  Neutrino telescopes allow powerful probes of high-energy astrophysics and
particle physics. Their power is increased when they can isolate different
event classes, e.g., by flavor, though that is not the only possibility. Here
we focus on a new event class for neutrino telescopes: dimuons, two energetic
muons from one neutrino interaction. We make new theoretical and observational
contributions. For the theoretical part, we calculate dimuon-production cross
sections and detection prospects via deep-inelastic scattering (DIS; where we
greatly improve upon prior work) and $W$-boson production (WBP; where we
present first results). We show that IceCube should have $\simeq 130$ dimuons
($\simeq 6$ from WBP) in its current data and that IceCube-Gen2, with a higher
threshold but a larger exposure, could detect $\simeq 620$ dimuons ($\simeq 30$
from WBP) in 10 years. These dimuons are almost all produced by atmospheric
neutrinos. For the observational part, we perform a simple but conservative
analysis of IceCube public data, finding 19 candidate dimuon events. Subsequent
to our paper appearing, visual inspection of these events by the IceCube
Collaboration revealed that they are not real dimuons, but instead arise from
an internal reconstruction error that identifies some single muons crossing the
dust layer as two separate muons. To help IceCube and the broader community
with future dimuon searches, we include the updated full details of our
analysis. Together, these theoretical and observational contributions help open
a valuable new direction for neutrino telescopes, one especially important for
probing high-energy QCD and new physics.
