Ph. Rosselet

Observation of a narrow state at 2.46 GeV/c2 — a candidate for the charmed strange Baryon A+☆

Abstract A narrow state has been observed in the reaction Σ − + Be → ( Λ K − π + π + ) + X in an experiment at the CERN SPS hyperon beam. At 2.46 GeV/ c 2 the effective ( Λ K − π + π + ) mass distribution shows an excess of 82 events above a background estimated to be 147, corresponding to a statistical significance of more than 6 standard deviations. The positive charge of the observed final state, which has strangeness −2, suggests the interpretation as a Cabibbo favoured decay of the charmed strange baryon, A + [quark content (csu)]. The cross section times branching ratio is measured to be σ · B = (5.3 ± 2.0) μ b/ (Be nucleus) for x > 0.6. The invariant production cross section is described by E d 3 σ /d p 3 ∞ (1 - x ) (1.7±0.7) exp[−(1.1 −0.4 +0.7 ) p T 2 ].

Evidence for narrow states decaying into (Λp + pions) at 3.1GeV / c2 with charges + 1, 0 and −1☆

Abstract Evidence for narrow states produced by Σ− interactions in beryllium, and decaying into ( Λ p + pions ), has been obtained in an experiment at the CERN SPS hyperon beam. At 3.1 GeV/c2, the ( Λ p π + π + ), ( Λ p π + π + π − ) and ( Λ p π + π − ) effective mass distributions show an excess of 45, 19 and 62 events above a background of 50, 28 and 187, respectively. The possibility that these three signals are statistical fluctuations is remote. The observed widths of the signals are compatible with the mass resolution of the apparatus, 24 MeV/c2 FWHM. We have not been able to find an interpretation of the quantum numbers of the final states, which are baryon number 0, strangeness −1 and charge +1, 0 and −1.

Measurement of the lifetime of the charmed strange baryon A

Abstract The lifetime of the charmed strange baryon A+ has been determined in an experiment at the CERN SPS hyperon beam from the distribution of distances between production and decay of A+ candidates of known momentum. The result is: τ = (4.8 −1.8 +2.9 ) × 10 −13 s .

Measurements of the total cross sections of Σ− and Ξ− on protons and deuterons between 74 and 137 GeV/c

The Σ− p and Σ− d total cross sections have been measured to a statistical accuracy of ±1% and ±0.5%, respectively, at five momenta from 74.5 to 136.9 GeV/c, using the hyperon beam at the CERN SPS. The Ξ−p and Ξ− d total cross sections have also been measured to the same statistical accuracy at 101.5 and 133.8 GeV/c. The systematic uncertainty at each momentum is estimated to be of the order of ±0.5%. The hyperon-nucleon cross sections are shown to be rising with energy, and the data are compared with various phenomenological models.

The reaction\bar pp \to \bar \Lambda \Lambda between 1.50 and 2.06 GeV/e

SummaryThe reaction

Properties of the charmed strange baryonA + and evidence for the charmed doubly strange baryonT 0 at 2.74 GeV/c2

\bar pp \to \bar \Lambda \Lambda

Ξ− and Ξ− inclusive production in Ξ− Be interactions at 116 GeV/c

has been studied in a bubble chamber experiment at eight incident momenta between 1.50 and 2.06 GeV/c. The differential cross-section, the polarization and the spin correlation coefficients have been measured. They have been compared with the prediction of two theoretical models: the K-meson conspiracy and the exchange of the K*K** degenerate trajectory associated with a Regge cut. The latter model gives the best representation of the data.RiassuntoSi è studiata la reazione