Search

The final results on the pionic annihilation of 1.6 GeV/ c antiprotons on free protons in the heavy liquid bubble chamber Gargamelle are presented here. Branching ratios of the various channels (including multi-π 0 channels) as well as multiplicity distributions for charged and neutral pions are given which are for the most part compatible with the prediction of the isospin statistical model.

The heavy liquid bubble chamber Garamelle has been used to study the rate of production of neutral pions in the pionic annihilation of 1.6 GeV/ c antiprotons on free protons. Preliminary results are presented on the relative cross-sections for most channels together with the mean π 0 multiplicity and the first moments for annihilation into 0-prongs, 2-prongs, 4-prongs and 6-prongs.

A method is presented, which has been used to determine the pion multiplicity distributions for p annihilations on free protons from a sample of events obtained in a heavy liquid bubble chamber experiment. The method uses data obtained in the experiment in question together with the usual invariance principles satisfied by strong interactions. Furthermore no particular nuclear model is assumed.

A beam dump experiment has been performed at CERN in Gargamelle using the neutrino facility to look for penetrating particles produced either directly in the beam interaction or by prompt decay of new particles. A total of 32 interactions with a visible energy greater than 10 GeV has been found, classified, aftercorrections, into 18 charged current ν μ or ν μ , 5.1 neutral current and 8.9 ν e or ν e charged current events. An excess of ν e events remains after all subtractions from any established sources. Results are presented in terms of the product of the cross section and the leptonic decay branching ratio of the possible source.

A study has been made of the individual channels that contribute to the reaction K−p → Λ0 + neutrals in the K− momentum range from 525 to 820 MeV/c. Total cross sections are presented for the K−p → Λ0η0, Σ0Σ0π0, Λ0π0, Σ0π0 and Σ0π0 π0 channels and differential cross sections for K−p → Λ0π0. The data were obtained in a heavy liquid bubble chamber experiment with an average gamma detection efficiency of 70%. Only events with all decay gammas detected were used for analysis. This is the first of a series of papers on this subject and presents the experimental technique in detail.

The reaction nu /sub mu /e to nu /sub mu /e has been investigated in the bubble chamber Gargamelle exposed to the wide-band neutrino beam of the CERN SPS. Nine electron candidates of which 0.5 are expected to be background, were found in a total statistics available of 64000 charged current neutrino events. Results are given in terms of vector and axial vector coupling constants. The present results agree with the standard SU(2)(X)U(1) model for current values of sin/sup 2/ Theta /sub w/. A critical comparison is made with the previous result based on statistics which were smaller by a factor 2.6 and which led to a rather higher cross section. (10 refs).

A search for the reaction nu /sub mu /+e/sup -/ to nu /sub mu /+e/sup -/ was made in the bubble chamber Gargamelle exposed to the wide- and neutrino beam of the CERN-SPS. Ten isolated e/sup -/ were found above 2 GeV energy. All of them were emitted at an angle smaller than 1.5 degrees with respect to the beam. The background is 0.2+or-0.2 events. Results on cross section are given in terms of vector and axial vector coupling constants. A comparison is made with the standard SU(2)(X)U (1) model: no agreement is found with the currently accepted value of the mixing angle. Possible sources other than the above reaction are discussed. (10 refs).

This letter reports a study of 117 opposite-sign and 41 like-sign dimuons, in a wide-band neutrino exposure of Gargamelle at CERN SPS. No signal is found in the μ − μ − channel. The μ − μ + channel is found to be dominated by D-meson production and decay. There is evidence in these events for missing energy which may be interpreted as an unseen neutrino. The V 0 multiplicities, K 0 /event=0.53 −0.20 +0.25 and Λ /event=0.03 −0.04 +0.06 show only evidence for charmed meson production. Information on the D-meson fragmentation function is presented. In a specific model, a rate σ (μ − μ + ) σ(μ − ) =(0.72±0.14×10 −2 is found, independent of the energy. An investigation of these events for visible D-decays sets a limit on the life-time τ D −12 s at 90% C.L.