase transition at lower collision energies and cavitation due to the sudden rise of the bulk viscosity at the crossover probed at RHIC and at the LHC. Our study is performed on samples of Monte Carlo events. The correlation function in relative rapidity appears to be a sensitive probe of fragmentation. We show that resonance decays make the strength of the correlation even stronger.

The effect of momentum deposition during fireball evolution on flow anisotropy

The highest LHC energies give rise to the production of many pairs of hard partons which deposit four-momentum into the expanding fireball matter. We argue that it is necessary to include momentum deposition during fireball evolution into 3 + 1 dimensional hydrodynamic simulations of the collision. This influence cannot be accounted for simply by modifying the initial conditions of the simulation. The resulting contribution to flow anisotropy is correlated with the fireball geometry and causes an increase of the elliptic flow in non-central collisions. The results are presented for various scenarios with energy and momentum deposition to clearly demonstrate this effect.

Observables of non-equilibrium phase transition⋆

Abstract.A rapidly expanding fireball which undergoes first-order phase transition will supercool and proceed via spinodal decomposition. Hadrons are produced from the individual fragments as well as the left-over matter filling the space between them. Emission from fragments should be visible in rapidity correlations, particularly of protons. In addition to that, even within narrow centrality classes, rapidity distributions will be fluctuating from one event to another in case of fragmentation. This can be identified with the help of the Kolmogorov-Smirnov test. Finally, we present a method which allows to sort events with varying rapidity distributions, in such a way that events with similar rapidity histograms are grouped together.

Flow anisotropy due to momentum deposition in ultra-relativistic nuclear collisions

Minijets and jets are produced in large numbers in nuclear collisions at TeV energies, so that there are many of them in a single fireball. They deposit non-negligible amount of momentum and energy into the hydrodynamically expanding bulk and cause anisotropies of the expansion. Moreover, due to their multiple production in a single event the resulting anisotropies are correlated with the collision geometry and thus contribute positively also to event-averaged anisotropies in non-central collisions. Using simulations with three-dimensional ideal hydrodynamic model we demonstrate the importance of this effect. It must be taken into account if conclusions about the properties of the hot matter are to be drawn.

Stimulation of static deconfined medium by multiple hard partons

We investigate the response of non-expanding deconfined hot matter to energy and momentum deposition from a pair of partons moving with high energies. Several situations are examined with partons moving so that the generated wakes in the medium interact. It is shown that the streams generated in the wakes, which carry deposited momentum, interact and merge if the hard partons are close enough to each other. Such cases are relevant for nuclear collisions at the Large Hadron Collider, where several hard partons are produced in a single collision. The observed effect itself could lead to elliptic flow at the level of a few per cent.