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23 rd ECRS, 3 – 7 July 2012. Muon problem in UHECR investigations. A.A.Petrukhin, A.G.Bogdanov, R.P.Kokoulin National Research Nuclear University MEPhI, Russia. Contents : Introduction Muon number measurements Muon energy measurements Possible explanation of results Conclusion.
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23rd ECRS, 3 – 7 July 2012 Muon problem in UHECR investigations A.A.Petrukhin, A.G.Bogdanov, R.P.Kokoulin National Research Nuclear University MEPhI, Russia • Contents: • Introduction • Muon number measurements • Muon energy measurements • Possible explanation of results • Conclusion
Introduction Muon problem – the excess of muon number in UHECR experiments compared to calculations – in many talks at International Symposium on Future Detections in UHECR Physics (13 – 16 February, CERN) was discussed: A.Yushkov (Auger): “Deficit of muons in simulations, harder muon spectra in data”. P.Sokolsky: “Muon content of showers in HiRes/MIA higher than expected”. M.Fukushima: “esp. muon (hard) sector is un-healthy”. P.Lipary: “The muon problem”. etc. But really this problem begins at lower energies.
Primary Cosmic Ray Energy < 1015 eV This PCR energies correspond to muon energies < 100 TeV At these energies no serious deviations from predictions. PCR energies in the interval 1015 – 1017 eV In this interval the increasing N/Ne - ratio in EAS experiments compared to calculations is observed. This increasing can be explained by changing the mass composition in favor of heavy nuclei. This change is in a good agreement with galactic model of GR origin which is dominating model for these energies.
PCR above 1017 eV At transition from compact EAS arrays to giant ones some difficulties of comparison of experimental data obtained at different arrays appear. Of course, the best approach is to obtain necessary data in one experiment. Experiment NEVOD-DECOR (Oscar Saavedra talk at today session) gives such possibility, since the results in the interval 1015 – 3 1018 eV were obtained at a single array by the same methods of data treatment.
Low angles: around the “knee” θ = 50º : 1016 – 1017 eV Large angles: around 1018 eV θ = 65º : 1016 – 1018 eV
Results of muon energy measurements above 100 TeV
Possible decision of muon problem Apparently it is possible to develop some interaction model which can explain the excess of total number of muons. But for explanation of excess of muons with energy > 100 TeV new process of muon generation is required. Since 1999 we develop a new approach to explanation of various results of cosmic ray investigations, in which production of new massive (~ TeV) state of matter in nuclei-nuclei interaction (e.g., a blob of QGM)is considered. This approach can explain excess of both total muon number and muon number with energy > 100 TeV.
Conclusion Of course available statistics is not too big to announce that new physics in cosmic rays is discovered. But the increasing amount of new experimental data which appeared during last years gives hope that, may be, in the 2nd century the CR investigations at energies > 1015 eV will be performed on a new basis.
