All Questions
Tagged with standard-model pions
76
questions
-3
votes
1
answer
95
views
Parity transformation of the $\pi^{0}\rightarrow\gamma\gamma$ process
I want to prove that the amplitude
$$\mathcal{M}^{\mu\nu}=\epsilon^{\mu\nu\alpha\beta}q_{1\alpha}q_{2\beta}$$
is violating parity. Here $q_{i=1,2}$ are the external momenta of the photons. The total ...
- 475
0
votes
2
answers
116
views
Why does the up and anti-up quark combine into a pion and not a photon?
im currently studying a level particle physics and im confused about this. Particle annihilation occours when a particle meets its corresponding particle, converting their mass energy into two photons,...
- 3
1
vote
1
answer
98
views
Quark condensate and VEV of $\pi^0$
In David Tong's lectures on the Standard Model I saw that there is a quark condensate, which is just a Vacuum Expectation Value (VEV) of the $\bar{q}_{Li}\, q_{Ri}$ operator,
$$
\left< \bar{q}_{Li}...
- 1,611
1
vote
0
answers
49
views
How are $\pi$ Mesons Created in the Residual Strong Interaction?
Watching this episode of PBS Space Time, they run an animation of how pi mesons are exchanged by nucleons as the residual strong interaction to overcome proton electromagnetic repulsion.
https://youtu....
- 23
0
votes
1
answer
132
views
Kinematics in the pion decay
If a charged pion decays via a charged current $W$, the $W$ boson is much heavier than the pions. How is this not a problem? Could the processes be off-shell in such a drastic manner?
It is tempting ...
- 126
0
votes
0
answers
114
views
How to obtain the amplitude for the leptonic pion decay?
Consider the leptonic decay of the pion
$$\pi^{+}\rightarrow l^{+}\nu_{l}$$
In my notes there's written that in order to compute the associated rate we can use the effective Lagrangian
$$\mathcal{L}^{\...
- 475
3
votes
1
answer
109
views
How is this equation about pion decay derived?
I'm reading Peskin's Concepts of Elementary Particle Physics and these equations confuse me.
What are the $\pi^1$ and $\pi^2$ in (15.49) and why $\pi^-$ equals to this?
I don't understand the ...
- 43
1
vote
0
answers
139
views
Can a $\phi$ meson decay into a pair of charged pions ($\pi^-$ and $\pi^+$)?
I understand that $\phi^0 \to \pi^+ \pi^- \pi^0$ is OZI suppressed.
But how about $\phi^0 \to \pi^+ \pi^-$?
Wikipedia doesn't list this decay path but $\phi^0 \to K^+ K^-$. Why? $\phi^0$ is a mixing ...
- 99
0
votes
1
answer
661
views
Energy distribution of photon from neutral pion ($\pi^0$) decay
The laboratory-frame energy $E_\gamma$ of either photon is uniformly distributed between $E_{min} = \frac{1}{2}E_{\pi}(1-\beta)$ and $E_{max} = \frac{1}{2}E_{\pi}(1+\beta)$, where $E_\pi$ is the ...
- 3
2
votes
2
answers
713
views
Deriving the charged pion decay matrix element
From M Schwarz's QFT (p 570), Goldstone's theorem indicates that pions are created from the vacuum by the chiral ${\rm SU}(2)$ current $J_\mu^{5a}$,
$$
\langle
\Omega|
J_\mu^{5a}(x)|\pi^b(p)
\rangle
=...
- 574
3
votes
1
answer
135
views
Why does the trace of the pion operator vanish?
I am working my way through Srednicki's QFT book. Currently I'm in chapter 94.
Between equations 94.20 and 94.21, Srednicki says that the following expression vanishes in the case of two light ...
- 143
0
votes
2
answers
555
views
Understanding depiction of gluons in the nuclear force Feynman diagram
In this Feynman diagram for the nuclear force, it labels this exchange as a pion. However, I was under the impression that this force was mediated by gluons. In the caption for this picture, it says ...
- 1,261
0
votes
1
answer
379
views
On neutral Kaon mixing
Kaons are not eigenstates of $CP$:
$$
CP|K\rangle =|\overline K\rangle\\
$$
Why do we need to mix them?
One answer I read is "since they both decay into $2$ or $3$ pions". Couldn't they ...
- 1,644
1
vote
2
answers
3k
views
Confused about helicity suppression in the decay $\pi^- \rightarrow \mu^- \overline{\nu}_\mu$
I know this question has been asked a few times before here in various ways, but I haven't found answers which helped me a lot. For one, the class I am in is not using any of the underlying math, so ...
- 508
7
votes
1
answer
972
views
Where do pions get angular momentum from?
If a neutral meson carrying intrinsic spin equal to 1 decays into a pair of charged pions, how can they possibly conserve angular momentum? Pions have no spin and if they originate from the same point ...
- 1,297