S. Ragazzi

Experimental Study of Atmospheric Neutrino Flux in the NUSEX Experiment

The fully contained events detected in the NUSEX nucleon stability experiment have been analysed to search for possible anomalies in the fluxes of atmospheric neutrinos. The measured flux of muon neutrinos is in very good agreement with predictions and no anomaly has been found in the ratio between the rate of electron and muon neutrino events.

Observation of a time modulated muon flux in the direction of Cygnus X-3

Abstract The analysis of angular and phase distribution is reported for high energy muons recorded in the NUSEX nucleon decay detector, located in the Mont Blanc tunnel at a depth of about 5000 hg of standard rock. Evidence is found for a signal correlated to the direction and time modulation of Cygnus X-3.

The NUSEX detector

Abstract We present in this paper the characteristics, trigger system and performance of the NUSEX detector, designed to study nucleon stability, running in the Mt. Blanc laboratory.

Nucleon stability, magnetic monopoles and atmospheric neutrinos in the Mont-Blanc experiment

Abstract Ten totally confined events have been found in the Mont-Blanc Nucleon Stability Experiment. While nine can be interpreted as interactions of atmospheric neutrinos, one could be a proton decay. Limits are given for nucleon stability, n- n oscillations, magnetic monopoles and monopole catalysis of nucleon decay.

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.

Search for neutrino oscillations in “Gargamelle” at SPS

Abstract The ν events collected in “Gargamelle” exposed at the CERN SPS wide band beam are reanalyzed to search for possible ν μ → ν e oscillations. No effect is found and an upper limit of 1.2 eV at 68% c.l. is determined for the mass parameters Δm = (m 1 2 − m 2 2 ) 1 2 in the case of maximum neutrino mixing. A limit on the ν μ → ν τ transition probability is also quoted, but the sensitivity is smaller.

An experimental study of the neutrino background in underground experiments on nucleon decay

Abstract In order to investigate experimentally the background induced by atmospheric neutrinos in nucleon decay experiments we have simulated very closely the expected spectrum by means of an accelerator produced neutrino beam and exposed to it a test module of a fine train calorimeter. Two runs have been performed with the detector axis placed at 0° and 45° with respect to the neutrino beam direction, and a total of 400 events have been detected and measured. The background induced by atmospheric neutrinos into various nucleon decay channels has been deduced from these data. These results can be applied to the present or planned nucleon decay experiments.

Multielement Proportional Chamber for 136Xe ββ decay

Abstract A Multielement Proportional Chamber designed to investigate ββ decay of 136 Xe is described. The detector consists of 61 cells. arranged in a honeycomb structure. Each cell is 80 cm long and has a hexagonal cross section of 2.5 cm side. The anodes are 20 μm diameter gold plated tungsten wires. Each cathode consists of 24 copper-beryllium wires of 100 μm diameter. This structure is mounted in a titanium vessel of 40 cm diameter and 110 cm length. In order to obtain a very low background all the materials used were selected for their low intrinsic activities. The detector is operated with Xe at 10 bar; a purification system keeps the oxygen like impurities below 0.2 ppm. The electronics consists of 61 hybrid charge sensitive preamplifiers followed by 7 bit CAMAC flash-ADCs to digitize and store the pulses. An auxiliary output of the preamplifier is used to drive a trigger module that can be preset to any configuration of total energy and/or anode pattern. The chamber, presently under test, will soon be installed in the Gran Sasso underground Laboratory for data taking. Measurements on energy resolution over several cells and on charge transport are described.