Y.A. Alexandrov

Study of D+ and D− Feynman's x distributions in π−-nucleus interactions at the SPS

Abstract Experiment WA82 studied charm production by a π− beam of 340 GeV/c at the CERN Ω′ spectrometer, using a silicon microstrip vertex detector and an impact parameter trigger. Results on the xF distributions of D+ and D− mesons are presented and discussed. A clear excess of D− over D+, increasing at high xF, is observed.

Measurements of charmed-meson production in interactions between 350 GeV/c π− particles and nuclei

Abstract Charmed-meson production by 350 GeV/c π − particles incident on copper and tungsten targets has been studied in the WA92 experiment, performed at the CERN Ω′ spectrometer. Results obtained are reported and discussed. Reconstruction of decays from the set D 0 → K − π + D 0 → K − π − π + π + , D s + → φπ + and charge conjugates has yielded a sample of 7280 ± 108 charmed mesons, produced with χ F > 0, ( χ F ) = 0.18 and〈 p T 2 〉 = 1.86 ( GeV / c ) 2 . Assuming a relationship σ = σ 0 A α between the cross section, σ, per nucleus of mass A and the nucleonic cross section, σ 0 the α value found for the detected charmed particles is 0.95 ± 0.06 ± 0.03. Taking α = 1, the measured cross sections per nucleon for χ F > 0 production are 7.78 ± 0.14 ± 0.52 μ b for D 0 / D 0 , 3.28 ± 0.08 ± 0.29 μ b for D + /D − and 1.29 ± 0.16 ± 0.33 μ b for D s + /D s − . Differential cross sections with respect to χ F and p T 2 have been determined for the various types of charmed meson, and particle-antiparticle asymmetries have been analysed.

Scaling properties of charged particle multiplicity distributions in oxygen induced emulsion interactions at 14.6, 60 and 200 A GeV

Abstract The multiplicity distributions of shower particles (ns) are measured in inclusive inelastic oxygen emulsion interactions. Scaling is observed in the normalized variable ns/〈ns〉 for 14.6, 60 and 200 AGeV. The dependence of 〈ns〉 on the charge flow in the forward direction (QZD) and the distribution of the number of participating projectile protons is examined. The normalized multiplicities as a function of QZD seem also to be independent of incident energies. A comparison with the Lund model Fritiof yields satisfactory agreement.

Rapidity densities and their fluctuations in central 200 A GeV 32S interactions with Au and Ag, Br nuclei EMU01 collaboration

The pseudo-rapidity density distributions of shower particles (n s ) are measured in central inelastic S + Au and S + Ag,Br inter-actions. The extracted maximum energy densities, while being higher for Au than for Ag.Br interactions, were found to be similar to those obtained for oxygen emulsion interactions. The correlation between rapidity density and shower particle multiplicity shows a small deviation from the Lund Model Fritiof for the highest energy densities in S + Au interactions, whereas the bulk of the data yields satisfactory agreement.

Multiplicities and rapidity densities in 200 A GeV 16O interactions with emulsion nuclei

Abstract We report on an experiment in which emulsion chambers were exposed to a beam of 200 A GeV 16 O at the CERN SPS. Pseudo-rapidity distributions are measured with high precision. Pseudo-rapidity densities of 140 particles per unit rapidity corresponding to an energy density of about 3 GeV/fm3 are observed. Pseudo-rapidity density distributions and fluctuations are found to satisfactorily agree with the Lund Monte Carlo model Fritiof, although new and unknown sources for fluctuations might still be present.

On intermittency in heavy-ion collisions and the importance of γ-conversion in a multi-dimensional intermittency analysis

Non-statistical fluctuations are used to probe the dynamical behaviour of multi-particle production in heavy-ion interactions at ultra-relativistic energies. In a one-dimensional analysis a 1〈ϱ〉-scaling is established and it is furthermore found that effects from higher-order particle correlations are small. In a two-dimensional analysis it is shown that a small background of particle pairs with a narrow opening angle can distort the observed signal. As an example we estimate the influence of γ-conversion and find that in our experiment γ-conversion alone gives results consistent with the experimental observations from a two-dimensional analysis. Whereas a two-dimensional analysis filters events where two particles are extremely close in phase space, the one-dimensional analysis picks out events with particles clustered in pseudorapidity, which are at the same time diluted in the azimuthal plane.

Measurement of the Ds→μνμ branching fraction and of the Ds decay constant

Abstract Using interactions of 350 GeV /c π − in copper and tungsten targets, the branching fraction for the leptonic decay B ( D s → μν μ ) is measured to be (0.83±0.23 stat. ±0.06 syst. ±0.18 B ( D s → ϕπ ) )%. The resulting value for the D s decay constant is f D s =323±44±12±34.

A study of the semileptonic decay

Abstract The decay D+→K−π+e+νe has been studied by the hadroproduction experiment WA82. The decay is dominated by the K ∗0 (892) resonance. The ratio of branching ratios, B( D + → K ∗0 e + ν e )/B( D + → K − π + π + ) , is found to be 0.62±0.15±0.09. The K ∗0 mesons have a ratio of longitudinal to transverse polarization of 0.6±0.3+0.3−0.1.

A search for non-statistical particle density fluctuations in 16O + Ag(Br) and 32S + Au interactions at 200 A GeV

Abstract Fluctuations in particle densities of non-statistical origin are studied in central 16 O+Ag(Br) and 32 S+Au interactions at 200 A GeV. Non-statistical fluctuations in the 32 S-induced interactions seem to enhance the local particle densities, and suggest the presence of intermittancy. The fluctuations are found to be accompanied by a clustering tendency also in the azimuthal plane. A new method for the study of azimuthal correlations is proposed.

Nuclear dependence of charm production by a 340 GeV π- beam

Abstract Charmed mesons, produced on silicon, copper and tungsten by 340 GeV π - , have been identified as peaks in invariant mass distributions. The comparison of the yields of charmed particles originating from interactions in Si, Cu and W allows the mass number dependence of the charm hadroproduction cross section to be measured. Assuming the usual parametrization σ c = σ 0 A α , we find α =0.92±0.06 for charmed mesons with 〈 x F 〉=0.24. We do not find any decrease of α with increasing x F in contrast to the case of the production of particles containing only light quarks.