GHOST PARTICLES

Why in the news? 

Scientists at Ice Cube Neutrino Observatory in Antarctica have detected seven tau neutrinos (ghost particles), which passed through the Earth. 

What are neutrinos/Ghost Particles?

• About: They are subatomic particles with no electrical charge and negligible mass. 
  • High-energy neutrinos which are released from cosmic sources at the Milky Way's edge are known as "astrophysical neutrinos". 
  • They are also known as Ghost Particles because nearly 100 trillion of neutrinos pass through the human body every second without us noticing.
• Classification: Under the Standard Model of particle physics, they’re classified as a "lepton." 
  • Standard Model of physics is the theory of particles, fields and the fundamental forces that govern them.

The Standard Model of Particle Physics Describe the most basic building blocks of the universe.  Explains how particles called quarks (which make up protons and neutrons) and leptons (which include electrons) make up all known matter.  Also explains how force carrying particles (bosons) influence the quarks and leptons. Also, explains three of the four fundamental forces that govern the universe: electromagnetism, the strong force, and the weak force.  Electromagnetism is carried by photons and involves the interaction of electric fields and magnetic fields.  The strong force, which is carried by gluons, binds together atomic nuclei to make them stable.  The weak force, carried by W and Z bosons, causes nuclear reactions that have powered our Sun and other stars for billions of years.  The fourth fundamental force is gravity, which is not adequately explained by the Standard Model.

• 3 types or flavours: electron, muon, and tau, and they oscillate between these flavours as they propagate.
• Possible sources of high-energy neutrinos: Events like supernovas and objects like active galactic nuclei and black holes.
  • Sun’s nuclear reactions, particle decay in Earth, Beta decay, particle accelerators and nuclear power plants all release neutrinos.
• Properties of neutrinos:
  • Travel at nearly the speed of light. 
  • Neither get deflected by magnetic fields, nor scattered or easily absorbed. Thus, are very difficult to detect. 
  • Travel in straight lines from their source.
  • Neutrinos are the most abundant particles that have mass in the universe. 
• Due to their properties, they are excellent messengers of information about the objects or events in which they originate.
  • Gamma rays and cosmic rays are other observed messengers.
• Note: It is different from the ‘God Particle’ or Higgs boson. 
  • Higgs boson is the fundamental particle associated with the Higgs field which gives mass to other fundamental particles.
  • It was discovered in 2012 at the Large Hadron Collider, world’s most powerful particle accelerator in the world, CERN, Switzerland.

About Ice Cube Observatory  It is a cubic-kilometre neutrino particle detector buried deep beneath the ice surface (~2500 metres). Aim: Observe cosmic rays that interact with the Earth’s atmosphere and study the nature of dark matter and the properties of the neutrino. Location: Near the Amundsen-Scott South Pole Station in Antarctica. The observatory was built on the South Pole as it needs clear, pure, and stable ice to make its discoveries and be shielded from radiation at the Earth’s surface. It is the first gigaton neutrino detector ever built and was primarily designed to observe neutrinos from the most violent astrophysical sources. The astrophysical neutrinos were first detected by the observatory in 2013. How does the Ice Cube Observatory detect neutrinos? Neutrinos are not observed directly, but through their interaction with the other matter.  When neutrinos interact with molecules in the ice, they produce electrically charged secondary particles traveling at high speeds (faster than light in the ice). It leads to emission of blue light (Cherenkov light). The observatory uses strings/cables of digital optical modules (DOMs) which are embedded deep into the Antarctic ice. The instruments then convert the messages into light patterns which reveal the direction and energy of neutrinos.

Significance of studying neutrinos

• Understanding universe's evolution: They can provide us insights into the early stages of the universe, soon after the Big Bang.
  • E.g., China is using its supercomputer, Tianhe-2, to create a simulation involving neutrinos to understand the origin of the universe.
• Better understanding of dark matter and dark energy: 95% of our universe is comprised of dark matter (27%) and dark energy (68%).
• Study the structure of nucleons: Studying protons and neutrinos present in nucleus of atoms may explain how matter evolved from simple particles into more complex ones.
• Neutrinos emitted from stars: Astronomers can study Neutrinos emitted from stars to understand the interior of stars, including the sun, and discover new planets.
• Medical Applications: They may have applications in medical imaging, similar to X-ray machines and MRI scans.
• Monitoring of nuclear proliferation: The process of fission inside of the nuclear reactor or from nuclear explosions leads to the birth of neutrinos through beta decay. 
  • Distant nuclear reactions can be observed and monitored with detectors filled with purified water to spot these neutrinos.
  • E.g., U.S.-U.K. collaboration- WATCHMAN aims to demonstrate remote monitoring of nuclear reactors using neutrino.