Abstract
The average profiles of cosmic ray shower development as a function of atmospheric depth are measured for the first time with the Fluorescence Detectors at the Pierre Auger Observatory. The profile shapes are well reproduced by the Gaisser-Hillas parametrization at the 1% level in a 500 g/cm2 interval around the shower maximum, for cosmic rays with log(E/eV) > 17.8. The results are quantified with two shape parameters, measured as a function of energy. The average profiles carry information on the primary cosmic ray and its high energy hadronic interactions. The shape parameters predicted by the commonly used models are compatible with the measured ones within experimental uncertainties. Those uncertainties are dominated by systematics which, at present, prevent a detailed composition analysis.
Highlights
The average profiles of cosmic ray shower development as a function of atmospheric depth are measured for the first time with the Fluorescence Detectors at the Pierre Auger Observatory
The profile shapes are well reproduced by the Gaisser-Hillas parametrization at the 1% level in a 500 g/cm2 interval around the shower maximum, for cosmic rays with log(E/eV) > 17.8
The Fluorescence Detector (FD) of the Pierre Auger Observatory [1] has collected unprecedented statistics of high quality data, imaging the longitudinal profile of the electromagnetic component of showers induced by ultra-high energy cosmic rays
Summary
The Fluorescence Detector (FD) of the Pierre Auger Observatory [1] has collected unprecedented statistics of high quality data, imaging the longitudinal profile of the electromagnetic component of showers induced by ultra-high energy cosmic rays. A fiducial field of view is defined as a function of energy to ensure a uniform acceptance of most of the Xmax distribution observed in the data; for each shower track, at least 300 g/cm must be observed. This should include the Xmax position, for. The main goal of this contribution is to present a precise measurement of the shape of the longitudinal electromagnetic profile of cosmic ray showers [4], and of the remaining information that it can carry about the interactions of primary cosmic rays
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