Lifetime of rho meson and Kaon

Tags:
1. Apr 13, 2015

unscientific

1. The problem statement, all variables and given/known data

(a) What is a meson?
(b) State what these mesons are made up of and explain their quantum numbers and interactions.
(c) Find the lifetimes of rho meson and kaon.
(d) Find the dominant decay mode and explain why.
(e) Why is decay to 2 neutral pions forbidden?
(f) Explain how an a1 (1260) meson can be formed and a valid decay.

2. Relevant equations

3. The attempt at a solution

Part(a)

A meson is a composite hadron formed by a quark and an anti-quark. There are three generations of quarks - (u,d), (s,c) and (t,b).

Part(b)
Textbook problem.

Part (c)
How do I find the lifetime from these graphs? I can see that the graphs peak at 1300 decays/bin and 2500 decays/bin respectively. How do I convert that into lifetimes?

Part (d)
Dominant decay mode is in fact decay to 2 Kaons $K^+$ and $K^-$. The decay to 3 pions is OZI suppressed. We expect lifetime to be 1000 times longer than lifetime of kaons.

Part (e)
In short, because 2 neutral pions cannot have L = 1, otherwise they are anti-symmetric in exchange (which cannot be, since they are bosons that must be symmetric under exchange).

Part (f)
It is possible for L =S=J=1 through L-S coupling to give total J=1. They exist as a spin tripplet. A valid decay would be $a_1 \rightarrow K + \bar K$.

2. Apr 13, 2015

BvU

(c) You don't. Instead, you use the uncertainty in the energy, so the width, not the height. Here or here

3. Apr 13, 2015

unscientific

Thanks alot for the links, I'll read that up. Are my other parts to the question OK?

4. Apr 13, 2015

BvU

I like part (b)

5. Apr 16, 2015

unscientific

So since $\Delta E \delta t = \frac{\hbar}{2}$, I take that the lifetime is the uncertainty $\delta t$ so I simply estimate the half-width $\Delta E$ from the graphs to calculate $\Delta t$?

6. Apr 16, 2015

BvU

Yes. Nice, isn't it ?

7. Apr 16, 2015

unscientific

These questions appear to be harder than they are..