Abstract
Muons produced in atmospheric cosmic ray showers account for the by far dominant part of the event yield in large-volume underground particle detectors. The IceCube detector, with an instrumented volume of about a cubic kilometer, has the potential to conduct unique investigations on atmospheric muons by exploiting the large collection area and the possibility to track particles over a long distance. Through detailed reconstruction of energy deposition along the tracks, the characteristics of muon bundles can be quantified, and individual particles of exceptionally high energy identified. The data can then be used to constrain the cosmic ray primary flux and the contribution to atmospheric lepton fluxes from prompt decays of short-lived hadrons. In this paper, techniques for the extraction of physical measurements from atmospheric muon events are described and first results are presented. The multiplicity spectrum of TeV muons in cosmic ray air showers for primaries in the energy range from the knee to the ankle is derived and found to be consistent with recent results from surface detectors. The single muon energy spectrum is determined up to PeV energies and shows a clear indication for the emergence of a distinct spectral component from prompt decays of short-lived hadrons. The magnitude of the prompt flux, which should include a substantial contribution from light vector meson di-muon decays, is consistent with current theoretical predictions. The variety of measurements and high event statistics can also be exploited for the evaluation of systematic effects. In the course of this study, internal inconsistencies in the zenith angle distribution of events were found which indicate the presence of an unexplained effect outside the currently applied range of detector systematics. The underlying cause could be related to the hadronic interaction models used to describe muon production in air showers.
| Original language | English |
|---|---|
| Pages (from-to) | 1-27 |
| Number of pages | 27 |
| Journal | Astroparticle Physics |
| Volume | 78 |
| DOIs | |
| State | Published - May 1 2016 |
| Externally published | Yes |
Funding
We acknowledge the support from the following agencies: U.S. National Science Foundation -Office of Polar Programs, U.S. National Science Foundation -Physics Division, University of Wisconsin Alumni Research Foundation, the Grid Laboratory Of Wisconsin (GLOW) grid infrastructure at the University of Wisconsin-Madison , the Open Science Grid (OSG) grid infrastructure; U.S. Department of Energy , and National Energy Research Scientific Computing Center, the Louisiana Optical Network Initiative (LONI) grid computing resources; Natural Sciences and Engineering Research Council of Canada , WestGrid and Compute/Calcul Canada; Swedish Research Council , Swedish Polar Research Secretariat , Swedish National Infrastructure for Computing (SNIC), and Knut and Alice Wallenberg Foundation , Sweden; German Ministry for Education and Research ( BMBF ), Deutsche Forschungsgemeinschaft ( DFG ), Helmholtz Alliance for Astroparticle Physics (HAP), Research Department of Plasmas with Complex Interactions (Bochum), Germany; Fonds De La Recherche Scientifique - FNRS , FWO Odysseus programme, Flanders Institute to encourage scientific and technological research in industry ( IWT ), Belgian Federal Science Policy Office ( BELSPO ); University of Oxford , United Kingdom; Marsden Fund, New Zealand; Australian Research Council ; Japan Society for Promotion of Science ( JSPS ); the Swiss National Science Foundation (SNSF), Switzerland; National Research Foundation of Korea ( NRF ); Danish National Research Foundation , Denmark ( DNRF ).
Keywords
- Atmospheric muons
- Cosmic rays
- Prompt leptons