GZK cutoff

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GZK cutoff (after the physicists Kenneth Greisen , Georgi Sazepin and Wadim Kusmin , who they calculated in 1966) is the upper limit ( cutoff ) for the energy of cosmic rays from very distant sources.

Charged particles of very high energy “see” the photons ( ) of the cosmic background radiation strongly blue-shifted and can be scattered by them. Besides elastic scattering, there are two inelastic processes for protons (p), also those bound in atomic nuclei

and

with an energy threshold of 6 × 10 19  eV for the generation of the delta resonance ( ), which in turn decays into a proton or neutron and a charged ( ) or neutral ( ) pion . The proton loses about 20% of its energy and changes its direction. If the energy of the proton is still above this threshold, the reaction can take place again. For sources that are very distant (> 100 million light years ), the probability of getting through without a shock is very low. One speaks of GZK suppression or GZK effect.

At the highest energies, cosmic radiation does not only consist of protons, but also a mixture of different atomic nuclei, but these are also slowed down by interaction with the cosmic background radiation. The GZK effect is therefore expected to be independent of the exact composition of the cosmic radiation, the extent and threshold energy of the GZK suppression depending on the only imprecisely known mass composition of the cosmic radiation.

The experimental results with regard to the highest energy cosmic rays initially appeared contradictory. While the AGASA experiment at the University of Tokyo claims to have registered particles above the GZK energy, the data from the HiRes collaboration are compatible with the GZK cutoff. The Pierre Auger Observatory and the Telescope Array Project have since confirmed that there is indeed a break in the energy spectrum of cosmic rays, the energy of which corresponds to the expected GZK cutoff within the scope of the measurement and prediction uncertainties.

The extremely rare events that were measured at energies beyond the GZK limit must have come from sources close by. In fact, the observed directional distribution correlates with potential sources known from the optical field. However, it is not yet clear whether the GZK cutoff is actually the main reason why significantly fewer particles reach the earth at higher energies. An alternative explanation is that the maximum energy of the cosmic ray sources could be of a similar energy. The current upgrade of the Pierre Auger Observatory is intended to increase its measurement accuracy to such an extent that this scenario can be distinguished from the GZK cutoff.

Exact measurements in the area of ​​the GZK energy can also be used to test theories for as yet unknown physical effects, for example scenarios of loop quantum gravity . This predicts a higher energy threshold than 6 × 10 19  eV.

References

  1. ↑ Kenneth Greisen: End to the Cosmic-Ray Spectrum? . In: Physical Review Letters . 16, No. 17, 1966, pp. 748-750. doi : 10.1103 / PhysRevLett.16.748 .
  2. ^ GT Zatsepin, Kuz'min, VA: Upper Limit of the Spectrum of Cosmic Rays . In: Journal of Experimental and Theoretical Physics Letters . 4, 1966, pp. 78-80. bibcode : 1966JETPL ... 4 ... 78Z .
  3. ^ A b The Pierre Auger Collaboration: The Pierre Auger Observatory Upgrade - Preliminary Design Report , 2016, arxiv : 1604.03637 [astro-ph]
  4. ↑ M. Takeda et al .: Energy determination in the Akeno Giant Air Shower Array experiment Astropart, Phys. 19 (2003) 447-462, arxiv : astro-ph / 0209422v3
  5. ^ HiRes Collaboration: First Observation of the Greisen-Zatsepin-Kuzmin Suppression Phys. Rev. Lett. 100, 101101 (2008), arxiv : astro-ph / 0703099v2
  6. ↑ The Pierre Auger Collaboration: Observation of the suppression of the flux of cosmic rays above 4x10 ^ 19eV. Phys. Rev. Lett. 101, 061101 (2008), arxiv : 0806.4302v1
  7. ^ The Telescope Array Collaboration: The Cosmic-Ray Energy Spectrum Oberved with the Surface Detector of the Telescope Array Experiment. Astrophysical Journal Letters 768 (2013) 1, arxiv : 1205.5067
  8. ^ The Pierre Auger Collaboration: Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter. Astropart.Phys. 34 (2010), pp. 314–326, arxiv : 1009.1855v2 [astro-ph]
  9. ↑ Jorge Alfaro, Gonzalo Palma: Loop Quantum Gravity and Ultra High Energy Cosmic Rays . In: Phys. Rev. D . tape 67 , 2003, p. 083003 , doi : 10.1103 / PhysRevD.67.083003 , arxiv : hep-th / 0208193 .

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