y***u
发帖数: 25 | 1 我不是学粒子的。这两道题回答起来有点麻烦。第一题我知道怎么做，第二道
不是很肯定问的是什么。
1) suppose spin part as +,- corresponding to up and down states respectively.
r,y,g represent the three states of color degrees of freedom.
u,d,s represent the flavor degrees of freedom.
1,2,3 represent the three quarks.
First we require color singlet, so for the color part of the wavefunction, it
is SUM q * P_{123} r(1)y(2)g(3). This state is antisymmetric for changing any
pair of quarks (q=1 for 123, q=-1 for 132 .... is the sign for different ord | p******g
发帖数: 347 | 2 A brief answer for the 2nd problem:
we know there's pi^{0} and pi^{\pm}, pi^{0} doesn't have anti-particle. So
it should be a unit representation of SU(3), cause under SU(3) transform-
ation it remains unchanged. Similiarly, pi^{\pm} obey SU(2) flavor symmtry
transformation, since they are anti-particle of each other. And we know
U(1) and SU(2) is the subset of SU(3).
Since pions are the lightest meson, and we know meson's consist of 2 valence
quarks(quark and antiquark, quark model), it gotta b |
|
