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Investigating the hadron nature of high-energy photons with PeVatrons
by Giuseppe Di Sciascio
Submission summary
| Authors (as registered SciPost users): | Giuseppe Di Sciascio |
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| Preprint Link: | scipost_202410_00058v1 (pdf) |
| Date submitted: | 2024-10-28 14:33 |
| Submitted by: | Di Sciascio, Giuseppe |
| Submitted to: | SciPost Physics Proceedings |
| Proceedings issue: | 22nd International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2024) |
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| Academic field: | Physics |
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| Approach: | Experimental |
Abstract
In high energy Gamma-Ray Astronomy with shower arrays the most discriminating signature of the photon-induced showers against the background of hadron-induced cosmic-ray is the content of muons in the observed events. In the electromagnetic $\gamma$-showers the muon production is mainly due to the photo-production of pions followed by the decay $\pi\to\mu\nu$, with a small relative probability of order $\alpha$ ($\simeq$ 1/137). Therefore, the number of muons is typically a few percent of that in a hadron showers where muons are abundantly generated by charged pions decay.\\ In high energy photo-production process the photon exhibits an internal structure which is very similar to that of hadrons. Indeed, photon-hadron interactions can be understood if the physical photon is viewed as a superposition of a bare photon and an accompanying small hadronic component which feels conventional hadronic interactions.\\ Information on photo-production $\gamma$p and $\gamma\gamma$ cross-sections are limited to $\sqrt{s}\leq$ 200 GeV from data collected at HERA. Starting from $E_{lab}\approx$100 TeV the difference between different extrapolations of the cross sections increases to more than 50\% at $E_{lab}\approx$10$^{19}$ eV, with important impact on a number of shower observables and on the selection of the photon-initiated air showers. \\ Recently, the LHAASO experiment opened the PeV-sky to observations detecting 40 PeVatrons in a background-free regime starting from about $E_{lab}\approx$ 100 TeV. This result provides a beam of pure high energy primary photons allowing to measure for the first time the photo-production cross section even at energies not explored yet. The future air shower array SWGO in the Southern Hemisphere, where the existence of Super-Pevatrons emitting photons well above the PeV is expected, could extend the study of the hadron nature of the photons in the PeV region.\\ In this contribution the opportunity for a measurement of the photo-production cross section with air shower arrays is presented and discussed.