A new discovery in the realm of cosmic rays has emerged from the GRAPES-3 experiment in Ooty, India, operated by the Tata Institute of Fundamental Research. The experiment has revealed a previously unseen feature in the cosmic-ray proton spectrum at approximately 166 tera-electron-volt (TeV) energy, shedding light on the origins and behavior of these high-energy particles.
Headed by Pravata K. Mohanty, the Principal Investigator of the GRAPES-3 experiment, the study has implications for our understanding of cosmic-ray sources, acceleration mechanisms, and their propagation within our galaxy. The findings have been published in Physical Review Letters.
Cosmic rays, the most energetic particles in the universe, have been bombarding our planet from outer space for over a century. These particles enter Earth’s atmosphere, inducing a shower of various particles that reach the ground at nearly the speed of light, including electrons, photons, muons, protons, and neutrons.
Spanning an energy range from 50 TeV to just over 1 peta-electron-volt (PeV), the observed feature in the cosmic-ray proton spectrum challenges existing models and theories. This discovery could prompt a re-evaluation of our current understanding of cosmic-ray phenomena, offering new insights into their sources and acceleration processes.
The GRAPES-3 experiment utilized a dense array of plastic scintillator detectors and a large-area muon detector to collect data, resulting in a collection area thousands of times larger than space-based detectors. This allowed for a comprehensive analysis of cosmic rays above 100 TeV, where space-based measurements lack precision due to low statistics.
The observation of this new feature, positioned above 100 TeV and below the previously known ‘Knee’ at about 3 PeV, challenges the long-held single power law description of the cosmic ray spectrum. The ‘Knee’ has been regarded as the upper limit for cosmic-ray acceleration within Galactic sources for the past seven decades, and this new finding could potentially reshape our understanding of these high-energy particles.
This groundbreaking discovery opens up new avenues for research into cosmic-ray phenomena, offering a deeper understanding of their properties, origins, and behavior. The GRAPES-3 experiment’s findings mark a significant milestone in the quest to unravel the mysteries of cosmic rays and their impact on the universe.
