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 (>100TeV) 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.