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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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Why is isospin utilized in determining the branching fraction of $K_1(1270)\to K\pi\pi$ final states?

The branching fraction of $\mathcal{B}_{K_1 \rightarrow K^{+} \pi^{+}\pi^{-}}$ is determined by $$\mathcal{B}_{K_1 \rightarrow K^{+} \pi^{+}\pi^{-}}=\frac{1}{3} \times \mathcal{B}_{K_1 \rightarrow K \...
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Quark Combination of Hadrons

I am trying to understand the different combinations of quarks in a hadron. I have seen that the positive pion is written as $\pi^{+}=u\bar{d}$, but I have not seen it written in the opposite order. ...
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Next-to-leading $1/N$ contributions to Feynman diagrams in large $N$

I want to understand $1/N$ contributions to quark bilinear operators $J(x)$ in large $N$, for instance, operators of the form $q\bar{q}$ or $\bar{q}\gamma^\mu q$. As pointed out by E. Witten, in the ...
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What is the difference between a meson and quarkonium?

I read that quarkonium is a "flavourless" meson. However what does it mean for a meson to be flavourless? I thought composite particles don't have "flavour" in the first place, and ...
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Does the kaon participate in the weak interaction?

I'm looking at a physics textbook for A-level and in the book it states that kaons are only affected by the strong force and the electromagnetic force. Isn't this incorrect? Aren't kaons affected by ...
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What is vector meson dominance and why is that related to QCD having a repulsive potential?

At long distances QCD is said to give rise to attractive force between nucleons by pion exchange and to give rise to repulsive force at short distance mediated by vector mesons. Is there a ...
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Clarifying with Dirac equation

The Dirac equation has a solution, $\Psi(x^\mu) = Ae^{-ip_\mu x^\mu / \hbar} u(p^\mu)$ and $\Psi(x^\mu) = Ae^{+ip_\mu x^\mu / \hbar} \nu(p^\mu)$, where $u(p^\mu)$ corresponds to the particle ...
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If a $J/\psi$ decays to an electron-positron pair 5% of the time, how often would a $\phi$ meson decay to a electron-positron pair?

I know the mass of $J/\psi$ to be 3097 mev and the mass of phi to be 1018 mev. I know that $J/\psi$ decays to electron and positron 5% of the time. I also know the full width of j/psi to be 0.092mev ...
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Lagrangian for quarks and pions

I need to understand how starting from the free Lagrangian $$ \mathscr{L} = \bar{q}(i \not\partial - \hat{m})q $$ and based on the chiral angle associated with the pion field and the quark field ...
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How would I estimate the partial width for the decay of upsilon meson into an electron-positron pair?

I cam across a question that stated the total decay width for the phi meson was 4300 kev and the partial decay of it into an electron-positron pair was 1.3kev. How would I estimate the partial width ...
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How Fast Can Toponium Form?

I understand that Toponium is only theoretical because the T quark decays too quickly. My question is this, would a right handed T quark live long enough to form a meson? If not, how long would it ...
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Why does the Yukawa potential fail for the strong force? [duplicate]

The gluon is a massless particle, so according to the Yukawa potential the strong force should have a $r^{-1}$ potential. However, that is clearly not the case. Is it because the gluons themselves can ...
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Mass of the kaon (1460)

When looking at the particle listing in PDG most of the hadron masses and excitation include an experimental error. But this is not the case for the Kaon (1460), does anybody know why? This means the ...
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Mesons as a two-body problem is semiclassical QCD?

In particle physics and quantum field theory, mesons are interpreted as a system composed of a quark and an anti-quark, and the color charge of both must be at each opposite moment (green/anti-green, ...
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Why there are no pseudoscalar mesons like $\eta_u = u\bar{u}$, $\eta_d = d\bar{d}$, etc?

Consulting the list of pseudoscalar mesons, we found that for charm and bottom quarks there are two mesons with quark content given by: $$\eta_c=c\bar{c},\qquad \eta_b = b\bar{b}$$ on the other hand, ...
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Why is the branching fraction of strange $D$ mesons to tau leptons so high?

From the PDG (https://pdg.lbl.gov/2008/listings/s031.pdf & https://pdg.lbl.gov/2010/listings/rpp2010-list-Ds-plus-minus.pdf) the branching rate for strange D mesons to tau leptons is about 3 ...
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Why are vector mesons heavier than pseudoscalar mesons?

From the hyperfine calculation we find that the mass of the vector mesons are heavier than pseudoscalar meson, as the following proves. The magnetic moment is proportional to the spin and inversely ...
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ELi5- How do pions hold nuclei together if they are so short-lived?

I need help understanding how particles do what they do and maintain the structures they maintain if so many of them exist for such a short time? In the case of the nucleus and pions, pions only exist ...
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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 ...
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On the Terent'ev, M V original article

I am in a Phd program and I want to read the Terent'ev, M V original article "On the structure of the wave functions of mesons considered as bound states of relativistic quarks" or, in ...
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Mass of $B$ Meson

This is a question from Griffith's Introduction to Elementary Particles, Chapter 2: The upsilon meson, $b\bar b$, is the bottom-quark analog to the $\psi$, $c\bar c$. Its mass is 9460 MeV/$c^2$ and ...
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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 ...
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Intrinsic Parity of the $𝐾^+$ Meson

Why it is not possible to determine intrinsic parity of the $𝐾^+$ mesons from the $𝐾^+ → 𝜋^+ 𝜋^0$ decay?
Hassan Ghavidel's user avatar
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What is the secret behind the striking similarity between a quark pair and a bar magnet?

If one tries to split a pair of quark and an anti quark, one ends up with two pairs, in the same way, when one tries to break a magnet in half, one end up in the same way with two magnets, so is this ...
Jack's user avatar
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How can scalar mesons have even parity?

From my understanding a pseudo-scalar meson has: $$J^P=0^-$$ That makes sense since the total spin $S=0$ and $l$ must be $l=0$ which makes the parity: $$ P=(-1)^{l+1}=-1 $$ uneven. Now, for scalar ...
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Meson-Meson Scattering Data

Recently, I have been interested in the scattering amplitudes of mesons in the high-energy fixed-angle regime. I have come across a simple result, due to Brodsky et al., that predicts the scaling of ...
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Quark structure of Baryons

I was studying Particle Physics then suddenly I came up with a question that why only Baryons are made up of three quarks, at first I thought to to conserve Baryon number which is $\frac{1}{3}$ for ...
Bishal Sarkar's user avatar
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Wilson Coefficients in the Standard Model

I'm not particularly knowledgeable in this area of physics. From my understanding as an undergraduate, Wilson coefficients are sets of parameters that arise from an effective field theory which ...
probablysid's user avatar
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Structure functions for mesons

I was researching about structure functions and understand how it's a probability density function that describes the distribution of quarks inside hadrons. However, since mesons also have quark gluon ...
Jungwoon Song's user avatar
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How can a meson beam be created?

I was reading this thread where the answer states that to use deep inelastic scattering on mesons, we have to "generate a meson beam (which is a bit of a trick in and of itself) and direct it ...
Jungwoon Song's user avatar
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How Does QCD Explain Nuclear Fission?

This question is brief and simple. As a layman, it is my understanding that QCD (Quantum Chromodynamics) explains the nuclear force as a "residual" force, mediated by pions (mesons), which ...
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Why did Yukawa theorize a neutral pion? Was it necessary or a guess?

At the time, neutrons had just been discovered, but were only needed to explain the extra mass inside nuclei... We now know that the strong force isn't strong enough to hold positive protons together ...
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How to use the quark model to explain that the $D^+$ won't be a strange particle?

For the system of $K^-,\pi^+,\pi^+$, with the invariant mass spectrum peaking about 1.87 GeV, call this resonant peak $D^+$; we find its spin to be zero by experiment. Using the quark model, how ...
jun xiang's user avatar
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When can spinless "particles" have dipole moments?

While fundamental point particles with zero spin cannot have a dipole moment because spin is their only directional property, this does not seem to be true for spinless composite "particles"....
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Are Kaons and Pions (mesons) made up of quarks?

I have tried to reasearch this and google says yes. But i learnt that pions decay into muons and netrinos (and the antiparticle versions) which are basically electrons and neutrinos Which are ...
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How does one calculate the decay width of an a1 Meson into a $\pi$ and a $\rho$?

I'm trying to make a theoretical prediction of the decay width (and by extension lifetime) of an a1 Meson into a rho⁰ and a pi⁻ (the rho⁰ then decays into a pi⁺⁻ pair). I can't seem to find the ...
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How do mesons explain nuclear stability?

I understand that nuclear stability is explained by the presence of the residual nuclear force, which in turn is a result of the strong nuclear force, which I believe, is mediated between quarks via ...
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Mesons wavefunction symmetry

Is it possible to write the valence quark wavefunction for mesons which is overall symmetric in nature? Because acc. to me, we can not say directly that flavor and color wavefunction is symmetric as ...
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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 ...
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$\rho$ and $\omega$ mesons decays

As far as I understand, typical decay for $\omega$ meson is into $3\pi$, while for $\rho^0$ is into $2\pi$. In fact they are quite similar particles (same spin, parity, similar masses). Why this ...
Antonio19932806's user avatar
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What prevents $K^0$ from decaying into $K^+ e^- \overline{\nu}_e$?

Energetically it is just possible for a neutral kaon to decay into a charged kaon, electron and antineutrino, namely: $$K^0 \rightarrow K^+ e^- \overline{\nu}_e$$ Indeed a mass difference of a few ...
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1 answer
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(Coleman QFT notes) Physical vacuum has no one-meson content?

I'm looking at Lecture 14 in Coleman's QFT notes. In defining the renormalized field $\phi'(x)$ corresponding to the meson field $\phi(x)$, Coleman notes first that \begin{equation*} \langle k | \phi(...
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Identifying mesons with Goldstone modes

In QCD, due to the work of ‘t Hooft and Vafa-Witten, we know that confinement implies chiral symmetry breaking (David Tong’s gauge theory notes have a clear discussion of this). It is then said that ...
Konder's user avatar
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In the history of the development of the standard model was there a version in which quark-antiquark pairs or flux tubes were the fundamental particle [closed]

Based on the observations of color confinement and no free quarks, I'm wondering if instead of a having quarks as fundamental particles, during development of the Standard Model was there ever a ...
dllahr's user avatar
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Spin dependence of wavefunction of meson states bound by a certain potential

Lets assume two spin half particles, for example a charm quark and a charm anti-quark are bound by a spherical harmonic oscillator potential to form bound meson states. The possible ground state ...
Utsab Dey's user avatar
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Mass counterterms in Yukawa-type meson-nucleon theory (Coleman's notes)

On page 102 of his QFT notes (https://arxiv.org/abs/1110.5013) Coleman uses the following reasoning for calculating the counterterms to the meson and nucleon masses in what he calls "quantum ...
mpc's user avatar
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Feynman diagram

In this picture first diagram, can't the gluon be a $Z$ boson? Similarly, can't the $Z$ boson in the second diagram be a gluon?
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Why $R(D)$ is not measured in LHCb and only $R(D^*)$ is measured?

Measurement of $R(D)$ and $R(D^*)$ are important probe of lepton universality violation. They are defined as the ratios of branching fractions: $$R(D^{(*)}) = \frac{\mathcal{B}(B\rightarrow D^{(*)}\...
Ahtra's user avatar
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Cause of Strong force

What is the origin and cause of the strong interaction which occurs between the nucleons? I have read that it is caused by the exchange of mesons but what then ultimately causes this meson exchange to ...
Scientific Co 's user avatar
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1 answer
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Particles composed of square roots?

There are some particles which require square roots when telling their compositions. Mostly mesons, not baryons. e.g. $$ρ^0=\frac{u\bar{u}-d\bar{d}}{\sqrt{2}}.$$ Could you explain me how to make sense ...
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