Higgs Boson Decay

Context: Recently, physicists working with the Large Hadron Collider (LHC) particle smasher at CERN, in Europe, reported that they had detected a Higgs boson decaying into a Z boson particle and a photon.
  • This is a very rare decay process that tells us important things about the Higgs boson as well as about our universe.
Image Source: The Hindu What is a Higgs boson?
  • The Higgs boson is a type of boson, a force­ carrying subatomic particles. 
  • It carries the force that a particle experiences when it moves through an energy field, called the Higgs field, that is believed to be present throughout the universe.
  • The stronger a particle’s interaction with the Higgs boson, the more mass it has. This is why electrons have a certain mass, protons have more of it, and neutrons have just a little bit more than protons.
  • A Higgs boson can also interact with another Higgs boson — this is how we know that its mass is greater than that of protons or neutrons.
    • For example, when an electron interacts with the Higgs field, the effects it experiences are said to be due to its interaction with Higgs bosons.
  • Since all the matter in the universe is made of these particles, working out how strongly each type couples to Higgs bosons, together with understanding the properties of Higgs bosons themselves.
The results of the recent study: LHC experiment: 
  • The LHC creates a Higgs boson by accelerating billions of highly energetic protons into a head-on collision, releasing a tremendous amount of energy that condenses into different particles.
  • As it is a heavy particle, the Higgs boson is unstable and decays into lighter particles.
  • The Higgs boson can decay to a lepton pair and a photon in three ways.
  • This is the first evidence that shows Higgs boson decays into a Z boson, the electrically neutral carrier of the weak force, and a photon, the carrier of the electromagnetic force.
  • It can’t always be said which combination of particles it will decay into.
  • Although the Standard Model predicts what happens to the Higgs boson when it dies, until now, researchers hadn’t observed the particle decay before the recent study.
Additional Information  Quantum field theory: 
  • According to quantum field theory, space at the subatomic level is not empty.
  • It is filled with virtual particles, which are particles that quickly pop in and out of existence.
  • They can’t be detected directly, but according to physicists their effects sometimes linger.
    • (Quantum field theory describes the microscopic world of particles very differently to everyday life. Fundamental quantum fields fill the universe and dictate what nature can and cannot do.)
  Standard Model of Particle Physics:
  • It says that a Higgs boson will decay to a Z boson and a photon 0.1% of the time.
  • This means the LHC needed to have created at least 1,000 Higgs bosons to have been able to spot one of them decaying to a Z boson and a photon.
Image source: energy.gov
  • The Standard Model of Particle Physics is scientists’ current best theory to describe the most basic building blocks of the universe.
  • It explains how particles called quarks (which make up protons and neutrons) and leptons (which include electrons) make up all known matter.
  • It also explains how force carrying particles, which belong to a broader group of bosons, influence the quarks and leptons.
  • The Standard Model explains three of the four fundamental forces that govern the universe: electromagnetism, the strong force, and the weak force.
    1. Electromagnetism is carried by photons and involves the interaction of electric fields and magnetic fields.
    2. The strong force, which is carried by gluons, binds together atomic nuclei to make them stable.
    3. The weak force, carried by W and Z bosons, causes nuclear reactions that have powered our Sun and other stars for billions of years.
    4. The fourth fundamental force is gravity, which is not adequately explained by the Standard Model.
Limitations of Standard Model
  • It does not explain how gravity is mediated. There is currently no experimental evidence supporting the existence of the hypothesised gravitons.
  • The Standard Model of Matter is incompatible with the Theory of General Relativity (whose basis focuses on gravity).
  • The Standard model currently cannot explain why the mass of sub-atomic particles is greater than the sum of its constituents.
    • For example, the mass of a proton is greater than 3 quarks combined.
  • It does not explain the disproportion between matter and anti-matter.
  • It does not explain the composition of dark matter, which makes up the majority of the universe.
Source: The Hindu, Science Ready
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