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.

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138 views

What exactly is the pi-rho-omega meson interaction vertex?

In the literature that I am currently aware of, the pi-rho-omega meson interaction vertex in chiral perturbation theory is stated as: $$ (1) \;\;\;\;\;\;\;\;\;\;\; g_{\rho \pi \omega} \; \...
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Effective theory for ω → π + γ → 3γ radiative meson decay?

Looking for accounts of omega-mesons decaying, eventually, into three photons, I found (just) the old M. Feldman et. al.: "Neutral Decay of the ω Meson", Phys. Rev. 159, 1219 (1967) (doi:10.1103/...
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Resourcs on learning about 2-body resources

As a part of my Particle Physics Course, I will need to give a talk on 2-body resonances - What are they? Some examples like 𝐽(Ψ), Z boson and significance of those discoveries. I am looking for ...
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Delta+ Baryon decay to proton and photon?

I was reading about delta + baryon decay modes and found a EM decay mode Delta+ (uud) -> Proton (uud) + photon However when I attempt at making Feynman diagram of this, I got this And a similar ...
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33 views

Where can I find the mesonic decay constants in the particle data group listings?

I can't seem to find the mesonic decay constants in any of the relevant particle data group (PDG) listings. I'm specifically looking for the neutral Kaon decay constants. Link to the PDG interactive ...
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What is a/the $K^*$ meson, and why is it important?

I know that the standard pseudoscalar $K$ mesons are: $K^+$: valence quark content $u\bar s$; electric charge $+1$; spin $0$; parity $-1$; $K^-$: valence quark content $\bar u s$; electric charge $-1$...
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Positive Kaon decay into $\pi^+$ and $\pi^0$ suppressed

I am looking at the reactions of positive Kaons and am looking at $$K^+\to\pi^++\pi^0$$ Since the strangeness is not conserved, this has to be a Weak decay. When I try to make the Feynman diagrams ...
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What are the minimum/realistic energies needed for positron/electron annihilation to form $D$ mesons?

High energy positrons and electrons can form $D$ mesons when they interact with each other and annihilate, but I was wondering what those energy levels would have to be. Specifically, would a fixed ...
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How do I show that the tensor product of $\mathbf{3} \otimes \mathbf{\bar{3}}=\mathbf{1} \oplus \mathbf{8}$? [duplicate]

It's often stated that the tensor product of the representations of $SU(3)$ satisfies $\mathbf{3} \otimes \mathbf{\bar{3}}=\mathbf{1} \oplus \mathbf{8}$, and that this implies that if flavour $SU(3)$ ...
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Can quark tunnel out and if so where do the energy used to form new meson come from? [closed]

If we give a quark enough energy to pull it out of a proton the energy can then creates more quarks but what happens if the quark quantum tunnel out, is it possible or the potential is simply too big ...
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Why is a quarkonium any different from a meson?

Quarkonium states are bound states of a quark-antiquark pair but so do the mesons. What is the difference between a quarkonium (e.g., charmonium, and bottomonium) and a meson then? Why use a separate ...
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Where do the mass and volume of the two quarks go when they create a meson?

A quark and an antiquark are fermionic particles with mass. Where do this said mass go when they bind to create a meson? If there's annihilation at play, how do mesons even be in the first place? ...
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Only two-particle Fock states contribute to the decay amplitude - meaning?

From the definition of the hadronic decay amplitude $f_h$, $$ f_h P^\mu=\langle 0 | J^\mu(0)|P\rangle $$ it follows that it is only the two-particle Fock states which contribute to $f_h$. Indeed, the ...
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Evaluation of an equation including Levi-Civita symbols

How can I obtain the result of the right-hand side in the Equation \begin{equation} i\epsilon_{\mu\nu\alpha\beta} \varepsilon^{\mu(\pm)}_{2}\varepsilon^{\nu(\pm)}_{1} p^{\alpha}_{B} p_{1}^{\beta}=\pm ...
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1answer
81 views

Why do this meson state (consisting with $ u,s,d$) are acceptable by nature?

I am new in Particle Physics and try to understand "Quark-Antiquark States:Meson article in Quarks & Leptons by Halzen and Martin(p=46) Why do this meson states are are acceptable by nature $$A=\...
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If a particle and its antiparticle annihilate upon contact, how do they form bound states?

I am reading about some old discoveries in particle physics and early collider experiments from Perkin's Introduction to High Energy Physics. However, I didn't get the answers to all my questions. If ...
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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 ...
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Meson decay constants from PDG

I've been looking for data for meson decay constants (pseudoscalar and vector), but in the latest release of PDG review I only find information about these parameters for charged pseudoscalar mesons. ...
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1answer
112 views

Why does the parity of a meson have a “+1” in it?

The parity of a meson is defined as $ P = (-1)^{L+1} $ where $L$ is the angular momentum. What does the "1" in the exponent represent?
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67 views

Why is the decay $\omega \rightarrow \eta \pi^0$ forbidden?

I understand that it is due to C conservation, but I'd like some more information - perhaps it's simpler than I'm imagining. Similarly for the decay $\omega \rightarrow \rho \gamma$. Thanks!
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Why is usual matter made up of $n,p$ and $e^-$?

We have six leptons and six quarks. Yet most of what we see around us is made of only neutrons, protons and electrons. For $\mu^-$ and $\tau^-$, I think the reason is that these are unstable particles ...
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Understanding some lines from 't Hooft's paper on large-N QCD in 1+1d

In 't Hooft's paper "A two-dimensional model for mesons", the author shows that two-dimensional (1+1) QCD in the large-N limit interestingly gives a theory of mesons. 't Hooft calculates the "mesonic ...
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How to understand the makeup of neutral pi and eta mesons?

I know that mesons are bosons made up of quark-antiquark pairs. But when I see the list of mesons, I can see that the makeup of neutral pions and eta mesons are noted in a strange way. $$\pi^0=(u\bar{...
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What is meant by “Since the exchange of (mesons) occurs frequently, the nuclear force is stronger than the electromagnetic force”?

This is from a book written by Y. Nambu. What role does the mass of mesons (versus mass of photons) have in making the strong force strong? How does this relate to "frequent exchanges" of mesons? ...
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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 ...
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Feynman loop diagrams

I am learning about Feynman diagrams, and I have trouble interpreting loop diagrams. The picture below shows a loop-induced decay of the neutral pion. $\pi^0 \rightarrow e^+ + e^-$. I understand that ...
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Feynman diagrams of phi-meson decay

I am learning how to make Feynman diagrams, and I have a couple of questions about two possible decays of the phi-meson. The first question relates to the reaction $\phi \rightarrow\text{K}^+ + \...
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Is there violation of energy conservation when a particle transforms to its anti-particle, for example $B^0\to\bar{B}^0$, or $K^0\to\bar{K}^0$

additive information : $B^0$ and $\bar{B}^0$ don't have the same mass, $K^0$ and $\bar{K}^0$ don't have the same mass. is there energy violation? if yes, is the key explanation of this coming from the ...
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Mass of the mesons in a universe with massless quarks

As I propose in this post, About the mass of the particles, imagine a universe with massless quarks due to Higgs' VEV is exactly zero. In our universe, where quarks are massive, we have consider ...
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Why are mesons only made of a quark-antiquark pair? [duplicate]

Why can't we have a meson made of two quarks, why does there have to be the antiquark too?
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53 views

Possible decay modes of Pion

I am aware that the following decay mode may happen: $$\pi^- → e^-\overline\nu $$ My question is why is the following decay mode not possible $$\pi^- → e^-\nu $$
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Energy conservation when exchanging meson

In Prob 1.2 of Griffith's "Introduction to Elementary Particles" 2nd ed., it says that: However, I don't understand why it states that "they must temporarily violate the conservation of energy by ...
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114 views

How can matter and anti-matter coexist in a meson?

Whilst learning about the nature of subatomic particles, I came along a pion zero meson. What really stumbled me was that the quark configuration of the particles was up and anti-up or down and anti-...
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How we know that the $\rho(1700)$ meson is in D-wave?

I was reading about Regge radial trajectories for $\rho$ meson and I found that we have two given by the values of the orbital angular momentum, $L=0$ and $L=2$. With this part, I feel OK. But, when ...
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Comparison between $\rho^0$ and $J/\psi$ decay mode

Why must a hadronic decay of the $J/\psi$ meson include (at least) three gluons? Why is the decay mediated by a single gluon allowed for the $\rho^0$ meson?
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What's the mass of $D_1(2430)^{\pm}$?

What's the mass of $D_1(2430)^{\pm}$? The standard reference http://pdglive.lbl.gov/ParticleGroup.action?init=0&node=MXXX035 only shows the data for $D_1(2430)^0$ but not for $D_1(2430)^{\pm}$. ...
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How does the nuclear interaction keep protons and neutrons together?

The strong force holds atoms hadrons together by using gluons to change the color charge of quarks and making the hadrons color nutral. But how does the nuclear force keep protons together, I heard ...
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Orbital parity of simple bound states in atomic and particle physics

The parity operator commutes with the Hydrogen atom Hamiltonian. The energy eigenfunctions are parity eigenstates with orbital parity $(-1)^\ell$ which follows from the fact that $Y_{\ell m}(\theta,\...
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Conversion of gluons into hadrons

Why and how does a gluon become a hadron when it leaves a hadron? Is this an analogous process to the way a quark becomes a meson, when it is "forced" out of (let's say) a proton?
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Confusion regarding the orbital angular momentum of mesons in an excited state

I came across the statement that Mesons can have a spin of a whole number (e.g. 1 or 2) instead of the regular 0, as a result of the orbital angular momentum they have in their excited states, with ...
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331 views

Rho and Omega meson mixing

I am new to particle physics. So this might seem to be a trivial question. I read about $\omega$ and $\phi$ meson states being written in terms of octet and singlet state. In the same way, can $\...
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Mixing Parameters of the $D^{0}$ Meson

Consider mixing in the $D^{0}$ charm meson system as discussed, for example here. Such mixing is characterised by the mixing parameters $x=\frac{\Delta m}{\Gamma}$, and $y=\frac{\Delta\Gamma}{2\Gamma}$...
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What is the time period in which an interaction with a π-meson takes place?

The longer-range inter-nucleon force is not a direct result of the gluon field, but is indirectly affected by a quark-antiquark pair (meson). If this ‘residual’ strong interaction between nucleons ...
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What meson influences the nucleon-nucleon interaction at a far range and why?

What meson influences the nucleon-nucleon interaction at a far range and why? Nucleon-Nucleon (NN) interaction is divided up into three parts a) long range (>2fm) b) medium range (1 to 2fm) c) ...
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Use of energy–momentum relation for virtual particle deriving Klein Gordon equation

Here it is claimed that A virtual particle does not precisely obey the energy–momentum relation $m^2c^4 = E^2 − p^2c^2$ But then why is Klein Gordon relation (in the context of Yukawa theory) ...
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Mass of mesons and baryons

In my introduction to nucleons and particles (basic) course, we were given the following formula to compute the mass of mesons and baryons : \begin{eqnarray} M(\text{meson}) & = & m_1 + m_2 ...
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144 views

Does the decay of $\rho^0$ meson imply that charged pions have non-integer orbital angular momentum?

In the decay $\rho_0\rightarrow \pi^+ + \pi^-$ the $\rho_0$ has total angular momentum 1 and the $\pi^\pm$ both have spin zero. In order to conserve total angular momentum, the pions must therefore ...
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240 views

Width of the J/$\psi$ resonance

The J/$\psi$ resonance has a mass of ~3 GeV but its width is only of 100 keV, why is it so narrow compared to the total mass? How can the width of these resonances be calculated?
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What is the process transforming $K_L$ mesons into $K_S$ mesons?

First of all, I could not find any good book/webpage where I can read about K mesons, can somebody point me to a good reading? The second point is about $K_L$ and $K_S$ mesons. As I can read, they are ...
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146 views

Can somebody explain the relation of Young diagrams and particle physics?

I have the mesons octet and there are Young diagrams below them. how are they drawn? what do they represent?