F. Jacquet

Observation of an excess of νe, νe events in a beam dump experiment at 400 GeV

Abstract 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.

Observation of an Excess of electron-neutrino, anti-electron-neutrino Events in a Beam Dump Experiment at 400-GeV

Abstract 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.

Observation and study of the νμe− → νμe− reaction in gargamelle at high energy

Abstract A search for the reaction ν μ + e − → ν μ + e − was made in the bubble chamber Gargamelle exposed to the wide-band neutrino beam of the CERN-SPS. Ten isolated e − were found above 2 GeV energy. All of them were emitted at an angle smaller than 1.5° with respect to the beam. The background is 0.2 ± 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) ⊗ 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.

Observation of "elastic" hyperon production by antineutrinos

Abstract The production of Λ and Σ0 hyperons by antineutrinos has been observed. These events have been used to estimate the production cross-section on protons. The result is compared with the predictions of the Cabibbo theory for the process ν p → μ + Λ .

Experimental study of the reaction νμ + e− → μ− + νe

Abstract The first observation of the reaction ν μ + e − → μ − + ν e has been made in the bubble chamber Gargamelle exposed to the CERN SPS wide-band neutrino beam. A signal of 26 ± 6 events has been found. This is 0.90 ± 0.20 times the prediction of the V - A theory.

Study of neutrino-indiced dimuon events in gargamelle at CERN SPS

Abstract 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.

High energy elastic νμ scattering off electrons in gargamelle

Abstract The reaction ν μ e → ν μ 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 64 000 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) ⊗ U(1) model for current values of sin 2 θ 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.

S-wave ππ scattering from the reaction π+p → π+pπ0π0 at 3.5 GeV/c

Abstract We have studied the 2π 0 system produced in the reaction π + p → π + p π 0 π 0 at 3.5 GeV/ c , using the heavy-liquid bubble chamber technique. The cross section of the reaction π + π − → π 0 π 0 saturates the S-wave unitarity limit around 750 MeV/ c 2 and near threshold is indicative of an I =0 S-wave scaterring length larger than expected.

Search for the decay mode ηO → πOγγ

Abstract A study of 4γ events has been made in the production reaction π + p → π + p + 4γ using a hydrogen target inside a heavy liquid bubble chamber. The analysis shows no evidence for the decay mode η O → π O γγ. With 90% of confidence, we find (η O → π O γγ)/(η O → all modes)

Further results in direct search for C violating decay mode η0 → π0e+e−

No example of this decay has been found in a sample of film containing 752 η0 → π0π+π− with π0 detected. The pictures were taken with the Ecole Polytechnique heavy liquid bubble chamber exposed to a 950 MeVc π− beam at Saclay. With 90% of confidence the decay fraction is less than 0.9 × 10−3 of all η0 decays.