O. Saavedra

On the event observed in the Mont Blanc Underground Neutrino Observatory during the occurrence of supernova 1987A

We discuss here the characteristics of the event detected in the Mont Blanc Underground Neutrino Observatory on February 23, 1987, consisting of 5 interactions recorded during 7s. The measured energies of the 5 pulses, the duration of the burst, and the advance of the detection time in comparison with the first optical observations give evidence that the event can be explained in terms of detection of neutrinos emitted during the stellar collapse in the Large Magellanic Cloud.

Comments on the Two Events Observed in Neutrino Detectors during the Supernova 1987a Outburst

Before optical detection of supernova SN 1987a, two events, separated in time by 4.72 hours, have been detected in underground laboratories: the first in the Mont Blanc Underground Neutrino Observatory (UNO), the second in Kamiokande II. In this letter we wish to emphasize that these results are not contradictory from the experimental point of view, and can be explained within reasonable theoretical expectations.

The limit to the UHE extraterrestrial neutrino flux from the observations of horizontal air showers at EAS-TOP

Abstract Extensive Air Showers at large zenith angles θ > 70° (Horizontal Air Showers, HAS) are observed at the EAS-TOP array at Campo Imperatore (Gran Sasso Laboratories). The rate of these events exceeds the one due to primary cosmic rays (at this angles) and therefore these showers have to be generated by penetrating particles. Assuming that they are produced by atmospheric muons we derived the muon flux as Fμ(> 30 TeV) = 1.1 × 10−11cm−2s−1sr−1, in good agreement with the underground measurements. The upper limits for diffuse neutrino radiation from these measurements is Iν(> 105GeV) dI ν e (E 0 )/dE ν e −18 cm −2 s −1 sr −1 GeV −1 , for the resonant ( E 0 = m W 2 2m e = 6.4 × 10 6 GeV ) neutrinos.

A limit on charm produced cosmic ray muon and atmospheric neutrino fluxes

Abstract An analysis of cosmic ray muon data at high energies can be used to draw an information on charm production. An empirical model discribing experiment data is proposed. The model is based on the data on behavior of inclusive cross-sections for charm production received in accelerator experiments and ideas on charm production at high energies in the frames of some modern theoretical models based on QCD. Fluxes of neutrinos produced in the atmosphere in decays of charmed particles are calculated. These fluxes can be considered at least as an upper limit on prompt atmospheric neutrino fluxes.

On the possibility of a search for a supersymmetric channel of proton decay p→K+ν, with lifetime around 1033 years

A search for a characteristic supersymmetric channel of proton decay, p→K+ν, is discussed in the paper. From calculations of background produced by atmospheric neutrinos, the lifetime τ(p→K+ν)<3×1032 y is derived as the upper limit for possible measurements using water-Cherenkov detectors. It is shown that liquid-scintillation detectors have a much better signature for this channel of proton decay. At the same time background produced by atmospheric neutrinos with a signature of p→K+ν decay in liquid-scintillation detectors is lower and can be further suppressed using some observational criteria. The possibility of searching for p→K+ν proton decay with lifetime ∼1033 y using a 4–10 kiloton (kt) liquid-scintillation detector is discussed.

CNGS beam monitor with the LVD detector

Abstract The importance of an adequate CNGS beam monitor at the Gran Sasso Laboratory has been stressed in many papers. Since the number of internal ν μ CC and NC interactions in the various detectors will not allow to collect statistics rapidly, one should also be able to detect the ν μ CC interactions in the upstream rock. In this study, we have investigated the performances of the LVD detector as a monitor for the CNGS neutrino beam. Thanks to its wide area ( 13×11 m 2 orthogonal to the beam direction) LVD can detect about 120 muons per day originated by ν μ CC interactions in the rock. The LVD total mass is ∼2 kt . This allows to get 30 more CNGS events per day as internal (NC+CC) ν μ interactions, for a total of ∼150 events/day . A 3% statistical error can be reached in 7 days. Taking into account the time characteristics of the CNGS beam, the cosmic muon background can be reduced to a negligible level, of the order of 1.5 events/day .

Correlation Analysis of the Data Recorded by the Baksan, Kamioka, and Mont Blanc Detectors during SN 1987A

Results are presented on the correlation analysis of data recorded by the Baksan, Kamioka, and Mont Blanc underground detectors during the explosion of the SN 1987. The analysis was performed in order to reinvestigate the observations of two burst of several pulses each occurring several hours before first optical observations. The Mont Blanc computer detected a burst of five pulses about 8 hrs before the first optical observation, followed by a second burst of three pulses about 2 hrs later; Kamioka and Baksan reported observations of a burst made by eleven and five pulses, respectively, delayed by 4.7 hrs in comparison with the Mont Blanc burst. The results of the analysis strongly suggest that the event was real, occurring a few hours before the first optical observation of SN 1987A. 9 refs.

Search for nuclearites using the TL stack detector

It is shown that a thermoluminescent (TL) sheet stack detector, consisting of TL sheets and medical x-ray films, is an effective nuclearite detector. Nuclearite energy loss is not explicitly used for the estimation of the TL stack sensitivity to nuclearites, but implicitly by considering ways of energy deposition. The 90% confidence level flux limit obtained with the TL stack detector is given for a certain β-M range of nuclearites. For nuclearites of β = 10-3 at sea level and M≥2×1015 GeV c-2, the limit is 1.3×10-13 s-1 cm-2 sr-1.

THE EFFECT OF WAVELENGTH SHIFTERS ON WATER CHERENKOV DETECTORS

Abstract We report the results of a test showing that concentrations of ≈2 mg/l of wavelength shifter in water give almost the maximum efficiency of detection without losing the directionality of Cherenkov light.

Study of the low energy background radiation and the effects of the 222Rn in the LSD underground experiment

Abstract A systematic study of the low energy background radiation has been performed under several conditions in the underground experiment at Mt. Blanc laboratory. The information gathered using three different types of detectors: LSD (90 tons of liquid scintillator) with energy threshold E th > 800 KeV , Nal (5” × 5”) with E th > 220 KeV and a Radon-meter (alpha spectrometer) running at the same time, has been analyzed during long and continuous time periods. It was found that the variations in counting rate of the low energy background is due to the presence of 222Rn in the laboratory room. Three types of variations were found: 1) a correlation with the tunnel ventilation system, 2) a daily modulation and 3) a sporadic increase in the counting rate not correlated to any man-made intervention. We emphasize the importance of knowing the background and its variations in underground laboratories dedicated to low energy neutrinos and dark matter searches.