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Register a new userEnergy dependence of kaon-to-proton ratio fluctuations in central Pb+Pb collisions from $sqrt{s_{NN}}$ = 6.3 to 17.3 GeV
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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.
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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$(stat.)^{+0.44}_{-0.16}(syst.) fm.
A novel approach, the identity method, was used for particle identification and the study of fluctuations of particle yield ratios in Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the moments of the unknown multiplicity distributions of protons (p), kaons (K), pions ($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.
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.
There is event by event geometric as well as quantum fluctuations in the initial condition of heavy-ion collisions. The standard technique of analysing heavy-ion collisions in bins of centrality obtained from final state multiplicity averages out the various initial configurations and thus restricts the study to only a limited range of initial conditions. In this paper, we propose an additional binning in terms of total spectator neutrons in an event. This offers us a key control parameter to probe events with broader range of initial conditions providing us an opportunity to peep into events with rarer initial conditions which otherwise get masked when analysed by centrality binning alone. We find that the inclusion of spectator binning allows one to vary $varepsilon_2$ and $varepsilon_3$ independently. We observe that the standard scaling relation between $displaystyle{v_2/varepsilon_2}$ and $frac{1}{S}frac{dN_{text{ch}}}{deta}$ exhibited by centrality bins is broken by the spectator neutron bins. However, the acoustic scaling relation between $displaystyle{lnleft( v_n/varepsilon_nright)}$ and transverse system size holds for both centrality as well as spectator bins for central to mid-central collisions. The introduction of the spectator binning allows us to tune over a wide range viscosity driven effects for events with varying initial states but similar final state multiplicity.
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.
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