Search Results (11 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.

We present the first measurement of fluctuations from event to event in the production of strange particles in collisions of heavy nuclei. The ratio of charged kaons to charged pions is determined for individual central Pb+Pb collisions. After accounting for the fluctuations due to detector resolution and finite number statistics we derive an upper limit on genuine nonstatistical fluctuations, which could be related to a first- or second-order QCD phase transition. Such fluctuations are shown to be very small.

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt[s_NN]  =  130  GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v₂, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.

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.

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.

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.

The NA35 experiment has collected a high statistics set of momentum analyzed negative hadrons near and forward of midrapidity for central collisions of 200A  GeV/c ³²S+S, Cu, Ag, and Au. Using momentum space correlations to study the size of the source of particle production, the transverse source radii are found to decrease by ∼40% at midrapidity and ∼20% at forward rapidity while the longitudinal radius R_L is found to decrease by ∼50% as p_T increases over the interval 50<p_T<600  MeV/c. Calculations using a microscopic phase space approach (relativistic quantum molecular dynamics) reproduce the observed trends of the data.

The transverse momentum and rapidity distributions of negative hadrons and participant protons have been measured for central ³²S+ ³²S collisions at p_lab=200 GeV/c per nucleon. The proton mean rapidity shift 〈Δy〉∼1.6 and mean transverse momentum 〈p_T〉∼0.6 GeV/c are much higher than in pp or peripheral AA collisions and indicate an increase in the nuclear stopping power. All p_T spectra exhibit similar source temperatures. Including previous results for K_s⁰ Λ, and Λ¯, we account for all important contributions to particle production.

The inclusive α spectra from the reaction ⁹Be(d,α) have been measured at E_d=50 MeV. The spectra were analyzed with a combination of phase space distributions and resonances. The result of the analysis suggests the evidence for a broad level in ⁷Li at E_x∼18 MeV. The position and width correspond to the analog state found in ⁷Be at ∼17 MeV excitation.