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Register a new userPhase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy
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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 ($pi$) and electrons (e). Using these moments the excitation function of the fluctuation measure $ u_{text{text{dyn}}}$[A,B] was measured, with A and B denoting different particle types. The obtained energy dependence of $ u_{text{dyn}}$ agrees with previously published NA49 results on the related measure $sigma_{text{dyn}}$. Moreover, $ u_{text{dyn}}$ was found to depend on the phase space coverage for [K,p] and [K,$pi$] 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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New measurements by the NA49 experiment of the centrality dependence of event-by-event fluctuations of the particle yield ratios (K$^{+}$+K$^{-}$)/($pi^{+}+pi^{-}$), (p+$bar{text p}$)/($pi^{+}+pi^{-}$), and (K$^{+}$+K$^{-}$)/(p+$bar{text p}$) are presented for Pb+Pb collisions at 158$A$ GeV. The absolute values of the dynamical fluctuations of these ratios, quantified by the measure $sigma_{text{dyn}}$, increase by about a factor of two from central to semi-peripheral collisions. Multiplicity scaling scenarios are tested and found to apply for both the centrality and the previously published energy dependence of the (K$^{+}$+K$^{-}$)/($pi^{+}+pi^{-}$) and (p+$bar{text p}$)/($pi^{+}+pi^{-}$) ratio fluctuations. A description of the centrality and energy dependence of (K$^{+}$+K$^{-}$)/(p+$bar{text p}$) ratio fluctuations by a common scaling prescription is not possible since there is a sign change in the energy dependence.
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 $sigma_{mathrm{dyn}}$, a measure of non-statistical fluctuations, around $sqrt{s_{NN}}$ = 8 GeV. Below this energy, $sigma_{mathrm{dyn}}$ is positive, indicating higher fluctuation compared to a mixed event background sample, while for higher energies, $sigma_{mathrm{dyn}}$ 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.
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.
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.
We present results on transverse momentum correlations of charged particle pairs produced in Pb-Au collisions at 158$A$ GeV/$c$ at the Super Proton Synchrotron. The transverse momentum correlations have been studied as a function of collision centrality, angular separation of the particle pairs, transverse momentum and charge sign. We demonstrate that the results are in agreement with previous findings in scale-independent analyses at the same beam energy. Employing the two-particle momentum correlator $<Delta p_{t,i}, Delta p_{t,j}>$ and the cumulative $p_t$ variable $x(p_t)$, we identify, using the scale-dependent approach presented in this paper, different sources contributing to the measured correlations, such as quantum and Coulomb correlations, elliptic flow and mini-jet fragmentation.
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