Geology

Shower

Atomic physics

Astrophysics

Oceanography

Muon

Hadron

Ultra-high-energy cosmic ray

Thermodynamics

Particle physics

Air shower

Nuclear physics

Particle (ecology)

Pierre Auger Observatory

Nozzle

Auger

Cosmic ray

Physics

Observatory

Physical Review Letters

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.

Measurement of the Fluctuations in the Number of Muons in Extensive Air Showers with the Pierre Auger Observatory