Synopsis: Air showers from ultrahigh-energy cosmic rays

Cascades created by cosmic rays interacting with the atmosphere provide clues about the mass composition of ultrahigh-energy cosmic rays.
Synopsis figure
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


Announcements

More Announcements »

Subject Areas

Particles and FieldsAstrophysics

Previous Synopsis

Atomic and Molecular Physics

Better timing with aluminum ions

Read More »

Next Synopsis

Superconductivity

Keep it local

Read More »

Related Articles

Synopsis: Testing Quantum Physics with Neutrinos
Quantum Physics

Synopsis: Testing Quantum Physics with Neutrinos

An experiment similar to the Bell inequality test confirms that neutrino oscillation is a quantum physics effect that is incompatible with alternative classical models. Read More »

Viewpoint: Of Gluons and Fireflies
Nuclear Physics

Viewpoint: Of Gluons and Fireflies

Improved models of gluon fluctuations within protons have been developed and applied to particle collision data, pointing to strong gluon fluctuations at high energies. Read More »

Synopsis: Solar Cycle Affects Cosmic Ray Positrons
Astrophysics

Synopsis: Solar Cycle Affects Cosmic Ray Positrons

Discrepancies in the positron content of cosmic rays measured at different times are explained by the periodic reversal of the solar magnetic field’s direction. Read More »

More Articles