All-particle primary energy spectrum in the 3-200 PeV energy range

TL;DR

This paper presents a detailed measurement of the cosmic-ray energy spectrum between 3 and 200 PeV, revealing a significant irregularity ('bump') at around 74 PeV, with robust analysis and minimal bias.

Contribution

It introduces a new multi-parametric event-by-event energy evaluation method using EAS simulations, achieving high accuracy and revealing a notable spectral feature.

Findings

Observed a 'bump' at ~74 PeV exceeding smooth spectrum predictions.

Achieved energy estimation accuracy of 10-15% across the studied range.

Confirmed the spectral feature is unlikely due to systematic uncertainties.

Abstract

We present all-particle primary cosmic-ray energy spectrum in the 3-200 PeV energy range obtained by a multi-parametric event-by-event evaluation of the primary energy. The results are obtained on the basis of an expanded EAS data set detected at mountain level (700 g/cm^2) by the GAMMA experiment. The energy evaluation method has been developed using the EAS simulation with the SIBYLL interaction model taking into account the response of GAMMA detectors and reconstruction uncertainties of EAS parameters. Nearly unbiased (<5%) energy estimations regardless of a primary nuclear mass with an accuracy of about 15-10% in the 3-200 PeV energy range respectively are attained. An irregularity ('bump') in the spectrum is observed at primary energies of ~74 PeV. This bump exceeds a smooth power-law fit to the data by about 4 standard deviations. Not rejecting stochastic nature of the bump completely, we examined the systematic uncertainties of our methods and conclude that they cannot be responsible for the observed feature.