Measurements of the reaction pˉp→ϕη\bar{p}p \to \phi \eta of antiproton annihilation at rest at three hydrogen target densities

The proton-antiproton annihilation at rest into the $\phi\eta$ final state was measured for three different target densities: liquid hydrogen, gaseous hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in the liquid hydrogen target is smaller than in the low-pressure gas target. The branching ratios of the $\phi\eta$ channel were calculated on the basis of simultaneous analysis of the three data samples. The branching ratio for annihilation into $\phi\eta$ from the $^3S_1$ protonium state turns out to be about ten times smaller as compared to the one from the $^1P_1$ state.Comment: 10 pages, 3 Postscript figures. Accepted by Physics Letters

New data on OZI rule violation in bar{p}p annihilation at rest

The results of a measurement of the ratio R = Y(phi pi+ pi-) / Y(omega pi+ pi-) for antiproton annihilation at rest in a gaseous and in a liquid hydrogen target are presented. It was found that the value of this ratio increases with the decreasing of the dipion mass, which demonstrates the difference in the phi and omega production mechanisms. An indication on the momentum transfer dependence of the apparent OZI rule violation for phi production from the 3S1 initial state was found.Comment: 11 pages, 3 PostScript figures, submitted to Physics Letter

The laser calibration system of the Obelix spectrometer

The realization of a laser-based system for calibrating the scintillator array of the Obelix spectrometer is described. The system allows a very precise timing of all the signals, which is needed for a first-level trigger based on time-of-flight information. Details of the optical system and of the calibration procedures are given

The trigger control system for the Obelix experiment

The trigger control system for the Obelix experiment at the low-energy antiproton ring (LEAR) at CERN is described. This system operates in a distributed environment and provides an easy to use mechanism for trigger selection. Automatic consistency checks and bookkeeping of all changes are performed. The integration with the run control system ensures proper synchronization with the other procedures

Hypernuclear physics at DAφNE, the frascati φ-factory

The low-energy, background free and tagged K−s from the φ(1020) decay produced at the DAφNE φ-factory in Frascati offer a unique opportunity for high resolution hypernuclei spectroscopy with K−at rest. In this paper we outline the general problematics of this interesting field, expose the physics motivations that support our proposal and, finally, describe the techniques foreseen for precise measurements of the hypernuclear level energies and their decay modes. In this regard we investigated the performances of a magnetic spectrometer foreseen for] one of the interaction region of the DAφNE machine. Details on the detector characteristics as well as on its response to all the particles in the final state will be extensively discussed

The VME based OBELIX TOF on-line system

The OBELIX spectrometer is dedicated to meson spectroscopy and to antinucleon-nucleon and antinucleon-nucleus interaction studies. The time-of-flight (TOF) apparatus consists of two concentric arrays (30+90) of plastic scintillators. The OBELIX online architecture is designed to allow centralized data acquisition as well as independent data taking for each detector. The TOF online system is described. Software and hardware aspects are discussed. This system is being employed in test runs on the TOF apparatus and, integrated with other components of the whole detector, in beam tests