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D. L. Olson

Publications and source records attributed to D. L. Olson.

10 recordsLinked to original sources

Near-threshold production of the multi-strange $Ξ^-$ hyperon

The yield for the multi-strange $Ξ^{-}$ hyperon has been measured in 6 AGeV Au+Au collisions via reconstruction of its decay products $π^{-}$ and $Λ$, the latter also being reconstructed from its daughter tracks of $π^{-}$ and p. The measurement is rather close to the threshold for $Ξ^{-}$ production and therefore provides an important test of model predictions. The measured yield for $Ξ^{-}$ and $Λ$ are compared for several centralities. In central collisions the $Ξ^{-}$ yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multi-strange hadron production approaches chemical equilibrium in high baryon density nuclear matter.

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Comparison of Source Images for protons, $π^-$'s and $Λ$'s in 6 AGeV Au+Au collisions

Source images are extracted from two-particle correlations constructed from strange and non-strange hadrons produced in 6 AGeV Au + Au collisions. Very different source images result from pp vs p$Λ$ vs $π^-π^-$ correlations. These observations suggest important differences in the space-time emission histories for protons, pions and neutral strange baryons produced in the same events.

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Longitudinal Flow of Protons from 2-8 AGeV Central Au+Au Collisions

Rapidity distributions of protons from central $^{197}$Au + $^{197}$Au collisions measured by the E895 Collaboration in the energy range from 2 to 8 AGeV 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, $<βγ>_{L}$, as a function of the logarithm of beam energy.

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Laying the groundwork at the AGS: Recent results from experiment E895

The E895 Collaboration at the Brookhaven AGS has performed a systematic investigation of Au+Au collisions at 2-8 AGeV, using a large-acceptance Time Projection Chamber. In addition to extensive measurements of particle flow, spectra, two-particle interferometry, and strangeness production, we have performed novel hybrid analyses, including azimuthally-sensitive pion HBT, extraction of the six-dimensional pion phasespace density, and a first measurement of the Lambda-proton correlation function.

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Anti-flow of K$^0_s$ Mesons in 6 AGeV Au + Au Collisions

We have measured the sideward flow of neutral strange ($K^0_s$) mesons in 6 AGeV Au + Au collisions. A prominent anti-flow signal is observed for an impact parameter range (b $\lesssim 7$ fm) which spans central and mid-central events. Since the $K^0_s$ scattering cross section is relatively small in nuclear matter, this observation suggests that the in-medium kaon vector potential plays an important role in high density nuclear matter.

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Directed Flow of $Λ$-Hyperons in 2-6 AGeV Au+Au Collisions

Directed flow measurements for $Λ$-hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2, 4, and 6 AGeV; $b < 5 - 6$ fm). The measurements indicate that $Λ$-hyperons flow consistently in the same direction and with smaller magnitudes than those of protons. Such a strong positive flow [for $Λ$s] has been predicted in calculations which include the influence of the $Λ$-nucleon potential. The experimental flow ratio $Λ$/p is in qualitative agreement with expectations ($\sim 2/3$) from the quark counting rule at 2 AGeV but is found to decrease with increasing beam energy.

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Azimuthal Dependence of Pion Interferometry at the AGS

Two-pion correlation functions, measured as a function of azimuthal emission angle with respect to the reaction plane, provide novel information on the anisotropic shape and orientation of the pion-emitting zone formed in heavy ion collisions. We present the first experimental determination of this information, for semi-central Au+Au collisions at 2-6 AGeV. The source extension perpendicular to the reaction plane is greater than the extension in the plane, and tilt of the pion source in coordinate space is found to be opposite its tilt in momentum space.

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Lambda Hyperons in 2 A*GeV Ni + Cu Collisions

A sample of Lambda's produced in 2 A*GeV Ni + Cu collisions has been obtained with the EOS Time Projection Chamber at the Bevalac. Low background in the invariant mass distribution allows for the unambiguous demonstration of Lambda directed flow. The transverse mass spectrum at mid-rapidity has the characteristic shoulder-arm shape of particles undergoing radial transverse expansion. A linear dependence of Lambda multiplicity on impact parameter is observed, from which a total Lambda + Sigma^0 production cross section of $112 +/- 24 mb is deduced. Detailed comparisons with the ARC and RVUU models are made.

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The Evolution of Nuclear Multifragmentation in the Temperature-Density Plane

The mean transverse kinetic energies of the fragments formed in the interaction of 1 A GeV Au+C have been determined. An energy balance argument indicates the presence of a collective energy which increases in magnitude with increasing multiplicity and accounts for nearly half of the measured mean transverse kinetic energy. The radial flow velocity associated with the collective energy yields estimates for the time required to expand to the freeze-out volume. Isentropic trajectories in the temperature-density plane are shown for the expansion and indicate that the system goes through the critical region at the same multiplicities as deduced from a statistical analysis. Here, the expansion time is approximately 70 fm/c.

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Radial Flow in Au+Au Collisions at E=0.25-1.15 A GeV

A systematic study of energy spectra for light particles emitted at midrapidity from Au+Au collisions at E=0.25-1.15 A GeV reveals a significant non-thermal component consistent with a collective radial flow. This component is evaluated as a function of bombarding energy and event centrality. Comparisons to Quantum Molecular Dynamics (QMD) and Boltzmann-Uehling-Uhlenbeck (BUU) models are made for different equations of state.

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