GRAPES-3 experiment

GRAPES-3 experiment in Ooty discovers a new feature in the cosmic-ray proton spectrum at approximately 166 tera-electron-volt (TeV).

About the discovery:

• Researchers have discovered a new feature in the cosmic-ray proton spectrum at an energy level of approximately 166 tera-electron-volt (TeV).
• This discovery, covering a measurement range from 50 TeV to slightly over one peta-electron-volt (PeV), has the potential to reshape the understanding of cosmic ray origins, their acceleration processes, and their movement within the Milky Way.

About Cosmic rays:

• Cosmic rays, discovered over a century ago, are the most energetic particles in the universe.
• They consistently bombard Earth from all directions, penetrating the atmosphere and creating a cascade of secondary particles, including electrons, photons, muons, protons, and neutrons, which reach the ground at nearly light speed.
• The study of cosmic rays covers a broad energy spectrum, ranging from 10^8 to 10^20 eV.
• The flux of cosmic rays exhibits a steep decline at higher energies, traditionally following a single power-law up to the “knee” around 3 PeV.
  • This knee signifies a significant change in the energy spectrum, suggesting a limitation to Galactic cosmic-ray acceleration.

Recent findings:

• Contrary to the traditional model, recent findings from the GRAPES-3 experiment have identified a new feature in the cosmic-ray spectrum between 100 TeV and the knee.
• This breakthrough was made possible by creatively using a dense array of plastic scintillator detectors in conjunction with a large-area muon detector.
• This experimental setup allowed the researchers to collect data from approximately eight million cosmic ray shower events, a scale of observation several thousand times larger than what space-based detectors can achieve in this energy range, often limited by data precision.

Significance of discovery:

• Discovery indicates complexities in cosmic ray production and propagation within our galaxy yet to be fully comprehended.

Role of Ground-Based Observatories:

• Underscores the critical role of ground-based observatories in advancing astrophysical research.
• GRAPES-3 expands the observable cosmic ray spectrum with unprecedented precision.

About GRAPES-3:

• GRAPES-3 (Gamma Ray Astronomy PeV EnergieS phase-3) is designed to study cosmic rays using an array of air shower detectors and a large-area muon detector.
• It aims to investigate the acceleration of cosmic rays infour astrophysical settings:
  • ~100 MeV in atmospheric electric fields through muons
  • ~10 GeV in the Solar system through muons
  • ~1 PeV in our galaxy through the nuclear composition of cosmic rays
  • ~100 EeV in the nearby universe through the measurement of diffuse γ-ray flux.
• It is a collaboration of the Indian Tata Institute of Fundamental Research and the Japanese Osaka City University, and now also includes the Japanese Nagoya Women’s University.
• Observations began in 2000 with 217 plastic scintillators and a 560 m² area muon detector.
  • The scintillators are designed to detect charged particles in extensive air showers generated by the interaction of high-energy cosmic rays in the atmosphere.

Ref: Source