Ultra High Energy Cosmic Particles Research Articles

Ultra High Energy Cosmic Particles observation from space: Perspectives for next-generation experiments

After the Pierre Auger Observatory, it is likely that space-based experiments will be required for next-generation studies of Ultra-High Energy Cosmic Particles. An overview of this challenging task is presented, emphasising the path and the intermediate steps required to make this challenging task a reality.

Frequency spectrum of Cherenkov radiation and radioastronomical method for measuring the flux of ultrahigh-energy cosmic particles

The frequency spectrum of a radio pulse generated by a cascade shower in the Moon’s regolith has been calculated with the inclusion of the transverse sizes of the shower and the inhomogeneous distribution of excess electrons over the disc radius. The character of the spectrum differs significantly from the previous results that were obtained by E. Zas et al., Phys. Rev. D 45, 362 (1992), and J. Alvarez-Munis et al., astro-ph/0003315, and were more recently used by T. H. Hankins et al., Mon. Not. R. Astron. Soc. 283, 1027 (1996); P. W. Gorham et al., astro-ph/9906504; and P. W. Gorham et al., astro-ph/0310232. The maximum-intensity region lies in a range of 500–600 MHz. In a frequency range of 1.5–2 GHz, the radiation intensity decreases by several orders of magnitude. This seems to be one of the causes of the absence of events in experimental works of T. H. Hankins et al., Mon. Not. R. Astron. Soc. 283, 1027 (1996); P. W. Gorham et al., astro-ph/9906504; and P. W. Gorham et al., astro-ph/0310232, which closed Z-burst models.

FORTE satellite constraints on ultrahigh energy cosmic particle fluxes

The FORTE (Fast On-orbit Recording of Transient Events) satellite records bursts of electromagnetic waves arising from near the Earth's surface in the radio frequency (rf) range of 30 to 300 MHz with a dual polarization antenna. We investigate the possible rf signature of ultrahigh energy cosmic-ray particles in the form of coherent Cherenkov radiation from cascades in ice. We calculate the sensitivity of the FORTE satellite to ultrahigh energy neutrino (UHE $\ensuremath{\nu})$ fluxes at different energies beyond the Greisen-Zatsepin-Kuzmin cutoff. Some constraints on supersymmetry model parameters are also estimated due to the limits that FORTE sets on the UHE neutralino flux. The FORTE database consists of over 4 million recorded events to date, including in principle some events associated with UHE $\ensuremath{\nu}.$ We search for candidate FORTE events in the period from September 1997 to December 1999. The candidate production mechanism is via coherent VHF radiation from a UHE $\ensuremath{\nu}$ shower in the Greenland ice sheet. We demonstrate a high efficiency for selection against lightning and anthropogenic backgrounds. A single candidate out of several thousand raw triggers survives all cuts, and we set limits on the corresponding particle fluxes assuming this event represents our background level.

Ultra high energy cosmic ray sources and experimental results

Here we discuss the latest developments in the debate, where the ultrahigh energy cosmic ray particles come from. In this brief review, we emphasize the predictions that necessarily follow from the various concepts proposed. We discuss both sources and propagation, and spend some space on the by now most conservative model, giant radio galaxies and their hot spots and jets, because it allows more steps in the reasoning to be checked, and is more tightly constrained than any other model. It has survived about forty years of debate already. We summarize the task ahead of us at the end, including the development of new technologies to observe ultra high energy cosmic rays, e.g., with the radio emission of air showers, which may lead to an alternative to the fluorescence detectors with their small duty cycle. Due to HiRes, AUGER, and the plans for EUSO, the future is bright, and the ultra high energy cosmic ray particles may yet allow us to explore new physics.