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Title: F γ: A new observable for photon-hadron discrimination in hybrid air shower events

To search for ultra-high-energy photons in primary cosmic rays, air shower observables are needed that allow a good separation between primary photons and primary hadrons. In this paper, we present a new observable, F γ, which can be extracted from ground-array data in hybrid events, where simultaneous measurements of the longitudinal and the lateral shower profile are performed. The observable is based on a template fit to the lateral distribution measured by the ground array with the template taking into account the complementary information from the measurement of the longitudinal profile, i.e. the primary energy and the geometry of the shower. F γ shows a very good photon-hadron separation, which is even superior to the separation given by the well-known X max observable (the atmospheric depth of the shower maximum). At energies around 1 EeV (10 EeV), F γ provides a background rejection better than 97.8 % (99.9 %) at a signal efficiency of 50 %. Advantages of the observable F γ are its technical stability with respect to irregularities in the ground array (i.e. missing or temporarily non-operating stations) and that it can be applied over the full energy range accessible to the air shower detector, down to its threshold energy. Finally and furthermore, F γ complements nicely to X max such that both observables can well be combined to achieve an even better discrimination power, exploiting the rich information available in hybrid events.
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4]
  1. Univ. of Siegen (Germany). Dept. of Physics
  2. Univ. of Siegen (Germany). Dept. of Physics; Univ. of Paris (France). Lab. of Nuclear and High-Energy Physics (LPNHE)
  3. Univ. of Siegen (Germany). Dept. of Physics; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Univ. of Siegen (Germany). Dept. of Physics; Inst. of Technologies in Detection and Astroparticles, Buenos Aires (Argentina)
Publication Date:
Report Number(s):
LA-UR-17-29807
Journal ID: ISSN 0927-6505; TRN: US1802889
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Astroparticle Physics
Additional Journal Information:
Journal Volume: 97; Journal ID: ISSN 0927-6505
Publisher:
Elsevier
Research Org:
Univ. of Siegen (Germany); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE; German Federal Ministry of Education and Research (BMBF); Helmholtz Alliance for Astroparticle Physics (HAP) (Germany)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 79 ASTRONOMY AND ASTROPHYSICS; photons; cosmic rays; hybrid detector; lateral distribution function; LDF
OSTI Identifier:
1430011

Niechciol, M., Risse, M., Ruehl, P., Settimo, M., Younk, P. W., and Yushkov, A.. Fγ: A new observable for photon-hadron discrimination in hybrid air shower events. United States: N. p., Web. doi:10.1016/j.astropartphys.2017.10.004.
Niechciol, M., Risse, M., Ruehl, P., Settimo, M., Younk, P. W., & Yushkov, A.. Fγ: A new observable for photon-hadron discrimination in hybrid air shower events. United States. doi:10.1016/j.astropartphys.2017.10.004.
Niechciol, M., Risse, M., Ruehl, P., Settimo, M., Younk, P. W., and Yushkov, A.. 2017. "Fγ: A new observable for photon-hadron discrimination in hybrid air shower events". United States. doi:10.1016/j.astropartphys.2017.10.004. https://www.osti.gov/servlets/purl/1430011.
@article{osti_1430011,
title = {Fγ: A new observable for photon-hadron discrimination in hybrid air shower events},
author = {Niechciol, M. and Risse, M. and Ruehl, P. and Settimo, M. and Younk, P. W. and Yushkov, A.},
abstractNote = {To search for ultra-high-energy photons in primary cosmic rays, air shower observables are needed that allow a good separation between primary photons and primary hadrons. In this paper, we present a new observable, Fγ, which can be extracted from ground-array data in hybrid events, where simultaneous measurements of the longitudinal and the lateral shower profile are performed. The observable is based on a template fit to the lateral distribution measured by the ground array with the template taking into account the complementary information from the measurement of the longitudinal profile, i.e. the primary energy and the geometry of the shower. Fγ shows a very good photon-hadron separation, which is even superior to the separation given by the well-known Xmax observable (the atmospheric depth of the shower maximum). At energies around 1 EeV (10 EeV), Fγ provides a background rejection better than 97.8 % (99.9 %) at a signal efficiency of 50 %. Advantages of the observable Fγ are its technical stability with respect to irregularities in the ground array (i.e. missing or temporarily non-operating stations) and that it can be applied over the full energy range accessible to the air shower detector, down to its threshold energy. Finally and furthermore, Fγ complements nicely to Xmax such that both observables can well be combined to achieve an even better discrimination power, exploiting the rich information available in hybrid events.},
doi = {10.1016/j.astropartphys.2017.10.004},
journal = {Astroparticle Physics},
number = ,
volume = 97,
place = {United States},
year = {2017},
month = {10}
}