Dimuons in Neutrino Telescopes: New Predictions and First Search in IceCube*

Neutrino telescopes are 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 $\simeq 400$ dimuons ($\simeq 8$ from WBP) in its current data and that IceCube-Gen2, with a higher threshold but a larger exposure, can detect $\simeq 1200$ 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 the first candidate dimuon events (19 events).  Though some IceCube experts we consulted argue these events cannot be real dimuons, (A) these events match well all aspects of our predictions and (B) no other compelling hypotheses have been raised.  Whether these 19 events are real dimuons or some new background (or signal!), it is important to understand them.  Here we share full details to help IceCube and to attract scrutiny from the broader community. 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.