Abstract
The Extreme Universe Space Observatory (EUSO) on–board the Japanese Experimental Module (JEM) of the International Space Station aims at the detection of ultra high energy cosmic rays from space. The mission consists of a UV telescope which will detect the fluorescence light emitted by cosmic ray showers in the atmosphere. The mission, currently developed by a large international collaboration, is designed to be launched within this decade. In this article, we present the reconstruction of the energy of the observed events and we also address the X max reconstruction. After discussing the algorithms developed for the energy and X max reconstruction, we present several estimates of the energy resolution, as a function of the incident angle, and energy of the event. Similarly, estimates of the X max resolution for various conditions are presented.
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Notes
The Cherenkov reflection will be modelled as a Lambertian reflector with an albedo of 5 %.
A small note should be given on the peaks on GTUs 18 and 20. These peaks are identified given the very unlikely case of peaks of exactly the same amplitude within ± 2 GTUs. The condition chosen for a bin to be accepted as peak is ≥.
A complete explanation on the iteration procedure is out of the scope of this publication. The iteration will be performed by variating the shower parameters obtained through the first reconstruction run. The reconstruction will be applied backward and the detector response obtained in this way will be compared with what originally detected by JEM–EUSO. The deviation of this test from the data will define a confidence interval in the parameter space and possibly deliver a better set of parameters than what was found in the first run.
According to the standard theory the Cherenkov yield is equal to \(C_{\mathrm {Y}}(E,h) = 2 \pi \alpha \left (2 \delta - \left (\frac {m_{\mathrm {e}} c^{2}}{E}\right )^{2}\right )\left (\frac {1}{\lambda _{\min }}-\frac {1}{\lambda _{\max }}\right )\) where α is the fine structure constant, δ is n-1 (n is the refractive index), E the electron’s energy, λ min and λ max are the integration extremes.
The backscattered component is therefore not distinguishable from fluorescence and has to be corrected.
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Acknowledgments
We wish to thank the RIKEN Integrated Cluster of Clusters facility for the computer resources used for the calculations. We wish to thank the IPA program of RIKEN (Japan) for its support. This work has been partially supported by the Italian Ministry of Foreign Affairs, General Direction for the Cultural Promotion and Cooperation. We also wish to thank the original ESAF developers for their work.
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The JEM-EUSO Collaboration., Adams, J.H., Ahmad, S. et al. Performances of JEM–EUSO: energy and X max reconstruction. Exp Astron 40, 183–214 (2015). https://doi.org/10.1007/s10686-014-9427-9
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DOI: https://doi.org/10.1007/s10686-014-9427-9