The GRAPES-3 experiment, conducted at Ooty, India, and operated by the Tata Institute of Fundamental Research, has made a significant discovery in the cosmic-ray proton spectrum. This discovery, observed at about 166 tera-electron-volt (TeV) energy, challenges our existing understanding of cosmic-ray sources, acceleration mechanisms, and their propagation within the galaxy.
Principal Investigator and Study Lead
The study was led by Pravata K. Mohanty, the Principal Investigator of the GRAPES-3 experiment and a faculty member at the Tata Institute of Fundamental Research, Mumbai.
Background on Cosmic Rays
Cosmic rays, the most energetic particles in the universe, were discovered over a century ago. These particles constantly bombard Earth from outer space, penetrating the atmosphere and inducing showers of particles. These showers include electrons, photons, muons, protons, neutrons, among others.
Cosmic Ray Energy Range
Cosmic rays have been observed over a broad energy range, spanning from 10^8 to 10^20 electron volts (eV). The flux of cosmic ray particles follows a power law, decreasing steeply with increasing energy.
The Cosmic-Ray Proton “Knee”
Approximately seven decades ago, a kink in the cosmic-ray proton spectrum, known as the “Knee” at about 3 peta-electron-volt (PeV), was discovered. It has been considered the maximum energy for cosmic-ray acceleration within Galactic sources. Previous models explained the cosmic ray spectrum up to the Knee with a single power law.
New Feature Discovery
The GRAPES-3 experiment’s observation reveals a new feature above 100 TeV and below the Knee, challenging the traditional understanding of cosmic-ray acceleration.
The researchers utilized a combination of a dense array of plastic scintillator detectors and a large-area muon detector. This experimental setup provided a collection area several thousand times larger than space-based detectors, enabling a more detailed examination of cosmic rays above 100 TeV.
Fahim Varsi and the research team analyzed a subset of about 8 million cosmic ray shower events recorded by the detectors. They employed CPU-intensive computer simulations to measure the cosmic-ray spectrum, offering insights into the observed feature.
Multiple-Choice Questions (MCQs):
- Who led the study on the new feature in the cosmic-ray proton spectrum discovered by the GRAPES-3 experiment?
- A) Fahim Varsi
- B) Pravata K. Mohanty
- C) Tata Institute of Fundamental Research
- D) GRAPES-3 experiment
- What is the “Knee” in the context of cosmic rays?
- A) A kink in the cosmic-ray proton spectrum
- B) The maximum energy for cosmic-ray acceleration
- C) Discovered seven decades ago
- D) All of the above
- At what energy was the new feature in the cosmic-ray proton spectrum observed by the GRAPES-3 experiment?
- A) 3 PeV
- B) 50 TeV
- C) 166 TeV
- D) 1 PeV
- What is the primary method used by the GRAPES-3 experiment for data collection?
- A) Space-based detectors
- B) Muon detectors
- C) Dense array of plastic scintillator detectors
- D) Radio telescopes
- Why is the experimental setup of GRAPES-3 with plastic scintillator detectors and a muon detector significant?
- A) Provides low statistics
- B) Allows for a more detailed examination of cosmic rays above 100 TeV
- C) Measures cosmic-ray spectrum below 50 TeV
- D) Limited collection area