What is Meson: Definition and 114 Discussions

In particle physics, mesons ( or ) are hadronic subatomic particles composed of an equal number of quarks and antiquarks, usually one of each, bound together by strong interactions. Because mesons are composed of quark subparticles, they have a meaningful physical size, a diameter of roughly one femtometer (1×10−15 m), which is about 0.6 times the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Heavier mesons decay to lighter mesons and ultimately to stable electrons, neutrinos and photons.
Outside the nucleus, mesons appear in nature only as short-lived products of very high-energy collisions between particles made of quarks, such as cosmic rays (high-energy protons and neutrons) and baryonic matter. Mesons are routinely produced artificially in cyclotrons or other accelerators in the collisions of protons, antiprotons, or other particles.
Higher-energy (more massive) mesons were created momentarily in the Big Bang, but are not thought to play a role in nature today. However, such heavy mesons are regularly created in particle accelerator experiments, in order to understand the nature of the heavier types of quark that compose the heavier mesons.
Mesons are part of the hadron particle family, which are defined simply as particles composed of two or more quarks. The other members of the hadron family are the baryons: subatomic particles composed of odd numbers of valence quarks (at least 3), and some experiments show evidence of exotic mesons, which do not have the conventional valence quark content of two quarks (one quark and one antiquark), but 4 or more.
Because quarks have a spin 1/2, the difference in quark number between mesons and baryons results in conventional two-quark mesons being bosons, whereas baryons are fermions.
Each type of meson has a corresponding antiparticle (antimeson) in which quarks are replaced by their corresponding antiquarks and vice versa. For example, a positive pion (π+) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion (π−), is made of one up antiquark and one down quark.
Because mesons are composed of quarks, they participate in both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction. Mesons are classified according to their quark content, total angular momentum, parity and various other properties, such as C-parity and G-parity. Although no meson is stable, those of lower mass are nonetheless more stable than the more massive, and hence are easier to observe and study in particle accelerators or in cosmic ray experiments. The lightest group of mesons is less massive than the lightest group of baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher-energy phenomena more readily than do baryons. But mesons can be quite massive: for example, the J/Psi meson (J/ψ) containing the charm quark, first seen 1974, is about three times as massive as a proton, and the upsilon meson (ϒ) containing the bottom quark, first seen in 1977, is about ten times as massive.

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  1. S

    Feynman Diagram of Meson decay

    I have trouble understanding the diagram and the answer key. 1) I am thinking time is the horizontal axis. Since A is π+, the quark composition will be ##u## and ##\bar{d}##. There are 2 vertices, let say P (on the left) and Q (on the right). I don't understand the conservation of charge at...
  2. imgamedeving

    I How often would a ϕ meson decay to a electron-positron pair?

    I know the mass of J/ψ to be 3097 mev and the mass of phi to be 1018 mev. I know that J/ψ decays to electron and positron 5% of the time. I also know the full width of j/psi to be 0.092mev and that the phi meson lives 50 times longer than J/ψ . My professor claims that if I am given that info...
  3. E

    I Steps behind Meson decay amplitudes

    I am a graduate student with a somewhat basic level of exposure to qft. As part of my degree I have been tasked with calculating meson decay amplitudes in a paper provided to me by my supervisor but unfortunately I seem to be lacking some prior knowledge to understand why certain expressions are...
  4. PeroK

    I Are Hadrons and Gluons Symmetric Against Interchange of Colours?

    This is from Griffiths' Elementary Particles, section 8.4.1. By analysing the colour factor, the conclusion is that a quark/anti-quark pair attract in the colour singlet configuration: $$\frac 1 {\sqrt 3}(r\bar r + b \bar b + g \bar g)$$ And this explains (to some extent) why mesons are...
  5. JD_PM

    Understanding the Math behind meson decay computations

    Homework Statement:: I am studying how to compute the meson-decay amplitude worked out in Tong's notes (pages 55 and 56; I attached the PDF). Relevant Equations:: $$<f|S|i>=-ig<f| \int d^4 x \psi^{\dagger} (x) \psi (x) \phi (x) |i>$$ The initial and final states are given by $$|i > = \sqrt{2...
  6. P

    Electron and positron collision producing a b0 meson pair

    Conservation of Energy: 9GeV + E = 5.3GeV + 5.3GeV Therefore E = 1.6GeV for the threshold energy. How would I find the velocity of B0 mesons so that I can calculate their mean distance? Then it would just be distance = velocity of b0 * mean proper lifetime Right?
  7. lLehner95

    Why is eta meson decay into 3 neutral pions forbidden?

    I started combining 2 pions: ##|\pi ^{0},\pi ^{0} >=\sqrt{\frac{2}{3}}|2,0>-\sqrt{\frac{1}{3}}|0,0>## What should i do now? Should i continue combining the third pion or can i already say that it's forbidden? If yes, why? Is it because the state antisymmetric, impossible for two bosons?
  8. K

    I Why do some mesons have = sign while others have ≈ in their composition?

    Hello! I am reading Modern Particle Physics by Mark Thomson and in chapter 9.6.2 he writes the composition of certain mesons. However for some of them he uses an equality sign: $$|\rho^0> = \frac{1}{\sqrt{2}}(u\bar{u}-d\bar{d})$$ while for others he writes: $$|\omega> \approx...
  9. S

    What is the range and time period of this particle?

    Homework Statement The longer-range inter-nucleon force is not a direct result of the gluon field, but is indirectly affected by a quark-antiquark pair (i.e. meson). If this ‘residual’ strong interaction between nucleons is mediated by a π-meson, then what is the maximum time period in which...
  10. S

    I Time period in which an interaction with a π-meson happens?

    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 is mediated by a π-meson, then what is the maximum time period in which the interaction takes...
  11. C

    I Are resonances formed in the scattering of a baryon and a meson?

    Consider the following reaction of strong interaction (in a scattering process) $$n+\pi^+\to \Lambda_0+K^+\tag{1}$$ Then the particle ##\Lambda_0## formed decays with weak interaction $$\Lambda_0\to \pi^+ +p\tag{2}$$ For each decay process I measure the four momenta of ##K^+##, ##\pi^+##...
  12. C

    I Strong force as exchange of mesons, or 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 nucleon "gives" a quark and receive an antiquark and it's the opposite for the other I do...
  13. P

    A Why does sd replace sγ5d ee in the amplitude of meson decay?

    is the amplitude of pure leptonic decay of pseudo scalar meson(say K→ee), while is the amplitude of the semileptonic decay of K→π ee. Kindly explain why does sd replace sγ5d ee in the amplitude?
  14. Bikash Kumar Das

    B Meson particles emitted from neutrons and protons

    Neutron and proton are themselves not composed of mesons, then how do they emit these particles inside the nucleus?
  15. ohwilleke

    I Excited hadrons v. fundamental particles

    Mesons and baryons have both a ground state and excited states involving the same valence quarks but a higher mass (which can in principle be calculated from QCD). Fundamental fermions and bosons, however, do not appear to display this behavior. They have a ground state, and while there are...
  16. S

    A Meson Compostions: Difference Between π0 and η

    The composition of the π0 is (uu_bar - dd_bar/√2; while the composition of the η meson is (uu_bar + dd_bar)/√2. Why is there a - sign in π0 while is there a + sign in η? How are the signs determined? By the way, can I type Latex symbols on this site? I tried to type the anti up quark by typing...
  17. M

    A Question about the matrix of a pseudoscalar meson

    Hi everyone, I have a question about the ##q_{1}\bar{q_{2}}## to vacuum : $$ \langle 0 |\bar{q_{2}}\gamma_{\mu}\gamma_{5}q_{1}| q_{1}\bar{q_{2}}\rangle$$ That is the first time I try to solve the question like this. How do we calculate the matrix about this question ? Thank you so much!
  18. AsadaShino92

    Finding the total energy of a Pi meson

    Homework Statement A K meson (an elementary particle with approximately 500 Mev rest mass) traveling through the laboratory breaks up into two Pi mesons (elementary particles with 140 Mev rest energies). One of the Pi mesons is left at rest. What is the total energy of the remaining Pi meson...
  19. R

    I Lightest Vector Meson Mass for Bottom Quarks and Antiquarks

    What is the mass of the lightest vector meson formed by bottom quarks and antiquarks?
  20. N

    I D meson decay and invariant mass

    Considering a D0->π+K- where the D meson decays from rest. If one was to want to calculate the invariant mass of the D meson by measuring the momenta of the pion and kaon, following from conservation of momentum: m2=(Eπ+EK)2-(pπ+pK)2 However by inputting numerical data Eπ=137MeV EK=493MeV...
  21. K

    I Decay of the Bs0 meson latest LHC results 7.8 sigma

    https://www.eurekalert.org/pub_releases/2017-04/thni-tma041217.php In its most recent analysis the LHCb experiment team took into account not only the first but also the second phase of operation of the LHC. The larger statistics helped achieve exceptional accuracy of the measurement of the...
  22. M

    Issue calculating the velocity of pions from K-meson decay

    Homework Statement We were supplied with several images of hydrogen bubble chamber tracks, from which we measured the length of the (invisible) K0 track, angles of departure from the K0 meson's track and curvature. As a way to limit the amount of data we're talking about, I'll only discuss the...
  23. R

    Pi meson decay (relativistic momentum)

    Homework Statement A charged π meson (rest mass = 273me) decays into a neutrino (zero rest mass) and a μ meson (rest mass = 207me). Find the kinetic energies of the neutrino and the mu meson. Homework Equations E = moγc2 K = mo(γ-1)c2 v = pc2/E p = moγv The Attempt at a Solution In the rest...
  24. B

    How can a pi_0 meson decay into 2 photons?

    Homework Statement Earlier my teacher put this equation on the board, π_0 --> γ+γ It appears to work until you consider spin. Homework Equations a quick google search reveals that the spin of a photon is +1 and the spin of a pi meson is 0 The Attempt at a Solution This appears to work for...
  25. M

    J/psi Meson Detection: ΔEΔt≈h

    Homework Statement See Image The bit about Spectral lines, I couldn't explain why[/B] Homework Equations ΔEΔt≈h The Attempt at a Solution I expected the histogram to peak at the given mass in question and to have a width of about 0.08 MeV calculated as ΔE from the Energy-time uncertainty...
  26. E

    Can meson decay be determined using rest frames and momentum conservation?

    Homework Statement Homework Equations E^2=m^2~p^2 k mass = 497.7Mev/c^2 pion mass = 139.6 Mev/c^2 The Attempt at a Solution Using the rest frame i figured that E_pi=m_k/2 so P_pi = sqrt(E_pi^2 - m_pi^2) the pion energy is half of the k meson mass so substituting that i end up with 206Mev/c...
  27. Garlic

    A Possibility of a stable mesonic nucleus

    Hello everyone, If a nucleus consisting solely of mesons has enough mesons in it, will it be stable? Mesons are bosons, therefore (unlike baryons) they aren't effected by the pauli exclusion principle, so they all can acquire the lowest energy state. In theory, if there are enough mesons, the...
  28. S

    Could a Meson Beam Weapon from Sword of the Stars Ever Be Realistic?

    There's this game called sword of the stars and one of the most interesting weapons is the meson beam. Essentially what happens is that mesons are generated and accelerated close to the speed of light so that they decay once they're inside an enemy ship, thus bypassing all defenses and creating...
  29. J

    Speed of an antimuon in a pi meson decay

    Homework Statement I'm trying to confirm the speed of an antimuon in the \pi^+ \rightarrow \mu^+ \nu_{\mu} decay through the laws of conservation but it doesn't add up. Homework Equations [/B] 1.Energy-momentum relation: E^2 = (pc)^2 + (mc^2)^2 2. Rest masses: m_{\pi} = 139.6 \...
  30. D

    Understanding the Spin States of Vector Mesons

    Hi All Thanks for welcoming me to the physics forum. I am reading Greiner and Mueller's Quantum Mechanics: Symmetries and am stuck at not understanding the vector meson ( rho meson)'s spin states. For S=1 we get three states -1, 0, and 1. Prof. Mueller separated them as a rho +/-1, and rho 0 ...
  31. T

    Understanding Meson Mixed States & Why They Don't Use Imaginary Phase

    Why mesons mixed states are defined as SOMETHING +/- SOMETHING [+/- SOMETHING] normalized by 1/sqrt(2) or 1/sqrt(3), So the sum uses quotient +1 or -1. But in electroweak symmetry breaking charged W boson is defined as W1 (+/-) i*W2, so the quotient is +i or -i. So why mesons never use...
  32. Vinci128

    Understanding CP Violation in Two-Body Decay of K Mesons

    Hi everyone, i was reading the article of Cristenson,Cronin,Fitch and Turlay of 1964, the one that discovered CP violation in the system of neutral K mesons. There is one point in it that i don't get it. They say "the angle should be zero for two body decay and is, in general, different from...
  33. ChrisVer

    CKM matrix and meson oscillations [book]

    Do you know any books or reviews that explains these in sufficient detail? I am having some small problems in understanding the triangles of the CKM matrix elements and experiments conducted for their measurement...
  34. ChrisVer

    Neutral Meson Oscillations (probabilities)

    I am looking into the probability for : \mathcal{P}(B^0 \rightarrow B^0). I said that if I start from a state |B^0> = \frac{1}{\sqrt{2}} (|B_L> +|B_H>) with L(ight)/H(heavy) are the mass eigenstates, then after some time t the state will evolve: |B^0(t) > = e^{-iHt} |B^0>= \frac{1}{\sqrt{2}} (...
  35. Dilatino

    Why can the omega meson not decay to 3 neutral pions?

    What reasons prevent the decay $\omega \rightarrow \pi^0 \pi^0 \pi^0$ from happening?
  36. E

    Neutral meson vs. neutrino oscillations

    Hello, I need to research online about the difference between neutral meson and neutrino oscillations. However I've found this difficult. I haven't found anywhere any comments on the differences between the two. The only thing which comes to mind is that the mesons can interact in their mass...
  37. U

    Upsilon Meson Decays and B Meson Decays: Feynman Diagrams and Distance Traveled

    Homework Statement (a)Draw feynman diagrams of upsilon meson. Why is decay to ##q\bar q## states suppressed? Explain why width for 4s is much wider. (b) How do B mesons decay? Why is no other type of interaction possible? Draw feynman diagrams. (c) Find the distance traveled by 1s and 4s. (d)...
  38. U

    Why don't a charm-anticharm meson decay to pair of leptons?

    If you consider the ##\chi_0 ## with a mass of ## 3.4 GeV/c^2## meson, why doesn't it decay to a pair of charged leptons? Technically it is possible though the weak interaction (Z boson) or EM interaction, right? Is it because it is so heavily suppressed because the strong interactions are...
  39. U

    Psi Meson Decay Modes: Spin, Parity, Quark Content & More

    Homework Statement (a) Explain spin and parity of mesons (b) State their quark content (c) Draw a feynman diagram of J/psi decay (d) Why doesn't ##\chi## undergo leptonic decay? (e) What is the minimum centre of mass? [/B] Homework EquationsThe Attempt at a Solution Part(a)[/B] Spin is...
  40. U

    Lifetime of rho meson and Kaon

    Homework Statement (a) What is a meson? (b) State what these mesons are made up of and explain their quantum numbers and interactions. (c) Find the lifetimes of rho meson and kaon. (d) Find the dominant decay mode and explain why. (e) Why is decay to 2 neutral pions forbidden? (f) Explain how...
  41. A

    Why Mesons Can't Be Made of 2 Quarks Alone

    As far as I know a Baryon is made of three Quarks (eg uud, udd etc) and a Meson of two Quarks, a Quark/Antiquark pair. As I am not a student / scholar in Physics but very deeply interested in this field, I couldn't find any explanation, why a Meson is omly made up by a Quark/Antiquark pair. What...
  42. Safinaz

    BR of semileptonic B meson decay

    Hi there, In a reference as 1303.5877v1 [hep-ph ] the SM branching ratio of ## B \to \tau \nu ## is given by: ## \frac{m_B G_F^2 m_\tau^2 \tau_B f^2_B } { 8 \pi } V_{ub}^2 ( 1 - \frac{m_\tau^2}{m_B^2} )^2 ## . In the SM model the value of this BR ## \sim 0.7 \times 10^{-4} ## . But I don't...
  43. Z

    Could Excited Baryon decay into omega meson and baryon?

    Excited baryon could decay into photon and ground state baryon,but could it decay into omega meson and ground state baryon?Could you introduce me some articles about it,experimental or theoretical?
  44. Matt atkinson

    Beta+ meson, decay - Relativistic kinematics

    Homework Statement The ##B^+## meson decays through the weak interaction. One of its decay channels is . If a ##B^+## is traveling with a total energy of 9.90 GeV, calculate the range of possible energies the produced may have. (i.e. determine the minimum and maximum values of its energy.)...
  45. zubair

    Having trouble combing through PDG's site

    Hey Folks, I wanted to put together a single spreadsheet of subatomic particles (e-, ν, b, t, π Ξ, Σ, Δ, etc.) and their properties that have been measured (mass, mean lifetime, valence quark content, charge, spin, parity, etc.). I have been looking through the PDG website for some way to...
  46. edguy99

    Is a Ds3*(2860)ˉ Meson? Analysis of CERN LHC Quarks

    There has been news lately on Ds3*(2860)ˉ from the CERN LHC of spin3 particles made from quarks. One example at http://news.yahoo.com/exotic-particle-could-help-explain-holds-matter-together-111405002.html The article says: " The Ds3* particle is made of one charm antiquark and one strange...
  47. B

    Quarkonium: General Information

    So I've been set a computational problem regarding applying the Shroedinger equation to quarkonium and I'm just trying to do some research around the subject because it's nothing like I've ever covered before and quite fascinating. There's quite a few questions that I can't find answers to...
  48. B

    Drawing Feynman Graphs for D→KK Meson - Need Help!

    Hi there, I need to draw the Feynman graphs for D→KK meson . I would be appreciate if anyone can help me. Thank you so much.
  49. G

    Eta prime meson as SU(3) singlet

    I understand that when the quark theory was being developed that SU(3) was used to explain the mesons that were ultimately found to be composed of the up, down, and strange quarks. I also get that the SU(3) is grouped as an octet and a singlet, with the eta prime meson being the singlet. But I'm...