Title

Evidence for a mixed mass composition at the ‘ankle’ in the cosmic-ray spectrum

Authors

A. Aab, Universität Siegen
P. Abreu, Instituto Superior Técnico
M. Aglietta, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
E. J. Ahn, Fermi National Accelerator Laboratory
I. Al Samarai, Laboratoire de Physique Nucléaire et de Hautes Energies
I. F.M. Albuquerque, Universidade de Sao Paulo - USP
I. Allekotte, Centro Atomico Bariloche
P. Allison, The Ohio State University
A. Almela, Centro Atomico Constituyentes
J. Alvarez Castillo, Universidad Nacional Autónoma de México
J. Alvarez-Muñiz, Universidad de Santiago de Compostela
M. Ambrosio, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
G. A. Anastasi, Gran Sasso Science Institute
L. Anchordoqui, Lehman College
B. Andrada, Centro Atomico Constituyentes
S. Andringa, Instituto Superior Técnico
C. Aramo, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
F. Arqueros, Universidad Complutense de Madrid
N. Arsene, Universitatea din Bucuresti
H. Asorey, Centro Atomico Bariloche
P. Assis, Instituto Superior Técnico
J. Aublin, Laboratoire de Physique Nucléaire et de Hautes Energies
G. Avila, Pierre Auger Observatory
A. M. Badescu, University Politehnica of Bucharest
A. Balaceanu, Horia Hulubei National Institute of Physics and Nuclear Engineering
C. Baus, Karlsruhe Institute of Technology
J. J. Beatty, The Ohio State University
K. H. Becker, Bergische Universitat Wuppertal
J. A. Bellido, The University of Adelaide
C. Berat, Universite Grenoble Alpes
M. E. Bertaina, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
X. Bertou, Centro Atomico Bariloche

Document Type

Article

Publication Date

11-10-2016

Abstract

© 2016 The Author(s) We report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the ‘ankle’ at lg⁡(E/eV)=18.5–19.0 differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass A> 4. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavored as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth.

Publication Title

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

Share

COinS