ABSTRACT
The yield for the multistrange Xi(-) hyperon has been measured in 6A GeV Au+Au collisions via reconstruction of its decay products pi(-) and Lambda, the latter also being reconstructed from its daughter tracks of pi(-) and p. The measurement is rather close to the threshold for Xi(-) production and therefore provides an important test of model predictions. The measured yield for Xi(-) and Lambda are compared for several centralities. In central collisions the Xi(-) yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multistrange hadron production approaches chemical equilibrium in high baryon density nuclear matter.
ABSTRACT
Source images are extracted from two-particle correlations constructed from strange and nonstrange hadrons produced in 6A GeV Au+Au collisions. Very different source images result from pp vs p Lambda vs pi(-)pi(-) correlations. Scaling by transverse mass can describe the apparent source size ratio for p/pi(-) but not for Lambda/pi(-) or Lambda/p. These observations suggest important differences in the space-time emission histories for protons, pions, and neutral strange baryons produced in the same events.
ABSTRACT
Rapidity distributions of protons from central 197Au+197Au collisions measured by the E895 Collaboration in the energy range from (2-8)A GeV at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity,
ABSTRACT
We report a particle source imaging analysis based on two-pion correlations in high multiplicity Au+Au collisions at beam energies between 2A and 8A GeV. We apply the imaging technique introduced by Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. The extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional Hanburg-Brown-Twiss analysis.
ABSTRACT
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.
ABSTRACT
Directed flow measurements for Lambda hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2A, 4A, and 6A GeV; b<5-6 fm). The measurements indicate that Lambda hyperons flow consistently in the same direction but with smaller magnitudes. A strong positive flow [for Lambdas] has been predicted in calculations which include the influence of the Lambda-nucleon potential. The experimental flow ratio Lambda/p is in qualitative agreement with expectations (approximately 2/3) from the quark counting rule at 2A GeV but is found to decrease with increasing beam energy.
ABSTRACT
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 square root(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.
ABSTRACT
Quantitative nonradioactive methods to measure the human immunodeficiency virus (HIV) in individually infected cells are needed for the direct assessment of HIV infection, for the evaluation of antiviral chemotherapy and for testing the efficacy of vaccines. As a first step in accomplishing this goal, we built an argon ion laser-based computerized image cytofluorometry (ALCIC) system and determined this instrument's ability to quantitatively measure HIV nucleotides in infected lymphocytes. ALCIC consisted of a 43-mW argon ion laser connected to a Zeiss Universal microscope via a fiberoptic cable, a charged coupled-device video camera, a video frame grabber and array processor and a Micro Vax II computer using computer programs written in FORTRAN. HIV RNA and DNA were detected in infected CEM lymphocytes in culture by in situ hybridization using acetylaminofluorene (AAF)-labeled HIV-DNA probes, a rabbit anti-AAF antibody and a fluorescein-labeled goat anti-rabbit antibody. ALCIC measurements showed that 61% of the CEM cells were infected and that quantitative differences were distinguishable within this group. The levels of fluorescein isothiocyanate (FITC) fluorescence were sixfold or more greater than that observed with the same system using a 100-W mercury lamp for illumination; the improved intensity of the laser-based system is due to greater excitation intensity of the laser and the matching of the excitation spectrum to the peak wavelength of FITC. ALCIC has potential clinical value for determining the effect of antiviral agents on HIV infection and for assessing the susceptibility of different cell types to infection.
