On the trace of the product of Pauli and Dirac matrices

Sarkar, Sasabindu

doi:10.1007/bf03157082

Cited by 9 publications

(8 citation statements)

References 4 publications

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“…From considerations of QCD fragmentation, 16,17,18,19 copious photons are then expected to be produced. 20,21,22 In the Z-burst scenario 23,24,25 (ZB), photons are generated via the resonant production of Z bosons by UHE neutrinos annihilating on the relic neutrino background. In more "conventional" cosmic-ray models, nuclear primaries are accelerated at suitable astrophysical sites to ultra-high energy.…”

Section: Uhe Photons As Cosmic Raysmentioning

confidence: 99%

Search for Ultra-High Energy Photons Using Air Showers

2007

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The observation of photons with energies above 10 18 eV would open a new window in cosmic-ray research, with possible impact on astrophysics, particle physics, cosmology and fundamental physics. Current and planned air shower experiments, particularly the Pierre Auger Observatory, offer an unprecedented opportunity to search for such photons and to complement efforts of multi-messenger observations of the universe. We summarize motivation, achievements, and prospects of the search for ultra-high energy photons.

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Section: Uhe Photons As Cosmic Raysmentioning

confidence: 99%

Search for Ultra-High Energy Photons Using Air Showers

2007

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“…A significant fraction of the UHE cosmic rays are predicted by these models to be photons (see e.g. [4,5]). For instance, UHE photons may be produced uniformly in the universe by the decay/annihilation of relic topological defects (TD) [11].…”

Section: Photons As Cosmic-ray Primariesmentioning

confidence: 99%

“…It should be noted that the photon flux arriving at Earth for a specific source model is subject to uncertainties arising from photon propagation: assumptions concerning the very low frequency (few MHz) radio background and inter-galactic magnetic fields must be made [4,5]. The typical range of energy loss lengths usually adopted for photons are 7-15 Mpc at 10 EeV and Average depth of shower maximum <X max > versus energy simulated for primary photons, protons and iron nuclei.…”

Section: Photons As Cosmic-ray Primariesmentioning

confidence: 99%

“…Photons are expected to dominate over nucleon primaries in non-acceleration ("top-down") models of UHE cosmic-ray origin [3,4,5] which have been invoked in particular to account for a continuation of the flux above E GZK without a spectral feature as indicated by AGASA data [6]. Thus, the determination of the photon contribution is a crucial probe of cosmic-ray source models.…”

Section: Introductionmentioning

confidence: 99%

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An upper limit to the photon fraction in cosmic rays above 1019eV from the Pierre Auger Observatory

Abraham

Aglietta

Aguirre

et al. 2007

Astroparticle Physics

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107

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An upper limit of 16% (at 95% c.l.) is derived for the photon fraction in cosmic rays with energies greater than 10 19 eV, based on observations of the depth of shower maximum performed with the hybrid detector of the Pierre Auger Observatory. This is the first such limit on photons obtained by observing the fluorescence light profile of air showers. This upper limit confirms and improves on previous results from the Haverah Park and AGASA surface arrays. Additional data recorded with the Auger surface detectors for a subset of the event sample support the conclusion that a photon origin of the observed events is not favored.

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“…Also in the Z-burst model [5], large photon fractions are predicted. Stringent upper limits to photons would disfavour many realizations of these topdown models, although some uncertainty exists in calculating the propagation of UHE photons [6].…”

Section: Cosmic-ray Photonsmentioning

confidence: 99%

Photon air showers at ultra-high energy and the photonuclear cross-section

Risse¹,

Homola

Engel³

et al. 2006

Czech J Phys

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Experimental conclusions from air shower observations on cosmic-ray photons above 10 19 eV are based on the comparison to detailed shower simulations. For the calculations, the photonuclear cross-section needs to be extrapolated over several orders of magnitude in energy. The uncertainty from the cross-section extrapolation translates into an uncertainty of the predicted shower features for primary photons and, thus, into uncertainties for a possible data interpretation. After briefly reviewing the current status of ultra-high energy photon studies, the impact of the uncertainty of the photonuclear cross-section for shower calculations is investigated. Estimates for the uncertainties in the main shower observables are provided. Photon discrimination is shown to be possible even for rapidly rising crosssections. When photon-initiated showers are identified, it is argued that the sensitivity of photon shower observables to the photonuclear cross-section can in turn be exploited to constrain the cross-section at energies not accessible at colliders. : 96.40.Pq,13.85.Tp PACS

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On the trace of the product of Pauli and Dirac matrices

Cited by 9 publications

References 4 publications

Search for Ultra-High Energy Photons Using Air Showers

Search for Ultra-High Energy Photons Using Air Showers

An upper limit to the photon fraction in cosmic rays above 1019eV from the Pierre Auger Observatory

Photon air showers at ultra-high energy and the photonuclear cross-section

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