arXiv subjects

Maciej Rybczynski

Publications and source records attributed to Maciej Rybczynski.

35 records · Page 2Linked to original sources

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

Explanation of hadron transverse-momentum spectra in heavy-ion collisions at sqrt(sNN) = 2.76 TeV within chemical non-equilibrium statistical hadronization model

Chemical non-equilibrium version of the statistical hadronization model combined with a single-freeze-out scenario is used to analyze the transverse-momentum spectra of pions, kaons and protons produced in heavy-ion collisions at sqrt(sNN) = 2.76 TeV. With the statistical parameters found in earlier studies of hadronic ratios and two new geometric parameters determined by the absolute normalization and slopes of the spectra, we obtain a very good agreement between the data and the model predictions. In particular, the enhancement of pions observed at the very low transverse-momenta is very well reproduced. In the chemical non-equilibrium approach, this effect may be naturally interpreted as the onset of pion condensation in heavy-ion collisions. We further stress that the chemical non-equilibrium explains not only the proton yield but the proton spectra as well.

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arXiv2014

Transverse-momentum spectra of strange particles produced in Pb+Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV in the chemical non-equilibrium model

We analyze the transverse-momentum spectra of strange hadrons produced in Pb+Pb collisions at the collision energy $\sqrt{s_{\rm NN}}=2.76$ TeV. Our approach combines the concept of chemical non-equilibrium with the single-freeze-out scenario. The two ideas are realized in the framework of the Cracow model, whose thermodynamic parameters have been established in earlier studies of the ratios of hadron multiplicities. The geometric parameters of the model are obtained from the fit to the spectra of pions and kaons, only. Using these parameters, we obtain an excellent description of the spectra of protons and the $K_S^0$, $K^*(892)^0$, and $ϕ(1020)$ mesons. A satisfactory description is also obtained for the $Λ$, $Ξ$ and $Ω$ hyperons. Further improvement of the hyperon spectra may be achieved if we assume that they are emitted from a smaller, internal part of the system but at the same thermodynamic conditions. Our work not only includes all particle species measured up to now in heavy-ion collisions at the LHC energies but, in addition, discusses the centrality dependence of the particle production.

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arXiv2014

Tsallis statistics approach to the transverse momentum distributions in p-p collisions

Transverse momentum distributions of negatively charged pions produced in p-p interactions at beam momenta 20, 31, 40, 80 and 158 GeV/c are studied using the Tsallis distribution as a parametrization. Results are compared with higher energies data and changes of parameters with energy are determined. Different Tsallis-like distributions are compared.

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arXiv2013

GLISSANDO 2: GLauber Initial-State Simulation AND mOre..., ver. 2

We present an extended version of GLISSANDO, a Monte-Carlo generator for Glauber-like models of the initial stage of relativistic heavy-ion collisions. The increased functionality of the code incorporates a parametrization of shape of nuclei, including light nuclei needed in the NA61 experiment, the nuclear deformation, a possibility of using correlated distributions of nucleons in nuclei read from external files, an option of overlaying distributions of produced particles dependent on the space-time rapidity, the inclusion of the core-corona effect, or the output of the source distributions that can be used in event-by-event hydrodynamics. Together with other features, such as incorporation of various variants of Glauber models, or the implementation of a realistic NN collision profile, the generator offers a realistic and practical approach to describe the early phase of the collision in 3+1 dimensions; the predictions may later be used in modeling the intermediate evolution phase, e.g., with hydrodynamics. The software is integrated with the ROOT platform. The supplied scripts compute and plot numerous features of the distributions, such as the multiplicity distributions and centrality classes, harmonic asymmetry coefficients and their correlations, forward-backward correlations, etc. The code can also be used for the proton-nucleus and deuteron-nucleus collisions.

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arXiv2013

Nucleon-nucleon collision profile and cross section fluctuations

The nucleon-nucleon collision profile, being the basic entity of the wounded nucleon model, is usually adopted in the form of hard sphere or the Gaussian shape. We suggest that the cross section fluctuations given by the gamma distribution leads to the profile function which smoothly ranges between the both limiting forms. Examples demonstrating sensitivity of profile function on cross section fluctuations are discussed.

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arXiv2013

Energy dependence of identified hadron spectra and event-by-event fluctuations in p+p interactions from NA61/SHINE at the CERN SPS

NA61/SHINE at the CERN SPS is a fixed-target experiment pursuing a rich physics program including measurements for heavy ion, neutrino and cosmic ray physics. The main goal of the ion program is to explore the most interesting $T, mu_{B}$ region of the phase diagram of strongly interacting matter. We plan to study the properties of the onset of deconfinement and to search for the signatures of the critical point. The search is performed by varying collision energy (13A-158A GeV/c) and system size (p+p, Be+Be, Ar+Ca, Xe+La). Thanks to its large acceptance and excellent particle identification capability NA61/SHINE is well suited for performing high-precision particle production measurements as well as for studying event-by-event fluctuations in p+p, p+nucleus and nucleus+nucleus collisions. Preliminary results on p+p interactions at 20, 31, 40, 80 and 158 GeV/c are presented. They include inclusive spectra of pi+, pi-, K- and protons as a function of transverse momentum/mass and rapidity as well as event-by-event fluctuations of transverse momentum, azimuthal angle and chemical composition. The new NA61 measurements are compared with the corresponding results of NA49 on central Pb+Pb collisions and with predictions of Monte Carlo models. Finally, the future plans of NA61/SHINE are summarised.

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arXiv2012

Onset of deconfinement and search for the critical point of strongly interacting matter at CERN SPS energies

The exploration of the QCD phase diagram particularly the search for a phase transition from hadronic to partonic degrees of freedom and possibly a critical endpoint, is one of the most challenging tasks in present heavy-ion physics. As observed by the NA49 experiment, several hadronic observables in central Pb+Pb collisions at the CERN SPS show qualitative changes in their energy dependence. These features are not observed in elementary interactions and indicate the onset of a phase transition in the SPS energy range. The existence of a critical point is expected to result in the increase of event-by-event fluctuations of various hadronic observables provided that the freeze-out of the measured hadrons occurs close to its location in the phase diagram and the evolution of the final hadron phase does not erase the fluctuations signals. A selection of NA49 results on di-pion and proton intermittency from the scan of the phase diagram will be discussed.

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arXiv2012

Influence of initial fluctuations on geometry measures in relativistic U-U and Cu-Au collisions

In the framework of the Glauber approach we investigate the influence of the initial fluctuations on various measures of the initial-state geometry in 63Cu+197Au and 238U+238U relativistic ion collisions. Comparing variants of Glauber model (the wounded-nucleon model, the mixed model, and the hot-spot model) we indicate sensitivity of certain observables, in particular for the azimuthal eccentricity parameters as well as for the correlation of directions of the principal axes associated with the Fourier components. We apply GLISSANDO in our analysis.

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arXiv2012

On the possibility of q-scaling in high energy production processes

It has been noticed recently that transverse momenta (p_T) distributions observed in high energy production processes exhibit remarkably universal scaling behaviour. This is the case when a suitable variable replaces the usual p_T. On the other hand, it is also widely known that transverse momentum distributions in general follow a power-like Tsallis distribution, rather than an exponential Boltzmann-Gibbs, with a (generally energy dependent) nonextensivity parameter q. Here we show that it is possible to choose a suitable variable such that all the data can be fitted by the same Tsallis distribution (with the same, energy independent value of the q-parameter). Thus they exhibit q-scaling.

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arXiv2010

Two-body nucleon-nucleon correlations in Glauber-like models

We investigate the role of the central two-body nucleon-nucleon correlations on typical quantities observed in relativistic heavy-ion collisions. Basic correlation measures, such as the fluctuations of the participant eccentricity, initial size fluctuations, or the fluctuations of the number of sources producing particles, are sensitive at the level 10-20% to the inclusion of the two-body correlations. However, the realistic correlation function gives virtually indistinguishable results from the {\em hard-core repulsion} with the expulsion distance set to $\sim 0.9$ fm. In the second part of the talk we compare the spherical and Gaussian wounding profiles and find that the latter, which is more realistic, leads to reduced eccentricity and fluctuations. This has significance for precision studies of the elliptic flow.

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arXiv2010

Two-body nucleon-nucleon correlations in Glauber models of relativistic heavy-ion collisions

We investigate the influence of the central two-body NN correlations on several quantities observed in relativistic heavy-ion collisions. It is demonstrated with explicit Monte Carlo simulations, that the basic correlation measures, such as the fluctuations of participant eccentricity, initial size fluctuations, or the fluctuations of the number of sources producing particles, are all sensitive to the inclusion of the two-body correlations. The effect is at the level of about 10-20%. Moreover, the realistic (Gaussian) correlation function gives indistinguishable results from the hard-core repulsion, with the expulsion distance set to 0.9 fm. Thus, for investigations of the considered correlation measures, it is sufficient to use the Monte Carlo generators accounting for the hard-core repulsion.

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arXiv2009

Fluctuations in relativistic heavy-ion collisions from the Glauber models

In the first part of the talk we discuss the role of the two-body nucleon-nucleon correlations on signatures of the heavy-ion collisions which are a priori expected to be sensitive to these effects. We find that while the fluctuations of the number of produced particles are indeed affected, other quantities (v_2 fluctuations, size fluctuations) are insensitive to the presence of the NN correlations in the nucleon distributions. In the second part we show that the fluctuations of the transverse size of the initial source cause, after a suitable hydrodynamic evolution, fluctuations of the transverse flow velocity at hadronic freeze-out. This in turn yields the event-by-event fluctuations of the transverse momentum of the produced particles, p_T. Our results demonstrate that practically all of the observed event-by-event p_T fluctuations may be explained this way.

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arXiv2008

GLISSANDO: GLauber Initial-State Simulation AND mOre

GLISSANDO is a Glauber Monte-Carlo generator for early-stages of relativistic heavy-ion collisions, written in c++ and interfaced to Root. Several models are implemented: the wounded-nucleon model, the binary collisions model, the mixed model, and the model with hot-spots. Subtleties of the distribution of nucleon in the nucleus are discussed. The original geometric distribution of sources in the transverse plane can be superimposed with a statistical distribution simulating the dispersion in the generated transverse energy in each individual collision. The program generates inter alia the fixed axes (standard) and variable-axes (participant) two-dimensional profiles of the density of sources in the transverse plane and their Fourier components. These profiles can be used in further analyses of physical phenomena, such as the the jet quenching, event-by-event hydrodynamics, or analysis of the elliptic flow and its fluctuations. Characteristics of the event (multiplicities, eccentricities, Fourier coefficients, etc.) are evaluated and stored in a file for further off-line studies. A number of scripts is provided for that purpose. Supplied variants of the code can also be used for the proton-nucleus and deuteron-nucleus collisions.

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arXiv2008

Glauber Monte-Carlo predictions for LHC

In the framework of various Glauber-like models we compute several correlation observables in nuclear collisions at the SPS, RHIC, and LHC energies. We analyze fluctuations of the eccentricity of the fireball created in the collision, in particular the {variable-axes} harmonic moments $ε^\ast$, as well as the fluctuations of multiplicity of charged particles. We find moderate model dependence of the scaled standard deviation $σ(ε^\ast)/ε^\ast$ on the choice of the particular Glauber model. For all considered models the values of $σ(ε^\ast)/ε^\ast$ range from $\sim$~0.5 for central collisions to $\sim$~0.3-0.4 for peripheral collisions. The results are confronted to the recent measurement of the elliptic-flow fluctuations at RHIC. We also find that the dependence of multiplicity fluctuations on the centrality of the collision is too weak to explain the measurements at the SPS energies. The magnitude of the Glauber multiplicity fluctuations increases by about 20% from the RHIC to LHC energies.

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arXiv2007

Fluctuation of the initial condition from Glauber models

We analyze measures of the azimuthal asymmetry, in particular the participant harmonic moments, epsilon*, in a variety of Glauber-like models for the early stage of collisions at RHIC. Quantitative comparisons indicate substantial model dependence for epsilon*, reflecting different effective number of sources, while the dependence of the scaled standard deviation sigma(epsilon*)/epsilon* on the particular Glauber model is weak. For all the considered models the values of sigma(epsilon*)/epsilon* range from ~0.5 for the central collisions to ~0.3-0.4 for peripheral collisions. These values, dominated by statistics, change only by 10-15% from model to model. For central collisions and in the absence of correlations between the location of sources we obtain through the use of the central limit theorem the simple analytic formula sigma(epsilon*)/epsilon*(b=0) ~ \sqrt{4/pi-1} ~ 0.52$, independent on the collision energy, mass number, or the number of sources. We investigate the shape-fluctuation effects for jet quenching and find they are important only for very central events. Finally, we list some remarks and predictions from smooth hydrodynamics on higher flow coefficients and their fluctuations, in particular sigma(v_4)/v_4=2 sigma(v_2)/v_2.

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arXiv2007

Fluctuating initial conditions in heavy-ion collisions from the Glauber approach

In the framework of the Glauber approach we analyze the shape parameters of the early-formed system and their event-by-event fluctuations. We test a variety of models: the conventional wounded nucleon model, a model admixing binary collisions to the wounded nucleons, a model with hot spots, as well as the hot-spot model where the deposition of energy occurs with a superimposed probability distribution. We look in detail at the so-called participant multipole moments, obtained by an averaging procedure where in each event the system is translated to its center of mass and aligned with the major principal axis of the ellipse of inertia. Quantitative comparisons indicate substantial relative effects for eccentricity in variants of Glauber models. On the other hand, the dependence of the scaled standard deviation of the participant eccentricity on the chosen model is weak. For all models the values range from about 0.5 for the central collisions to about 0.3-0.4 for peripheral collisions, both for the gold-gold and copper-copper collisions. They are dominated by statistics and change only by 10-15% from model to model. We provide an approximate analytic expansion for the multipole moments and their fluctuations given in terms of the fixed-axes moments. For central collisions and in the absence of correlations it gives the simple formula for the scaled standard deviation of the participant eccentricity: sqrt(4/pi-1). Similarly, we obtain expansions for the radial profiles of the multipole distributions. We investigate the relevance of the shape-fluctuation effects for jet quenching and find them important only for very central events. Finally, we argue how smooth hydro leads to the known result v_4 ~ v_2^2, and further to the prediction Delta v_4/v_4 = 2 Delta v_2/v_2.

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