544 10 Particle Physics – II
matrix element, the general form being (q^2 +m^2 )−^1 , where m is the mass of the
exchanged particle and q is the four-momentum transfer.
In general, the same end result is obtained from a number of Feynman diagrams.
The transition matrix element includes the superposition of amplitudes of all such
diagrams.
For the weak interaction the exchanged particle is a massive boson,W±orZ^0 ,
indicated by a wavy or broken line. For the strong interaction, the exchanged particle
is a gluon indicated by a spring.
10.2 Problems..................................................
10.2.1 ConservationLaws.................................
10.1 Are the following particle interactions allowed by the conservation
rules? If so, state which force is involved and draw a Feynman diagram for
the process.
[University of Aberystwyth 2003]
(i) μ−→e−+νμ+νe
(ii) Λ→π++π−
(iii) νe+n→p+e−
(iv) π^0 →τ++τ−
(v)e++e−→μ++μ−10.2 Indicate, with an explanation, whether the following interactions proceed
through the strong, electromagnetic or weak interactions, or whether they
do not occur.
(i) π−→μ−+νμ
(ii) τ−→μ−+ντ
(iii)Σ^0 →Λ+γ
(iv) p→n+e++νe
(v)π−+p→π^0 +Σ^0
(vi) π−+p→K^0 +Σ^0
(vii) e++e−→μ++μ−
10.3 Consider the decay ofK^0 meson of momentumP 0 intoπ+ andπ−of
momentap+andp−in the opposite direction such thatp+= 2 p−. Deter-
minep 0.
[Mass ofK^0 is 498 MeV/c^2 ;massofπ±is 140 MeV/c^2 ]
10.4 Indicate, with an explanation, whether the following interactions proceed
through the strong, electromagnetic or weak interactions, or whether they
do not occur.
(i)Ξ−→Σ−+π^0
(ii)τ−→e−+νe+ντ
(iii)τ+→μ++γ