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Publications and source records attributed to The Soudan 2 Collaboration.
The effects of oscillations of atmospheric muon neutrinos are observed in the 5.90 fiducial kiloton-year exposure of the Soudan 2 detector. An unbinned maximum likelihood analysis of the neutrino L/E distribution has been carried out using the Feldman-Cousins prescription. The probability of the no oscillation hypothesis is 5.8x10-4. The 90% confidence allowed region in the sin**(2theta), Delta m**2 plane is presented.
A search for nucleon decay into two-body final states containing K^0 mesons has been conducted using the 963 metric ton Soudan 2 iron tracking calorimeter. The topologies, ionizations, and kinematics of contained events recorded in a 5.52 kiloton-year total exposure (4.41 kton-year fiducial volume exposure) are examined for compatibility with nucleon decays in an iron medium. For proton decay into the fully visible final states μ^+K^0_s and e^+K^0_s, zero and one event candidates are observed respectively. The lifetime lower limits (τ/B) thus implied are 1.5 \times 10^{32} years and 1.2 \times 10^{32} years, respectively. Lifetime lower limits are also reported for proton decay into l^+K^0_l, and for neutron decay into νK^0_s.
A shadow of the moon, with a statistical significance of 5 sigma, has been observed in the underground muon flux at a depth of 2090 mwe using the Soudan 2 detector. The angular resolution of the detector is well described by a Gaussian with a sigma of less than 0.3 degrees. The position of the shadow confirms that the alignment of the detector is known to better than 0.15 degrees and has remained stable during ten years of data taking.
We report a measurement of the atmospheric neutrino flavor ratio, R, using a sample of quasi-elastic neutrino interactions occurring in an iron medium. The flavor ratio (tracks/showers) of atmospheric neutrinos in a 3.9 fiducial kiloton-year exposure of Soudan 2 is 0.64 +- 0.11 (stat.) +- 0.06 (syst.) of that expected. Important aspects of our main analysis have been checked by carrying out two independent, alternative analyses; one is based upon automated scanning, the other uses a multivariate approach for background subtraction. Similar results are found by all three approaches.