arXiv subjects

G. Stefanek

Publications and source records attributed to G. Stefanek.

14 recordsLinked to original sources

arXiv2026

$K^{*}(892)^0$ production and the time between freeze-outs in $^{40}$Ar+$^{45}$Sc collisions by NA61/SHINE at the CERN SPS

The analysis of the production of strange $K^{*}(892)^0$ resonances allows us to better understand the temporal evolution of high-energy nucleus--nucleus collisions. In particular, the ratio of $K^{*}(892)^0$ to charged kaon yields is used to determine the time interval between chemical and kinetic freeze-outs. In this paper, the first measurements of $K^{*}(892)^0$ production in central $^{40}$Ar+$^{45}$Sc collisions at the CERN Super Proton Synchrotron are reported. They were performed by NA61/SHINE at collision center-of-mass energies per nucleon pair $\sqrt{s_\mathrm{NN}}$ = 8.8, 11.9, 16.8 GeV. The obtained $\langle K^{*}(892)^0 \rangle/\langle K^{+} \rangle $ and $\langle K^{*}(892)^0 \rangle/\langle K^{-} \rangle$ mean multiplicity ratios are compared with corresponding results in $p$+$p$ collisions, allowing for an estimate of the time interval between chemical and thermal freeze-outs in the $^{40}$Ar+$^{45}$Sc system. These are the first such results reported for $^{40}$Ar+$^{45}$Sc collisions.

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arXiv2018

Influence of target material impurities on physical results in relativistic heavy-ion collisions

This paper presents the studies on the influence of the target material impurities on physical observables registered in heavy ion collisions collected by fixed target experiments. It mainly concerns the measures of multiplicity fluctuations which can be used to searches for critical point of strongly interacting matter, e.g. in the {NA61/SHINE} fixed-target experiment at CERN SPS. The elemental composition of the targets used in the NA61/SHINE experiment was determined applying wavelength dispersive X-ray fluorescence (WDXRF) technique. The influence of measured target impurities on multiplicity distributions and scaled variance was estimated using simulation events. The modification of the standard analysis was proposed to reduce this influence.

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arXiv2016

Production of deuterium, tritium, and $^3$He in central Pb+Pb collisions at 20A, 30A, 40A, 80A, and 158A GeV at the CERN SPS

Production of $d$, $t$, and $^3$He nuclei in central Pb+Pb interactions was studied at five collision energies ($\sqrt{s_{NN}}=$ 6.3, 7.6, 8.8, 12.3, and 17.3 GeV) with the NA49 detector at the CERN SPS. Transverse momentum spectra, rapidity distributions, and particle ratios were measured. Yields are compared to predictions of statistical models. Phase-space distributions of light nuclei are discussed and compared to those of protons in the context of a coalescence approach. The coalescence parameters $B_2$ and $B_3$, as well as coalescence radii for $d$ and $^3$He were determined as a function of transverse mass at all energies.

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arXiv2015

Critical fluctuations of the proton density in A+A collisions at $158A$ GeV

We look for fluctuations expected for the QCD critical point using an intermittency analysis in the transverse momentum phase space of protons produced around midrapidity in the 12.5\% most central C+C, Si+Si and Pb+Pb collisions at the maximum SPS energy of 158$A$~GeV. We find evidence of power-law fluctuations for the Si+Si data. The fitted power-law exponent $ϕ_{2} = 0.96^{+0.38}_{-0.25}\text{ (stat.)}$ $\pm 0.16\text{ (syst.)}$ is consistent with the va\-lue expected for critical fluctuations. Power-law fluctuations had previously also been observed in low-mass $π^+ π^-$ pairs in the same Si+Si collisions.

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arXiv2015

Measurement of event-by-event transverse momentum and multiplicity fluctuations using strongly intensive measures $Δ[P_T, N]$ and $Σ[P_T, N]$ in nucleus-nucleus collisions at the CERN Super Proton Synchrotron

Results from the NA49 experiment at the CERN SPS are presented on event-by-event transverse momentum and multiplicity fluctuations of charged particles, produced at forward rapidities in central Pb+Pb interactions at beam momenta 20$A$, 30$A$, 40$A$, 80$A$, and 158$A$ GeV/c, as well as in systems of different size ($p+p$, C+C, Si+Si, and Pb+Pb) at 158$A$ GeV/c. This publication extends the previous NA49 measurements of the strongly intensive measure $Φ_{p_T}$ by a study of the recently proposed strongly intensive measures of fluctuations $Δ[P_T, N]$ and $Σ[P_T, N]$. In the explored kinematic region transverse momentum and multiplicity fluctuations show no significant energy dependence in the SPS energy range. However, a remarkable system size dependence is observed for both $Δ[P_T, N]$ and $Σ[P_T, N]$, with the largest values measured in peripheral Pb+Pb interactions. The results are compared with NA61/SHINE measurements in $p+p$ collisions, as well as with predictions of the UrQMD and EPOS models.

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arXiv2013

Phase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy

A novel approach, the identity method, was used for particle identification and the study of fluctuations of particle yield ratios in Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the moments of the unknown multiplicity distributions of protons (p), kaons (K), pions ($π$) and electrons (e). Using these moments the excitation function of the fluctuation measure $ν_{\text{\text{dyn}}}$[A,B] was measured, with A and B denoting different particle types. The obtained energy dependence of $ν_{\text{dyn}}$ agrees with previously published NA49 results on the related measure $σ_{\text{dyn}}$. Moreover, $ν_{\text{dyn}}$ was found to depend on the phase space coverage for [K,p] and [K,$π$] pairs. This feature most likely explains the reported differences between measurements of NA49 and those of STAR in central Au+Au collisions.

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arXiv2012

System-size and centrality dependence of charged kaon and pion production in nucleus-nucleus collisions at 40A GeV and158A GeV beam energy

Measurements of charged pion and kaon production are presented in centrality selected Pb+Pb collisions at 40A GeV and 158A GeV beam energy as well as in semi-central C+C and Si+Si interactions at 40A GeV. Transverse mass spectra, rapidity spectra and total yields are determined as a function of centrality. The system-size and centrality dependence of relative strangeness production in nucleus-nucleus collisions at 40A GeV and 158A GeV beam energy are derived from the data presented here and published data for C+C and Si+Si collisions at 158A GeV beam energy. At both energies a steep increase with centrality is observed for small systems followed by a weak rise or even saturation for higher centralities. This behavior is compared to calculations using transport models (UrQMD and HSD), a percolation model and the core-corona approach.

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arXiv2011

Energy dependence of kaon-to-proton ratio fluctuations in central Pb+Pb collisions from $\sqrt{s_{NN}}$ = 6.3 to 17.3 GeV

Kaons and protons carry large parts of two conserved quantities, strangeness and baryon number. It is argued that their correlation and thus also fluctuations are sensitive to conditions prevailing at the anticipated parton-hadron phase boundary. Fluctuations of the $(\mathrm{K}^+ + \mathrm{K}^-)/(\mathrm{p}+\bar{\mathrm{p}})$ and $\mathrm{K}^+/\mathrm{p}$ ratios have been measured for the first time by NA49 in central Pb+Pb collisions at 5 SPS energies between $\sqrt{s_{NN}}$= 6.3 GeV and 17.3 GeV. Both ratios exhibit a change of sign in $σ_{\mathrm{dyn}}$, a measure of non-statistical fluctuations, around $\sqrt{s_{NN}}$ = 8 GeV. Below this energy, $σ_{\mathrm{dyn}}$ is positive, indicating higher fluctuation compared to a mixed event background sample, while for higher energies, $σ_{\mathrm{dyn}}$ is negative, indicating correlated emission of kaons and protons. The results are compared to UrQMD calculations which which give a good description at the higher SPS energies, but fail to reproduce the transition to positive values.

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arXiv2011

Proton -- Lambda Correlations in Central Pb+Pb Collisions at sqrt(s_{NN}) = 17.3 GeV

The momentum correlation between protons and lambda particles emitted from central Pb+Pb collisions at sqrt(s_{NN}) = 17.3 GeV was studied by the NA49 experiment at the CERN SPS. A clear enhancement is observed for small relative momenta (q_{inv} < 0.2 GeV). By fitting a theoretical model, which uses the strong interaction between the proton and the lambda in a given pair, to the measured data a value for the effective source size is deduced. Assuming a static Gaussian source distribution we derive an effective radius parameter of R_G = 3.02 \pm 0.20$(stat.)^{+0.44}_{-0.16}(syst.) fm.

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arXiv2010

Centrality dependence of proton and antiproton spectra in Pb+Pb collisions at 40A GeV and 158A GeV measured at the CERN SPS

The yields of (anti-)protons were measured by the NA49 Collaboration in centrality selected Pb+Pb collisions at 40A GeV and 158A GeV. Particle identification was obtained in the laboratory momentum range from 5 to 63 GeV/c by the measurement of the energy loss dE/dx in the TPC detector gas. The corresponding rapidity coverage extends 1.6 units from mid-rapidity into the forward hemisphere. Transverse mass spectra, the rapidity dependences of the average transverse mass, and rapidity density distributions were studied as a function of collision centrality. The values of the average transverse mass as well as the midrapidity yields of protons when normalized to the number of wounded nucleons show only modest centrality dependences. In contrast, the shape of the rapidity distribution changes significantly with collision centrality, especially at 40A GeV. The experimental results are compared to calculations of the HSD and UrQMD transport models.

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arXiv2009

Inclusive production of protons, anti-protons and neutrons in p+p collisions at 158 GeV/c beam momentum

New data on the production of protons, anti-protons and neutrons in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The charged baryons are identified by energy loss measurement in a large TPC tracking system. Neutrons are detected in a forward hadronic calorimeter. Inclusive invariant cross sections are obtained in intervals from 0 to 1.9 GeV/c (0 to 1.5 GeV/c) in transverse momentum and from -0.05 to 0.95 (-0.05 to 0.4) in Feynman x for protons (anti-protons), respectively. pT integrated neutron cross sections are given in the interval from 0.1 to 0.9 in Feynman x. The data are compared to a wide sample of existing results in the SPS and ISR energy ranges as well as to proton and neutron measurements from HERA and RHIC.

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arXiv2008

Energy dependence of phi meson production in central Pb+Pb collisions at sqrt(s_nn) = 6 to 17 GeV

Phi meson production is studied by the NA49 Collaboration in central Pb+Pb collisions at 20A, 30A, 40A, 80A and 158A GeV beam energy. The data are compared with measurements at lower and higher energies and to microscopic and thermal models. The energy dependence of yields and spectral distributions is compatible with the assumption that partonic degrees of freedom set in at low SPS energies.

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arXiv2008

Event-by-event transverse momentum fluctuations in nuclear collisions at CERN SPS

The latest NA49 results on event-by-event transverse momentum fluctuations are presented for central Pb+Pb interactions over the whole SPS energy range (20A - 158A GeV). Two different methods are applied: evaluating the $Φ_{p_{T}}$ fluctuation measure and studying two-particle transverse momentum correlations. The obtained results are compared to predictions of the UrQMD model. The results on the energy dependence are compared to the NA49 data on the system size dependence. The NA61 (SHINE, NA49-future) strategy of searching of the QCD critical end-point is also discussed.

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arXiv2007

Elliptic flow of Lambda hyperons in Pb+Pb collisions at 158A GeV

The elliptic flow of Lambda hyperons has been measured by the NA49 collaboration at the CERN-SPS in semi-central Pb+Pb collisions at 158A GeV. The standard method of correlating particles with the event plane was used. Measurements of v2 near mid-rapidity are reported as a function of rapidity, centrality and transverse momentum. Elliptic flow of Lambda particles increases both with the impact parameter and with the transverse momentum. It is compared with v2 for pions and protons as well as with model calculations. The observation of significant elliptic flow and its mass dependence suggest strong collective behaviour of the matter produced in collisions of heavy nuclei already at the SPS. Scaling properties of elliptic flow of different particle species have been tested at 158A GeV. The limited pT range of the data does not allow for a decisive test of the coalescence model.

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