Muon puzzle in cosmic ray experiments and its possible solution

The term “muon puzzle” was formulated at International Symposium on Future Directions in UHECR Physics in CERN 13–16 February 2012. In this paper, various aspects of muon puzzle are considered. Obtained experimental data can be divided into two types: muon bundle excess compared to simulations which is increasing with the increase of primary particle energy, and the excess of very-high-energy muons ( > 100 TeV ) in the muon energy spectrum. One of the possible (and realistic) solutions of the muon puzzle is the hypothesis about production of blobs of quark-gluon matter with large orbital momentum in nucleus–nucleus interactions at energies more than several PeV. Possibilities of the check of this hypothesis are discussed.