1000 Solved Problems in Modern Physics

536 10 Particle Physics – II

Table 10.1 Mass Common Particle (MeV/c^2 ) τ(s) decay mode

Hadrons

⎧ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎨ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎩

Mesons

⎧ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎨ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎩

Pions

{ π−,π+ 139 2. 5 × 10 −^8 μν π^01351. 8 × 10 −^16 γγ

Kaons

⎧ ⎪⎪⎪ ⎪⎪⎨

⎪⎪⎪ ⎪⎪⎩

K−,K+ 494 1. 2 × 10 −^8 μν K^0498 π±π^0 Mixture ofK 1 ,K 2 K 1 0. 89 × 10 −^10 π+π− π^0 π^0 K 2 5. 18 × 10 −^8 π^0 π^0 π^0 π+π−π^0 πμν πμeν ̄ η 550 10 −^18 γ+γ π++π−+π^0

Baryons

⎧ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎪ ⎪⎪⎨

⎪⎪⎪ ⎪⎪⎪ ⎪⎪ ⎪⎪⎪ ⎩

Nucleons

{ p 938.2 > 1038 stable n 939.5 103 pe−ν

Hyperons

⎧ ⎪⎪⎪ ⎪⎪⎪ ⎪⎨ ⎪⎪ ⎪⎪⎪ ⎪⎪⎩

Λ 1,115 2. 6 × 10 −^10 pπ−,nπ^0 Σ+ 1,189 0. 8 × 10 −^10 pπ^0 ,nπ+ Σ^0 1,192 10 −^20 Λγ Σ− 1,197 1. 6 × 10 −^10 nπ− Ξ^0 1,314 3 × 10 −^10 Λπ^0 Ξ− 1,321 1. 8 × 10 −^10 Λπ− Ω− 1,675 1. 3 × 10 −^10 Ξπ ΛK− Photon γ 0 ∞ Stable

Leptons

⎧ ⎪⎪⎪ ⎪⎪⎪ ⎪⎨ ⎪⎪⎪ ⎪⎪⎪ ⎪⎩

τ− 1,784 3. 4 × 10 −^13 Electrons and neutrinos μ− 105 2 × 10 −^6 eν ̄ν e− 0.51 ∞ Stable νe 0 ∞ Stable νμ < 0 .5Stable ντ < 164 ∞ Stable Graviton ?0–Stable

Here we will be concerned with only the first three types. Table 10.2 summarizes
the characteristics of the interactions.
Coupling constant: Particles interact through strong electromagnetic or weak charges.
The square of the charge is known as the coupling constant. It enters the interaction
matrix which determines the cross-sections and decay rates. Strictly speaking, the
coupling constants are not constant but vary very gradually with the particle energy.
They are called running constants.
QED (quantum electrodynamics)is the quantum field theory of the electro mag-
netic interaction whose predictions have been verified to a precision of one part in a
billion.
QCD (quantum chromo dynamics)is the field theory of the strong color interaction
between quarks.

1000 Solved Problems in Modern Physics

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