Aab, A.Zepeda, A.Álvarez Muñiz, JaimeParente Bermúdez, Gonzalo2024-02-092024-02-092021-02-12Aab et al. (Pierre Auger Collaboration), Measurement of the Fluctuations in the Number of Muons in Extensive Air Showers with the Pierre Auger Observatory, Phys. Rev. Lett. 126, 1520020031-9007http://hdl.handle.net/10347/32680We 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.engPublished by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.http://creativecommons.org/licenses/by-nc-nd/4.0/Particle interactionsParticle productionStrong interactionjournal article10.1103/PhysRevLett.126.1520021079-7114open access