J. Bartke

Polish Academy of Sciences, Warszawa, Masovian Voivodeship, Poland

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Publications (456)

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    [Show abstract] [Hide abstract] ABSTRACT: We report the transverse energy (ET) measured with ALICE at midrapidity in Pb-Pb collisions at√sNN=2.76 TeV as a function of centrality. The transverse energy was measured using identified single-particle tracks.The measurement was cross checked using the electromagnetic calorimeters and the transverse momentum distributions of identified particles previously reported by ALICE. The results are compared to theoretical models as well as to results from other experiments. The mean ET per unit pseudorapidity (η), dET/dη, in 0%–5% central collisions is 1737±6(stat.)±97(sys.) GeV. We find a similar centrality dependence of the shape dET/dη as a function of the number of participating nucleons to that seen at lower energies. The growth in dET/dη at the LHC energies exceeds extrapolations of low-energy data. We observe a nearly linear scaling of dET/dη with the number of quark participants. With the canonical assumption of a 1 fm/c formation time, we estimate that the energy density in 0%–5% central Pb-Pb collisions at√sNN=2.76 TeV is 12.3±1.0 GeV/fm3 and that the energy density at the most central 80 fm2 of the collision is at least 21.5±1.7 GeV/fm3.This is roughly 2.3 times that observed in 0%–5% central Au-Au collisions at√sNN=200 GeV.
    Full-text Article · Sep 2016
  • [Show abstract] [Hide abstract] ABSTRACT: The elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity (|y| < 0.7) is measured in Pb-Pb collisions at \( \sqrt{s_{\mathrm{NN}}}=2.76 \) TeV with ALICE at the LHC. The particle azimuthal distribution with respect to the reaction plane can be parametrized with a Fourier expansion, where the second coefficient (v2) represents the elliptic flow. The v2 coefficient of inclusive electrons is measured in three centrality classes (0–10%, 10–20% and 20–40%) with the event plane and the scalar product methods in the transverse momentum (pT) intervals 0.5–13 GeV/c and 0.5–8 GeV/c, respectively. After subtracting the background, mainly from photon conversions and Dalitz decays of neutral mesons, a positive v2 of electrons from heavy-flavour hadron decays is observed in all centrality classes, with a maximum significance of 5.9σ in the interval 2 < pT < 2.5 GeV/c in semi-central collisions (20–40%). The value of v2 decreases towards more central collisions at low and intermediate pT (0.5 < pT < 3 GeV/c). The v2 of electrons from heavy-flavour hadron decays at mid-rapidity is found to be similar to the one of muons from heavy-flavour hadron decays at forward rapidity (2.5 < y < 4). The results are described within uncertainties by model calculations including substantial elastic interactions of heavy quarks with an expanding strongly-interacting medium.
    Article · Sep 2016 · Journal of High Energy Physics
  • [Show abstract] [Hide abstract] ABSTRACT: The measurement of prompt D-meson production as a function of multiplicity in p-Pb collisions at \( \sqrt{s_{\mathrm{NN}}}=5.02 \) TeV with the ALICE detector at the LHC is reported. D0, D+ and D∗+ mesons are reconstructed via their hadronic decay channels in the centre-of-mass rapidity range −0.96 < ycms< 0.04 and transverse momentum interval 1<pT<24 GeV/c. The multiplicity dependence of D-meson production is examined by either comparing yields in p-Pb collisions in different event classes, selected based on the multiplicity of produced particles or zero-degree energy, with those in pp collisions, scaled by the number of binary nucleon-nucleon collisions (nuclear modification factor); as well as by evaluating the per-event yields in p-Pb collisions in different multiplicity intervals normalised to the multiplicity-integrated ones (relative yields). The nuclear modification factors for D0, D+ and D∗+ are consistent with one another. The D-meson nuclear modification factors as a function of the zero-degree energy are consistent with unity within uncertainties in the measured pT regions and event classes. The relative D-meson yields, calculated in various pT intervals, increase as a function of the charged-particle multiplicity. The results are compared with the equivalent pp measurements at \( \sqrt{s}=7 \) TeV as well as with EPOS 3 calculations.
    Article · Aug 2016 · Journal of High Energy Physics
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    [Show abstract] [Hide abstract] ABSTRACT: The production of charged pions, kaons and (anti)protons has been measured at mid-rapidity (−0.5<y<0) in p–Pb collisions at sNN=5.02 TeV using the ALICE detector at the LHC. Exploiting particle identification capabilities at high transverse momentum (pT), the previously published pT spectra have been extended to include measurements up to 20 ,GeV/c for seven event multiplicity classes. The pT spectra for pp collisions at s=7 TeV, needed to interpolate a pp reference spectrum, have also been extended up to 20 GeV/c to measure the nuclear modification factor (RpPb) in non-single diffractive p–Pb collisions.
    Full-text Article · Jul 2016 · Physics Letters B
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    [Show abstract] [Hide abstract] ABSTRACT: We present measurements of the elliptic (v2), triangular (v3) and quadrangular (v4) anisotropic azimuthal flow over a wide range of pseudorapidities (−3.5<η<5). The measurements are performed with Pb–Pb collisions at sNN=2.76 TeV using the ALICE detector at the Large Hadron Collider (LHC). The flow harmonics are obtained using two- and four-particle correlations from nine different centrality intervals covering central to peripheral collisions. We find that the shape of vn(η) is largely independent of centrality for the flow harmonics n=2−4, however the higher harmonics fall off more steeply with increasing |η|. We assess the validity of extended longitudinal scaling of v2 by comparing to lower energy measurements, and find that the higher harmonic flow coefficients are proportional to the charged particle densities at larger pseudorapidities. Finally, we compare our measurements to both hydrodynamical and transport models, and find they both have challenges when it comes to describing our data.
    Full-text Article · Jul 2016 · Physics Letters B
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    [Show abstract] [Hide abstract] ABSTRACT: 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.
    Full-text Article · Jun 2016
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    [Show abstract] [Hide abstract] ABSTRACT: The pseudorapidity density of charged particles, dN_{ch}/dη, at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=5.02 TeV. For the 5% most central collisions, we measure a value of 1943±54. The rise in dN_{ch}/dη as a function of sqrt[s_{NN}] is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of dN_{ch}/dη as a function of the average number of participant nucleons, ⟨N_{part}⟩, calculated in a Glauber model, is compared with the previous measurement at sqrt[s_{NN}]=2.76 TeV. A constant factor of about 1.2 describes the increase in dN_{ch}/dη from sqrt[s_{NN}]=2.76 to 5.02 TeV for all centrality classes, within the measured range of 0%-80% centrality. The results are also compared to models based on different mechanisms for particle production in nuclear collisions.
    Full-text Article · Jun 2016 · Physical Review Letters
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    [Show abstract] [Hide abstract] ABSTRACT: We report on the first measurement of an excess in the yield of J/ψ at very low transverse momentum (p_{T}<0.3 GeV/c) in peripheral hadronic Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J/ψ in the rapidity range 2.5<y<4 reaches about 7 (2) in the p_{T} range 0-0.3 GeV/c in the 70%-90% (50%-70%) centrality class. The J/ψ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J/ψ is the underlying physics mechanism. If confirmed, the observation of J/ψ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nuclear radius opens new theoretical and experimental challenges and opportunities. In particular, coherent photoproduction accompanying hadronic collisions may provide insight into the dynamics of photoproduction and nuclear reactions, as well as become a novel probe of the quark-gluon plasma.
    Full-text Article · Jun 2016 · Physical Review Letters
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    [Show abstract] [Hide abstract] ABSTRACT: The inclusive production of the ψ(2S) charmonium state was studied as a function of centrality in p-Pb collisions at the nucleon-nucleon center of mass energy √sNN = 5.02 TeV at the CERN LHC. The measurement was performed with the ALICE detector in the center of mass rapidity ranges −4.46 < ycms< −2.96 and 2.03 < ycms< 3.53, down to zero transverse momentum, by reconstructing the ψ(2S) decay to a muon pair. The ψ(2S) production cross section σψ(2S) is presented as a function of the collision centrality, which is estimated through the energy deposited in forward rapidity calorimeters. The relative strength of nuclear effects on the ψ(2S) and on the corresponding 1S charmonium state J/ψ is then studied by means of the double ratio of cross sections [σψ(2S)/σJ/ψ]pPb/[σψ(2S)/σJ/ψ]pp between p-Pb and pp collisions, and by the values of the nuclear modification factors for the two charmonium states. The results show a large suppression of ψ(2S) production relative to the J/ψ at backward (negative) rapidity, corresponding to the flight direction of the Pb-nucleus, while at forward (positive) rapidity the suppressions of the two states are comparable. Finally, comparisons to results from lower energy experiments and to available theoretical models are presented.
    Full-text Article · Jun 2016 · Journal of High Energy Physics
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    [Show abstract] [Hide abstract] ABSTRACT: Three- and four-pion Bose-Einstein correlations are presented in pp,p-Pb, and Pb-Pb collisions at the LHC. We compare our measured four-pion correlations to the expectation derived from two- and three-pion measurements. Such a comparison provides a method to search for coherent pion emission. We also present mixed-charge correlations in order to demonstrate the effectiveness of several analysis procedures such as Coulomb corrections. Same-charge four-pion correlations in pp and p-Pb appear consistent with the expectations from three-pion measurements. However, the presence of non-negligible background correlations in both systems prevent a conclusive statement. In Pb-Pb collisions, we observe a significant suppression of three- and four-pion Bose-Einstein correlations compared to expectations from two-pion measurements. There appears to be no centrality dependence of the suppression within the 0%-50% centrality interval. The origin of the suppression is not clear. However, by postulating either coherent pion emission or large multibody Coulomb effects, the suppression may be explained.
    Full-text Article · May 2016
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    [Show abstract] [Hide abstract] ABSTRACT: The multi-strange baryon yields in Pb–Pb collisions have been shown to exhibit an enhancement relative to pp reactions. In this work, Ξ and Ω production rates have been measured with the ALICE experiment as a function of transverse momentum, , in p–Pb collisions at a centre-of-mass energy of = 5.02 TeV. The results cover the kinematic ranges 0.6 GeV/c < < 7.2 GeV/c and 0.8 GeV/c < < 5 GeV/c, for Ξ and Ω respectively, in the common rapidity interval -0.5 0. Multi-strange baryons have been identified by reconstructing their weak decays into charged particles. The spectra are analysed as a function of event charged–particle multiplicity, which in p–Pb collisions ranges over one order of magnitude and lies between those observed in pp and Pb–Pb collisions. The measured distributions are compared to the expectations from a Blast-Wave model. The parameters which describe the production of lighter hadron species also describe the hyperon spectra in high multiplicity p–Pb collisions. The yield of hyperons relative to charged pions is studied and compared with results from pp and Pb–Pb collisions. A continuous increase in the yield ratios as a function of multiplicity is observed in p–Pb data, the values of which range from those measured in minimum bias pp to the ones in Pb–Pb collisions. A statistical model qualitatively describes this multiplicity dependence using a canonical suppression mechanism, in which the small volume causes a relative reduction of hadron production dependent on the strangeness content of the hyperon.
    Full-text Article · May 2016 · Physics Letters B
  • [Show abstract] [Hide abstract] ABSTRACT: The production of J/psi and psi (2S) was studied with the ALICE detector in Pb-Pb collisions at the LHC. The measurement was performed at forward rapidity (2.5 < y < 4) down to zero transverse momentum (p(T)) in the dimuon decay channel. Inclusive J/psi yields were extracted in different centrality classes and the centrality dependence of the average p(T) is presented. The J/psi suppression, quantified with the nuclear modification factor (R-AA), was measured as a function of centrality, transverse momentum and rapidity. Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/psi production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization. Results on the psi(2S) suppression are provided via the ratio of psi(2S) over J/psi measured in pp and Pb-Pb collisions.
    Article · May 2016 · Journal of High Energy Physics
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    [Show abstract] [Hide abstract] ABSTRACT: We present a Bayesian approach to particle identification (PID) within the ALICE experiment. The aim is to more effectively combine the particle identification capabilities of its various detectors. After a brief explanation of the adopted methodology and formalism, the performance of the Bayesian PID approach for charged pions, kaons and protons in the central barrel of ALICE is studied. PID is performed via measurements of specific energy loss (dE/dx) and time of flight. PID efficiencies and misidentification probabilities are extracted and compared with Monte Carlo simulations using high-purity samples of identified particles in the decay channels K0S→ π-π+}, ɸ → K-K+, and Λ → p π- in p-Pb collisions at √sNN=5.02 TeV. In order to thoroughly assess the validity of the Bayesian approach, this methodology was used to obtain corrected pT spectra of pions, kaons, protons, and D0 mesons in pp collisions at √s=7 TeV. In all cases, the results using Bayesian PID were found to be consistent with previous measurements performed by ALICE using a standard PID approach. For the measurement of D0 → K-π+, it was found that a Bayesian PID approach gave a higher signal-to-background ratio and a similar or larger statistical significance when compared with standard PID selections, despite a reduced identification efficiency. Finally, we present an exploratory study of the measurement of Λc+ → p K-π+ in pp collisions at √s=7 TeV, using the Bayesian approach for the identification of its decay products.
    Full-text Article · May 2016 · European Physical Journal Plus
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    [Show abstract] [Hide abstract] ABSTRACT: Measurements of charged jet production as a function of centrality are presented for p–Pb collisions recorded at √sNN = 5.02 TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon–nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti-kT algorithm for resolution parameters R= 0.2 and R= 0.4 in the transverse momentum range 20 to 120 GeV/c. The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in p–Pb collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.
    Full-text Article · May 2016 · European Physical Journal C
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    [Show abstract] [Hide abstract] ABSTRACT: The production of K∗(892)0 and ϕ(1020) mesons has been measured in p–Pb collisions at sNN= 5.02 TeV. K∗ 0 and ϕ are reconstructed via their decay into charged hadrons with the ALICE detector in the rapidity range - 0.5 < y< 0. The transverse momentum spectra, measured as a function of the multiplicity, have a pT range from 0 to 15 GeV/c for K∗ 0 and from 0.3 to 21 GeV/c for ϕ. Integrated yields, mean transverse momenta and particle ratios are reported and compared with results in pp collisions at √s= 7 TeV and Pb–Pb collisions at sNN= 2.76 TeV. In Pb–Pb and p–Pb collisions, K∗ 0 and ϕ probe the hadronic phase of the system and contribute to the study of particle formation mechanisms by comparison with other identified hadrons. For this purpose, the mean transverse momenta and the differential proton-to-ϕ ratio are discussed as a function of the multiplicity of the event. The short-lived K∗ 0 is measured to investigate re-scattering effects, believed to be related to the size of the system and to the lifetime of the hadronic phase.
    Full-text Article · May 2016 · European Physical Journal C
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    [Show abstract] [Hide abstract] ABSTRACT: We report on measurements of a charge-dependent flow using a novel three-particle correlator with ALICE in Pb-Pb collisions at the CERN Large Hadron Collider (LHC), and discuss the implications for observation of local parity violation and the chiral magnetic wave (CMW) in heavy-ion collisions. Charge-dependent flow is reported for different collision centralities as a function of the event charge asymmetry. While our results are in qualitative agreement with expectations based on the CMW, the nonzero signal observed in higher harmonics correlations indicates a possible significant background contribution. We also present results on a differential correlator, where the flow of positive and negative charges is reported as a function of the mean charge of the particles and their pseudorapidity separation. We argue that this differential correlator is better suited to distinguish the differences in positive and negative charges expected due to the CMW and the background effects, such as local charge conservation coupled with strong radial and anisotropic flow.
    Full-text Article · Apr 2016
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    [Show abstract] [Hide abstract] ABSTRACT: We report the first results of elliptic (v_{2}), triangular (v_{3}), and quadrangular (v_{4}) flow of charged particles in Pb-Pb collisions at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurements are performed in the central pseudorapidity region |η|<0.8 and for the transverse momentum range 0.2<p_{T}<5 GeV/c. The anisotropic flow is measured using two-particle correlations with a pseudorapidity gap greater than one unit and with the multiparticle cumulant method. Compared to results from Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV, the anisotropic flow coefficients v_{2}, v_{3}, and v_{4} are found to increase by (3.0±0.6)%, (4.3±1.4)%, and (10.2±3.8)%, respectively, in the centrality range 0%-50%. This increase can be attributed mostly to an increase of the average transverse momentum between the two energies. The measurements are found to be compatible with hydrodynamic model calculations. This comparison provides a unique opportunity to test the validity of the hydrodynamic picture and the power to further discriminate between various possibilities for the temperature dependence of shear viscosity to entropy density ratio of the produced matter in heavy-ion collisions at the highest energies.
    Full-text Article · Apr 2016 · Physical Review Letters
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    [Show abstract] [Hide abstract] ABSTRACT: We report on the inclusive production cross sections of (Formula presented.) , (Formula presented.) , (Formula presented.) (1S), (Formula presented.) (2S) and (Formula presented.) (3S), measured at forward rapidity with the ALICE detector in (Formula presented.) collisions at a center-of-mass energy (Formula presented.) TeV. The analysis is based on data collected at the LHC and corresponds to an integrated luminosity of 1.23 pb (Formula presented.). Quarkonia are reconstructed in the dimuon-decay channel. The differential production cross sections are measured as a function of the transverse momentum (Formula presented.) and rapidity y, over the (Formula presented.) ranges (Formula presented.) GeV/c for (Formula presented.) , (Formula presented.) GeV/c for all other resonances, and for (Formula presented.). The cross sections, integrated over (Formula presented.) and y, and assuming unpolarized quarkonia, are (Formula presented.) (Formula presented.) b, (Formula presented.) (Formula presented.) b, (Formula presented.) nb, (Formula presented.) nb and (Formula presented.) nb, where the first uncertainty is statistical and the second one is systematic. These values agree, within at most (Formula presented.) , with measurements performed by the LHCb collaboration in the same rapidity range.
    Full-text Article · Apr 2016 · European Physical Journal C
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    [Show abstract] [Hide abstract] ABSTRACT: We report on results obtained with the event-shape engineering technique applied to Pb-Pb collisions at sNN=2.76 TeV. By selecting events in the same centrality interval, but with very different average flow, different initial-state conditions can be studied. We find the effect of the event-shape selection on the elliptic flow coefficient v2 to be almost independent of transverse momentum pT, which is as expected if this effect is attributable to fluctuations in the initial geometry of the system. Charged-hadron, -pion, -kaon, and -proton transverse momentum distributions are found to be harder in events with higher-than-average elliptic flow, indicating an interplay between radial and elliptic flow. ©2016 CERN, for the ALICE Collaboration. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
    Full-text Article · Mar 2016
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    [Show abstract] [Hide abstract] ABSTRACT: Transverse momentum (pT) spectra of pions, kaons, and protons up to pT=20GeV/c have been measured in Pb-Pb collisions at sNN=2.76TeV using the ALICE detector for six different centrality classes covering 0%-80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT≈3GeV/c in central Pb-Pb collisions that decreases for more peripheral collisions. For pT>10GeV/c, the nuclear modification factor is found to be the same for all three particle species in each centrality interval within systematic uncertainties of 10%-20%. This suggests there is no direct interplay between the energy loss in the medium and the particle species composition in the hard core of the quenched jet. For pT<10GeV/c, the data provide important constraints for models aimed at describing the transition from soft to hard physics.
    Full-text Article · Mar 2016

Publication Stats

9k Citations

Institutions

  • 2008-2014
    • Polish Academy of Sciences
      • Henryk Niewodniczański Institute of Nuclear Physics
      Warszawa, Masovian Voivodeship, Poland
  • 2012-2013
    • Lawrence Livermore National Laboratory
      • Physics Division
      Livermore, California, United States
  • 2010
    • University of Bergen
      • Department of Physics and Technology
      Bergen, Hordaland Fylke, Norway
  • 1973-2009
    • Institute of Nuclear Physics
      Cracovia, Lesser Poland Voivodeship, Poland
  • 2006
    • Sofia University "St. Kliment Ohridski"
      • Department of Atomic Physics
      Sofia, Oblast Sofiya-Grad, Bulgaria
  • 2005
    • University Hospital Frankfurt
      Frankfurt, Hesse, Germany
  • 1999
    • University of Birmingham
      • School of Physics and Astronomy
      Birmingham, England, United Kingdom
  • 1989-1999
    • Philipps University of Marburg
      Marburg, Hesse, Germany
  • 1992
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States
  • 1988
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
  • 1983-1985
    • Joint Institute for Nuclear Research
      Dubno, Moskovskaya, Russia
  • 1962-1976
    • CERN
      Genève, Geneva, Switzerland
  • 1970
    • Institut de Physique du Globe de Paris
      Lutetia Parisorum, Île-de-France, France
  • 1966
    • Foundry Research Institute in Cracow
      Cracovia, Lesser Poland Voivodeship, Poland