Search Results (7 total)

We show that Σ⁺ hyperons produced by 800 GeV/c protons on targets of Be and Cu have significant polarizations (15–20%). These polarizations persist at values of p_t≈2  GeV/c and a wide range of x_F. The polarizations from the Cu target are consistently less than from Be. The average ratio of the Σ⁺ polarization from Cu to that from Be is 0.68±0.08.

We report the first observation of a charm-strange meson D_sJ⁺(2632) at a mass of 2632.5±1.7  MeV/c² in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D_s⁺η and D⁰K⁺. In the D_s⁺η decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4±3.3  MeV/c². There is a corresponding peak of 21 events over a background of 6.9 at 2631.5±2.0  MeV/c² in the decay mode D⁰K⁺. The decay width of this state is <17  MeV/c² at 90% confidence level. The relative branching ratio Γ(D⁰K⁺)/Γ(D_s⁺η) is 0.14±0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D_s⁺η decay mode.

Pion virtual compton scattering (VCS) via the reaction π^-e→π^-eγ was observed in the Fermilab E781 SELEX experiment. SELEX used a 600 GeV/c π^- beam incident on target atomic electrons, detecting the incident π^- and the final state π^-, electron and γ. Theoretical predictions based on chiral perturbation theory are incorporated into a Monte Carlo simulation of the experiment and are compared to the data. The number of reconstructed events (=9) and their distribution with respect to the kinematic variables (for the kinematic region studied) are in reasonable accord with the predictions. The corresponding π^- VCS experimental cross section is σ=38.8±13 nb, in agreement with the theoretical expectation of σ=34.7 nb.

We observe a signal for the doubly charmed baryon Ξ_cc⁺ in the charged decay mode Ξ_cc⁺→Λ_c⁺K^-π⁺ in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1±0.5 events, a statistical significance of 6.3σ. The observed mass of this state is 3519±1  MeV/c². The Gaussian mass width of this state is 3  MeV/c², consistent with resolution; its lifetime is less than 33 fs at 90% confidence.

We report new precision measurements of the lifetimes of the Λ_c⁺ and D⁰ from SELEX, the charm hadroproduction experiment at Fermilab. Based upon 1630 Λ_c⁺ and 10 210 D⁰ decays we observe lifetimes of τ[Λ_c⁺]  =  198.1±7.0±5.6 fs and τ[D⁰]  =  407.9±6.0±4.3 fs.

We report the first observation of the Cabibbo-suppressed charm baryon decay Ξ_c⁺→pK^-π⁺. We observe 150±22±5 events for the signal. The data were accumulated using the SELEX spectrometer during the 1996–1997 fixed target run at Fermilab, chiefly from a 600 GeV/c Σ^- beam. The branching fractions of the decay relative to the Cabibbo-favored Ξ_c⁺→Σ⁺K^-π⁺ and Ξ_c⁺→Ξ^-π⁺π⁺ are measured to be B(Ξ_c⁺→pK^-π⁺)/B(Ξ_c⁺→Σ⁺K^-π⁺)  =  0.22±0.06±0.03 and B(Ξ_c⁺→pK^-π⁺)/B(Ξ_c⁺→Ξ^-π⁺π⁺)  =  0.20±0.04±0.02, respectively.

Collective transverse flow of nuclear matter was measured as a function of the ratio of neutrons to protons ( N/Z) of the interacting system for the first time. The collisions of three isotopically pure beams of A  =  58 nuclei with two A  =  58 targets were studied at 55 MeV/nucleon. The results for the flow variables demonstrate the sensitivity of transport models to elementary aspects of the nucleon-nucleon collisions.