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4 th Round Table, December 16 - 17, 2011. What we do know about cosmic rays at energies above 10 15 eV?. A.A.Petrukhin. National Research Nuclear University MEPhI, Russia. Contents. 1. Introduction. 2. How these CR are investigated. 3. Results and questions.
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4th Round Table, December 16 - 17, 2011 What we do know about cosmic rays at energies above 1015 eV? A.A.Petrukhin National Research Nuclear University MEPhI, Russia Contents 1. Introduction. 2. How these CR are investigated. 3. Results and questions. 4. New approach to CR investigations. 5. NEVOD-DÉCOR experiment. 5. Further steps. 6. Conclusion.
Introduction Why these energies are interesting? 1015 eV in p-p – interactions corresponds to ~ 1 TeV in the center-of-mass system. Interval 1015 – 1017 eV corresponds to LHC energies 1.4 – 14 TeV. There are no direct measurements of CR energy spectrum and mass composition above 1015 eV. In indirect experiments above 1015 eV changes in CR energy spectrum and mass composition have been observed.
Extensive Air Shower (EAS) • EAS– the single source about PCR at energies above 1015 eV. • EAS consists of hadrons, muons, electrons, positrons, photons, neutrinos. • EASradiates Cherenkov fluorescent, radio, acoustic radiations.
Fermi LAT Pierre Auger Observatory AGASA 0 4km AMS2 1 particle/m2 s ~ 5104 m2 KASCADE Direct measurements Ground based measurements 50 km 100 km2 “Knee” 1 particle/m2 year “Ankle” 1 particle/ km2 year 3000 km2 1 particle/ km2 century
CR mass composition at low energies < lnA > 1.5
Existing explanation of CR spectrum Jörg R. Hörandel, 2007
Conclusion - 1 Satisfactory description of primary CR in the whole measured interval of energies is absent, especially at highest energies. (May be any processes around BH are sources of these CR?) There are contradictions between different mass composition measurements.. One of possible reasons is a short dynamic interval of measured energies (~ 102) by EAS detectors. Therefore the development of new approaches to CR investigations which can give new information in a wide energy interval is required.
Inclined EAS detection(local muon density measurements) Advantages: - practically pure muon component; - large area of showers, which increases with energy; - strong dependence of EAS energy on zenith angle.
μ-EAS transverse section VS zenith angle Number of detected EAS depends on: array dimensions shower dimensions
Traditional EAS detection technique (E ~ 1018 eV) ~ 500 m EAS counters (~ 1 m2)
Local muon density spectra detection technique E ~ 1018 eV, θ=80º Muon detector ~ 10 km
Contribution of primary energies at different zenith angles Wide angular interval – very wide range of primary energies !
New technique of Local Muon Density Spectra was realized by means of Experimental complex NEVOD-DECOR Russian-Italian Collaboration National Research Nuclear University MEPhI, Russia Istituto di Fisica dello Spazio Interplanetario, INAF, Torino, Italy Dipartimento di Fisica Generale dell’ Universita di Torino , Italy
General view of NEVOD-DECOR complex Coordinate-tracking detector DECOR (~115 m2) Cherenkov water detector NEVOD (2000 m3) • SideSM: 8.4 m2 each • σx1 cm; σψ 1°
A typical muon bundle event in Side DECOR( 9 muons, 78 degrees) Y-projection X-projection
A “record” muon bundle event Y-projection X-projection
DECOR data. Muon bundle statistics (*) For zenith angles < 60°, only events in two sectors of azimuth angle (with DECOR shielded by the water tank) are selected.
Effective primary energy ranges Lower limit ~ 1015 eV (limited by DECOR area). Upper limit ~ 1019 eV (limited by statistics).
Local muon density spectra Low angles: around the “knee” θ = 50º : 1016 – 1017 eV Large angles: around 1018 eV θ = 65º : 1016 – 1018 eV
Conclusion - 2 A new method of EAS investigations allows investigate cosmic ray energy spectrum in very wide interval from 1015 to 1018 eV and even higher. The following results were obtained: - detection of the knee (this can be considered as energy scale calibration), - observation of the second knee, - some excess of muon bundles in comparison with predictions, which increases with energy. The last result was confirmed in fact in LHC experiment.
Discussion Apparently the change of hadron interaction model at least in multiplicity of secondary particles in nuclei-nuclei collisions has been observed. More interesting is another question: This change of multiplicity is a simple increasing of number of secondary particles (and as the consequence – number of muons) or it is a change of energy distribution in favor of high energies? Muon energy is the single parameter which is not measured at existing EAS arrays. But there are other experimental results which allow get answer this question. They were obtained in BUST and IceCube experiments..
IceCube Collaboration, 32nd ICRC, 2011, Beijing Muons in IceCube Candidate shower with a high pT muon. The cosmic ray bundle is on the left and the high pT muon is on the right.
Patrick Berghaus, 31st ICRC, 2009, Lodz IceCubemuon energy spectrum - 2009
Patrick Berghaus, Chen Xu, 32nd ICRC, 2011, Beijing IceCubemuon energy spectrum - 2011
Conclusion - 3 New(?) physics in cosmic rays: In CR experiments have been observed: - not only increasing of number of muons in EAS with the increasing of their energies, which has been confirmed in LHC experiments, - but the excess of very high energy muons (>100 TeV)! The excess of very high energy muons (>100 TeV) can be produced in decays of heavy particles (or other states of matter) with mass~ 1 Tev only. This is a new task for both cosmic ray andLHC experiments
Conclusion - 4 Measurements of local muon density spectra with coordinate detector DECOR and muon bundle energy deposit with Cherenkov water detector NEVOD compose a new promising method of the search of new processes of muon generation in cosmic rays. This experiment will start in the beginning of 2012.
