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Elementary Particle, Meson Family

Explore the Meson Family of subatomic particles and their significant role in understanding particle physics. Learn about their properties and interactions.
authorImageAbhishek Kumar14 Nov, 2023
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Meson Family

  • Boson and Antiboson have the same parity.

  • Spin S = 0
  • Parity P = -1
Particles Antiparticles Charge Rest Mass Mean Life
+ - +1 140 2.6 x 10 -8
o o 0 135 8.9 x 10 -17
k + k - +1 494 1.2 x 10 -8
k o k o 0 499 0.9 x10 -10
πœ‚ πœ‚ 0 549 5.1 x10 -19
Baryon Family
Particles Antiparticles Charge Mean Life Rest Mass Spin
p p +1 ∞ 938 1 2
n n 0 886 940 1 2
0 2.6 x 10 -10 1116 1 2
+ Ξ£ + +1 8 x10 -11 1189 1 2
- Ξ£ - -1 1.5 x 10 -10 1197 1 2
o Ξ£ 0 0 7.4 x 10 -20 1193 1 2
o 0 0 2.7 x 10 -10 1315 1 2
- - -1 1.6 x 10 -10 1322 1 2
𝛺 - 𝛺 - -1 8.2 x 10 -11 1672 3 2
Conservation Laws
  • Exact Conservation Law
  • Non Exact Conservation Law
  • Universal / Exact Conservation Law
  1. Energy conservation law (E)
  2. Linear momentum conservation law (p)
  3. Total angular momentum conservation law (J)
  4. Charge Conservation law (Q)
  5. Lepton Number conservation law
  6. Baryon Number conservation law
  7. CPT (Charge, parity & time)
Note :-
  • Energy Conservation Law
Let's have a reaction. A + B β†’ C + D m A m B m C m D So according to energy conservation law E A + E B = E C + E D m A c 2 + m B c 2 = m C c 2 + m D c 2
  • Linear momentum conservation law (p)
Let a reaction A + B β‡’ C + D p A + p B = p C + p D Example : e + + e - β†’ Ξ³ + Ξ³ If e - is Coming from left towards right and positron is coming from right towards left and if Ξ³Β  is emitting upwards then to conserve momentum another Ξ³ emitted towards downward direction.
  • Angular momentum conservation law (J)
J i = J f
  • Charge conservation law Q
Q i = Q f Example:- n β†’ p + e - + e 0 Β  Β  +1 Β  -1Β  Β  0 Q i = 0 Q f = 0 So Q is conserve here
  • Lepton Number conservation law
  1. e + & 𝝂 e have lepton no.1
L e - = +1, L 𝝂 e = +1
  1. e + & 𝜈 e have lepton number -1
L 𝜏 - = -1 , L 𝜈 e = -1
  1. - , 𝜈 𝜏 have lepton number = +1
L 𝜏 - = +1, L 𝜈 𝜏 = +1
  1. + , 𝜈 𝜏 have lepton number = -1
L 𝜏 + + = -1, L 𝜈 𝜏 = -1
  1. πœ‡ - & 𝜈 πœ‡ have lepton number +1
L πœ‡ - = +1, L 𝜈 𝜏 = +1
  1. u + & 𝜈 πœ‡ have lepton number -1
L πœ‡ + = -1 , L 𝜈 πœ‡ = 1 Note : All Baryons and mesons have lepton number = 0
  • In any process, lepton number for e - family, muon family and tauon family should be separately conserved.
Example:
  1. πœ‹ - β†’ - + 𝜈 ΞΌ
L πœ‡ 0 Β  Β  +1 -1 So L πœ‡ = 0
  1. 𝜈 e + p β†’ e + + n + -
L e +1  0       -1    0    0 L 𝜏 0     0       0    0   +1 here L 𝜏 0, L e 0 So this reaction is not possible
  • Baryon number conservation law
  1. In any reaction, the total baryon number must be conserved.
  2. All Baryons have baryon number B = +1
  3. All antibaryons have B = -1
  4. All means and leptons (Non Baryons) have B = 0
Example:-
  1. p + p β†’ p + p + p + p -
1Β  Β  1Β  Β  Β  1Β  Β  1Β  Β  1 Β  -1 B = 0, So reaction is possible

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