12-20 July 2017
BEXCO
Asia/Seoul timezone
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Contribution

BEXCO - Room F(201/202/203/204)

[GA038] Detection of primary photons in high energy cosmic rays using v{C}erenkov imaging and surface detectors

Speakers

  • Fausto CASABURO

Primary authors

Description

lettrine[nindent=0em,lines=3]{D}iscovered by Hess during some experiments about air ionization, cosmic rays are constituted by particles coming from the space. In the past, cosmic rays allowed the development of Particle Physics; indeed, thanks to their high energy not achievable in laboratories, they enabled new particles discovery. Today, interest about this radiation concerns both Astrophysics and Particle Physics. Indeed on the one hand, their knowledge allows formulation about new models of Universe structure and evolution or to acquire new knowledge about final objects of stars evolution; on the other hand cosmic rays allows us to study fundamental processes, as for example acceleration and interaction mechanisms of particles at energies not achievable in laboratories. Although it has passed more than a century after their discovery, there are many questions to which it isn't possible to answer yet or to which there isn't certainty about formulated theories. Some examples are about objects that can accelerate particles to high energy and acceleration mechanisms; indeed, even if there are some theories, we don't have experimental certainty. Moreover, although measured in many experiments, energy spectrum shows, especially in the region called "Knee", some differences between measuring made by experiments. Since magnetic fields deflect charged particles, their observation doesn't allow to go back to the source, so in cosmic rays study it's very important $gamma$ rays observation because they aren't deflected by magnetic fields. In 1989 extit{ extbf{Whipple}} experiment allowed to observe, for the first time, $unit{TeV}$ energy $gamma$ rays coming from Crab Nebula. Thanks to many experiments made to answer questions about cosmic rays, more than 100 extit{ extbf{ac{VHE}}} $gamma$ rays sources were observed since then; 60 out of 100 have galactic origin, as for instance Supernova Remnants or Pulsars; for the rest, apart from those not identified, they have extra-galactic origin. In this perspective, extit{ extbf{ac{LHAASO}}} experiment is currently in planning phase; it will be composed by ac{LHAASO-KM2A} (it will be composed by extit{ extbf{ac{ED}}} and extit{ extbf{ac{MD}}}) to measure number and arrival time of particles, ac{LHAASO-WCDA} a water v{C}erenkov detector to study cosmic rays of energies higher than $unit[1]{TeV}$ and ac{LHAASO-WFCTA} a v{C}erenkov telescope system to measure longitudinal development of cosmic rays and to obtain information about primary cosmic rays. After the building at Daochen in China, ac{LHAASO} will allow to study the extit{"High Energy Universe"}, allowing observation of $gamma$ rays of energies in the range $unit[300]{GeV}divunit[1]{PeV}$ observing secondary particles of showers called extit{ extbf{ac{EAS}}}, result of interaction between primary particles and atmosphere. One other important experiment, currently in planning phase, it's extit{ extbf{ac{CTA}}}. It will be built in two sites, at La Palma in Spain and at Parana in Chile. It will be the biggest v{C}erenkov imaging telescope array built so far and, although using different kind of detectors, ac{CTA} final goals are the same of ac{LHAASO}. Improving instrumentation respect to current and past experiments, they will allow observations not possibile up to now and they will improve results as well. To allow observation of $gamma$ rays of energies in the range $unit[20]{GeV}divunit[300]{TeV}$, ac{CTA} will be composed by three kind of telescopes, the extit{ extbf{ac{LST}}} to make observations in the range $unit[20]{GeV}divunit[100]{GeV}$, the extit{ extbf{ac{MST}}} for observations in the range $unit[100]{GeV}divunit[10]{TeV}$ and the extit{ extbf{ac{SST}}} for observations in the range $unit[10]{TeV}divunit[300]{TeV}$. Although ac{LHAASO} and ac{CTA} will have same final goals, since they will have different detectors, they will offer distinct opportunities to Astroparticle Physics; for example, ac{LHAASO} will have a better resolution at energies higher than $unit[30]{TeV}$ and it will allow observation of high section of the sky, ac{CTA} at energies approximately $unit[1]{TeV}$ and focused about single source. Thanks to specific simulation software it's possible to simulate ac{EAS} on the basis of theoretical models and to use simulations both to study detector performances during fulfillment phase and to compare simulation results to experimental data in order to prove models during detector data acquisition; one of these software is, for example, extit{ extbf{ac{CORSIKA}}}. Since in $gamma$ astronomy experiments it's very important adrons rejection, some simulations made by ac{CORSIKA} were analyzed to compare ac{EAS} induced by protons in the range $unit[1]{GeV}divunit[1000]{GeV}$ and power law $frac{dN}{dE}propto E^{-2}$ to ac{EAS} induced by $gamma$ in the same energetic range and same power law. First of all, it was studied first interaction height of primary particles showing that, due to different values of radiation length about electromagnetic showers and interaction length about adronic showers, $gamma$ rays interact previous to protons in atmosphere; in addition, by calculating mean values of first interaction heights in the ranges $left[unit[20]{GeV}divunit[50]{GeV} ight]$, $left[unit[50]{GeV}divunit[100]{GeV} ight]$, $left[unit[100]{GeV}divunit[200]{GeV} ight]$, $left[unit[200]{GeV}divunit[350]{GeV} ight]$, $left[unit[350]{GeV}divunit[600]{GeV} ight]$ and $left[unit[600]{GeV}divunit[1000]{GeV} ight]$ it was showed that first interaction height of gamma rays is almost constant in energy; instead, due to $pp$ cross section, protons first interaction height mean values are a bit higher for energies $E