[en] Using pp→p+ all charged particles at 800 GeV/c and 27.5 GeV/c incident protons at Fermilah and Brookhaven, respectively, the mass of the Σ⁰ hyperon has been measured with an uncertainty of 7 times smaller than the best previous result. This result, M_Σ⁰=1192.65±0.020±0.014 MeV/c² is based on 16 times the statistics of previous results. copyright 1998 American Institute of Physics

[en] This article describes the fiber-optic-based calibration system installed at the High Resolution Fly's Eye (HiRes) astro-particle physics observatory. The HiRes detectors measure ultra violet scintillation light from distant extensive air showers. This automated calibration system delivers light from a frequency tripled 355 nm YAG laser to the 10,752 photo-multiplier tubes of the 42 HiRes-II detectors

[en] The High-Resolution Fly's Eye (HiRes) is an observatory for the highest energy cosmic rays. It detects the nitrogen fluorescence light induced by the passage of giant cosmic ray extensive air showers through the atmosphere. A two-site prototype of the observatory was operated from September 1994 to November 1996. In this paper we describe the components of that detector, and the procedures used to calibrate the detector and characterise the atmosphere. Data collected by the HiRes prototype are being used for physics studies, including an analysis of the cosmic ray mass composition in the energy range from 10¹⁷ to 10¹⁸ eV

[en] Stable, robust ultraviolet light sources for atmospheric monitoring and calibration pose a challenge for experiments that measure air fluorescence from cosmic ray air showers. One type of light source in use at the High Resolution Fly's Eye (HiRes) cosmic ray observatory features a xenon flashbulb at the focal point of a spherical mirror to produce a 1 μs pulse of collimated light that includes a strong UV component. A computer-controlled touch tone radio system provides remote operation of bulb triggering and window heating. These devices, dubbed 'flashers', feature stand-alone operation, ±5% shot-to-shot stability, weather proof construction and are well suited for long-term field use. This paper describes the flashers, the radio control system, and a 12-unit array in operation at the HiRes cosmic ray observatory

[en] In Λ⁰ close-quote s created from the specific reactions: pp→pΛ⁰K⁺π⁺π^-, pp→pΛ⁰K⁺π⁺π^-π⁺π^-, pp→pΛ⁰K⁺π⁺π^-π⁺π^-π⁺π^-, and pp→pΛ⁰K⁺π⁺π^-π⁺π^-π⁺π^-π⁺π^-, using 27.5 GeV/c proton beam incident on a liquid hydrogen target, we measured Λ⁰ polarization as a function of x_F and P_T. We found that Λ⁰ polarization is independent of any particular final state and of any specific mechanism responsible of producing Λ⁰. copyright 1998 American Institute of Physics

[en] We report a measurement of the x_F and P_TΛ⁰ polarization dependence; Λ⁰ close-quote s were produced in the specific channels: pp→pΛ⁰K⁺π⁺π^-, pp→pΛ⁰K⁺π⁺π^-π⁺π^-, pp→pΛ⁰K⁺π⁺π^-π⁺π^-π⁺π^-, and pp→pΛ⁰K⁺π⁺π^-π⁺π^-π⁺π^-π⁺π^- with 27.5 GeV/c protons incident on a liquid hydrogen target. We find that Λ⁰ polarization is independent of the final state. copyright 1998 American Institute of Physics

[en] We have measured the x_F and P_T dependence of the polarization of Λ⁰ hyperons produced in exclusive final states pp→pΛ⁰K⁺π⁺ π^- , pp→pΛ⁰K⁺π⁺ π^-π⁺π^- , pp→pΛ⁰K⁺ π⁺π^-π⁺ π^-π⁺π^- , and pp→pΛ⁰K⁺π⁺ π^-π⁺π^-π⁺π^-π⁺π^- at 27.5thinspthinspGeV/c . We present an empirical parametrization for Λ⁰ polarization as a function of x_F and P_T : P=(-0.443±0.03 7)x_FP_T for -1≤x_F≤1 and 0≤P_T≤1.8 GeV/ c . This parametrization is independent of the final state and provides a good description of the data. We note that the mechanism responsible for Λ⁰ polarization appears to be independent of the production mechanism. copyright 1999 The American Physical Society

[en] We have obtained precise measurements of the Σ⁰ mass and the Σ⁰-Λ⁰ mass difference from a fit to the Λ⁰γ invariant mass distribution of 3327 Σ⁰→Λ⁰+γ decays. Our measurements yield M_Σ⁰=1192.65±0.020±0.014 MeV/c² and M_Σ⁰-M_Λ⁰=76.966±0.020±0.013 MeV/c², where the uncertainties are statistical and systematic in that order. This represents a significant improvement over all previous determinations and is the first direct measurement of the Σ⁰ mass itself. copyright 1997 The American Physical Society

[en] A precision measurement of the masses of the Λ⁰ and bar Λ⁰ hyperons is obtained from Gaussian fits to the invariant mass distributions for 20 138 Λ⁰'s and 18 309 bar Λ⁰'s. The Gaussians have standard deviations of 0.49 and 0.51 MeV/c² for the Λ⁰ and bar Λ⁰, respectively. Systematic errors were reduced by calibrating the spectrometer with 60 000 exclusive events containing a K_S⁰. We find M_Λ=1115.678±0.006±0.006 MeV/c² and M_barΛ=1115.690±0.008±0.006 MeV/c². The Λ^0-bar Λ⁰ mass difference testing CPT invariance is -0.012±0.010 MeV/c²

[en] We measured the polarization of 51195 Λ⁰ close-quote s produced in the specific reaction pp→pΛ⁰K⁺π⁺π^-π⁺π^- with 27.5GeV/c protons incident on a liquid hydrogen target. Because the reaction was measured completely, the polarization was studied versus the following: x_F(-1to+1), Λ⁰ transverse momentum (0 to 1.32GeV/c), correlations with the momentum vectors of the other particles in the reaction, and the invariant mass of combinations of particles in the final state. The dependence of the polarization on these variables does not always agree with theoretical expectations. copyright 1995 The American Physical Society