Charm decays (pictured) are a particularly insidious background to DONUT neutrino
interacton identification. The charm (now indicated in red) has a decay length
comparable to that of the tau and is produced in %8.1 percent of electron and
muon neutrino interactions. Additionally, it often has similar decay
topologies. Donut physicists determine whether or not a decay is charm by
looking at the primary interaction vertex. If the vertex has more than one
charged lepton product it is dismissed from being a tau event because, due to
lepton number conservation, tau neutrinos do not interact to form other leptons.
However,if the lepton products are not identified, the event must be classified as
background. Physicists were able to estimate the approximate charm background
based on various interaction, detection and calculation parameters and determine
the probability of mistaking a tau deacy for a charm particle and use those
numbers for the overall data uncertainty. In this particular event, DONUT
analysts were able to identify an electron from the primary interaction vertex,
indicated by the green track, and thereby identify the red track as a tau (the
colors are purely used for convention's sake).
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Last updated: 6/29/01 comments