Abstract
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.
Highlights
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
Summary.—We have presented for the first time a measurement of the fluctuations in the number of muons in inclined air showers, as a function of the UHECR primary energy
Summary
Based on models of air shower development and given the gradual change of the composition in this energy range (single logarithmic dependence on energy) [8,21,22,23], the number of muons is related to the primary energy by a single power law hRμiðEÞ 1⁄4 a1⁄2E=ð1019 eVÞb; ð1Þ which can be fitted following a procedure described in the text below. The model assumes that measurements of E and Rμ follow Gaussian distributions centered at the true value, with widths given by the detector resolution sE and sμ, which are the uncertainties obtained in each individual event reconstruction [3,25]. Physical fluctuations are assumed to follow a Gaussian distribution of width σ Simulations have shown this is an acceptable approximation given the event number in each bin. The log-likelihood function is given by ln Lða; b; σ 1; ...; σ 6Þ
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