New ideas about cosmic ray investigations above the knee A.A.Petrukhin National Research Nuclear University MEPhI, Moscow, Russia • Contents: • Introduction. • Cosmophysical approach. • Nuclear-physical approach. • Explanation of unusual events in CR. • Role of nuclei-nuclei interactions. • How to check new approach? • Conclusion.
Introduction • 100 years of cosmic rays and 50 years of the knee. • In the 1st paper (Kulikov & Khristiansen, 1958) both possible interpretations of the knee origin (cosmophysical and nuclear-physical) were discussed. • Both these interpretations are connectedwith problem of cosmic ray origin (galactic or extragalactic). • But the knee itself is the result of interpretation of measured EAS parameters.
Basic ideas of the existing approach EAS energy is equal to the energy of primary particle. All changes of EAS characteristics in dependence on energy are results of energy spectrum or/and composition changes only. Primary cosmic rays have galactic origin. Their acceleration and keeping in Galaxy are determined by their charge Z or/and mass A. And the following results were obtained:
Results of energy spectrum “measurements” Really, in the best case, EAS energy can be evaluated.
Results of composition “investigations” Really, N / Ne – ratio and Xmax are measured.
Some remarks • In spite of interesting ideas and numerous calculations of not one generation of scientists, a satisfactory description of changes of the energy spectrum and mass composition above the knee in frame of thecosmophysical approachhas not been found. • Experimental results of N/Ne and Xmax measurements contradict this approach. • The problem of UHE cosmic ray origin is not clear. If the sources of such particles exist in other galaxies, why they do not exist in our Galaxy?
Basic ideas of nuclear-physical approach The knee is the result of inclusion of new processes of interaction or/and production of new particles, states of matter, etc. EAS energy is not equal to primary particle energy: EEAS = E2 < E1 Naturally, in this case primary cosmic ray spectrum and composition are not changed and their sources must be the same in the whole Universe.
Two main difficulties of nuclear physical approach • Large cross section of new processes which is requiredto change the cosmic ray energy spectrum. • Many physicists speak about new physics (new particles, etc.) in TeV energy region (in the center of mass system which corresponds to PeV energy region in cosmic ray experiments) but with low cross sections: nb or pb. • Where the difference between primary particle energy and EAS energy disappears? In favor of possibility of appearance of new processes (particles, states of matter, etc.) evident numerous unusual events which were detected in various experiments at energies above the knee.
List of unusual events • In hadron experiments: halos, alignment, penetrating cascades, Centauros (Pamir-Chacaltaya); long-flying component, Anti-Centauros (Tien-Shan). • In muon experiments: excess of VHE (~ 100 TeV) single (MSU) and multiple (LVD) muons; observation of VHE muons (Japan, NUSEX), the probability to detect which is very small. • In EAS investigations (in this approach we can consider): change of EAS energy spectrum in the atmosphere, which now is interpreted as a change of primary energy spectrum. changes of behavior of N(Ne) and Xmax(Ne) dependences, which now are explained as the heaving of composition. Important: Unusual events appear at PeV energies of primary particles.
The knee as a result of new interaction In this case a difference between primary and EAS energies, so-called missing energy, appears.
What do we need to explain all unusual data? Model of hadron interactions which gives: • Threshold behaviour (unusual events appear at • several PeV only). • 2. Large cross section (to change EAS spectrum slope). • 3. Large yield of leptons (excess of VHE muons, missing energy and penetrating cascades). • 4. Large orbital (or rotational) momentum (alignment). • 5. More quick development of EAS (for increasing the Nm / Ne ratio and decreasing Xmaxelongation rate).
Possible variants • Inclusion of new super-strong interaction. • Appearance of new massive particles (supersymmetric, Higgs-bosons, relatively long-lived resonances, etc.) • Production of blobs of quark-gluon plasma (QGP) • (better to speak about quark-gluon matter (QGM), • since usual plasma is a gas but quark-gluon is a liquid). We considered the last model since it allows demonstrably explain the inclusion of new interaction.
Quark-gluon matter • Production of QGM provides main conditions: • - threshold behavior, since for that large 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 2. But for explanation of other observed phenomena a large value of orbital angular momentum is required.
Orbital angular momentum in non-central ion-ion collisions Zuo-Tang Liang and Xin-Nian Wang, PRL 94, 102301 (2005); 96, 039901 (2006)
As was shown by Zuo-Tang Liang and Xin-Nian Vang, in non-central collisions a globally polarized QGP with large orbital angular momentum which increases with energy appears. • 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 less for top-quarks or other heavy particles. Centrifugalbarrier
How EAS development is changed in frame of a new model? • Simultaneous interactions of many quarks change the energy in the center of mass system drastically: where mcnmN. At threshold energy, n ~ 4 ( - particle) • Produced -quarks take away energy GeV, and taking into account fly-out energy,t> 4mt 700 GeV (in the center of mass system). • Decays of top-quarks W –bosons decay into leptons (~30%) and hadrons (~70%); b c s u with production of muons and neutrinos.
How the energy spectrum is changed? • One part of t-quark energy gives the missing energy (e, , , ), and another part changes EAS development, especially its beginning, parameters of which are not measured. • As a result, measured EAS energy E2 will not be equal to primary particle energy E1 and the measured spectrum will be differed from the primary spectrum. 3. Transition of particles from energy E1 to energy E2 gives a bump in the energy spectrum near E2.
How measured composition is changed in frame of the new approach Since for QGM production not only high temperature (energy) but also high density is required, threshold energy for production of new state of matter for heavy nuclei will be less than for light nuclei and protons. Therefore the heavy nuclei (f.e., iron) spectrum is changed earlier than light nuclei and proton spectra!!! To compare the changes of spectra of different nuclei, very simple model was used.
Relation between primary energy E1 and measured energy E2 n = 4 t = 700 GeV
Comparison with experimental data (without straggling)
Comparison with experimental data (with 10% straggling)
Discussion of results • Energy spectrum obtained in frame of the simplest model surprisingly well describes experimental data. • Changes of composition are explained: • a sharp increase of average mass at the expense of detection of EAS from heavy nuclei, • after that slow transition to proton composition. • Results of composition changes obtained by means of N measurements are explained, too. Number of muons is increased as result of not muon production in nuclei interaction but through decays of massive particles.
EAS simulations in frame of the new approach CORSIKA (version 6.960) was used. To introduce -quarks, PYTHIA (version 6.4.22)was used. Unfortunately, PYTHIA describes pp-interactions only, but in spite of this the obtained results are impressive. The following results were obtained: - changes of various particle spectra in EAS after introduction of t-quark; - changes of inclusive muon energy spectrum; - comparison of cascades from nuclei without t-quarks and cascades from protons with t-quarks.
Explanation of the ankle appearance On the face of it, the considered approach does not explain the behavior of the energy spectrum above the ankle, but this is not so. With increasing of primary particle energy the excitation level can exceed the centrifugal barrier, and the blob of QGM will decay into light quarks.
Illustration of the ankle appearance The knee 1017 eV 1018 eV The ankle In this case, there will be no missing energy and the measured spectrum begins to return to the initial form (g = 2.7).
How to check the new approach? There are several possibilities to check new approach as in LHC experiments so in cosmic ray investigations. Of course, the most convincing results in LHC experiments can be obtained, since QGM with described characteristics (excess of t-quarks, excess of VHE muons, sharp increasing of missing energy, etc.) doubtless will be observed. However these results unlikely can be obtained in pp-interactions even at full energy 14 TeV, which correspond 1017 eV in cosmic ray experiments (for pp-interaction), since for that collisions of sufficiently heavy nuclei are required.
How to check the new approach in cosmic ray experiments? One possibility is direct measurements of various nuclei spectra in space. Changes in spectra must begin from heavy nuclei. Two other possibilities are connected with VHE muon detection: - measurements of muon energy spectrum above 100 TeV; - measurements of energy deposit of EAS muon component below and above the knee. For that, existing muon and neutrino detectors can be used: BUST, NEVOD-DECOR, Baikal, ANTARES, IceCube etc.
Preliminary results of muon energy spectrum investigations in BaksanUnderground Scintillation Telescope (BUST)http://arxiv.org/pdf/0911.1692