Measurement of the UHECR energy spectrum using data from the Surface Detector of the Pierre Auger Observatory

TL;DR

This paper reports a measurement of the ultra-high-energy cosmic ray spectrum using the Pierre Auger Observatory's surface detector, employing robust, hybrid calibration methods that minimize reliance on simulations or composition assumptions.

Contribution

It introduces a new, simple, and robust method for measuring the cosmic ray spectrum using hybrid data, reducing dependence on detailed simulations and composition models.

Findings

High-statistics measurement of the UHECR spectrum

Calibration method leveraging hybrid fluorescence and surface data

Analysis of systematic uncertainties in spectrum measurement

Abstract

At the southern site of the Pierre Auger Observatory, which is close to completion, an exposure that significantly exceeds the largest forerunner experiments has already been accumulated. We report a measurement of the cosmic ray energy spectrum based on the high statistics collected by the surface detector. The methods developed to determine the spectrum from reconstructed observables are described. The energy calibration of the observables, which exploits the correlation of surface detector data with fluorescence measurements in hybrid events, is presented in detail. The methods are simple and robust, exploiting the combination of fluorescence detector (FD) and surface detector (SD) and do not rely on detailed numerical simulation or any assumption about the chemical composition. Besides presenting statistical uncertainties, we address the impact of systematic uncertainties.