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

  $n\to p+e^{-}+\overline{{\nu }_e}$ (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