B. J. Saunders

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 ].

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.

Production of hyperons and hyperon resonances inΞ−N interactions at 102 and 135 GeV/c*

AbstractΞ− interactions in hydrogen and deuterium are studied close to the forward direction using the CERN charged hyperon beam. The inclusive production of ∑*−(1385),Ξ−,Ξ*0(1530),Ξ*−(1700),Ξ*−(1830), and Ω− is observed, as well as an enhancement in theΞ−π+ channel at 1940 MeV/c2. The momentum distributions and the production cross sections are measured for ∑*−(1385),Ξ−,Ξ*0(1530), and Ω−.

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

Results are presented from experiment WA62, which searched for charmed strange baryon states produced inΣ− interactions in the SPS charged hyperon beam at CERN. Properties of theA+ (csu) baryon at 2.46 GeV/c2 are summarized and upper limits are given for decay branching ratios into various channels. Three events observed at 2.74 GeV/c2 in theΞ−K−π+π+ mass spectrum are interpreted as the first evidence for theT0 baryon with quark content css. Results of a search for theA0 (csd), the isospin partner of theA+, are presented. The results are discussed in the context of current theoretical understanding, and a comparison with other experiments on hadroproduction of charmed baryons is made.

Measurements of hyperon semileptonic decays at the CERN Super Proton Synchrotron: II. The 1-011-011-01decay modes

AbstractThe charged hyperon beam at the CERN Super Proton Synchrotron (SPS) has been used to collect data on semileptonic decays of Σ−, Ξ−, andΛ. A magnetic channel selected 100 GeV/c negatively charged particles produced in the forward direction by interaction of a 210 GeV/c proton beam on a BeO target. The Σ− and Ξ− hyperons were concurrently identified in a DISC Čerenkov counter, and their decay products were analysed by a magnetic spectrometer. Electron-hadron discrimination was achieved by the combined use of lead glass and lead/scintillator counters, transition radiation detectors, and a Čerenkov counter.In this article we report results on the

First observation ofΩ* resonances

\Xi \to \Lambda \pi (\Lambda \to pe\bar v), \Xi \to \Lambda e\bar v(\Lambda \to p\pi ),

Measurement of theΞ - p elastic cross section at 102 and 135 GeV/c

and