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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Meson operator treated as an elementary field in effective action?

I have seen in many papers, with this as the earliest example I can find, that the meson chiral order operator $M_j^{\,\,\,i}(x)=\overline{\psi}^i(1+\gamma_5)\psi_j(x)$ is treated as an elementary ...
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Is there such an effect in QCD?

I heard that one of the phenomena in Quantum Chromodynamics allows for the conversion of Mesons in to Baryons, if temporarily, namely by replacing the anti-quark in a meson with its equivalent ...
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Meson as hadron and boson

In wikipedia page about hadrons the following image appears: I can understand why the intersection between hadrons and fermions are baryons, as a way to say a baryon is a kind of hadron composed of ...
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Meson masses difference

I am reading some group theory applied to QCD and they show how by using the lightest 3 quarks in the $l=0$ state we get 9 pseudoscalar mesons and 9 vector mesons. The difference in masses between the ...
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Number of $\pi ^+$ and $\pi^-$ in collision experiments

My first idea is that number of $\pi ^+$ and $\pi ^-$ mesons in collision of heavy ions with some target made of heavy nuclei should be close to 50/50. But after that I start to think that mass of $d$ ...
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B mesons lifetime

I read about a technique called b-tagging in which one can check if a b meson was produced in a collision by looking for a jet which has a secondary vertex within it. The reason is that b mesons are ...
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Has there been research done on the dependence of particle decay to its immediate surroundings?

The meson particle, Kaon, can decay into pions or leptons + neutrinos. Each decay has its own probabilities as measured and confirmed during experiments. Has there been any research into the ...
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81 views

How to write quark composition of $\rm SU(3)$ mesons?

In $\rm SU(2)$, taking up quark and down quark as a doublet we can easily apply the isospin ladder operators to write the combination of 2 quark or 3 quark (baryon) systems. In $\rm SU(3)$ quark model,...
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4-point Green's function for mesons

Starting with $$ Z(J,\lambda)=\int D\varphi e^{ i\int \!d^4x\,\{ \frac{1}{2}[(\partial\varphi)^2-m^2\varphi^2 ]-\frac{\lambda}{4!} \varphi^4+J\varphi \} } . $$ I have a question about how ...
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Why the mesons $\pi^0$ and $\eta$ are “degenerate”

I don't know anything about elementary particles, but reading the book by Zeidler on p158, table 2.8 one can observe the quark content of baryons and mesons. It is strange that the $\pi^0$ meson has ...
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Is the decay of a neutral rho meson into a neutral pi meson and a photon forbidden?

is the decay of a neutral rho meson into a neutral pi meson and a photon forbidden? It doesn´t look like parity conservation or charge conservation is violated but I haven´t found this decay is ...
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How is the neutral kaon stable?

A neutral kaon is a mix of a particle and antiparticle, in layman's terms. In layman's terms, how is this possible without there being annihilation?
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59 views

Probability decay for rho meson

I have the following putative set of decays for the $\rho^0$ meson: $$\begin{array}{l} \rho^{0} \rightarrow \pi^{0} \pi^{0}:\text{STRONG} \\ \rho^{0} \rightarrow \pi^{-} \pi^{+}:\text{STRONG} \\ \rho^{...
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Does tau decay to rho meson + tau neutrino?

In the particle data group table: http://pdg.lbl.gov/2020/tables/rpp2020-sum-leptons.pdf ,only $\tau \rightarrow \pi + \nu_{\tau}$ is documented. But does $\tau \rightarrow \rho + \nu_{\tau}$ as well? ...
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Meson could include both matter and antimatter?

I wonder eta and pion could exist containing up quark (anti up quark)? Isn't there pair annihilation in this meson?
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Meson conservation [closed]

Why meson conservation doesn't exist?
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Paramagnetic susceptibility on mesonic gas

I'm trying to find the paramagnetic susceptibility on an ideal gas with spin = 1, and magnetic moment $\mu$ in the high-temperature regime. The paramagnetic susceptibility is given by $$ \chi = \...
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84 views

Decay of the Phi Meson: Error in Question?

I'm trying to draw Feynman diagrams for 'The decay of the pseudoscalar meson $\phi = |s \bar{s}\rangle $ into these final states: i) $\phi \rightarrow \pi^{+} \pi^{-},$ where $\pi^{+}=|u \bar{d}\...
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Question about the most probable decay mode

I want to understand which of the following possible decay modes for the B$^+$ meson is most probable: $$ B^+ \rightarrow \tau^+\upsilon_\tau $$ $$ B^+ \rightarrow \mu^+\upsilon_\mu $$ $$ B^+ \...
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119 views

Why are the lightest mesons (Goldstone bosons) pseudoscalar?

I get that the lightest mesons are generically the (approximate) Goldstone bosons of spontaneous chiral symmetry breaking in the quark sector. I understand that they are spin-0, but why are they ...
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Chiral WZW term for Hadron Supersymmetry?

Remarkably, an approximate supersymmetry not in the color- but in the flavor-sector is experimentally observed: hadron supersymmetry, relating mesons (the bosons) to baryons (the fermions). The most ...
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Are there any mesons with one charm antiquark?

Is there a meson with one charm antiquark, $\bar{c}$, so that $C=-1$? Can they exist?
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Anomalous K-K*-γ interaction and similar D-D*-γ and B-B*-γ?

In trying to better understand the chiral-anomaly WZW-term interaction of the heavy vector mesons, I have trouble finding much relevant literature, but maybe I am looking in the wrong place. One ...
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Skyrme model with both: vector & heavy mesons?

While the original Skyrmion model for effective hadrodynamics contained, of all mesons, only the pion, there are two well-studied directions in which it is successfully refined by incorporation of ...
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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 one ...
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55 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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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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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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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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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 ...