We present the measurement of two event samples induced by atmospheric v(μ) of average energy Ē(ν) ~ 4 GeV. In the first sample, a neutrino interacts inside the MACRO detector producing an upward-going muon leaving the apparatus. The ratio of the number of observed to expected events is 0.57 ± 0.05(stat) ± 0.06(syst) ± 0.14(theor) with an angular distribution similar to that expected from the Bartol atmospheric neutrino flux. The second is a mixed sample of internally produced downward-going muons and externally produced upward-going muons stopping inside the detector. These two subsamples are selected by topological criteria; the lack of timing information makes it impossible to distinguish stopping from downgoing muons. The ratio of the number of observed to expected events is 0.71 ± 0.05(stat) ± 0.07(syst) ± 0.18(theor). The observed deficits in each subsample is in agreement with neutrino oscillations, although the significance is reduced by the large theoretical errors. However, the ratio of the two samples causes a large cancellation of theoretical and of some systematic errors. With the ratio, we rule out the no-oscillation hypothesis at 95% c.1. Furthermore, the ratio tests the pathlength dependence of possible oscillations. The data of both samples and their ratio favor maximal mixing and Δm2 ~ 10-3-10-2 eV2. These parameters are in agreement with our results from upward throughgoing muons, induced by v(μ) of much higher energies.
Low energy atmospheric muon neutrinos in MACRO / Ambrosio, M., Antolini, R., Auriemma, G., Bakari, D., Baldini, A., Barbarino, G.C., Barish, B.C., Battistoni, G., Bellotti, R., Bemporad, C., Bernardini, P., Bilokon, H., Bisi, V., Bloise, C., Bower, C., Brigida, M., Bussino, S., Cafagna, F., Calicchio, M., Campana, D.l., et al.. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - STAMPA. - 478:1-3(2000), pp. 5-13. [10.1016/S0370-2693(00)00267-7]
Low energy atmospheric muon neutrinos in MACRO
Giglietto, N.;
2000
Abstract
We present the measurement of two event samples induced by atmospheric v(μ) of average energy Ē(ν) ~ 4 GeV. In the first sample, a neutrino interacts inside the MACRO detector producing an upward-going muon leaving the apparatus. The ratio of the number of observed to expected events is 0.57 ± 0.05(stat) ± 0.06(syst) ± 0.14(theor) with an angular distribution similar to that expected from the Bartol atmospheric neutrino flux. The second is a mixed sample of internally produced downward-going muons and externally produced upward-going muons stopping inside the detector. These two subsamples are selected by topological criteria; the lack of timing information makes it impossible to distinguish stopping from downgoing muons. The ratio of the number of observed to expected events is 0.71 ± 0.05(stat) ± 0.07(syst) ± 0.18(theor). The observed deficits in each subsample is in agreement with neutrino oscillations, although the significance is reduced by the large theoretical errors. However, the ratio of the two samples causes a large cancellation of theoretical and of some systematic errors. With the ratio, we rule out the no-oscillation hypothesis at 95% c.1. Furthermore, the ratio tests the pathlength dependence of possible oscillations. The data of both samples and their ratio favor maximal mixing and Δm2 ~ 10-3-10-2 eV2. These parameters are in agreement with our results from upward throughgoing muons, induced by v(μ) of much higher energies.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
