Rationale

In diffuse neutrino searches it is almost always necessary to estimate the background due to atmospheric muons from simulation. In IceCube this has typically been done directly, by simulating air showers to ground level with CORSIKA, propagating the muons in the shower through the firn and ice with PROPOSAL to a cylindrical sampling surface surrounding the detector, and then weighting the simulated events to an assumed cosmic-ray flux. Though this method offers the highest possible precision available from the chosen simulation software, it suffers from two key inefficiencies. First, since the simulation starts with cosmic-ray primaries rather than in-ice muons, one has only loose control over the characteristics of the muon bundles that actually reach the detector. For example, if one were interested only in single muons with a few TeV of energy, one would spend quite a lot of time simulating both showers whose muons never reached the detector those that result in high-multiplicity bundles. Second, the direct approach makes it necessary to repeat the entire simulation chain in order to change aspects of the air shower simulation such as atmospheric profile or hadronic model.

An alternative approach is to de-couple the air shower simulation and muon propagation from the remainder of the simulation by constructing a parametrization of the muon flux under the ice and drawing muon bundles from the parameterized distribution. This allows one to generate specific bundle configurations and weight them properly, and also to re-weight existing simulated events to a muon flux associated with different assumptions about interactions in the atmosphere.

The parametric approach is used heavily by ANTARES in the form of their MUPAGE event generator. The work described here is an attempt to apply the technique, described in a paper by Becherini et al, to IceCube simulation.