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Wojciech Broniowski

Publications and source records attributed to Wojciech Broniowski.

At least 73 records · Page 4Linked to original sources
arXiv2016

Irrelevance of $f_{0}(500)$ in bulk thermal properties

We discuss why the scalar-isoscalar resonance $f_{0}(500)$ should in practice not be included in thermal models describing the freeze-out of heavy-ion collisions. Its contribution into pion multiplicities is in principle relevant because it is light and it decays only into pions. However, it is cancelled to a very good numerical precision by the non-resonant scalar-isotensor repulsion among pions. Our approach is an application of a well-known theorem relating spectral function to phase shifts. The numerical results are solely based on pion-pion scattering data and thus model independent.

hep-ph↗
arXiv2016

Proton-Proton On Shell Optical Potential at High Energies and the Hollownes Effect

We analyze the usefulness of the optical potential as suggested by the double spectral Mandelstam representation at very high energies, such as in the proton-proton scattering at ISR and the LHC. Its particular meaning regarding the interpretation of the scattering data up to the maximum available measured energies is discussed. Our analysis reconstructs 3D dynamics from the effective transverse 2D impact parameter representation and suggests that besides the onset of gray nucleons at the LHC there appears an inelasticity depletion (hollowness) which precludes convolution models at the attometer scale.

hep-ph↗
arXiv2016

Generalized Valon Model for Double Parton Distributions

We show how the double parton distributions may be obtained consistently from the many-body light-cone wave functions. We illustrate the method on the example of the pion with two Fock components. The procedure, by construction, satisfies the Gaunt-Stirling sum rules. The resulting single parton distributions of valence quarks and gluons are consistent with a phenomenological parametrization at a low scale.

hep-ph↗
arXiv2015

A simple model for rapidity fluctuations in the initial state of ultra-relativistic heavy-ion collisions

Two-particle pseudorapidity correlations are analyzed in a simple model, where in the initial stage of the reaction multiple sources, extended in rapidity, are created. We show how the fluctuations of the length of the sources in rapidity generate correlations in the initial entropy deposition, which later contribute to the observed longitudinal correlations in hadron production. Our analysis, which is analytic and leads to straightforward formulas, allows us to understand the structure of the correlations, in particular to identify the component related to the fluctuation of the numbers of sources and the component from the length fluctuations. We also present the results in terms of the expansion in the basis of the Legendre polynomials. A number of further effects is discussed, such as smearing of the pseudorapidity distributions or resonance decays. Our results reproduce qualitatively and semiquantitatively the basic features of the recent measurements at the LHC.

nucl-th↗
arXiv2015

Fluctuations of flow harmonics in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$~TeV from the Glauber model

In the framework of the Glauber model as implemented in GLISSANDO 2, we study the fluctuations of flow harmonics in Pb+Pb collisions at the LHC centre-of-mass energy of 2.76 TeV. The model with wounded nucleons and the admixture of binary collisions leads to reasonable agreement for the ellipticity and triangularity fluctuations with the experimental data from the ATLAS, ALICE, and CMS collaborations, verifying the assumption that the initial eccentricity is approximately proportional to the harmonic flow of charged particles. While the agreement, in particular at the level of event-by-event distributions of eccentricities/flow coefficients in not perfect, it leads to a fair (at the level of a few percent for all centralities except the most peripheral collisions) description of the scaled standard deviation and the F measure which involve the four-particle cumulants. We also discuss the case of quadrangular flow. Computer scripts that generate our results from the GLISSANDO 2 simulations are provided.

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arXiv2015

Two-particle correlations in pseudorapidity in a hydrodynamic model

Two-particle pseudorapidity correlations of hadrons produced in Pb+Pb collisions at 2.76 TeV at the CERN Large Hadron Collider are analyzed in the framework of a model based on viscous 3+1-dimensional hydrodynamics with the Glauber initial condition. Based on our results, we argue that the correlation from resonance decays, formed at a late stage of the evolution, produce significant effects. In particular, their contribution to the event averages of the coefficients of the expansion in the Legendre basis explain 60-70% of the experimental values. We have proposed an accurate way to compute these coefficients, independent of the binning in pseudorapidity, and tested a double expansion of the two-particle correlation function in the azimuth and pseudorapidity, which allows us to investigate the pseudorapidity correlations between harmonics of the collective flow. In our model, these quantities are also dominated by non-flow effects from the resonance decays. Finally, our method can be used to compute higher-order cumulants for the expansion in orthonormal polynomials which offers a suitable way of eliminating the non-flow effects from the correlation analyses.

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arXiv2015

Cancellation of the sigma meson in thermal models

The by now well-established scalar-isoscalar resonance $f_{0}(500)$ (the $σ$ meson) seems potentially relevant in the evaluation of thermodynamic quantities of a hadronic gas, since its mass is low. However, we recall that its contribution to isospin-averaged observables is, to a surprising accuracy, canceled by the repulsion from the pion-pion scalar-isotensor channel. As a result, in practice one should not incorporate $f_0(500)$ in standard hadronic resonance-gas models for studies of isospin averaged quantities. In our analysis we use the formalism of the virial expansion, which allows one to calculate the thermal properties of an interacting hadron gas in terms of derivatives of the scattering phase shifts, hence in a model-independent way directly from experimentally accessible quantities. A similar cancellation mechanism occurs for the scalar kaonic interactions between the $I=1/2$ channel (containing the alleged $K_{0}^{\ast}(800)$ or the $κ$ meson) and the $I=3/2$ channel.

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arXiv2015

Multibin correlations in a superposition approach to relativistic heavy-ion collisions

Analysis of correlation of multiplicities between various rapidity bins is carried out in the framework of a superposition approach consisting of three phases of the ultra-relativistic nuclear collision: early partonic phase, intermediate collective evolution, and statistical hadronization. Simple relations between the moments of produced hadrons and the moments of the sources produced in the initial partonic phase are presented. They involve only a few effective parameters describing the of microscopic dynamics of the system. We illustrate the practicality of the approach with the Glauber model simulations. Our study carries direct relevance for the interpretation of the upcoming results for the multibin multiplicity correlations from the LHC, which will help in an assessment of the correlation features of the state formed in the earliest stage of the reaction.

nucl-th↗
arXiv2015

The torque effect and fluctuations of entropy deposition in rapidity in ultra-relativistic nuclear collisions

The decorrelation of the orientation of the event-plane angles in the initial state of relativistic Pb-Pb and p-Pb collisions, the "torque effect," is studied in a model of entropy deposition in the longitudinal direction involving fluctuations of the longitudinal source profile on large scales. The radiation from a single wounded nucleon is asymmetric in space-time rapidity. It is assumed that the extent in rapidity of the region of deposited entropy is random. Fluctuations in the deposition of entropy from each source increase the event-plane decorrelation: for Pb-Pb collisions they improve the description of the data, while for p-Pb collisions the mechanism is absolutely essential to generate any sizable decorrelation. We also show that the experimental data for rank-four flow may be explained via folding of the elliptic flow. The results suggest the existence of long range fluctuations in the space-time distribution of entropy in the initial stages of relativistic nuclear collisions.

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arXiv2015

Hydrodynamic modeling of pseudorapidity flow correlations in relativistic heavy-ion collisions and the torque effect

We analyze correlations between the event-plane angles in different intervals of pseudorapidity within the 3+1-dimensional viscous hydrodynamics with the Glauber-model initial conditions. As predicted earlier, the fluctuations in the particle production mechanism in the earliest stage, together with asymmetry of the emission profiles in pseudorapidity from the forward- and backward going wounded nucleons, lead to the torque effect, namely, decorrelation of the event-plane angles in distant pseudorapidity bins. We use two- or three-bin measures of correlation functions to quantify the effect, with the latter compared to the recent data from the CMS collaboration. We find a sizable torque effect, with magnitude larger at RHIC than at the LHC.

nucl-th↗
arXiv2015

Hydrodynamic modeling of 3He-Au collisions at sqrt(sNN)=200 GeV

Collective flow and femtoscopy in ultrarelativistic 3He-Au collisions are investigated within the 3+1-dimensional (3+1D) viscous event-by-event hydrodynamics. We evaluate elliptic and triangular flow coefficients as functions of the transverse momentum. We find the typical long-range ridge structures in the two-particle correlations in the relative azimuth and pseudorapidity, in the pseudorapidity directions of both Au and 3He. We also make predictions for the pionic interferometric radii, which decrease with the transverse momentum of the pion pair. All features found hint on collectivity of the dynamics of the system formed in 3He-Au collisions, with hydrodynamics leading to quantitative agreement with the up-to-now released data.

nucl-th↗
arXiv2014

Large-Nc Regge spectroscopy

This talk, dedicated to Eef van Beveren on the occasion of his birthday, reviews some of our results concerning the hadron spectroscopy, Regge trajectories, and the large-Nc meson-dominance of hadronic form factors.

hep-ph↗
arXiv2014

Low Energy Nuclear Structure from Ultra-relativistic Heavy-Light Ion collisions

The search for specific signals in ultra-relativistic heavy-light ion collisions addressing intrinsic geometric features of nuclei may open a new window to low energy nuclear structure. We discuss specifically the phenomenon of α-clustering in $^{12}$C when colliding with $^{208}$Pb at almost the speed of light.

nucl-th↗
arXiv2014

Alpha clusters and collective flow in ultra-relativistic carbon - heavy nucleus collisions

We investigate ultrarelativistic collisions of the 12C nucleus with heavy targets and show that the harmonic flow measures based on ratios of cumulant moments are particularly suited to study the intrinsic deformation of the 12C wave function. That way one can probe the expected alpha clusterization in the ground state, which leads to large initial triangularity in the shape of the fireball in the transverse plane. We show that the clusterization effect results in very characteristic behavior of the ratios of the cumulant moments as functions of the number of participant nucleons, both for the elliptic and triangular deformations. Thus the experimental event-by-event studies of harmonic flow in ultrarelativistic light-heavy collisions may offer a new window to look at the ground-state structure of light nuclei.

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arXiv2014

Correlations in the Monte Carlo Glauber model

Event-by-event fluctuations of observables are often modeled using the Monte Carlo Glauber model, in which the energy is initially deposited in sources associated with wounded nucleons. In this paper, we analyze in detail the correlations between these sources in proton-nucleus and nucleus-nucleus collisions. There are correlations arising from nucleon-nucleon correlations within each nucleus, and correlations due to the collision mechanism, which we dub twin correlations. We investigate this new phenomenon in detail. At the RHIC and LHC energies, correlations are found to have modest effects on size and eccentricity fluctuations, such that the Glauber model produces to a good approximation a collection of independent sources.

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arXiv2014

Collective flow in ultrarelativistic $^3$He-Au collisions

The triangular flow in ultrarelativistic $^3$He-Au collisions at RHIC energies is enhanced due to the triangular arrangement of the nucleon configurations in $^3$He. We study the fireball eccentricities in the Glauber Monte Carlo model and find that since the configurations of the projectile $^3$He are elongated triangles, the created fireball has a large ellipticity and a smaller triangularity. The dependence of the triangularity on centrality is weak, so it cannot be extracted from the centrality dependence of the triangular flow $v_3$, as it is dominated by the centrality dependence of the hydrodynamic response. We propose to look at the centrality dependence of the ratio $v_n\{4\}/v_n\{2\}$, where the uncertainties from the hydrodynamic response cancel, and show that the basic signature of the geometry-driven collective flow is the raise of the ratio $v_3\{4\}/v_3\{2\}$ with the number of participant nucleons for centralities less than 10%.

nucl-th↗
arXiv2014

Alpha clustering and flow in ultra-relativistic heavy-ion collisions

We show how ultra-relativistic collisions of light nuclei with heavy targets may be used to record snap-shots of the ground-state configurations and reveal information on cluster correlations. The development of collective flow in the formed fireball, which reflects the geometric correlations in the initial state, is essential for the method. As an illustration we analyze the 12C-208Pb collisions.

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