Search for proton decay in the Frejus experiment

The status of the Frejus experiment and the preliminary results obtained in the search for nucleon decay are discussed. A modular, fine grain tracking calorimeter was installed in the Frejus laboratory in the period extending from October 1983 to May 1985. The 3300 cubic meter underground laboratory, located in the center of the Frejus tunnel in the Alps, is covered in the vertical direction by 1600 m of rocks (4400 m w.e.). The average number of atmospheric muons in the lab is 4.2 square meters per day. The 912 ton detector is made of 114 modules, each one including eight flash chamber and one Geiger vertical planes of (6 x 6) square meters dimensions. The flash chamber (and Geiger) planes are alternatively crossed to provide a 90 deg. stereo reconstruction. No candidate for the nucleon decay into charged lepton is found in the first sample of events

Excitation des niveaux 15,1 Mev et 16,1 Mev du noyau c12 par diffusion d'électrons

The spectrum of electrons scattered at 135° from a carbon target has been studied as a function of incident electron energy. For several incident énergies between 46 and 154 MeV we have measured the elastic peak and the région of the spectrum from 13.5 to 17.5 MeV below the elastic peak. We have observed peaks corresponding to excitation of the 15.1 and 16.1 MeV levels. The cross-sections for these excitations, relative to the elastic peak, have been determined to an accuracy of the order of 15 %. The cross-section for excitation of the 15.1 MeV level falls from 2.6 x 10—32 cm2/steradian to 0.4 x 10—32 cm2/steradian as the energy increases from 46 to 100 MeV. The cross-section for excitation of the 16.1 MeV level varies little with energy, and is the order of 0.5 × 10—32 cm2/steradian for the énergies studied.Le spectre d'électrons diffusés à 135° par une cible de 12C a été étudié en faisant varier l'énergie des électrons incidents de 46 MeV à 154 MeV. Pour chaque valeur de l'énergie incidente nous avons analysé le pic élastique et la région du spectre située entre 13,5 MeV et 17,5 MeV au-dessous du pic élastique. Les pics correspondant aux niveaux de 15,1 MeV et 16,1 MeV ont été mis en évidence. Les sections efficaces, relatives à la section efficace de diffusion élastique, ont été déterminées pour ces deux niveaux avec une précision de l'ordre de 15 %. La section efficace du niveau 15,1 MeV décroît de 2,6.10—32 cm2/stéradian à 0,4 .10— 32 cm2/stéradian, quand l'énergie croît de 46 MeV à 100 MeV. La section efficace du niveau 16,1 MeV varie peu, elle est de l'ordre de 0,5.10—32 cm2/stéradian quand l'énergie varie de 62 MeV à 154 MeV

Electroproduction of pions near the Δ(1236)\Delta(1236) isobar and the form-factor GM∗(q2)G^*_M(q^2) of the (γNΔ)({\gamma} N\Delta) vertex

The cross section for inelastic electron-proton scattering was measured at incident electron energies of 1.5 to 6 GeV by magnetic analysis of the scattered electrons at angles between 10° and 35°. For invariant masses of the hardonic final state W ⩽ 1.4 GeV. the measured spectra are compared with theoretical predictions for electroproduction of the Δ(1236) isobar. The magnetic dipole transition form factor G ∗ M ( q 2 ) of the (γ N Δ)-vertex is derived for momentum transfers q 2 = 0.2 − 2.34 (GeV/ c ) 2 ard found to decrease more rapidly with q 2 than the proton form factors

Electroproduction of pions near the Δ(1236)\Delta(1236) - isobar and the form factor GM∗(q2)\mathrm{G^{∗}_M (q^2)} of the (γNΔ)\mathrm{(\gamma N \Delta)}-vertex

The cross section for inelastic electron-proton scattering was measured at incident electron energies of 1.5 to 6 GeV by magnetic analysis of the scattered electrons at angles between 10° and 35°. For invariant masses of the hardonic final state W ⩽ 1.4 GeV. the measured spectra are compared with theoretical predictions for electroproduction of the Δ(1236) isobar. The magnetic dipole transition form factor G ∗ M ( q 2 ) of the (γ N Δ)-vertex is derived for momentum transfers q 2 = 0.2 − 2.34 (GeV/ c ) 2 ard found to decrease more rapidly with q 2 than the proton form factors