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Questions tagged [mesons]

Μesons are unstable hadronic subatomic particles of integral spin, and hence bosons. They are composed of one quark and one antiquark, and bound together by the strong interaction to a physical size of roughly one fermi.

Μesons are unstable hadronic subatomic particles of integral spin, and hence bosons. They are composed of one quark and one antiquark, and bound together by the strong interaction to a physical size of roughly one fermi.

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What does it mean that the neutral pion is a mixture of quarks?

The quark composition of the neutral pion ($\pi^0$) is $\frac{u\bar{u} - d\bar{d}}{\sqrt{2}}$. What does this actually mean? I think it's bizarre that a particle doesn't have a definite composition. There's a difference of 2 MeV between the quark…
Kasper
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Are there any Baryons that have quark-antiquark combinations?

I'll be honest, I only have a Highschool education, so there might be something obvious I'm overlooking. However particle physics is of massive Interest to me. My question is, I know there are unstable quark-antiquark pairs that form Mesons, but…
RudyJD
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Probability of forming mesons vs baryons

When a heavy quark hadronizes it has some probability of forming a meson vs forming a baryon. I suspect there is a well known branching ratio for each type of hadron. Does anyone know what the probability is or, even better, a reference that…
JeffDror
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Does the Pauli exclusion principle apply to mesons?

According to the Pauli exclusion principle, two identical fermions cannot occupy the same quantum state simultaneously, but two bosons can. Mesons are bosons, but composed of two quarks, and quarks in turn are fermions. If two identical mesons were…
hilssu
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Why is the charmed eta meson its own antiparticle, but the neutral kaon is not?

I have a limited understanding of antiparticles, so this may be why I am unable to explain why certain mesons are their own antiparticles, while others are not. My understanding is that antiparticles have properties (ie. spin, charge, mass, etc)…
grizzly.bear
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Why is the decay of a neutral $\rho$ meson into two neutral pions forbidden?

Why is the decay of a neutral $\rho$ meson into two neutral pions forbidden? (Other modes of decay are possible though.) Is it something with conservation of isospin symmetry or something else? Please explain in a bit more detail.
Adeel
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Why does charmonium (and phi mesons) not decay via quark and antiquark annihilation?

The decay of heavy quark/antiquark pairs (say $c\bar{c}$, $s\bar{s}$) is supposedly 'suppressed because of the Zweig/OZI rule', see for instance Phi meson. And they certainly have a longer lifetime than expected. However, the Zweig suppression only…
Meep
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$B$-meson naming convention

An unbarred $B$-meson contains $\bar{b}$ (an anti-bottom quark), whereas a barred $\bar{B}$-meson contains $b$ (a bottom quark). What is the historical reason for this hellish naming convention?
innisfree
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What's the difference between a meson and a glueball?

There is a blog post by Matt Strassler about the structure of hadrons. He contrasts the "conventional" picture of hadrons shown below: with one that he considers to be more accurate: From the second figure, one would be led to believe that there…
Brian Bi
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Are mesons color polarized?

The binding of quarks in mesons baffles me. It's an Occam's Razor thing. Since a meson is a colorless, the simplest way to bind its two quarks together is to use a $U(1)$ Cartan subalgebra of $SU(3)$. That is, the two quarks would bind by exchanging…
Terry Bollinger
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How do we measure meson decay constants?

I'm trying to understand how people actually measure decay constants that are discussed in meson decays. As a concrete example lets consider the pion decay constant. The amplitude for $\pi ^-$ decay is given by, \begin{equation} \big\langle 0 | T …
JeffDror
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What is the difference between a charged rho meson and a charged pion?

They both seem to have the same quark content: $$\rho^{+} = u\bar{d} = \pi^{+}$$ and $$\rho^{-} = \bar{u}d = \pi^{-}$$ What is different about the two?
XYZT
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Quantum field theory meson scattering calculation (scalar yukawa theory)

Please see this question for a clear background of the notation I use. My issue is that I want to use Wick's theorem to calculate the amplitude of meson $\psi(p_1)\psi(p_2)\rightarrow\psi(p_1')\psi(p_2')$ scattering. I can quickly get to the point…
user5866
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Does the color of a quark matter in a meson?

QCD and confinement specify that hadrons must be color-neutral. My understanding is that this means you can have mesons (quark + antiquark) or baryons with 3 quarks, one of each color: Red+green+blue=neutral. In a meson, does the color of the quark…
Richardbernstein
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Derivation of Gell-Mann Okubo relation for mesons

In SU(3) quark model of hadronic structure one assumes that mass splitings between hadrons is due to difference between masses of $s$ quark and $u,d$. This is modeled by perturbation Hamiltonian $$ \delta H=\frac{m_s-m}{3}(1-3 Y),$$ where $m$ is…
Blazej
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