The successful installation, commissioning, and operation of the Pierre Auger Observatory would not have been possible without the strong commitment and effort from the technical and administrative staff in Malargue. We are very grateful to the following agencies and organizations for financial support: Argentina-Comision Nacional de Energia Atomica, Agencia Nacional de Promocion Cientifica y Tecnologica (ANPCyT), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Gobierno de la Provincia de Mendoza, Municipalidad de Malargue, NDM Holdings and Valle Las Lenas; in gratitude for their continuing cooperation over land access; Australia-the Australian Research Council; BrazilConselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Financiadora de Estudos e Projetos (FINEP), Fundacao de Amparo a Pesquisa do Estado de Rio de Janeiro (FAPERJ), Sao Paulo Research Foundation (FAPESP) Grants No. 2019/10151-2, No. 2010/07359-6, and No. 1999/05404-3, Ministerio da Ciencia, Tecnologia, Inovacoes e Comunicacoes (MCTIC); Ministry of Education, Youth and Sports of the Czech RepublicGrants No. MSMT CR LTT18004, No. LM2015038, No. LM2018102, No. CZ.02.1.01/0.0/0.0/16_013/0001402, No. CZ.02.1.01/0.0/0.0/18_046/0016010, and No. CZ.02.1.01/0.0/0.0/17_049/0008422; France-Centre de Calcul IN2P3/CNRS, Centre National de la Recherche Scientifique (CNRS), Conseil Regional Ile-de-France, Departement Physique Nucl ' eaire et Corpusculaire (PNC-IN2P3/CNRS), Departement Sciences de l'Univers (SDU-INSU/CNRS), Institut Lagrange de Paris (ILP) Grant No. LABEX ANR-10-LABX-63 within the Investissements d'Avenir Programme Grant No. ANR11-IDEX-0004-02; Germany-Bundesministerium fur Bildung und Forschung (BMBF), Deutsche Forschungsgemeinschaft (DFG), Finanzministerium Baden-Wurttemberg, Helmholtz Alliance for Astroparticle Physics (HAP), Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF), Ministerium fur Innovation, Wissenschaft und Forschung des Landes Nordrhein-Westfalen, Ministerium fur Wissenschaft, Forschung und Kunst des Landes Baden-Wurttemberg; Italy-Istituto Nazionale di Fisica Nucleare (INFN), Istituto Nazionale di Astrofisica (INAF), Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR), CETEMPS Center of Excellence, Ministero degli Affari Esteri (MAE); Mexico-Consejo Nacional de Ciencia y Tecnologia (CONACYT) Grant No. 167733, Universidad Nacional Autonoma de Mexico (UNAM), PAPIIT DGAPA-UNAM; The Netherlands-Ministry of Education, Culture and Science, Netherlands Organisation for Scientific Research (NWO), Dutch national e-infrastructure with the support of SURF Cooperative; Poland-Ministry of Science and Higher Education, Grant No. DIR/WK/2018/11, National Science Centre, Grants No. 2013/08/M/ST9/00322, No. 2016/23/B/ST9/01635, and No. HARMONIA 5-2013/10/M/ST9/00062, UMO-2016/22/M/ST9/00198; Portugal -Portuguese national funds and FEDER funds within Programa Operacional Factores de Competitividade through Fundacao para a Ciencia e a Tecnologia (COMPETE); Romania-Romanian Ministry of Education and Research, the Program Nucleu within MCI (PN19150201/16N/2019 and PN19060102), and project PN-III-P1-1.2-PCCDI-2017-0839/19PCCDI/2018 within PNCDI III; Slovenia-Slovenian Research Agency, Grants No. P1-0031, No. P1-0385, No. I00033, No. N1-0111; Spain-Ministerio de Economia, Industria y Competitividad (FPA2017-85114-P and FPA2017-85197-P), Xunta de Galicia (ED431C 2017/07), Junta de Andalucia (SOMM17/6104/UGR), Feder Funds, RENATA Red Nacional Tematica de Astroparticulas (FPA2015-68783-REDT), and Maria de Maeztu Unit of Excellence (MDM-2016-0692); U.S.Department of Energy, Awards No. DE-AC0207CH11359, No. DE-FR02-04ER41300, No. DE-FG0299ER41107, and No. DE-SC0011689, National Science Foundation, Grant No. 0450696, The Grainger Foundation, Marie Curie-IRSES/EPLANET, European Particle Physics Latin American Network, and UNESCO.
We present the first measurement of the fluctuations in the number of muons in extensive air showers produced by ultrahigh energy cosmic rays. We find that the measured fluctuations are in good agreement with predictions from air shower simulations. This observation provides new insights into the origin of the previously reported deficit of muons in air shower simulations and constrains models of hadronic interactions at ultrahigh energies. Our measurement is compatible with the muon deficit originating from small deviations in the predictions from hadronic interaction models of particle production that accumulate as the showers develop.
Argentina-Comision Nacional de Energia Atomica
ANPCyT
Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET)
Gobierno de la Provincia de Mendoza
Municipalidad de Malargue
NDM Holdings
Valle Las Lenas
Australian Research Council
Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ)
Fundacao de Apoio a Pesquisa do Distrito Federal (FAPDF)
Financiadora de Inovacao e Pesquisa (Finep)
Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio De Janeiro (FAPERJ)
Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) 2019/10151-2 2010/07359-6 1999/05404-3
Ministerio da Ciencia, Tecnologia, Inovacoes e Comunicacoes (MCTIC)
Ministry of Education, Youth & Sports - Czech Republic MSMT CR LTT18004 LM2015038 LM2018102 CZ.02.1.01/0.0/0.0/16_013/0001402 CZ.02.1.01/0.0/0.0/18_046/0016010 CZ.02.1.01/0.0/0.0/17_049/0008422
France-Centre de Calcul IN2P3/CNRS
Centre National de la Recherche Scientifique (CNRS)
Region Ile-de-France
Departement Sciences de l'Univers (SDU-INSU/CNRS)
French National Research Agency (ANR) LABEX ANR-10-LABX-63 ANR11-IDEX-0004-02
Federal Ministry of Education & Research (BMBF)
German Research Foundation (DFG)
Finanzministerium Baden-Wurttemberg
Helmholtz Alliance for Astroparticle Physics (HAP)
Helmholtz Association
Ministerium fur Innovation, Wissenschaft und Forschung des Landes Nordrhein-Westfalen
Ministerium fur Wissenschaft, Forschung und Kunst des Landes Baden-Wurttemberg
Italy-Istituto Nazionale di Fisica Nucleare (INFN)
Istituto Nazionale Astrofisica (INAF)
Ministry of Education, Universities and Research (MIUR)
CETEMPS Center of Excellence
Ministry of Foreign Affairs and International Cooperation (Italy)
Consejo Nacional de Ciencia y Tecnologia (CONACyT) 167733
Universidad Nacional Autonoma de Mexico (UNAM), PAPIIT DGAPA-UNAM
Netherlands-Ministry of Education, Culture and Science
Netherlands Organization for Scientific Research (NWO)
Dutch national e-infrastructure
SURF Cooperative
Poland-Ministry of Science and Higher Education DIR/WK/2018/11
National Science Centre, Poland 2013/08/M/ST9/00322 2016/23/B/ST9/01635 HARMONIA 5-2013/10/M/ST9/00062 UMO-2016/22/M/ST9/00198
Portugal -Portuguese national funds
FEDER funds within Programa Operacional Factores de Competitividade through Fundacao para a Ciencia e a Tecnologia (COMPETE)
Romania-Romanian Ministry of Education and Research, the Program Nucleu within MCI PN19150201/16N/2019 PN19060102
Romania-Romanian Ministry of Educatio n and Research, the Program Nucleu within PNCDI III PN-III-P1-1.2-PCCDI-2017-0839/19PCCDI/2018
Slovenian Research Agency - Slovenia P1-0031 P1-0385 I00033 N1-0111
Spain-Ministerio de Economia, Industria y Competitividad FPA2017-85114-P FPA2017-85197-P
Xunta de Galicia European Commission ED431C 2017/07
Junta de Andalucia SOMM17/6104/UGR
European Commission
RENATA Red Nacional Tematica de Astroparticulas FPA2015-68783-REDT
Maria de Maeztu Unit of Excellence MDM-2016-0692
United States Department of Energy (DOE) DE-AC0207CH11359 DE-FR02-04ER41300 DE-FG0299ER41107 DE-SC0011689
National Science Foundation (NSF) 0450696
Grainger Foundation
Marie Curie-IRSES/EPLANET
European Particle Physics Latin American Network
UNESCO