Context:
Recently, researchers used a magnetic field 2.7 lakh times stronger than the Earth’s to discover semi-Dirac fermions.
Fundamental Particles
- Atoms are composed of three types of particles: electrons (leptons), protons, and neutrons.
- Electrons revolve around the nucleus.
- Protons and neutrons are located inside the nucleus.
- Protons and neutrons are composite particles.
- They are made up of fundamental particles called up quarks and down quarks in different combinations.
- Fermions (quarks and leptons) and bosons are the actual fundamental particles.
Fermions
- Fermions: Fundamental particles of normal matter.
- Energy Transfer: Transfer discrete amounts of energy by exchanging bosons.
- Classification:
- Dirac Fermions: Fermions that may or may not have mass but are always different from their anti-particles.
- Majorana Fermions: Fermions that are also their own antiparticles (neutrinos are suspected to be Majorana fermions).
- 2 Types: Quarks and leptons.
- Characteristics:
- Pauli Exclusion Principle: No two fermions (e.g., electrons) can occupy the same space and have the same quantum numbers.
- Fermi-Dirac Statistics: Obeyed by fermions, unlike bosons.
Quarks and Leptons
| Property | Quarks | Leptons |
| Flavours and Colours | Six quarks – three generations (flavours) and three colour charges | No colour charges |
| Composite Particles | Combine to form hadrons (baryons and mesons) Baryons: Composed of three quarks (e.g., protons, neutrons) Mesons: Composed of two quarks, becoming a boson | Do not make composite particles |
| Identity Change | Can change identities due to weak force (via W and Z bosons) or combine to make composite particles (due to strong nuclear force via gluons) | Cannot change their identities |
| Interaction with Strong Nuclear Force | Interact with strong nuclear force | Do not interact with strong nuclear force |
| Types | Quarks | Six leptons – three negatively charged (electron, muon, tauon) and three neutral (neutrinos) |
| Location | Inside the nucleus | Do not reside inside the nucleus |
Neutrinos (Ghost Particles)
- Most Abundant: Most abundant particles in the universe with mass.
- Production: Produced during nuclear fusion (e.g., sun), in nuclear reactors, and radioactive decay.
- Type Change: Can change types through neutrino oscillation.
- Detectors: Neutrino detectors worldwide, including the INO Project of India, work towards understanding these particles.
Bosons
- Bosons: Force carrier particles and composite particles with integer spins (mesons).
- Types of Bosons: Mesons (Composite particles with integer spins), Vector Bosons, Higgs Bosons.
- Characteristics:
- Do not obey Pauli’s Exclusion Principle and Fermi-Dirac Statistics.
- Obey Bose-Einstein statistics (described by Satyendra Nath Bose and Albert Einstein).
- Bosons in the same quantum state can form a Bose-Einstein condensate.
- Observed in superfluid helium and potentially in neutron stars.
Vector Bosons
- Force Carrier Bosons: Mediate fundamental forces.
- Gluons: Mediate strong force.
- Photons: Mediate electromagnetic force.
- W and Z bosons: Mediate weak force.
- Graviton: Hypothetical particle believed to carry gravitational force (not part of Standard Model).
Higgs Bosons (God Particle)
- Responsible for the intrinsic mass of particles.
- Represents a wave in the Higgs field.
- Particles acquire mass through interactions with the Higgs field.
- The stronger the interaction, the more massive the particle.
Standard Model of Particle Physics
- The Standard Model: Theoretical framework describing fundamental particles and their interactions.
- Incorporates Three Fundamental Forces: Electromagnetism, weak nuclear force, and strong nuclear force.
- Excludes Gravity: Gravity is not included in this model.
Limitations of the Standard Model
- Quantum Numbers: Does not explain particle quantum numbers like electric charge (Q), weak isospin (I), hypercharge (Y), and colour.
- Incomplete Model: Unifies only three of the four fundamental forces, excluding gravity.
- Graviton: The carrier particle of gravity, not yet discovered by physicists.
- Dark Matter: Silent on dark matter and energy, which make up 95% of the universe.
- Mass of Composite Particles: Cannot explain why the mass of composite particles is greater than the sum of their constituents (e.g., proton mass > sum of 3 quarks).
- Mass of Neutrinos: The Higgs boson (God particle) gives mass to quarks, charged leptons, and W and Z bosons, but it is unknown if it gives mass to neutrinos (Ghost particles).
Source: TH
Previous Year Question
The efforts to detect the existence of Higgs boson particles have become frequent news in the recent past. What is/are the importance/importances of discovering this particle?
1. It will enable us to understand as to why elementary particles have mass.
2. It will enable us in the near future to develop the technology of transferring matter from one point to another without traversing the physical space between them.
3. It will enable us to create better fuels for nuclear fission.
Select the correct answer using the codes given below.
[UPSC CSE – 2013 Prelims]
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a)