Tensor or pseudo-tensor particles

[RedX]

Why are spin 0 mesons pseudo-scalar, and spin 1 mesons vector?

Why can't spin 0 mesons be scalar, and spin 1 mesons be pseudo-vector?

If observables are bilinear in the fields, then how can you even detect whether a field is pseudo-scalar, since $$\phi^2$$ is a scalar no matter if the meson field is pseudo-scalar or scalar?

Also, is it correct to assume that spin 0 mesons obey the Klein-Gordan equation, and spin 1 mesons obey the Maxwell equations but with a mass term, i.e., $$\mathcal L=-\frac{1}{4} F_{\mu \nu}F^{\mu \nu}-\frac{m}{2}A_\mu A^\mu$$?

 

[DrDu]

As these mesons have integer spin, they are bosons and the observables don't have to be bilinear but also linear operators may be observables. So you could detect the change of the sign of phi under parity.

 

[lpetrich]

It's possible for spin-0 particles to be scalar (positive parity). If it exists, the Standard-Model Higgs would be.

Pions are the like are negative parity because they are quark-antiquark composites in an orbital ground state.
Quark: +
Antiquark: -
Spin-0 orbit: +
Total: -

 

[Meir Achuz]

Why are spin 0 mesons pseudo-scalar, and spin 1 mesons vector?

Why can't spin 0 mesons be scalar, and spin 1 mesons be pseudo-vector?

If observables are bilinear in the fields, then how can you even detect whether a field is pseudo-scalar, since $$\phi^2$$ is a scalar no matter if the meson field is pseudo-scalar or scalar?

1. Spin zero mesons can be scalar. The (somewhat controversal) sigma meson is a spin zero scalar. In the quark model, the quark-antiquark combination has intrinsic negative parity. This makes the quark model mesons as 0^- and 1^-, pseudoscalar and vector.

2. Parity is determined experimentally in transitions.
The pion was originally determined to be a pseudoscalar from angular distributions in N+N-->N+N+pi/