P. Kirk

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.

Evidence for hard scattering of hadronic constituents of photons in photon-photon collisions of TRISTAN

Abstract We present results of an experimental study of e + e − + hadrons in the kinematic regime for which the process is interpreted as hadron production in collisions of almost-real photons. The data sample corresponds to an integrated luminosity of 27.5 pb − and covers center-of-mass energies from 55 to 61.4 GeV. We observe more events than expected from the incoherent sum of quark-parton and vector-meson-dominance models, and we give a quantitative explanation of the excess by including the hard scattering of the hadronic constituents of the photons calculated with QCD.

Improved measurement of the anti-d / anti-u asymmetry in the nucleon sea

Measurements of the ratio of Drell-Yan yields from an 800 \rm{GeV/c} proton beam incident on liquid hydrogen and deuterium targets are reported. Approximately 360,000 Drell-Yan muon pairs remained after all cuts on the data. From these data, the ratio of anti-down (

Measurements of the inclusive jet cross section in photon-photon interactions at TRISTAN

\bar{d}

A measurement of the photon structure function F2

) to anti-up (

A high-Q2 measurement of the photon structure function F2γ

\bar{u}

The dilepton spectrometer

) quark distributions in the proton sea is determined over a wide range in Bjorken-

Measurement of charm production in two-photon processes using inclusive lepton events at TRISTAN

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