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Ollitrault, Jean-Yves

Publications and source records attributed to Ollitrault, Jean-Yves.

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Measures of azimuthal anisotropy in high-energy collisions

Azimuthal anisotropy is a key observation made in ultrarelativistic heavy-ion collisions. This phenomenon has played a crucial role in the development of the field over the last two decades. In addition to its interest for studying the quark-gluon plasma, which was the original motivation, it is sensitive to the properties of incoming nuclei, in particular to the nuclear deformation and to the nuclear skin. The azimuthal anisotropy is therefore of crucial importance when relating low-energy nuclear structure to high-energy nuclear collisions. Furthermore, this article is an elementary introduction to the various observables used in order to characterize azimuthal anisotropy, which go under the names of v 2 {2}, v 3 {2}, v 2 {4}, etc. The intended audience is primarily physicists working in the field of nuclear structure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Non-Gaussian transverse momentum fluctuations from impact parameter fluctuations

The transverse momentum per particle, [p t ], fluctuates event by event in ultrarelativistic nucleus-nucleus collisions, for a given multiplicity. These fluctuations are small and approximately Gaussian, but a nonzero skewness has been predicted on the basis of hydrodynamic calculations, and seen experimentally. We argue that the mechanism driving the skewness is that, if the system thermalizes, the mean transverse momentum increases with impact parameter for a fixed collision multiplicity. We postulate that fluctuations are Gaussian at fixed impact parameter, and that non-Gaussianities solely result from impact parameter fluctuations. Using recent data on the variance of [p t ] fluctuations, we make quantitative predictions for their skewness and kurtosis as a function of the collision multiplicity. Here, we predict, in particular, a spectacular increase of the skewness below the knee of the multiplicity distribution, followed by a fast decrease.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Correlation between mean transverse momentum and anisotropic flow in heavy-ion collisions

The correlation between the mean transverse momentum of outgoing particles, $\langle{p_t}\rangle$, and the magnitude of anisotropic flow, v n , has recently been measured in Pb+Pb collisions at the CERN Large Hadron Collider, as a function of the collision centrality. Here, we confirm the previous observation that event-by-event hydrodynamics predicts a correlation between v n and $\langle{p_t}\rangle$ that is similar to that measured in data. We show that the magnitude of this correlation can be directly predicted from the initial condition of the hydrodynamic calculation, for n = 2, 3, if one replaces v n by the corresponding initial-state anisotropy, ε n , and $\langle{p_t}\rangle$ by the total energy per unit rapidity of the fluid at the beginning of the hydrodynamic expansion.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Skewness of mean transverse momentum fluctuations in heavy-ion collisions

We propose the skewness of mean transverse momentum, $\langle{p_t}\rangle$, fluctuations as a fine probe of hydrodynamic behavior in relativistic nuclear collisions. We describe how the skewness of the $\langle{p_t}\rangle$ distribution can be analyzed experimentally, and we use hydrodynamic simulations to predict its value. We predict in particular that $\langle{p_t}\rangle$ fluctuations have positive skew, which is significantly larger than if particles were emitted independently. We elucidate the origin of this result by deriving generic formulas relating the fluctuations of $\langle{p_t}\rangle$ to the fluctuations of the early-time thermodynamic quantities. We postulate that the large positive skewness of $\langle{p_t}\rangle$ fluctuations is a generic prediction of hydrodynamic models.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Determining initial-state fluctuations from flow measurements in heavy-ion collisions

We present a number of independent flow observables that can be measured using multiparticle azimuthal correlations in heavy-ion collisions. Some of these observables are already well known, such as v{sub 2}(2) and v{sub 2}(4), but most are new--in particular, joint correlations among v{sub 1}, v{sub 2}, and v{sub 3}. Taken together, these measurements will allow for a more precise determination of the medium properties than is currently possible. In particular, by taking ratios of these observables, we construct quantities that are less sensitive to the hydrodynamic response of the medium and thus more directly characterize the initial-state fluctuations of the event shape, which may constrain models for early-time, nonequilibrium QCD dynamics. We present predictions for these ratios using two Monte Carlo models and compare them to available data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Directed flow at midrapidity in event-by-event hydrodynamics

Fluctuations in the initial geometry of a nucleus-nucleus collision have been recently shown to result in a new type of directed flow (v{sub 1}) that, unlike the usual directed flow, is also present at midrapidity. We compute this new v{sub 1} versus transverse momentum and centrality for Au-Au collisions at RHIC using the hydrodynamic code NeXSPheRIO. We find that the event plane of v{sub 1} is correlated with the angle of the initial dipole of the distribution, as predicted, though with a large dispersion. It is uncorrelated with the reaction plane. Our results are in excellent agreement with results inferred from STAR correlation data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Directed Flow at Midrapidity in Heavy-Ion Collisions

It was recently shown that fluctuations in the initial geometry of a heavy-ion collision generally result in a dipole asymmetry of the distribution of outgoing particles. This asymmetry, unlike the usual directed flow, is expected to be present at a wide range of rapidity--including midrapidity. The first evidence of this phenomenon can be seen in recent two-particle correlation data by the STAR Collaboration, providing the last element necessary to quantitatively describe long-range dihadron correlations. We extract differential directed flow from these data and propose a new direct measurement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Event-plane flow analysis without nonflow effects

The event-plane method, which is widely used to analyze anisotropic flow in nucleus-nucleus collisions, is known to be biased by nonflow effects, especially at high p{sub t}. Various methods (cumulants, Lee-Yang zeros) have been proposed to eliminate nonflow effects, but their implementation is tedious, which has limited their application so far. In this article, we show that the Lee-Yang-zeroes method can be recast in a form similar to the standard event-plane analysis. Nonflow correlations are strongly suppressed by using the information from the length of the flow vector, in addition to the event-plane angle. This opens the way to improved analyses of elliptic flow and azimuthally sensitive observables at the Relativistic Heavy Ion Collider and the Large Hadron Collider.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗