What is Pions: Definition and 45 Discussions

In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: π) is any of three subatomic particles: π0, π+, and π−. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged pions π+ and π− decaying after a mean lifetime of 26.033 nanoseconds (2.6033×10−8 seconds), and the neutral pion π0 decaying after a much shorter lifetime of 85 attoseconds (8.5×10−17 seconds). Charged pions most often decay into muons and muon neutrinos, while neutral pions generally decay into gamma rays.
The exchange of virtual pions, along with vector, rho and omega mesons, provides an explanation for the residual strong force between nucleons. Pions are not produced in radioactive decay, but commonly are in high-energy collisions between hadrons. Pions also result from some matter–antimatter annihilation events. All types of pions are also produced in natural processes when high-energy cosmic-ray protons and other hadronic cosmic-ray components interact with matter in Earth's atmosphere. In 2013, the detection of characteristic gamma rays originating from the decay of neutral pions in two supernova remnants has shown that pions are produced copiously after supernovas, most probably in conjunction with production of high-energy protons that are detected on Earth as cosmic rays.The pion also plays a crucial role in cosmology, by imposing an upper limit on the energies of cosmic rays surviving collisions with the cosmic microwave background, through the Greisen–Zatsepin–Kuzmin limit.

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  1. B

    I Tau Decay: More Pions, Less Ratio?

    Hello! Tau decay has a branching ratio to a charged pion + neutral pion + tau neutrino much bigger than to a charged pion and a tau neutrino. Based on consideration of available phase space, I would imagine that adding an extra pion would decrease the branching ratio. Why is this happening...
  2. 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?
  3. T

    Axial Transformation of a pion

    Homework Statement I'm considering a non-linear chiral theory where the Lagrangian is in terms of the field #\Sigma = e^{\frac{2i\pi}{f}}# where #\pi# is my pion matrix containing pion, kaon, and #\eta#. I need to calculate the transformation of #\pi# up to order #\pi^2# under an axial...
  4. K

    Calculating the Maximum Kinetic Energy of pions

    Homework Statement The problem is to Use the rest energy values in table 1 to calculate the maximum kinetic energy of the pions assuming the kaon is at rest before it decays. Rest Energies of pions are π- 140, π0 135 and π+ 140. Rest energies of kaons K- 494, K0 498 K+ 494 Homework...
  5. Gene Naden

    I Why does the long-lived kaon only rarely decay to two pions?

    The weak interaction doesn't conserve CP, so it shouldn't care whether there are two neutral pions in the decay product or three. And the three-pion decay is slowed down by the lack of phase space since there is little mass in excess of that of three pions. So why don't we see more decays into...
  6. Kevin McHugh

    I Exploring Half Lives of Pions in Nuclei

    Do they exist in nature, i.e. in high Z nuclei, or are they only created in scattering experiments? Are the half lives increased in bound states? Why do positive pions get trapped in the potential well as well as negative pions?
  7. L

    Are pions produced in pairs?

    I thought only strange particles were produced in pairs via the strong interaction, however in my textbook it states 'kaons, like pions are produced in pairs via the strong interaction'. Can particles that are not strange also be produced in this way?
  8. 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...
  9. khelzor

    I Pion Detection: Finding a Film for Interference Experiment

    I'm a student in high school asking for suggestions for an experiment proposal. So far, our idea has been to recreate Young's interference experiment, but instead of using electrons, we will use a heavier particle. Charged pions have been the first choice so far. Aluminum is the current delegate...
  10. S

    I Photoproduction of pions off protons

    A meson can be produced by a high energy photon scattering off a nucleon in an interaction such as $$\gamma + p \rightarrow p + \pi^0$$ As long as the photon is sufficiently energetic, mesons heavier than the pion can be produced, as well as multiple mesons such as ##\pi^{+} + \pi^{-}##...
  11. 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...
  12. bcrowell

    Experimental Signatures of Neutral Pion Decay at High Energies

    A neutral pion decays into two gammas. In the rest frame of the pion, these are back to back and have energies of 67 MeV. I'm interested in the case where the pion's energy in the lab frame is on the order of a few hundred MeV. Can anyone point me to any source of information on what kind of...
  13. 1

    How does protons has mass and not pions?

    hi, I've heard that protons has most of their mass from their electromagnetic and strong interactions between their quarks, but specifically, how does that make mass? and if so, what is intrinsic mass then? and pions has 2 quarks and strong and electro interactions, why doesn't it has mass...
  14. 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?
  15. 1

    Time of flight experiment to distinguish muons from pions?

    If I wanted to design an experiment which would allow to distinguish muons from pions in the energy range from 200 MeV to 2 GeV, how would I do it in a simple way? Could I just use the Time of Flight experiment? What quantitative arguments can one make for the design of the detectors?
  16. P

    Velocity of pions after moving far away from each other?

    Homework Statement A proton and an antiproton, each with an initial speed of 5.90 107 m/s when they are far apart. When these two particles collide, they react to form two new particles: a positive pion (π+, charge +e) and a negative pion (π−, charge −e). Each pion has a rest mass of 2.5...
  17. A

    Mass of Pion in Gev/c^2: Calculate and Convert

    The mass of a pion is 2.5x10^-28kg. Calculate the mass of a pion in Gev/c^2. I really don't understand how to do these, as I always divide/multiply the wrong numbers etc. Does anyone have any ways to remember which way round you do it? (1eV = 1.6x10^-19J) I get confused whether to times or...
  18. G

    Momentum exchange of virtual pions

    I know that the strong force is viewed as the exchange of virtual pions between two nucleons, with the mass and range of them confirmed by the energy-time uncertainty principle. But if the momentum of the pion is transferred from one nucleon to the other in the interaction, wouldn't that give an...
  19. T

    Decay of a moving Kaon in to two charged Pions

    Homework Statement A Kaon (k0) decays into two charged pions (π+ & π-), what is the minimum momentum required for the kaon so that none of the pions move backwards (in the opposite direction of the kaon) in the laboratory frame. Homework Equations Conservation of momentum...
  20. D

    Understanding Neutral Pions: Superpositions, Particles, & Feynman Diagrams

    So apparently a neutral pion is a superposition of u\bar{u} and d\bar{d}. I'm having trouble understanding what this means. I have no problem understanding how the decay products of some scattering experiment could be a superposition of these two states, but how can we treat this superposition...
  21. F

    Pions vs. Fermi Dirac Statistics and Bose-Einstein Statistics

    Hello! I have a small question, and I am not sure if I am missing something: Today I glanced at the wikipedia page for Pions, and saw this: Statistics: Bosonic Can anyone explain to me why a quark paired with a anti-quark obey Bose-Einstein Statistics? If quarks obey Fermi-Dirac statistics...
  22. C

    Percentage of neutral pions created

    When bombarding a target with a high energy proton beam, of the pions produced, what determines the percentage of them that are neutral?
  23. F

    How are Pions Produced in Nuclei?

    How are Pions produced inside a nucleus? I've heard it was through gluons exchange but found nothing about it.
  24. J

    Explaining role of Pions in Strong force interactions.

    Let me start off by saying that I am no professor of any kind, i am simply a high school student in way over his head concerning particle interactions. Without a class to teach me, i have used the magic of the internet to attempt to get a rudimentary understanding of these interactions. I...
  25. A

    Why is the decay of a neutral ρ meson to two neutral π's disallowed?

    Hi all. I'm looking at the decay of a neutral ρ meson to two neutral π's. I think it is disallowed but I can't figure out why. The J^{P} of the ρ is 1^{-} and 0^{-} for the neutral π's. The formula P(ρ^{0})=(-1)^{L}P(π^{0})P(π^{0}) then says that the decay is allowed provided the π's are...
  26. A

    Why do charged pions have different masses from neutral pions?

    The charged pion particles (\pi^+ and \pi^-) have different masses from the neutral pion particle (\pi^0). Why? It's not like the pions are nuclei that they have binding energy.
  27. J

    Quarks effective masses and the pions

    Hi everybody :) A lagrangian of the u and d quarks where they don't have a mass, shares chiral SU(2) and U(1) symmetries. In the vacuum, we write <0| \bar{Q} Q | 0 > = \eta where Q is the douplet of u and d quarks. In such a way we break chiral symmetries. The current associated with...
  28. B

    Unceartianity and virtual pions.

    Hi, I'm 11 so I probably will not understand your answer if you use a lot of math without explaining it. I heard that Heisinburg's unceartianity principle was what made people believe Yukawa(spelled right?) that there are such things as virtual mesons that can be pulled out of a vaccum, you...
  29. J

    Why Do Pions Decay? Weak Force & Strong Force Explained

    I heard that (charged) Pions decay due to the weak force, but what does that have anything to do with it? Also, wouldn't the strong force hold them together? I actually came up with the idea of the Pion on my own before discovering that it had already been discovered. Also, could they be...
  30. J

    Is it possible the decay of rho neutral meson to two pions?

    ¿Is it possible the decay of rho neutral meson to two pions? Homework Statement We initially have the neutral rho meson -----> pion+ + pion- ¿Is this reaction possible? ¿What are the conserved quantities?¿Which is the interaction involved in the process? Homework...
  31. FeDeX_LaTeX

    Pions, Muons, Kaons, Tau, Neutrinos

    Hello; Are these particles all found in the atom? If so, whereabouts? Thanks.
  32. S

    Linear acceleration and speed of light and pions

    Homework Statement In a particle physics experiment a particle called pion is used to hit a target. The particle pion has a (rest) lifetime of 2.6x 10-8 second and is accelerated to a speed 0.99c with respect to the linear accelerator. A straight beam pipe is used to transport the pions to...
  33. E

    In SUSY, do pions have SUSY-partners?

    SUSY, (SUSY-MSSM, SUSY-GR, M-theory) doubles the number of particles in the SM, but what about SUSY partners for mesons like pions?
  34. matt_crouch

    Calculating the proper mean lifetime of pions

    Calculating the "proper mean lifetime" of pions Homework Statement The mean lifetime of pions at rest is to=2.6x10^-8. if a beam of pions has a speed v=0.85c a)what would their lifetime be in the laboratory? b)how far would they travel before they decay? c)what would your answer to b)...
  35. F

    Stuck with Kaon Decay: Finding Ek of Pions

    Homework Statement a neutral kaon at rest decays to pion- and pion+ , if kaon rest mass is 497.7MeV/c^2, and the pions rest mass is 139.6MeV/c^2, what are the kinetic energies of the resulting pions? Im very stuck with this, and not sure where to start, how can i find Ek of pions, if i don't...
  36. R

    Pion Constituents: Nucleon & Antinucleon Explained

    The nucleon and antinucleon are each about seven times more massive than the pion How is it conceivable that the pion could be a combination of nucleon and antinucleon
  37. S

    Exploring the Mystery of Particle Mass: The 3 Pions

    The 3 pions have different masses and we say this so because of the electro magnetic energy.if this is so then we can never measure a mass because the magnitude of the EM energy that a particle receives depends on the charged particles around it. if you help with this dilemma i would be grateful.
  38. C

    Special Rel. Creates pions decaying, most of question completed.

    Homework Statement I was wondering if I am getting anything like the right answers here to this: 12. A relativistic anti-proton, with total energy 30 GeV, travels 2.5 x i04 light years (2.36 x 1020 m) from the centre of the Milky Way galaxy and collides with a proton in the Earth's...
  39. J

    Pions - how they interact with Baryons

    hey, i was told that in a Atom's Nucleus, Nucleons keep changing from Proton state to Neutron state , and vice versa , by the means of Pions exchange. But how does this works I know : p+ : u u d n : u d d Positive pion (that turns neutron into proton ?) : (d) u u d d + (d) u = u u...
  40. Q

    Pions and Quarks: The Mystery of the Neutral Pion

    why is it that the pion with no charge (the one with the 0 in the top corner) actually exists? cos if it's made of an up anti-up or a down anti-down quark, shouldn't they annihilate each other?
  41. D

    Proton and anti-proton annihilation can produce extra pions

    Why do proton and anti-proton annihilation can produce extra pions, in addition to the photons; whereas the electron and positron interaction only gives photons?
  42. D

    Nuclear physics Pions and Parity?

    Nuclear physics Pions and Parity? Ignore, nevermind Why can: \pi^- + d \rightarrow n + n + \pi^0 not happen for pions at rest? work so far: \begin{array} {|c|c|c|c|c|c|}\hline&\pi^-&d&\rightarrow &n \ + \ n&\pi^0\\\hline{Spin}&0&1&\ \rightarrow &1/2 \...
  43. M

    Strong Force: Gluons vs. Pions

    I;ve heard 2 different things, and onw says that the strong force is mediated by the gluon, but also, I've also heard that it is mediated by pions. The strong force, AFAIK, is actually caused when the 3 quarks in a hadron, continually exchange gluons with each other. And if a red quark, emits a...
  44. curious george

    Why do different pions have different lifetimes?

    I don't understand why the pi(+) has such a long lifetime compared to the pi(0). Can anyone give me a simple qualitatiive explanation of this?