Search Results (9 total)

The NA44 experiment has measured single-particle inclusive spectra for charged pions, kaons, and protons as a function of transverse mass near midrapidity in 158A GeV/c Pb+Pb collisions. From the particle mass dependence of the observed m_T distributions, we are able to deduce a value of about 120 MeV for the temperature at thermal freeze-out. From the observed ratios of the rapidity densities, we find values of the chemical potentials for light and strange quarks and a chemical freeze-out temperature of approximately 140 MeV.

NA44 uses a 512-channel Si pad array covering 1.5<η<3.3 to study charged hadron production in 158A GeV Pb+Pb collisions at the CERN SPS. We apply a multiresolution analysis, based on a discrete wavelet transformation, to probe the texture of particle distributions event by event, allowing a simultaneous localization of features in space and scale. Scanning a broad range of multiplicities, we search for signals of clustering and of critical behavior in the power spectra of local density fluctuations. The data are compared with detailed simulations of detector response, using heavy-ion event generators, and with a reference sample created via event mixing. An upper limit is set on the probability and magnitude of dynamical fluctuations.

Two-particle interferometry of positive kaons is studied in Pb+Pb collisions at mean transverse momenta 〈p_T〉≈0.25 and 0.91 GeV/c. A three-dimensional analysis was applied to the lower p_T data, while a two-dimensional analysis was used for the higher p_T data. We find that the source-size parameters are consistent with the m_T scaling curve observed in pion-correlation measurements in the same collisions, and that the duration time of kaon emission is consistent with zero within the experimental sensitivity.

The invariant cross section as a function of transverse momentum for antideuterons produced in 158A GeV/c per nucleon Pb+Pb central collisions has been measured by the NA44 experiment at CERN. This measurement, together with a measurement of antiprotons, allows for the determination of the antideuteron coalescence parameter. The extracted coalescence radius is found to agree with the deuteron coalescence radius and radii determined from two particle correlations.

The NA44 Collaboration has measured charged kaon and pion distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and 450 GeV/c per nucleon, respectively. The inverse slopes of kaons, are larger than those of pions. The difference in the inverse slopes of pions, kaons, and protons, all measured in our spectrometer, increases with system size and is consistent with the buildup of collective flow for larger systems. The target dependence of both the yields and inverse slopes is stronger for the sulphur beam, suggesting the increased importance of secondary rescattering for SA reactions. The rapidity density dN/dy of both K⁺ and K^- increases more rapidly with system size than for π⁺ in a similar rapidity region. This trend continues with increasing centrality, and according to RQMD, it is caused by secondary reactions between mesons and baryons. The K^-/K⁺ ratio falls with increasing system size but more slowly than the p̅ /p ratio. The π^-/π⁺ ratio is close to unity for all systems. From pBe to SPb the K⁺/p ratio decreases while K^-/p̅ increases and sqrt[(K⁺⋅K^-)/(p⋅p̅ )] stays constant. These data suggest that as larger nuclei collide, the resulting system has a larger transverse expansion and baryon density and an increasing fraction of strange quarks.

Two-pion correlations from Pb+Pb collisions at 158 GeV/c per nucleon are measured by the NA44 experiment at CERN. Multidimensional fits characterize the emission volume, which is found to be larger than in S-induced collisions. Comparison to the RQMD model is used to relate the fit parameters to the actual emission volume.

Experiment NA44 has measured proton and antiproton distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and 450 GeV/c per nucleon respectively. The inverse slopes of transverse mass distributions increase with system size for both protons and antiprotons but are slightly lower for antiprotons. This could happen if antiprotons are annihilated in the nuclear medium. The antiproton yield increases with system size and centrality and is largest at midrapidity. The proton yield also increases with system size and centrality, but decreases from backward rapidity to midrapidity. The stopping of protons at these energies lies between the full stopping and nuclear transparency scenarios. The data are in reasonable agreement with RQMD predictions except for the antiproton yields from sulphur-nucleus collisions.

Transverse mass spectra of pions, kaons, and protons from the symmetric heavy-ion collisions 200 A GeV S+S and 158 A GeV Pb+Pb, measured in the NA44 focusing spectrometer at CERN, are presented. The mass dependence of the slope parameters provides evidence of collective transverse flow from expansion of the system in heavy-ion induced central collisions.

First results of the m_T dependence of π⁺π⁺ and K⁺K⁺ correlations from S+Pb collisions at 200 GeV /c per nucleon measured by the focusing spectrometer of the NA44 experiment at CERN are presented. Multidimensional fits characterize the pion and kaon emission volume. The pion radius parameter decreases with increasing p_T. Furthermore, the pion and kaon radii show a common 1/sqrt[m_T] dependence. This behavior can be interpreted as a result of a strong momentum-position correlation arising from collective flow.