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Atmospheric Neutrinos in AMANDA-B10

The atmospheric neutrino analysis concentrated on signal purity. The distribution show on the right is from our 1997 data sample. It is consistent with expectations from atmospheric neutrinos because 1) the observed events are distributed approximately isotropically, 2) the distribution of the number of OMs participating in the event (which is correlated with energy) is consistent with a soft spectra, 3) the shape of the zenith angle distribution of events is consistent with expectation (see figure for Diffuse Flux), 4) the absolute number of events is within 30% of expectation, consistent with systematic uncertainty of the predictions, and 5) upon visual inspection, the events topology is consistent with upgoing events.
 

This skyplot below shows the event distribution of neutrino candidates. The decreasing density of points near the equator is due to the decreasing efficiency of the AMANDA-B10 detector, which looks like a narrow cylindrical tube from the side. Muons from horizontal neutrinos travel through the shortest path. Consequently, the direction is not a well determined. Since AMANDA-II is much wider, it can see horizontal neutrinos far more easily than B10.

Atm nu sky map

Here is the RA-Dec plot of atm nu events for B10 data .  There are ~300 events in the sample

 The zenith angle distribution is shown below.  Horizontal events have cos(zenith)=0, and upward vertical events have cos(zenith)= -1. Note that AMANDA has very little sensitivity to neutrino oscillations due to its relatively large energy threshold, although we have included such effects in the predicted flux.zenith angle distribution

 
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Barwick Group
School of Physical Sciences
University of California Irvine