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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.

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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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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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146 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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Description of strong force as exchange of meson or as exchange of quark and antiquark

The (residual) strong force between nucleons can be desribed as The exchange of a meson (from a nucleon to the other), as in picture b) The exchange of a quark and an antiquark: in picture a) one ...
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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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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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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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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?
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If colour charge is like electric charge how do baryons hold together when all the colour charges have the same sign?

So a quark and an antiquark in a meson have colour charges of the same colour but opposite sign eg $r \bar{r}$, so I think this is like an electric charge with a positive and negative particle so ...
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Can a kaon decay into 4 pions?

Since a Kaon's wavefunction is composed of $K_S$ and $K_L$ which are CP-even and CP-odd respectively. The Kaon can decay into $\pi \pi \pi \pi$ through $K_S$ since the 4 pions have CP-parity $= (-1)^4 ...
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How can i predict the decay modes and branching ratios of the phi-meson (mass 1020 MeV)?

I have looked up the pdg and found different decay modes in which three of them are the most occurring in nature. They are $\rm\phi\rightarrow K^+K^-$, $\rm\phi\rightarrow K_0\bar K_0$, and $\rm\phi\...
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How are the 'physical' isospin zero states determined?

Consider the light mesons. Since $3 \times \bar{3} = 8 + 1$, the states should be grouped into $\mathfrak{su}(3)$ octets and singlets. In the case of the spin zero states (the pseudoscalars), the ...
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Calculating matrix elements for quarkonium decay amplitudes

In this paper (Appendix A) several decay amplitudes are calculated. How does this work? Note that $$ |n \bar n \rangle = \frac{1}{\sqrt{2}} (| u \bar u \rangle + |d \bar d\rangle ) \\ \eta = \cos \...
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vector mesons identified with positive parity

I have seen in some sources (like in https://arxiv.org/abs/1610.06090, page 11, footnote 11 but also in some few more) that vector mesons are assigned with positive parity $(J^P)=1^+$. In Particle ...
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Why can't omega meson decay into two neutral pions?

Here it says this decay mode is a violation of C-parity. I don't understand how that works. So $\omega$ has $C=-1$ and $J=1$ and $\pi^0$ has $C=1$ and $J=0$, that means the orbital angular momentum ...
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Which mesons are possible?

That's probably a plain question but I wonder: Which mesons can exist? The only limitation I'm aware of is the charge (antiparticle+particle). Ok, finally also the color (anticolor+color) but I assume ...
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Neutral kaon semileptonic decays, why is $\overline{K^0}\rightarrow l^+\nu\pi^-$ not allowed?

On several texts it is stated that the semileptonic decays are different for the $K^0$ and $\overline{K^0}$, and each only gives leptons of particular charges (see www.hep.ph.ic.ac.uk/~dauncey/will/...
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Wavefunctions of (Pseudo)-scalar/vector meson and Tensor meson

Two quarks can bound to form a meson, and the wavefunction consists of several quantum degrees of freedom: $$ \psi=\psi(\text{flavor})\psi(\text{color})\psi(\text{orbital})\psi(\text{spin}) $$ ...
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What is the matter anti-matter asymmetry in the decay of the neutral K meson?

In 1964 Cronin and Fitch discovered that there is asymmetry in the weak decay of the neutral K meson. What is this asymmetry and what causes it?
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Are bottomonium and charmonium the only quarkonium systems?

I had a question: Are bottomonium and charmonium the only quarkonium systems? I was searching the internet and found that these two systems have been experimetally observed but the toponium has ...
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What is a $D^{0 \ast}$ meson?

What are the quark contents of $D^{0 \ast}$ meson? How to distinguish between $D^{0 \ast}$ meson and $D^{0}$ meson as I guess both have same quark content.
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Scalar pseudo-Goldstones from hypothetical $SU(3)_V$ symmetry breaking in QCD

The eight light pseudoscalar mesons of QCD are the pseudo-Goldstone bosons of the spontaneously broken chiral (axial) $SU(3)_A$ quark flavor symmetry. If we consider the hypothetical case of also ...
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Applying ladder operators to Isospin states for quarks

I'm having trouble finding the isospin representation of the meson isospin triplet $|\rho\rangle$. Starting from the $|\rho^+\rangle$ meson $|u^\uparrow\bar d^\uparrow\rangle$ (where the arrows ...
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216 views

The right quark combination for a meson

If I have a meson nonet, it contains the octet and the singlet ($\eta'$). For example in the $J^P=0^-$-case, I have 'simple' mesons like $K^0$ with $d\bar{s}$, but I also have mesons, which are mixed ...
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Why do $I,J,P$ still need confirmation for the B mesons?

If I open the PDG (say here), and look at the quantum numbers of the $B$ mesons it says, for every $B$ meson, "I, J, P need confirmation". However, this disclaimer doesn't appear for any other type of ...
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Which particle decays are quickest?

The $ρ^0$ and $\pi^0$ mesons have the same quark content, (uu*-dd*)/sqrt(2) and have masses of 775 MeV/c^2 and 135 MeV/c^2 respectively. The ρ0 has a lifetime ~ 10^-24s while pi0 has a lifetiem of ~10^...
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Meson wave function

I have a basic question about pseudoscalar mesons wavefunction. As I understand it, mesons are bosons so they have a total symmetric wavefunction under exchange of particles. For pseudoscalar mesons,...
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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 ...
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Why can omega meson not decay into two charged pions?

Why is the decay of the $\omega$ meson similiar to the neutral $\rho^{0}$ meson into two charged $\pi$ prohibited? My first thought was that it has something to do with isospin conservation in the ...
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390 views

Why is a Kaon strange?

I've read that because Kaons are produced by the strong interaction and decay by the weak interaction that this makes them strange. However protons and neutrons decay by the weak interaction as well i....
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Why are there both scalar and vector mesons?

I understand that the term "vector meson" denotes a meson particle (composite particle with a quark and an antiquark) which transforms as a vector under the Lorentz group. Since both the quark and the ...
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Overall symmetry of pion wave function

Mesons are bosons, therefore their wavefunction must be symmetric under particle exchange. Overall, the meson wave function ($\text{WF}$) has the following contributions: $$\text{WF} = \lvert \text{...
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Why are all mesons unstable

My question is: why are all mesons unstable? Shouldn't the lightest mesons like the pion be stable because they are made from the lightest quarks (and anti-quarks)? Or could the they annihilate (the ...
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How can we explain that $\Sigma \pm$ have different masses whereas K$\pm$ have the same mass?

I guess it is because of the forces between the quarks inside them but I am not quite sure how to explain it.
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Physical significance of the decomposition $3\times \bar{3}=8+1$: Does the singlet state differs from the states in the octet?

Under $SU(3)$, $3\times \bar{3}=8+1$ i.e., the tensor product of the fundamental and the conjugate (to the fundamental) representation is reducible: 1 represents the singlet under $SU(3)$, and 8 ...
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Explicit construction of states from $3\times \bar{3}=8+1$

Under $SU(3)$, $3\times \bar{3}=8+1$ i.e., the tensor product of the fundamental and the conjugate (to the fundamental) representation is reducible: 1 represents the singlet under $SU(3)$, and 8 ...
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What is this notation using $\psi$ and $J$ to represent particles in a quark-based interaction?

The $c\bar{c}$ meson decays to a lighter meson in the following reactions: $$\psi(3686)\rightarrow J/\psi(3097)+\eta^0$$ $$\psi(3686)\rightarrow J/\psi(3097)+\pi^0.$$ My aim is to find out which ...
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Gluons and mesons

I just read somewhere that both gluons and mesons transmit the strong force, gluons between quarks inside hadrons, but mesons between nucleons. I thought that the strong force would have one field, ...