Results 1 - 10 of 11
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[en] The production of hadrons in heavy-ion collisions at high-pT provides an important information on mechanism of particle formation and constituent energy loss in medium. Such information is needed for search of a Critical Point and signatures of phase transition. Measurements by the STAR Collaboration of charged hadron production in Au + Au collisions at √sNN = 9.2 GeV over a wide transverse momentum pT = 0.2−4 GeV/c and at mid-rapidity range are reported. It allows for a first measurement of the spectra for charged hadrons at high pT at this energy. The spectra demonstrate the dependence on centrality which enhances with pT. The constituent energy loss and its dependence on transverse momentum of particle, and centrality of collisions are estimated in the z-scaling approach.
[en] New experimental data on inclusive cross section of neutral-vector-meson (ω0, φ, KS0) production in proton-proton collisions at √s = 200 GeV obtained at RHIC are analyzed in the framework of z scaling. Properties of z-presentation are used to predict hadron yields over a wide range of transverse momentum pT and collisions energy √s. The next-to-leading-order perturbative QCD calculations of inclusive cross sections of π0 mesons produced in pp and p-bar collisions over a wide range of √s and pT are compared with ISR, Sp-barpS, RHIC data and predictions of z scaling. The dependence of the spectra in pT and z presentations for different parton distribution and fragmentation functions is studied. The sensitivity of the obtained results to the choice of the renormalization (μR), initial-state factorization (μF), and final-state factorization (fragmentation) (μH) scales is verified. It is shown that self-similar features of particle production dictated by the z scaling give strong restriction on the asymptotic behavior of the inclusive spectra in high-pT region.
[en] The concept of z scaling reflecting the general regularities of high-pT particle production is reviewed. Properties of data z presentation are discussed. New data on high-pT particle spectra obtained at the RHIC are analyzed in the framework of z presentation. It was shown that these experimental data confirm z scaling. Predictions of strange particle spectra are considered to be useful for understanding of strangeness origin in mesons and baryons and search for new physics phenomena at the RHIC.
[en] The SePaC and BC methods are used for fractal analysis of mixed events containing incomplete fractals. Reconstruction of the distribution of events by dimension DF is studied. The procedures for analyzing incomplete fractals and correcting the determination of DF of combined fractals by the SePaC method are proposed. We find that the SePaC method fully reconstructs incomplete fractals and suppresses background, separation of incomplete fractals and background by the BC method depends on the basis of the formation of the fractal. The distribution of events by value of DF is more accurately reconstructed by the SePaC method in comparison with the BC method.
[ru]В работе использовались SePaC- и BC-методы для фрактального анализа смешанных событий, содержащих различные виды полных, неполных фракталов и примеси. Предложена процедура анализа SePaC-методом неполных фракталов, а также способ коррекции в определении размерности DF для фракталов с комбинированным делением частей. Установлено, что SePaC-методом полностью реконструируются неполные фракталы и подавляется фон, а разделение фракталов и фоновых событий BC-методом зависит от основания образования фракталов. Показано, что с помощью SePaC-метода более точно восстанавливается распределение фракталов по размерности DF по сравнению с BC-методом.
[en] New generalization of the z-scaling in inclusive particle production is proposed. The scaling variable z is a fractal measure which depends on kinematic characteristics of the underlying subprocess expressed in terms of the momentum fractions x1 and x2 of the incoming protons. In the generalized approach, x1 and x2 are functions of the momentum fractions ya and yb of the scattered and recoil constituents carried by the inclusive particle and recoil object, respectively. The scaling function ψ(z) for charged and identified hadrons produced in proton-proton collisions is constructed. The fractal dimensions and heat capacity of the produced medium entering definition of the variable z are established to restore energy, angular, and multiplicity independence of ψ(z). The proposed scheme allows a unique description of data on inclusive cross sections at high energies. Universality of the shape of the scaling function for various types of produced hadrons (π, K, p, Λ) is shown. Results of the analysis of experimental data are compared with the next-to-leading order (NLO) QCD calculations in pT and z-presentations. The obtained results suggest that the z-scaling may be used as a tool for searching for new physics phenomena of particle production in high transverse momentum and the high multiplicity region at proton-proton colliders RHIC and LHC
[en] Results of analysis of experimental data on inclusive spectra of charged hadrons produced in heavy-ion collisions at RHIC are shown in z presentation. The data indicate similarity as a characteristic feature of mechanism of hadron production at high energies. It is argued that this property includes structure of the colliding objects, interaction of their constituents, and character of the fragmentation process. Relation of the scaling variable z with the entropy and 'specific heat' of the interacting system is discussed. A microscopic scenario of the constituent interactions connected with the momentum distribution of hadrons in the final state is suggested. We estimate energy losses of particles in the produced matter characterized by the multiplicity density dNch/dη.
[en] The multiplicity dependence of inclusive spectra of identified hadrons (π, K, p-bar, KS0, and Λ) produced in high-energy p-barp and pp collisions is studied. Analysis of experimental data on high-pT hadron cross sections obtained at the Tevatron and RHIC is performed in the framework of z scaling. Independence of the scaling function ψ(z) on the multiplicity density dNch/dη is established. The multiplicity density measured in nucleon-nucleon collisions reaches much higher values than the corresponding quantity [1/(0.5Np)]dNch/dη obtained in heavy-ion collisions. Its influence on particle production reveals properties of self-similarity and fractality. The relation between the scaling variable z and thermodynamic quantities ('heat capacity' and 'temperature') of the medium associated with the produced inclusive particle is discussed. Search for z-scaling violation in p-barp and pp collisions at very high multiplicities as an indication of new-physics phenomena is suggested
[en] Experimental data on inclusive spectra measured in heavy-ion collisions at RHIC and SPS over a wide range of the energy √sNN = 9 - 200 GeV are analyzed in the framework of z scaling. A microscopic scenario of constituent interactions in the framework of this approach is discussed. Dependence of the energy loss on the momentum of the produced hadron, energy, and centrality of the collision, is studied. Self-similarity of the constituent interactions in terms of momentum fractions is used to characterize the nuclear medium by “specific heat” and colliding nuclei by fractal dimensions. Preferable kinematical regions for search for signatures of the phase transition of the nuclear matter produced inHIC are discussed. Discontinuity of “specific heat” is assumed to be a signature of the phase transition and the Critical Point.
[en] Experimental data on inclusive spectra of pions produced in heavy-ion collisions at RHIC are analyzed in the framework of z-scaling. The data indicate similarity as a characteristic feature of the mechanism of pion production at high energies. It is argued that this property includes structure of the colliding objects, interaction of their constituents, and character of the fragmentation process. A microscopic scenario of nucleus interactions at a constituent level in terms of momentum fractions is developed. The centrality dependence of the shape of the scaling function Ψ(z) and the fractal dimention εAA of the fragmentation process is studied. Energy losses of particles in the final state as a function of the collision energy, transverse momentum, and centrality are estimated. The scale dependence of the energy losses is discussed. A decreasing tendency of specific heat of the produced medium with the system size is established. The obtained results may be exploited to search for and study new physics phenomena in pion production in pp and AA collisions at high multiplicities.
[en] The hypothesis of the self-similarity of hadron production in relativistic heavy-ion collisions to search for the phase transition in nuclear matter is discussed. Using the established features of z -scaling is suggested to reveal the signatures of new physics in the cumulative region. It is noted that selecting events on centrality in the cumulative region could help localize the position of a critical point. The change in the parameters of the theory (a specific heat and fractal dimensions) near the critical point is considered a signature of new physics. The relationship between the power asymptotic of Ψ(z ) at high values of the similarity parameter z, the anisotropy of momentum space due to spontaneous symmetry breaking, and discrete (C, P, T) symmetries is emphasized.