Synopsis

Air showers from ultrahigh-energy cosmic rays

Physics 3, s26
Cascades created by cosmic rays interacting with the atmosphere provide clues about the mass composition of ultrahigh-energy cosmic rays.
Illustration: Courtesy of the Pierre Auger Observatory

The nature and origin of ultrahigh-energy ( >1018eV) cosmic rays remain a mystery. Astrophysicists hunt for clues regarding their mass composition, which, along with other properties such as the flux and arrival direction distribution, should help distinguish among the various models of the sources and propagation of cosmic rays. However, because of the low flux of ultrahigh-energy cosmic rays, the mass composition cannot be measured directly. Instead, it is inferred from measurements of the extensive air showers—the cascades of high-energy ions created when incident cosmic rays collide with atoms in the atmosphere. The atmospheric depth at which development of a shower reaches its maximum number of secondary particles depends on the mass and energy of the incident particle. Data on the depth of the maximum thus provide information about the mass composition.

The Pierre Auger Collaboration has presented in Physical Review Letters new measurements of extensive air showers from ultrahigh-energy cosmic rays. Their observations suggest a gradual increase in the average mass of cosmic rays in a region of energies around 1019eV. The data are the highest statistics measurements to date. – Stanley Brown


Subject Areas

Particles and FieldsAstrophysics

Related Articles

Dark Matter Detector Proves its Sensitivity
Cosmology

Dark Matter Detector Proves its Sensitivity

A new sensor provides world-leading sensitivity for distinguishing lightweight dark matter from background noise. Read More »

Looking for Dark Matter in Neutron Star Light
Cosmology

Looking for Dark Matter in Neutron Star Light

Radio observations of neutron stars demonstrate a way to search for axions through their expected conversion to electromagnetic waves in a star’s magnetic field. Read More »

Dark Matter Detector Delivers Enigmatic Signal
Particles and Fields

Dark Matter Detector Delivers Enigmatic Signal

Are the excess events detected by the XENON1T experiment a harbinger of new physics or a mundane background? Read More »

More Articles