Resonances and fluctuations of strange particle in 200 GeV Au-Au collisions

We perform an analysis of preliminary data on strange particles yields and fluctuations within the Statistical hadronization model. We begin by describing the theoretical disagreements between different statistical models currently on the market. We then show how the simultaneous analysis of yields and fluctuations can be used to differentiate between the different models, and determine if one of them can be connected to underlying physics. We perform a study on a RHIC 200 GeV data sample that includes stable particles, resonances, and the event-by-event fluctuation of the $K/\pi$ ratio. We show that the equilibrium statistical model can not describe the fluctuation, unless an unrealistically small volume is assumed. Such small volume then makes it impossible to describe the total particle multiplicity. The non-equilibrium model,on the other hand, describes both the $K/\pi$ fluctuation and yields acceptably due to the extra boost to the $\pi$ fluctuation provided by the high pion chemical potential. $\Lambda(1520)$ and $K^*$ abundance is described within error bars, but the $\Sigma^*$ is under-predicted to $\sim$ 1.5 standard deviations. We suggest further measurements that have the potential to test the non-equilibrium model, as well as gauge the effect of re-interactions between hadronization and freeze-out.Comment: References added, equations corrected. As accepted for publication by Journal of Physics

Centrality and system size dependence of multiplicity fluctuations in nuclear collisions at 158A GeV

The centrality and system size dependence of multiplicity fluctuations of charged particles produced in nuclear collisions at 158A GeV was studied by the NA49 Collaboration. Centrality selected Pb+Pb collisions, semicentral C+C and Si+Si collisions as well as inelastic p+p interactions were analyzed. The number of projectile participants determined on an event-by-event basis was used to characterize the collision centrality. The scaled variance of the multiplicity distribution obtained in the forward rapidity region (1.1 < y(c.m.)< 2.6) shows a significant increase toward peripheral collisions. The results are similar for negatively and positively charged particles and about 50% larger for all charged particles. String-hadronic models of nuclear reactions without the fusion process do not reproduce the rise of fluctuations from central toward peripheral collisions. The measured centrality dependence can be reproduced in superposition models with the assumption of contributions from target participants to particle production in the forward hemisphere or in string models with fusion

Pion and kaon production in central Pb plus Pb collisions at 20A and 30A GeV: Evidence for the onset of deconfinement

Results on charged pion and kaon production in central Pb+Pb collisions at 20A and 30A GeV are presented and compared to data at lower and higher energies. Around 30A GeV a rapid change of the energy dependence for the yields of pions and kaons as well as for the shape of the transverse mass spectra is observed. The change is compatible with the prediction that the threshold for production of a state of deconfined matter at the early stage of the collisions is located at low CERN Super Proton Synchroton energies

High transverse momentum hadron spectra at root s(NN)=17.3 GeV in Pb+Pb and p+p collisions

Transverse momentum spectra up to 4.5 GeV/c around midrapidity of pi(+/-), p, (p) over bar, and K-+/- in Pb+Pb reactions were measured at root s(NN) = 17.3 GeV by the CERN-NA49 experiment. The nuclear modification factors R-AA for pi(+/-) and R-CP for pi(+/-), p, (p) over bar, K-+/- were extracted and compared with results obtained at the BNL Relativistic Heavy Ion Collider (RHIC) at root s(NN) = 200 GeV. The modification factor R-AA shows a rapid increase with transverse momentum in the covered region. This indicates that the Cronin effect is the dominating effect in our energy range. The modification factor R-CP, in which the contribution of the Cronin effect is reduced, shows a saturation well below unity in the pi(+/-) channel. The extracted R-CP values follow the 200 GeV RHIC results closely in the available transverse momentum range, except for pi(+/-) above 2.5 GeV/c transverse momentum. There the measured suppression is smaller than that observed at RHIC

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 semicentral Pb+Pb collisions at 158A GeV. The standard method of correlating particles with the event plane was used. Measurements of v(2) near midrapidity 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 v(2) for pions and protons as well as with model calculations. The observation of significant elliptic flow and its mass dependence suggest strong collective behavior 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 p(T) range of the data does not allow for a decisive test of the coalescence model

Energy dependence of Lambda and Xi production in central Pb plus Pb collisions at 20A, 30A, 40A, 80A, and 158A GeV measured at the CERN Super Proton Synchrotron

Results on Lambda, (Lambda) over bar, Xi(-), and (Xi) over bar (+) production in central Pb+Pb reactions at 20A, 30A, 40A, 80A, and 158A GeV are presented. The energy dependence of transverse mass spectra, rapidity spectra, and multiplicities is discussed. Comparisons to string hadronic models (UrQMD and HSD) and statistical hadron gas models are shown. Although the latter provide a reasonable description of all particle yields, the first class of models fails to match the Xi(-) and (Xi) over bar (+) multiplicities

System size and centrality dependence of the balance function in A+A collisions at root S-NN=17.2 GeV

Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at root s(NN) = 17.2 GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions

Omega(-) and (Omega)over-bar(+) production in central Pb+Pb collisions at 40 and 158A GeV

Results are presented on Omega production in central Pb+Pb collisions at 40 and 158A GeV beam energy. For the first time in heavy ion reactions, rapidity distributions and total yields were measured for the sum Omega(-)+(Omega) over bar (+) at 40A GeV and for Omega(-) and (Omega) over bar (+) separately at 158A GeV. The yields are strongly underpredicted by the string-hadronic UrQMD model but agree better with predictions from hadron gas models

Directed and elliptic flow in 158GeV/nucleon Pb+Pb collisions

The directed and elliptic flow of protons and charged pions has been observed from the semicentral collisions of a 158 GeV/nucleon Ph beam with a Pb target. The rapidity and transverse momentum dependence of the flow has been measured. The directed flow of the pions is opposite to that of the protons but both exhibit negative flow at low p(t). The elliptic flow of both is fairly independent of rapidity but rises with p(t)

Spectator nucleons in Pb+Pb collisions at 158 A center dot GeV

The composition of forward-going projectile spectator matter in fixed-target Pb+Pb collisions at 158 A.GeV at the CERN SPS has been studied as a function of centrality. The data were measured with the NA49 veto calorimeter. We observe that forward-going spectator matter in central collisions consists of 9 neutrons, 7 protons, and half a deuteron on average. At large impact parameters most spectator nucleons are bound in fragments. The relative resolution of the average impact parameter derived from the measurement of spectator neutrons is roughly 19% in the range from zero to half maximum impact parameters