S.N. Tovey

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 ].

Recent results of radiation damage studies in silicon

Abstract The RD2 Collaboration is making preliminary studies on a silicon tracking detector for use at the LHC. It is a priority that this detector should withstand the high level of radiation to be expected for LHC operation. Therefore systematic studies on the change of the detector performance due to radiation damage have been made, or are in progress. Well established results on neutron related damage at room temperature have been extended to lower temperatures, as foreseen for operation at LHC. For comparison proton damage studies have also been started. The detector properties under investigation include the reverse current, the depletion voltage and the charge collection efficiency. With a compressed 10 year LHC operational scenario we have successfully checked the ability of silicon detectors to survive the period influences of high fluence irradiation and subsequent annealing.

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 .

Neutron irradiation of silicon diodes at temperatures of +20°C and −20°C

Abstract We report measurements of the behaviour of silicon diodes when exposed to integrated neutron doses of up to 5 × 10 13 neutron/cm 2 . The measurements have been made at diode temperatures between room temperature and −20°C. From measurements of the diode leakage current and depletion voltage, and consequent evaluations of the effective impurity concentration, the temperature dependence of these quantities is discussed in terms of the annealing behaviour of the diodes. Comments are made on the suitability of silicon as a detector medium for particle physics experiments at future accelerators.

K/π production ratios from 450 GeV/c protons on beryllium

Abstract This paper reports on the charged K / π production ratios and on the shape of the p T distributions of π fluxes measured by the SPY/NA56 experiment for 450 GeV/c proton interactions on beryllium targets. The present data cover a secondary momentum range from 7 GeV/c to 135 GeV/c in the forward direction and with p T values up to 600 MeV/c. An experimental accuracy of about 3% has been achieved. These results will reduce the uncertainty on the estimation of the ν e component of neutrino beams.

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.

Charged baryon and antibaryon production in the fragmentation region by 240 GeV protons

AbstractMeasurements of the production inp-BeO collisions of charged baryons and antibaryons with strangeness between −3 and +3 at

Resonance production in the reaction pd→psπ+π-π-π0 at 0.4 to 0.9 GeV/c antiproton momenta

\sqrt s = 21.2GeV