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Tuesday, December 13, 2011

elementary particles and fundamental interactions

  • Elementary particles are those microscopic elementary constituents out of which all matter in this universe is made of.
  • Bound neutron is stable but unbound neutron is unstable and it decays according to equation

    n p + e - + ν e ¯ (anti-nutrino)

    half life of free neutron is 14 min 49 sec.

Fundamental interactions

There are four fundamental interactions between particles

(1) strong

(2) electromagnetic

(3) week

(4) gravitational

Interaction Particles affected range relative strength particles exchanged Role in universe
(1) Strons Quarks ∼10-15m 1 gluons Holds quarks togather to form nucleus
Hadrons Mesons Holds nucleons togather to form atomic nuclei
(2) Electromagnetic charged particles infinite ∼10-2 photons determine structure of atoms, molecules , solids etc., Important factor in astronomical universe.
(3) Weak Quarks and leptons ∼10-17m ∼10-5m Intermediate bosons mediates transformations of quarks and leptons; helps determine composition of atomic nuclei
(4) Gravitational all infinite ∼10-39m gravitons Assemble matter into planet , galaxies and stars
  • Elementary particles can be divided into four groups

    (1) photons

    (2) leptons

    (3) mesons

    (4) baryons

Anti particles

  • A particle identical with proton except for negative charge, i.e., negative proton or antiproton was created by bombarding protons in a target with 6 GeV protons thereby inducing the reaction

    p+p+energy(6 GeV)→p+p+

  • Particle and anti particle annihilate each otherto give rise to a form of energy.
  • positron is the anti particle of electron.
  • There must be an anti oarticle corresponding to each particle.
  • From the collection of anti particles a world of anti matter could be created.

Reletionship between particle and anti particles is

property relationship
(1) mass same
(2) spin same
(3) magnetic monemt of opposite sign but same magnitude
(4) charge of opposite sign but same magnitude
(5) mean life in free decay same
(6) annihilation in pair
(7) creation in pair
(8) total isotopic spin same
(9) intrinsic parity same for bosons but opposite for fermions
(10) strangeness number of opposite sign but same magnitude

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