C. Rubbia

Observation of small angle proton proton elastic scattering at 30 gev and 45 gev center-of-mass energies

Abstract Small angle elastic scattering events have been observed at the CERN Intersecting Storage Rings. Directions of both particles as well as the collision vertex are reconstructed with the help of four sets of spark chambers, two for each of the two arms. The elastic nature of the events is demonstrated by a collinearity requirement. We find values for the (diffraction) slope parameter in disagreement with the simple linear extrapolation of lower energy (Surpukov) data.

Predictions for a liquid argon solar neutrino detector

Abstract A liquid argon time projection chamber can be used to make separate measurements of electron neutrinos and neutrinos of different flavors, to determine the incident neutrino spectrum, and to verify that neutrinos come from the direction of the sun. Resonant neutrino oscillation has a dramatic effect on the shape of the predicted spectrum of recoil electrons.

Diffractive production of the charmed baryon Λ+c at the CERN ISR☆

Abstract In a sample of diffractive events of high multiplicity a sharp five standard deviation signal is observed at M = 2255 MeV/c2 in the K−pπ+ mass distribution and, although with less statistical strength, at the same mass in the Λ0π+π+π− channel. These signals are identified as being due to the decay of the charmed baryon Λ+c which is produced with a cross section times branching ratio σcB in the range 0.7−1.8 μb for the K−π+p decay and 0.3−0.7 μb for the Λ-π+π+ π− system.

Further results on small-angle elastic proton-proton scattering at very high energies☆

Abstract This work extends our previous investigations at the CERN Intersecting Storage Rings, with improved statistics at three different energies, wider angular range and a better control over systematic errors. Values for the (diffraction) shape parameter b are given.

A Study of Ionization Electrons Drifting Large Distances in Liquid and Solid Argon

Abstract A two liter gridded ionization chamber was built and operated repeatedly to study electron transport in liquid and solid argon over distances up to 10 cm in drift fields of 0.01–2 kV/cm. A detailed analysis of the ionization pulse shape was performed, yielding information on both the degree of purity of the liquid and the electron drift velocity. Argon with an impurity concentration less than 0.2 ppb oxygen equivalent was obtained with a simple purification system. The measured attenuation length extrapolates to 7.5 m for liquid argon and to 1 m for solid argon at a drift field of 1 kV/cm.

Determination of the proton-proton elastic cross section at 30 GeV center of mass energy

Abstract The absolute luminosity of the CERN Intersecting Storage Rings has been determined by the Van der Meer method. Combining the measurement with small angle proton-proton elastic events, we find σ elastic = (6.8±0.6)mb.

A search for nucleon decay with multiple muon decays

Abstract A search was made for nucleon decays which result in multiple delayed muon decays using the HPW water Cerenkov detector. No contained events were found, which is consistent with the expected neutrino background of 0.7±0.2 events. Lower lifetime limits are calculated for eleven proton decay modes and five bound neutron decay modes, ranging from 2×10 30 yr to 1×10 31 yr.

Antiproton decay and the baryon number of the universe

Abstract It appears that the present universe has net positive baryon number. If the lifetime of the antiproton is less than the age of the universe, it is plausible that the initial universe had zero baryon number. The antiproton instability can be tested with a small antiproton storage ring.

Drifting electrons over large distances in liquid argon-methane mixtures

Abstract For large liquid image chambers argon was proven to be well suited, as it can be purified such that several meters of drift length are feasible. For several physics motivations free photons would be desirable within the detector liquid. A gridded ionization chamber used before for tests with liquid and solid argon was therefore repeatedly filled with argon-methane mixtures. Mixtures with up to 50 mol % CH 4 were used to drift electrons over distances up to 10 cm in drift fields of 0.01 to 0.2 kV/cm. A detailed analysis of the ionization pulse shape was performed, yielding information on the attenuation length due to attachment of drifting electrons to impurities. With a simple purification system the impurity level in the argon-methane mixtures could be reduced to reach attenuation lengths of many meters at a drift field of 1 kV/cm.

Production of charmed particles at the CERN intersecting storage rings in events triggered by an electron

Abstract Production of charmed particles has been investigated at √ s = 63 GeV usi ng the Lampshade Magnet detector triggered by electrons and positrons emitted at 30% from the ISR beam axis. The results of a search for Λ c and Λ c signals in the K − pπ + and K + p π − channels are presented. Cross sections for the reactions pp → D Λ c X and pp → Λ c Λ c X, and upper limits. for pp → D D X, are evaluated under various models and compared with other values obtained at the ISR.