A shadow of the moon, with a statistical significance of 5σ, 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 ≤ 0.3. The position of the shadow confirms that the alignment of the detector is known to better than 0.15 and has remained stable during ten years of data taking. PACS 96.40.Cd, 13.85.Tp, 96.40.Tv Typeset using REVTEX

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 have searched for nucleon decay into five two-body final states using a 4.4 kiloton-year fiducial exposure of the Soudan 2 iron tracking calorimeter. For proton decay into the fully visible final states mu (+) eta (0) and e(+) eta (0), we observe zero and one event, respectively, that satisfy our search criteria for nucleon decay. The lifetime lower limits (tau /B) thus implied are 89 x 10(30) years and 81 x 10(30) years at 90% confidence level. For neutron decay into <()over bar>eta0, we obtain the lifetime lower limit 71 x 10(30) years. Limits are also reported for neutron decay into <()over bar>pi (0), and for proton decay into <()over bar>pi (+).

A search for nucleon decay into two-body final states containing K-o 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 mu(+)K(S)(o) and e(+) K-S(o), zero and one event candidates are observed respectively. The lifetime lower limits (tau/B) thus implied are 1.5 x 10(32) yr and 1.2 x 10(32) yr, respectively. Lifetime lower limits are also reported for proton decay into l(+)K(l)(o), and for neutron decay into nu K-S(o).

We have searched for nucleon decay into five two-body final states using a 4.4 kiloton-year fiducial exposure of the Soudan 2 iron tracking calorimeter. For proton decay into the fully visible final states μ+η0 and e+η0, we observe zero and one event, respectively, that satisfy our search criteria for nucleon decay. The lifetime lower limits (τ/B) thus implied are 89×1030years and 81×1030years at 90% confidence level. For neutron decay into ν¯η0, we obtain the lifetime lower limit 71×1030years. Limits are also reported for neutron decay into ν¯π0, and for proton decay into ν¯π+. Received 7 January 2000DOI:https://doi.org/10.1103/PhysRevD.62.092003©2000 American Physical Society

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.

We have searched for the proton decay mode p --> nu K+ using the one-kiloton Soudan 2 high resolution calorimeter. Contained events obtained from a 3.56 kiloton-year fiducial exposure through June 1997 are examined for occurrence of a visible K+ track which decays at rest into mu(+)nu or pi(+)pi(0). We found one candidate event consistent with background, yielding a limit, tau/B(p --> nu K+)> 4.3 x 10(31) years at 90% CL with no background subtraction. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

The atmospheric neutrino flavour ratio measured using a 1.52 kton-year exposure of Soudan 2 is found to be 0.72 ± 0.19−0.07+0.05 relative to the expected value from a Monte Carlo calculation. The possible background of interactions of neutrons and photons produced in muon interactions in the rock surrounding the detector has been investigated and is shown not to produce low values of the ratio.

SOUDAN 2 is a 960-ton tracking calorimeter which has been constructed to search for nucleon decay and other phenomena. The full detector consists of 224 calorimeter modules each weighing 4.3 tons. The design and construction of the modules are described. The modules consist of finely segmented iron instrumented with 1 m long drift tubes of 15 mm internal diameter. The tubes enable three spatial coordinates and dE/dx to be recorded for charged particles traversing the tubes.

SOUDAN 2 is a 960-ton tracking calorimeter which has been constructed to search for nucleon decay and other phenomena. The full detector consists of 224 calorimeter modules each weighing 4.3 tons. The modules consist of finely segmented iron instrumented with 1 m long drift tubes of 15 mm internal diameter. The tubes enable three spatial coordinates and dEdx to be recorded for charged particles traversing the tubes. The spatial resolution is 0.38 cm in the x−y plane and 0.65 cm in the z, or drift, direction. The operation and performance of the modules are discussed.

The status of the Soudan 2 experiment is discussed. The detector parameters, running schedule, and physics program are presented. Limits on proton decay, the flux of highly ionizing magnetic monopoles and neutrinos from active galactic nuclei are given.

Atmospheric [nu][sub [mu]] and [nu][sub e] are created in cosmic ray interactions in the atmosphere, and can be detected in underground detectors. The Kamiokande and IMB water Cerenkov detectors have found fewer [nu][sub [mu]] interactions (relative to [nu][sub e]) than are expected. Results are usually expressed by the ratio: R[triple bond]([nu][sub [mu]]/[nu][sub [mu]]) measured ([nu][sub [mu]]/[nu][sub e]) predicted with R found to be less than 1. The Soudan 2 detector is an iron calorimeter, which has different systematic effects than the water Cerenkov counters. Results from the Frejus and NUSEX calorimeters do not suggest a deficit of [nu][sub [mu]]'s in iron, implying that perhaps there is a systematic effect in Cerenkov detectors or some unexpected nuclear effect. Here we report on a preliminary analysis of 0.5 kton-year of data in Soudan 2. We are presently analyzing our second 0.5 kt-year of data, and will present new results at the meeting.