1. Muon puzzle in cosmic ray experiments and its possible solution
RICAP 2013
Muon puzzle in cosmic ray experiments and its possible solution
Anatoly Petrukhin
National Research Nuclear University MEPhI, Moscow, Russia
Outline
Introduction
Muon bundle investigations
VHE muon investigations
Possible explanation
How to check the new approach
5. Conclusion

2. Introduction What does mean “muon puzzle”? Short answer:
Excess of muons in different experiments compared to expectations from corresponding calculations and simulations.
The term “muon puzzle” was finally formulated at International Symposium on Future Directions in UHECR Physics in CERN, February, 2012.

4. Short conclusions of talks
P. Sokolsky:
Muon content in showers in HiRes/MIA higher then expected
Pierre Auger Observatory:
Deficit of muons in simulations.
Harder muon spectra in data.
M. Fukushima:
Air shower at UHE is poorly understood, esp. muon (had) sector is un-healthy.
T. Pierog:
Discrepancy (baryon and pion spectra) between models = = Large differences in the number of muons.
P. Lipari:
The “muon problem”.

5. Muon bundle investigations

6. LEP Detectors (CERN) L3 ALEPH DELPHI
130 m depth (E  70 GeV) Hadron calorimeter, TPC 5 scintillator stations
100 m depth (E  50 GeV) Hadron calorimeter, TPC, TOF
40 m depth (E  15 GeV) Drift chambers, timing scintillators, EAS surface array

7. Multi-muon events (muon bundles)
C. Grupen et al., Nuclear Physics B (Proc. Suppl.) J. Abdallah et al., Astroparticle Physics 28 (2007) (2008) 286,
DELPHI
ALEPH

8. General view of NEVOD-DECOR complex
(Russian-Italian Project)
Coordinate-tracking detector DECOR (~115 m2)
Cherenkov water detector NEVOD (2000 m3)
Side SM: 8.4 m2 each
σx  1 cm; σψ  1°

9. A typical muon bundle event in Side DECOR ( 9 muons, 78 degrees)
Y-projection
X-projection

10. A “record” muon bundle event
Y-projection
X-projection

11. Muon bundle event (geometry reconstruction)

12. Low angles: around the “knee” Large angles: around 1018 eV

13. Muons in Auger

14. VHE (> 100 TeV) muon investigations

15. Baksan underground scintillation telescope

16. Preliminary results of muon energy spectrum investigations in Baksan Underground Scintillation Telescope (BUST) [A.G. Bogdanov et al., Astropart. Phys. 36 (2012) 224]

17. IceCube results Double Coincident CRs High pT Muons Single Showers
Bundle
Data
High pT
Muon
Double Coincident
CRs
High pT Muons
Single Showers 17

18. Patrick Berghaus, Chen Xu, 32nd ICRC, 2011, Beijing
Muon energy spectrum

19. Possible explanation

20. How to explain results of muon investigations?
Of course, excess of muon bundles can be explained by changing of interaction model (existing attempt - EPOS).
But it is more difficult to explain the excess of VHE muons, since very quick processes of muon generation are required.
Also it is necessary to explain of other unusual phenomena which were detected in cosmic rays:
unusual events in hadron experiments (halo, alignment, Centauros, penetrating cascades, etc.);
- some deviations in EAS (“young” and “old” showers, large Pt, Nm/Ne-ratio behavior, etc.).
It is important to mark that all unusual phenomena appear at primary energies between eV.

21. Possible new model
Production of blobs of quark-gluon matter (QGM) with large orbital momentum.
This model ensures two main conditions:
- threshold behavior, since for that high temperature (energy) is required;
- large cross section, since the transition from quark-quark interaction to some collective interaction of many quarks occurs:
where R, R1 and R2 are sizes of quark-gluon blobs.

22. Centrifugal barrier
Appearance of a globally polarized QGM with a large orbital angular momentum in non-central ion-ion collisions was predicted by Zuo-Tang Liang and Xin-Nian Wang.
In this case, such state of quark-gluon matter can be considered as a usual resonance with a large centrifugal barrier.
Centrifugal barrier will be large for light quarks but small for top-quarks.

23. Centrifugal barrier for different masses

24. Consequences of top-quark production
Top-quarks decay:
W –bosons decay into hadrons (~70%) and leptons (~30%).
In the first case, the increase of the number of secondary pions will lead to increasing muon number (muon multiplicity).
In the second case, the decay W  gives the excess of VHE muons in cosmic rays.

25. Muon energy spectrum

26. How to check the new approach?

27. How to check the new approach at LHC?
It is very interesting, but the first results of LHC experiments confirm the new approach.
There are a good agreement of obtained results with predictions for pp-interactions but it is observed some deviations for nuclei-nuclei interactions.
The last circumstance is very important, since in cosmic rays most part of interactions are nuclei-nuclei collisions.

29. ATLAS observes striking imbalance of jet energies in heavy ion collisions (CERN Courier, January/February 2011)
Highly asymmetric dijet event
Dijet asymmetry distributions

30. How to explain ATLAS results in frame of the considered approach?
t  W + + b
In the top-quark center-of-mass system:
Tb ~ 65 GeV, TW ~ 25 GeV.
If to take into account fly-out energy, Tb can be more than 100 GeV.
In the case, if b gives a jet and W  ~ 20 , the ATLAS experiment’s picture will be obtained.

31. How to check the new approach in CR?
There are two possibilities to check new interaction model:
detailed measurements of inclusive muon energy spectrum near and above 100 TeV (for that, IceCube and other large detectors can be used);
measurements of the energy deposit of muon bundles and changes of its behavior with increasing PCR energy (for that, NEVOD-DECOR complex must be complimented by an usual EAS array for independent evaluation of PCR energy).
This array will be constructed from Italian scintillation detectors which were used in KASCADE-Grande experiment.
This work will be fulfilled in collaboration with Torino Section of INFN (A.Chiavassa).

32. Shower array around NEVOD-DECOR

33. Expected results of muon energy deposit measurements

34. Conclusion
Considered approach of production of blobs of QGM with large orbital momentum in nuclei-nuclei interactions allows solve not only “muon puzzle” but
explain other unusual events observed in CR experiments (halo, alignment, Centauros, penetrating cascades, etc).
Seemingly, this is a good idea which with a high probability is realized in Nature.

35. Thank you for attention!