Data are reported on the momentum distributions of Λ, Λ (1520), φ (1020), Λ and p , inclusively produced between 1° and 2° with respect to one of the primary proton beams at the CERN Intersecting Storage Rings. In addition, the decay angular distribution of the Λ(1520), the ratio of the cross sections for the production of Σ − (1385) and Σ + (1385) and the ratios among different charge states of the pairs Λπ , Λ K, Δ ++ (1232) π and ππ have been measured. These data are confronted with current ideas on fragmentation.
In pp collisions at √ s = 44.7 and 62.3 GeV, where each proton fragments into at least one low- p T, high- x meson or baryon, no correlations between the particle momenta are found for ππ , π K, KK, and p π pairs. The ππ data show a preference for the formation of electrically neutral ππ systems. The KK data show the influence of strangeness conservation. For pp and pΛ final states, the momentum dependence of the correlation ratio R can be described by the scaling variable z = (1 − x 1 )(1 − x 2 ). Small deviations from factorization are discussed.
We report a measurement of the reaction γγ→K+K−π+π− in both tagged and untagged events at PEP. The cross section rises with invariant γγ mass to about 15 nb at 2 GeV and falls slowly at higher masses. We find clear evidence for the processes γγ→φπ+π− and γγ→K*0(892)Kπ. Upper limits (95% C.L.) of 1.5 and 5.7 nb in the mass range from 1.7 to 3.7 GeV are obtained for φρ0 and K*0K¯*0 production, respectively.
The two-photon production of the η meson has been observed, and a value has been determined for the two-photon η decay width by a measurement of the cross section σ(e+e−→e+e−η) where η→γγ. The measurement was made with the TPC/Two-Gamma facility at the SLAC e+e− collider PEP, with an accumulated data sample of 64.5 pb−1. The η→γγ events were both triggered and detected by the pole-tip calorimeter. The measured two-photon η decay width is Γη→γγ=0.64±0.14 (statistical) ±0.13 (systematic) keV, in agreement with earlier similarly determined values.
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.
This paper reports measurements of the hadrons produced in the inelastic scattering of 147-GeV muons by protons and deuterons in an experiment carried out at Fermi National Accelerator Laboratory. Both the scattered muon and the hadrons were measured in a large spectrometer. Properties of the hadron spectra are presented for proton, deuteron, and neutron targets and compared with theoretical models and with hadron spectra from related processes. Emphasis is placed on the quark-parton model and the data are found to be in substantial agreement with it. The average transverse momentum of the hadrons with respect to the virtual photon direction shows no dependence on the muon scattering variables. The data display "jet behavior" of the inclusive hadrons comparable to that found in e+e− annihilations.
The inclusive production of charged hadrons in the collisions of quasi-real photons e+e- -> e+e- +X has been measured using the OPAL detector at LEP. The data were taken at e+e- centre-of-mass energies from 183 to 209 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the hadrons are compared to theoretical calculations of up to next-to-leading order (NLO) in the strong coupling constant alpha{s}. The data are also compared to a measurement by the L3 Collaboration, in which a large deviation from the NLO predictions is observed.
New experimental data on antiproton production by carbon and deutron ions on copper and carbon nuclei at 3.65 GeV/nucleon and by proton at 3.65–8.1 GeV incident energy were obtained. Production angle is 24° and antiproton momentum is 0.8 GeV/c in the laboratory system.
Three-jet production in deep inelastic ep scattering and photoproduction was investigated with the ZEUS detector at HERA using an integrated luminosity of 127 pb-1. Measurements of differential cross sections are presented as functions of angular correlations between the three jets in the final state and the proton-beam direction. These correlations provide a stringent test of perturbative QCD and show sensitivity to the contributions from different colour configurations. Fixed-order perturbative QCD calculations assuming the values of the colour factors C_F, C_A and T_F as derived from a variety of gauge groups were compared to the measurements to study the underlying gauge group symmetry. The measured angular correlations in the deep inelastic ep scattering and photoproduction regimes are consistent with the admixture of colour configurations as predicted by SU(3) and disfavour other symmetry groups, such as SU(N) in the limit of large N.
Antiproton production near midrapidity has been studied in central collisions of 32 S with sulphur, silver and gold nuclei at 200 GeV per nucleon. The measured transverse mass distributions can be described by an exponential with inverse slope parameters of about 200 MeV, similar to those obtained from Λ spectra. The rapidity density increases weakly with the target mass, ranging from 0.4 to 0.7. The ratio Λ p near midrapidity is approximately 1.4 on average, significantly larger than the corresponding ratio observed in proton-proton and proton-nucleus collisions.
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