%AAab, A.%AAbreu, P.%AAglietta, M.%AAlbury, J.%AAllekotte, I.%AAlmela, A.%AAlvarez Castillo, J.%AAlvarez-Muñiz, J.%AAnastasi, G.%AAnchordoqui, L.%AAndrada, B.%AAndringa, S.%AAramo, C.%AAraújo Ferreira, P.%AAsorey, H.%AAssis, P.%AAvila, G.%ABadescu, A.%ABakalova, A.%ABalaceanu, A.%ABarbato, F.%ABarreira Luz, R.%ABecker, K.%ABellido, J.%ABerat, C.%ABertaina, M.%ABertou, X.%ABiermann, P.%ABister, T.%ABiteau, J.%ABlanco, A.%ABlazek, J.%ABleve, C.%ABoháčová, M.%ABoncioli, D.%ABonifazi, C.%ABonneau Arbeletche, L.%ABorodai, N.%ABotti, A.%ABrack, J.%ABretz, T.%ABriechle, F.%ABuchholz, P.%ABueno, A.%ABuitink, S.%ABuscemi, M.%ACaballero-Mora, K.%ACaccianiga, L.%ACalcagni, L.%ACancio, A.%ACanfora, F.%ACaracas, I.%ACarceller, J.%ACaruso, R.%ACastellina, A.%ACatalani, F.%ACataldi, G.%ACazon, L.%ACerda, M.%AChinellato, J.%AChoi, K.%AChudoba, J.%AChytka, L.%AClay, R.%ACobos Cerutti, A.%AColalillo, R.%AColeman, A.%AColuccia, M.%AConceição, R.%ACondorelli, A.%AConsolati, G.%AContreras, F.%AConvenga, F.%ACovault, C.%ADasso, S.%ADaumiller, K.%ADawson, B.%ADay, J.%Ade Almeida, R.%Ade Jesús, J.%Ade Jong, S.%ADe Mauro, G.%Ade Mello Neto, J.%ADe Mitri, I.%Ade Oliveira, J.%Ade Oliveira Franco, D.%Ade Souza, V.%ADebatin, J.%Adel Río, M.%ADeligny, O.%ADhital, N.%ADi Matteo, A.%ADíaz Castro, M.%ADobrigkeit, C.%AD’Olivo, J.%ADorosti, Q.%Ados Anjos, R.%ADova, M.%AEbr, J.%AEngel, R.%AEpicoco, I.%AErdmann, M.%AEscobar, C.%AEtchegoyen, A.%AFalcke, H.%AFarmer, J.%AFarrar, G.%AFauth, A.%AFazzini, N.%AFeldbusch, F.%AFenu, F.%AFick, B.%AFigueira, J.%AFilipčič, A.%AFreire, M.%AFujii, T.%AFuster, A.%AGalea, C.%AGalelli, C.%AGarcía, B.%AGarcia Vegas, A.%AGemmeke, H.%AGesualdi, F.%AGherghel-Lascu, A.%AGhia, P.%AGiaccari, U.%AGiammarchi, M.%AGiller, M.%AGlombitza, J.%AGobbi, F.%AGolup, G.%AGómez Berisso, M.%AGómez Vitale, P.%AGongora, J.%AGonzález, N.%AGoos, I.%AGóra, D.%AGorgi, A.%AGottowik, M.%AGrubb, T.%AGuarino, F.%AGuedes, G.%AGuido, E.%AHahn, S.%AHalliday, R.%AHampel, M.%AHansen, P.%AHarari, D.%AHarvey, V.%AHaungs, A.%AHebbeker, T.%AHeck, D.%AHill, G.%AHojvat, C.%AHörandel, J.%AHorvath, P.%AHrabovský, M.%AHuege, T.%AHulsman, J.%AInsolia, A.%AIsar, P.%AJohnsen, J.%AJurysek, J.%AKääpä, A.%AKampert, K.%AKeilhauer, B.%AKemp, J.%AKlages, H.%AKleifges, M.%AKleinfeller, J.%AKöpke, M.%AKukec Mezek, G.%ALago, B.%ALaHurd, D.%ALang, R.%ALeigui de Oliveira, M.%ALenok, V.%ALetessier-Selvon, A.%ALhenry-Yvon, I.%ALo Presti, D.%ALopes, L.%ALópez, R.%ALópez Casado, A.%ALorek, R.%ALuce, Q.%ALucero, A.%AMachado Payeras, A.%AMalacari, M.%AMancarella, G.%AMandat, D.%AManning, B.%AManshanden, J.%AMantsch, P.%AMariazzi, A.%AMariş, I.%AMarsella, G.%AMartello, D.%AMartinez, H.%AMartínez Bravo, O.%AMastrodicasa, M.%AMathes, H.%AMatthews, J.%AMatthiae, G.%AMayotte, E.%AMazur, P.%AMedina-Tanco, G.%AMelo, D.%AMenshikov, A.%AMerenda, K.-D.%AMichal, S.%AMicheletti, M.%AMiramonti, L.%AMockler, D.%AMollerach, S.%AMontanet, F.%AMorello, C.%AMostafá, M.%AMüller, A.%AMuller, M.%AMüller, S.%AMussa, R.%AMuzio, M.%ANamasaka, W.%ANellen, L.%ANiculescu-Oglinzanu, M.%ANiechciol, M.%ANitz, D.%ANosek, D.%ANovotny, V.%ANožka, L.%ANucita, A%ANúñez, L.%APalatka, M.%APallotta, J.%APanetta, M.%APapenbreer, P.%AParente, G.%AParra, A.%APech, M.%APedreira, F.%APȩkala, J.%APelayo, R.%APeña-Rodriguez, J.%APerez Armand, J.%APerlin, M.%APerrone, L.%APeters, C.%APetrera, S.%APierog, T.%APimenta, M.%APirronello, V.%APlatino, M.%APont, B.%APothast, M.%APrivitera, P.%AProuza, M.%APuyleart, A.%AQuerchfeld, S.%ARautenberg, J.%ARavignani, D.%AReininghaus, M.%ARidky, J.%ARiehn, F.%ARisse, M.%ARistori, P.%ARizi, V.%ARodrigues de Carvalho, W.%ARodriguez Rojo, J.%ARoncoroni, M.%ARoth, M.%ARoulet, E.%ARovero, A.%ARuehl, P.%ASaffi, S.%ASaftoiu, A.%ASalamida, F.%ASalazar, H.%ASalina, G.%ASanabria Gomez, J.%ASánchez, F.%ASantos, E.%ASantos, E.%ASarazin, F.%ASarmento, R.%ASarmiento-Cano, C.%ASato, R.%ASavina, P.%ASchäfer, C.%AScherini, V.%ASchieler, H.%ASchimassek, M.%ASchimp, M.%ASchlüter, F.%ASchmidt, D.%AScholten, O.%ASchovánek, P.%ASchröder, F.%ASchröder, S.%ASciutto, S.%AScornavacche, M.%AShellard, R.%ASigl, G.%ASilli, G.%ASima, O.%AŠmída, R.%ASommers, P.%ASoriano, J.%ASouchard, J.%ASquartini, R.%AStadelmaier, M.%AStanca, D.%AStanič, S.%AStasielak, J.%AStassi, P.%AStreich, A.%ASuárez-Durán, M.%ASudholz, T.%ASuomijärvi, T.%ASupanitsky, A.%AŠupík, J.%ASzadkowski, Z.%ATaboada, A.%ATaborda, O.%ATapia, A.%ATimmermans, C.%ATobiska, P.%ATodero Peixoto, C.%ATomé, B.%ATorralba Elipe, G.%ATravaini, A.%ATravnicek, P.%ATrimarelli, C.%ATrini, M.%ATueros, M.%AUlrich, R.%AUnger, M.%AUrban, M.%AVaclavek, L.%AValdés Galicia, J.%AValiño, I.%AValore, L.%Avan Vliet, A.%AVarela, E.%AVargas Cárdenas, B.%AVásquez-Ramírez, A.%AVeberič, D.%AVentura, C.%AVergara Quispe, I.%AVerzi, V.%AVicha, J.%AVillaseñor, L.%AVink, J.%AVorobiov, S.%AWahlberg, H.%AWatson, A.%AWeber, M.%AWeindl, A.%AWiencke, L.%AWilczyński, H.%AWinchen, T.%AWirtz, M.%AWittkowski, D.%AWundheiler, B.%AYushkov, A.%AZapparrata, O.%AZas, E.%AZavrtanik, D.%AZavrtanik, M.%AZehrer, L.%AZepeda, A.%AZiolkowski, M.%AZuccarello, F.%Anull Ed.%BJournal Name: The European Physical Journal C; Journal Volume: 80; Journal Issue: 8 %D2020%I %JJournal Name: The European Physical Journal C; Journal Volume: 80; Journal Issue: 8 %K %MOSTI ID: 10293509 %PMedium: X %TDirect measurement of the muonic content of extensive air showers between $$\mathbf { 2\times 10^{17}}$$ and $$\mathbf {2\times 10^{18}}~$$eV at the Pierre Auger Observatory %XAbstract The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between $$2\times 10^{17}$$ 2 × 10 17 and $$2\times 10^{18}$$ 2 × 10 18 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at $$10^{{17.5}}\, {\mathrm{eV}} $$ 10 17.5 eV and $$10^{{18}}\, {\mathrm{eV}} $$ 10 18 eV . We find that, for the models to explain the data, an increase in the muon density of $$38\%$$ 38 % $$\pm 4\% (12\%)$$ ± 4 % ( 12 % ) $$\pm {}^{21\%}_{18\%}$$ ± 18 % 21 % for EPOS-LHC , and of $$50\% (53\%)$$ 50 % ( 53 % ) $$\pm 4\% (13\%)$$ ± 4 % ( 13 % ) $$\pm {}^{23\%}_{20\%}$$ ± 20 % 23 % for QGSJetII-04 , is respectively needed. %0Journal Article