C. Lazzeroni

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 kinematical correlations between charmed particles produced in π-Cu interactions at s=26 GeV

Abstract A sample of 475 events, in which two charmed-particle decays are observed, is analyzed to determine distributions of two-particle kinematic variables. One charmed particle with x F > 0 is fully reconstructed and the other is at least partially recontructed. The distributions of Δo and p T 2 are compared with a next-to-leading order QCD calculation.

Measurement of the beauty production cross section in 350 GeV / c π-Cu interactions

Abstract Using a sample of 108 triggered events, produced in π−−Cu interactions at 350 GeV/c, we have identified 26 beauty events. The estimated background in this sample is 0.6 ± 0.6 events. From these data, assuming a linear A-dependence, we measure a beauty production cross section integrated over all χF of 5.7−1.1+1.3 (stat.)−0.5+0.6 (syst.) nb/N.

Azimuthal correlation between beauty particles produced in 350 GeV/c pi- Cu interactions

Abstract Using a sample of 108 triggered events, produced in 350 GeV /c π− interactions in a copper target, we have identified 26 bb events. These include 13 events where the decays of both B and B are well reconstructed. We measure the azimuthal correlation between beauty particles, and compare our result with predictions based on perturbative QCD.

Search for the flavour-changing neutral-current decay D0 → μ+μ−

Abstract We have searched for the decay D 0 → μ + μ − among 2.0 × 10 5 μ + μ − pair produced, in the WA92 experiment, by 350 GeV/ c π − particles interacting in copper and tungsten targets. Using a high-resolution silicon-microstrip detector followed by a large-acceptance magnetic spectrometer and a muon filter we are able to measure the momentum of the muons, to visualize the event topology near their point of origin, and thus to discriminate between prompt and non-prompt muons. No D 0 → μ + μ − candidate has been found. This result allows us to set an upper limit on the branching fraction B( D 0 → μ + μ − ) of 4.1 × 10 −6 at 90 % confidence level.

Search for the decay D0 → μ+μ−

Abstract We have searched for the decay D 0 → μ + μ − among 1.25 × 10 5 μ + μ − pairs produced by 350 GeV/ c π − particles interacting in copper and tungsten targets. Using a high-resolution silicon-microstrip detector followed by a large-acceptance magnetic spectrometer and a muon filter we are able to discriminate between prompt and non-prompt muons and to measure dimuon masses. No candidate compatible with a D 0 → μ + μ − decay has been found, allowing us to set an upper limit on the branching fraction B( D 0 → μ + μ − ) of 7.6 × 10 −6 at the 90% confidence level.

D* production in 350 GeV/c pi- N interactions

Abstract We report measurements of D ∗± production in interactions between 350 GeV/c π− particles and nuclei. Reconstruction of the decay D ∗+ → D 0 π + and charge conugate, with D0 identified via its decays to K−π+ and K−π−π+π+, has allowed isolation of a sample of 611 ± 28 D ∗± mesons, produced at positive xF. Assuming a linear A-dependence, the cross-section per nucleon in the region xF > 0 is measured to be 1.41 ± 0.10 ± 0.11 μ b for D ∗+ and 1.84 ± 0.12 ± 0.15 μ b for D ∗− . We present measurements of differential cross-sections with respect to xF and Pt2, and compare data for D ∗± (vector-meson) production with data for production of charmed pseudoscalar mesons.

Inclusive J/ψ and ψ′ production in π−-nucleus interactions at √s ⋍ 26 GeV

Abstract Charmonium production by 350 GeV/ c negative pions incident on tungsten, copper and silicon has been studied in the WA92 experiment. J / ψ and ψ′ mesons are identified through their decays into muon pairs and are selected in the Feynman-χ range χ F > 0. Inclusive J / ψ and ψ′ cross-sections and J / ψ differential cross-sections as functions of χ F and p T 2 are measured. Assuming the relation σ = σ 0 A α between the nuclear cross-section, σ, and the atomic mass, A , of a target nucleus, a fit to J / ψ data for different targets yields α = 0.87 ± 0.05 ± 0.04. Taking α = 0.87, the cross-sections per nucleon for J / ψ and ψ′ are σ 0 ( J / ψ ) = 216 ± 5 ± 13 nb and σ 0 ( ψ ′) = 28 ± 8 ± 11 nb, and their ratio is σ 0 ( ψ ′)/ σ 0 ( J / ψ ) = 0.13 ± 0.05 ± 0.01. The measurements of charmonium production are compared with results on open-charm production previously obtained in the same experiment. The ratio between the J / ψ cross-section and the charmed-meson cross-section, relating to the same experimental conditions, is found to be σ 0 (J/ψ)/σ 0 (D D − ) = 1.75±0.05±0.15) × 10 −2 .

Inclusive J/ψ and ψ′ production in π−-nucleus interactions at

Abstract Charmonium production by 350 GeV/ c negative pions incident on tungsten, copper and silicon has been studied in the WA92 experiment. J / ψ and ψ′ mesons are identified through their decays into muon pairs and are selected in the Feynman-χ range χ F > 0. Inclusive J / ψ and ψ′ cross-sections and J / ψ differential cross-sections as functions of χ F and p T 2 are measured. Assuming the relation σ = σ 0 A α between the nuclear cross-section, σ, and the atomic mass, A , of a target nucleus, a fit to J / ψ data for different targets yields α = 0.87 ± 0.05 ± 0.04. Taking α = 0.87, the cross-sections per nucleon for J / ψ and ψ′ are σ 0 ( J / ψ ) = 216 ± 5 ± 13 nb and σ 0 ( ψ ′) = 28 ± 8 ± 11 nb, and their ratio is σ 0 ( ψ ′)/ σ 0 ( J / ψ ) = 0.13 ± 0.05 ± 0.01. The measurements of charmonium production are compared with results on open-charm production previously obtained in the same experiment. The ratio between the J / ψ cross-section and the charmed-meson cross-section, relating to the same experimental conditions, is found to be σ 0 (J/ψ)/σ 0 (D D − ) = 1.75±0.05±0.15) × 10 −2 .