We present proton-nucleus dimuon-production cross sections for masses between 4 and 15 GeV, center-of-mass rapidities between -0.23 and 0.6 and incident energies of 200, 300, and 400 GeV. The data confirm scaling to the 20% level. The dependence of continuum 〈pT〉 on beam energy is also presented.
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The photonic part of multihadronice+e− annihilation events has been analyzed at a c.m. energy of 34 GeV. The photonic energy fraction per event is determined to befγ=0.251±0.003 (stat.) ±0.04 (syste.). The neutral and charged components of the events are analyzed separately revealing close similarity in thrust axis directions and momentum distributions in agreement with the hypothesis that most photons result from π0 decay. π0's are reconstructed separately and used to determine the inclusive cross section. Comparing these cross sections with lower energy data from SPEAR we find some indication for scaling violation.
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We have measured transverse momentum spectra up to 10 GeV/ c for charged particles produced centrally in proton-antiproton collisions at 540 GeV in the centre of mass at the CERN collider. Our results are compared with data at ISR energies and with the predictions of a QCD model. The charged particle spectrum shows a clear dependence on charged track multiplicity.
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Transverse particle momenta have been measured ine+e− annihilation into hadrons at c.m. energies between 9.4 and 31.6 GeV. The data are fully corrected for detector effects and radiation in the initial state. A comparison is made with recent QCD calculations.
MEASUREMENTS MADE WITH RESPECT TO THE SPHERICITY AXIS.
MEASUREMENTS MADE WITH RESPECT TO THE THRUST AXIS.
MEASUREMENTS MADE WITH RESPECT TO THE MOST ENERGETIC PARTON AXIS.
We present the general properties of jets produced bye+e− annihilation. Their production and fragmentation characteristics have been studied with charged particles for c.m. energies between 12 and 43 GeV. In this energy rangee+e− annihilation into hadrons is dominated by pair production of the five quarksu, d, s, c andb. In addition, hard gluon bremsstrahlung effects which are invisible at low energies become prominent at the high energies. The observed multiplicity distributions deviate from a Poisson distribution. The multiplicity distributions for the overall event as well as for each event hemisphere satisfy KNO scaling to within ∼20%. The distributions ofxp=2p/W are presented; scale breaking is observed at the level of 25%. The quantityxpdδ/dxp is compared with multigluon emission calculations which predict a Gaussian distribution in terms of ln(1/x). The observed energy dependence of the maximum of the distributions is in qualitative agreement with the calculations. Particle production is analysed with respect to the jet axis and longitudinal and transverse momentum spectra are presented. The angular distribution of the jet axis strongly supports the idea of predominant spin 1/2 quark pair production. The particle distributions with respect to the event plane show clearly the growing importance of planar events with increasing c.m. energies. They also exclude the presence of heavy quark production,e+e−→Q\(\bar Q\) for quark masses up to 5<mQ<20.3 GeV (|eQ|=2/3) and 7<mQ<19 GeV (|eQ|=1/3). The comparison of 1/σtotdδ/dpT measured at 14, 22 and 34 GeV suggests that hard gluon bremsstrahlung contributes mainly to transverse momenta larger than 0.5 GeV/c. The rapidity distribution forW≧22 GeV shows an enhancement away fromy=0 which corresponds to an increase in yield of 10–15% compared to the centre region (y=0). The enhancement probably results from heavy quark production and gluon bremsstrahlung. The particle flux around the jet axis shows with increasing c.m. energy a rapidly growing number of particles collimated around the jet axis, while at large angles to the jet axis almost noW dependence is observed. For fixed longitudinal momentump‖ approximate “fan invariance” is seen: The shape of the angular distribution around the jet axis is almost independent ofW. The collimation depends strongly onp‖. For smallp‖,p‖<0.2 GeV/c, isotropy is observed. With increasingp‖ the particles tend to be emitted closer and closer to the jet axis.
R VALUES BELOW 32.5 GEV ARE IDENTICAL TO THOSE GIVEN IN BRANDELIK ET AL., PL 113B, 499 (1982).
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CHARGED PARTICLE MULTIPLICITY DISTRIBUTIONS.
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We have measured 〈p⊥〉 as a function of multiplicity for the reaction proton (antiproton) on proton, neon, argon, and xenon. For all reactions, 〈p⊥〉 is independent of multiplicity. We observed that the pion-emission volume is the same for both hydrogen and xenon targets and has a radius about 1.5 fm. Our analysis shows no indication of a deconfinement phase transition in nuclear matter.
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Light ion collisions with carbon target at 4.2 GeV/c/N are studied. Pion multiplicity distributions, momentum and angular spectra are analysed. These data are described in terms of models assuming independent interactions of nucleons from the projectile nucleus with the target.
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