T. Hallman

Dielectron cross-section measurements in nucleus-nucleus reactions at 1-A/GeV

We present measured dielectron production cross sections for Ca+Ca, C+C, He+Ca, and d+Ca reactions at 1.0 A GeV . Statistical uncertainties and systematic effects are smaller than in previous dilepton spectrometer (DLS) nucleus-nucleus data. For pair mass M{le}0.35 GeV/c{sup 2} we obtain (1) the Ca+Ca cross section is larger than the previous DLS measurement and current model results, (2) the mass spectra suggest large contributions from {pi}{sup 0} and {eta} Dalitz decays, and (3) d{sigma}/dM{proportional_to}A{sub P}A{sub T}. For M{gt}0.5 GeV/c{sup 2} the Ca+Ca to C+C cross section ratio is significantly larger than the ratio of A{sub P}A{sub T} values. {copyright} {ital 1997} {ital The American Physical Society}

Dielectron production in Ca+Ca collisions at 1.0 and 2.0 A GeV

Abstract Dileptons should be a good probe of the early stage of nucleus-nucleus collisions and may carry information on pion dynamics in nuclear matter. We have observed a dielectron signal well above estimated contributions from Dalitz decays of particles or resonances. At 1.0 A GeV, the dielectron mass spectrum is significantly different for Ca+Ca and p+ Be reactions. The dielectron yield scales as the first power of the product of the projectile and target masses.

Inclusive dielectron cross sections in p + p and p + d interactions at beam energies from 1.04 to 4.88 GeV.

Measurements of dielectron production in p + p and p + d collisions with beamkinetic energies from 1.04 to 4.88 GeV are presented. The differential cross section is presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the mass spectra and their evolution with beam energy provide information about the relative importance of the various dielectron production mechanisms in this energy regime. The p + d to p + p ratio of the dielectron yield is also presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the transverse momentum and rapidity spectra from the p + d and p + p systems are found to be similar to one another for each of the beam energies studied. The beam energy dependence of the integrated cross sections is also presented.

Spectra of gamma rays and energetic neutrons from μ− capture in 165Ho

Abstract The neutron spectrum resulting from μ − capture in 165 Ho has been measured with a time-of-flight spectrometer. The exponential constant between 13 and 50 MeV is 10.5 ± 1 MeV. The intensity of neutrons with energy greater than 40 MeV is 0.019 ± 0.004/ μ − -stop. This represents the first measurement of the neutron spectra by a system capable of resolving neutron energies near 100 MeV. Neutron spectra from final nuclear state roughly identified by NaI pulse height are presented. Above 50 MeV, these spectra do not follow a simple exponential decrease. The photon spectrum measured by Ge(Li) detectors exhibits neutron multiplicites up to 5 with an intensity greater than expected.

Rapidity distributions of Ks0's and Λ's produced by 14.6×A GeV/cSi beams on Si and Pb targets

Abstract We present the first measurement at AGS energies of rapidity distributions of K s 0 and Λ production with silicon beams on silicon and lead targets. The measurements cover the rapidity region of 2.0 y K s 0 s and 1.4 y Λ s.

The dilepton spectrometer

Abstract The dilepton spectrometer (DLS) at Lawrence Berkeley Laboratorys Bevalac has been designed and constructed to investigate the production of electron-positron pairs with low mass and low transverse momentum in proton-nucleus and nucleus-nucleus collisions for incident-beam kinetic energies of 5 A GeV and less. This article briefly recalls the physics objectives of the program, discusses the methodology of the measurement, presents details of the design of the spectrometer and the detector elements, and reports on their performance. Selected experimental results are given to illustrate the capability of the DLS and to demonstrate the level to which it is possible to realize the physics objectives with the spectrometer.

Relative dielectron yields in p + p and p + d interactions from Ebeam = 1.0–4.9 GeV

Abstract The beam energy and invariant mass dependence of the dielectron yield in p + d interactions relative to the yield in p + p interactions is presented for incident kinetic energies from 1.0–4.9 GeV. The ratio of the yield in p + d interactions to that in p + p interactions decreases from 10.5±1.6 at 1.0 GeV to 1.96±0.08 at 4.9 GeV for electron pairs with invariant masses ⩾ 0.15 GeV/ c 2 . The large ratio at 1.0 GeV suggests that dielectron production in the p + d system is dominated by a p + n process. The beam energy dependence of the ratio indicates that this p + n contribution decreases with respect to the other dielectron sources as the incident energy is increased.

Neutral V production with 14.6 ×A GeV/c silicon beams

Abstract We present the results of a measurement of neutral V production with 14.6 × A GeV/ c Si beams on Au and Cu targets. The Λ and K s 0 yields were measured as a function of negative particle multiplicity. Effective temperatures were determined from an exponential fit to the transverse mass distributions.

Energetic neutron emission from μ−-capture in deuterium

Abstract The neutron spectrum from 25 to 52 MeV resulting from μ − -capture in liquid deuterium was measured by a time-of-flight technique. The spectrum near the end point exhibited an enhancement consistent with the meson-exchange-current calculations.

Neutral-pion production in central collisions of relativistic 12C and 40Ar on 208Pb☆

Abstract The production of π0 mesons in central collisions of 12C and 40Ar on 208Pb has been examined at a number of energies from 1. to 2.1 GeV/N, as part of the first systematic study as a function of beam energy and charged-particle multiplicity of the rate of neutral-pion production in relativistic heavy-ion collisions. For comparison, corresponding π± data acquired with the same detector system have also been presented. The results indicate that, for a given target-projectile combination, both neutral- and charged-pion production increase smoothly by a factor of approximately 2.9 in this energy range. The measurement of charged-particle multiplicity is discussed in order to indicate how the characteristic distributions observed in this study were used to parameterize the experimental results. The average multiplicity of both pions and nucleons projected from these data is found to disagree with statistical models of particle production. The significance of the Nπ±/Ncharge and Nπ±/Nπ0 ratios observed as a function of beam energy and charged-particle multiplicity is discussed in the context of understanding the nature of the collision process.