What is Particle decay: Definition and 67 Discussions

Particle decay is the spontaneous process of one unstable subatomic particle transforming into multiple other particles. The particles created in this process (the final state) must each be less massive than the original, although the total invariant mass of the system must be conserved. A particle is unstable if there is at least one allowed final state that it can decay into. Unstable particles will often have multiple ways of decaying, each with its own associated probability. Decays are mediated by one or several fundamental forces. The particles in the final state may themselves be unstable and subject to further decay.
The term is typically distinct from radioactive decay, in which an unstable atomic nucleus is transformed into a lighter nucleus accompanied by the emission of particles or radiation, although the two are conceptually similar and are often described using the same terminology.

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  1. S

    I Can proton/neutron decay be avoided in some conditions?

    I was wondering whether the decay of neutrons and protons (if they happen to be able to decay, as it is predicted by some GUTs) could be avoided in some cases. Let's begin with neutrons: In principle neutrons have a very short time when they are isolated (around 10 minutes) and they suffer...
  2. nightvidcole

    A Decay Modes of J/psi: Understanding Gamma and Hadron Decays

    Everywhere I look, I see the claim that J/psi decays to "g g g" about 64% of the time, and to "gamma -----> hadrons" about 13% of the time. My question is, exactly how does one distinguish between (1) J/psi -----> g g g ------> hadrons, and (2) J/psi -----> gamma ------> hadrons? If you...
  3. O

    I Question on Baryons and Specific Decays

    1) We know in case of beta decay if there is excess of protons or neutrons in the nucleus beta decay take place. Force involved - weak interaction Reason involved - to stabilize, to obtain proton neuton 1:1 ratio in the nucleus. E. g., Beta minus - Carbon 14 transforms into Nitrogen 14 2) Case...
  4. RicardoMP

    A How to reduce an integral in phase space to a one-dimensional form?

    I've been trying for a very long time to show that the following integral: $$ I_D=2{\displaystyle \int} \, {\displaystyle \prod_{i=1}^3} d \Pi_i \, (2\pi )^4\delta^4(p_H-p_L-p_R) |{\cal M}({e_L}^c e_R \leftrightarrow h^*)|^2 f_{L}^0f_{R}^0(1+f_{H}^0). $$ can be reduced to one dimension: $$ I_D...
  5. W

    How Does Conservation of Momentum Apply to Particle Decay?

    Attempt at solution: By conservation of momentum: $$P = (M,0,0,0) = p_1 + p_2 = (E_1 + E_2, 0, 0,0)$$ thus $$ M = E_1 + E_2 = 2k^2 + m_1^2 + m_2^2$$ Now $$E_1^2 - E_2^2 = m_1^2 - m_2^2 = (m_1 + m_2)(m_1-m_2)$$ $$ = M(m_1-m_2) = (2k^2+m_1^2+m_2^2)(m_1-m_2)$$ Isolating k: $$ k =...
  6. Cocoleia

    Particle decay, Lorentz transformations with angles

    Homework Statement I have a mother particle at rest, which decays to a daughter particle. The daughter has mass m, momentum p and energy E and is at an angle θ1. Now I have to assume that the daughter is emitted at an angle θ2, and the mother is moving along the x-axis with velocity βc. I need...
  7. F

    Relativistic Decay: Calculating Pion Momentum

    Homework Statement A Sigma^+ decays at rest into a neutron and a pion^+ meson, i.e. according to the reaction $$\Sigma \rightarrow n + \pi$$ The n and π masses are assumed known. The kinetic energy of the π + is measured to be 92 MeV. Determine the momentum of the pion. Homework Equations...
  8. J

    I On the decay of the neutral Sigma particle

    Hello! I wanted to ask why does the neutral Σ decay almost always to one γ(or two) and a neutral Λ. Why can't it decay to anything else? Thanks!
  9. LarryS

    I Conservation laws during particle decay?

    I believe that conservation laws, like for energy and momentum, are obeyed during the particle decay process, e.g. the total energy of the new output particles is equal to the energy of the one input particle. But is that relationship subject to quantum fuzziness? Suppose we, somehow, prepare...
  10. E

    A Hadrons with significant branching ratios to muons

    Hi, I'm undergraduate researcher and my professor is interested in the answer to this question. He's kind of left me in the dark on why this is important to us, but that is another matter. We want hadrons that are produced at LHC conditions and decay before reaching the detector. So far all...
  11. R

    Energy of the photon emitted in a gamma ray decay

    Homework Statement An Fe nucleus (A=57) decays from an excited stated to the ground state by emitting a gamma ray. The energy of the photon is 14.4 KeV when the nucleus is held fixed. If the nucleus is free to recoil then the energy of the photon emitted will be? Homework Equations ## E =...
  12. R

    Calculating the energy of anti neutrino

    Homework Statement A free neutron is unstable and decays into proton electron and an anti neutrino. The rest masses of these particles are ##m_n = 939.6 MeV, m_p = 938.3 MeV m_e = 0.51 MeV ##and ##m_{\nu} = 0 ## so that the change in the total rest mass in the decay is 0.79 MeV. If in a...
  13. F

    Possible webpage title: How does energy factor into the decay of particles?

    Homework Statement [/B] A particle detector shows tracks produced by two particles X and Y that were created by the decay of a lambda particle at O. Which of the following is a correct statement about energy at the decay? The energy of X must be greater than that of Y. The combined energy...
  14. T

    I Why Does Unstable Particle Decay Follow an Exponential Curve?

    Given that an unstable particle has a constant probability of decaying per unit time, why is it said that its chance of surviving falls exponentially?
  15. Isomorphism

    Particle decay: Relativistic or classical?

    This question was asked in an competitive exam in India. The relevant equations are momentum conservation in the classical sense and the 4 momentum conservation. My attempt: Classical momentum conservation would seem inaccurate since the kinetic energies are high. However, a straightforward...
  16. P

    Particle Decay After a Certain Distance

    Homework Statement A certain elementary particle lives only a time [T][/0] = 5 sec (proper time) before disintegrating. What velocity must the particle have if it is to reach the Earth from the Sun before disintegrating? Distance between the Earth and Sun is 1.5x10^11 meters.[/B]Homework...
  17. Elvis 123456789

    Another relativistic particle decay question

    Homework Statement Unstable particles cannot live very long. Their mean life time t is defined by N(t) = N0e−t/τ , i.e., after a time of t, the number of particles left is N0/e. (For muons, τ=2.2µs.) Due to time dilation and length contraction, unstable particles can still travel far if their...
  18. Elvis 123456789

    How Fast Must Muons Travel to Reach a Distant Target Without Decaying?

    Homework Statement Unstable particles cannot live very long. Their mean life time t is defined by N(t) = N0e−t/τ , i.e., after a time of t, the number of particles left is N0/e. (For muons, τ=2.2µs.) Due to time dilation and length contraction, unstable particles can still travel far if their...
  19. R

    I What is the role of entropy in particle decay theory?

    Maybe my question is a bit more philosophical than scientific. In the macroscopic world entropy means that things become more chaotic and less orderly as they decay. It seems to me somewhat paradoxical that in the quantum world lower generation particles "decay" into the first generation...
  20. P

    Calculate the energy of the neutrino in the following decay

    Homework Statement Stopped pions provide a useful mono-energetic source of neutrinos. For a pion at rest, calculate the energy of the neutrino in the decay $$\pi^+\rightarrow \mu^++\nu_{\mu}$$ You do not need to consider the subsequent decay of the ##\mu^+## and you can assume that the...
  21. Xico Sim

    I Method to know if a reaction is allowed

    Hi guys. This is my first post here. Here it goes. I'm attending an introductory course on particle physics. By now, I'm supposed to know how to find out if a given reaction, say νμ+p→μ++n (for example) is possible or not. Unfortunately, the rules by which a reaction must abide are still foggy...
  22. S

    Unraveling Hadronization: Understanding Particle Decay and Feynman Diagrams

    Hello everyone, I've been wondering for a while how is it possible to determine which decays are possible from a particle or, given a decay be sure that the given decay is possible and hence draw a Feynman diagram of it. I know I have to take into account conservation charge, energy...
  23. T

    Why Does Particle Decay? | Explained with Fermi

    For instancr like neutron decaying into proton electron and antineutrino. I read it in a book that says that according to Fermi, each of these particles are vibrations in different quantum fields and that each field exerted a tiny influence on the others. Because of quantum mechanics, we can't...
  24. W

    Relativistic Particle Decay: Momentum Conservation

    A particle with mass M a rest decays into two particles a and b. I know that Ea + Eb = Mc2, from conservation of energy. But I'm pretty confused about signs in the conservation of momentum equation, and I've actually seen two versions! pa + pb = 0, so pa = - pb. But I've also seen pa = pb! I...
  25. JG1009

    CP Violation in Neutral Kaon Decays

    I was recently reading an article that attempted to explain how the results of the Cronin-Fitch experiment illustrated CP violation. (http://hyperphysics.phy-astr.gsu.edu/hbase/particles/cronin.html) However, it wasn't very well explained. Could someone please explain this to me?
  26. QuantumKangaroo

    Difference between Photons and the Higgs Boson?

    I'm new to quantum physics, and this might be a stupid question. What is the difference between Photons and the Higgs Boson? I know that neither of them interact with the Higgs field. And that when CERN found the Higgs Boson, it decayed into other particles INCLUDING photons. So what's the...
  27. 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?
  28. U

    Tau leptonic decay - Lifetimes and modes

    Homework Statement [/B] (a) Explain lepton universality. (b) Explain why decay mode is forbidden and find hadronic branching ratios. (c) Find the lifetime of tau lepton. (d) What tau decay mode would be suitable? (e) Find the precision. (f) How do you improve the results? (g) Why is it much...
  29. U

    Why is this tau decay not allowed?

    Why is the decay ##\tau^{-} \rightarrow \mu^+ + \mu^- + \mu^-## not allowed? Charge, lepton number are conserved. I have a feeling it is something really basic. I'm thinking in weak interactions you only go from a ##l^- \rightarrow \nu_{l}## and not 'hop' from one muon to another non-neutrino muon.
  30. Phynos

    Relativistic kinetic energy - particle decay

    Homework Statement A pion at rest (mπ = 273me) decays into a muon (mμ = 207me) and an antineutrino (mn ≈ 0). Find (a) the kinetic energy of the muon and (b) the energy of the antineutrino in electron volts. Homework Equations K = (γ-1)mc2 E = γmc2 ER = mc2 E2 = p2c2 + (mc2)2 I didn't...
  31. 1

    Angle of photon emission from particle decay (Particle Phys)

    Homework Statement a) Particle A decays at rest into two photons. Calculate, in terms of the rest mass of A, the energy and momentum of each photon. b) In a different reference frame, particle A is initially in motion such that its kinetic energy is equal to its rest energy. Find the momentum...
  32. ORF

    Can we find EM radiation in charged particle's decays?

    Hello. I was taught that a charge which changes its velocity must radiate (at least, in classical electrodynamics). Let's consider a charged particle which decays into another charged particle (and, maybe, others neutral particles; but not photons). In this case, can we find electromagnetic...
  33. P

    Relativistic Particle Decay of Higgs Boson

    Homework Statement A Higgs boson has mass 125 GeV/c2, decaying into a pair of Z bosons, mass 91 GeV/c2. In the lab frame, one of the Z bosons is at rest. Determine the kinetic energy for the other Z boson in this laboratory frame. Homework Equations E = γmc2 γ=1/√(1-β2) The Attempt at a...
  34. Safinaz

    Off-shell Particle Decay: Does Mass Affect Cross Section?

    Hi all, I think that the off shell decay dosn't decrease the decay cross section, I mean if a particle X decays into a jet pair has mass for example Mjj ~ 130 GeV, being X has mass M ~ 130 GeV so decay in resonance or on shell into jj or being MX even much greater ~ 2000 GeV , this...
  35. C

    Particle Decay: Radioactivity & Reversibility

    In the process of particle decay (eg carbon-14 ---> nitrogen-14), is there any relations with radioactivity? Is it reversible? ( up quark + 2 x down quark + W positive boson = down quark + 2 x up quark + electron, so that carbon-14 turns to nitrogen-14. Is it possible that down quark + 2 x up...
  36. PsychonautQQ

    How Do You Calculate the Kinetic Energy of Particles in Relativistic Decay?

    Homework Statement A K_0 particle has a mass of 497.7 MeV/c^2. It decays into a -∏ and +∏, each having a mass of 139.6 MeV/c^2. Following the decay of the K_0, one of the pions is at rest in the laboratory. Determine the kinetic energy of the other pion after the decay and of the K_0 prior to...
  37. J

    Physics Particle Decay Question (Cons. of Momentum?)

    Physics Particle Decay Question (Cons. of Momentum??) Homework Statement An isotope of Polonium 210Po with mass 3.49x10^-25 kg can decay into an alpha-particle(He Nucleus) with mass of 6.64x10^-27 kg and an isotope of lead 206Pb with a mass of 3.42x10^-25. If the polonium decays at rest. and...
  38. PsychonautQQ

    Special Relativity particle decay.

    Homework Statement An accelerator produces a beam of Un that travels to a detector located 100m away. The particles travel with a velocity of .866c, so in the laboratory frame it takes the particles .385*10^-6 seconds to get to the detector. By the time the particles get to the detector, half...
  39. sunrah

    Particle decay rates, CKM matrix etc

    Homework Statement Calculate following decay rate \frac{\Gamma(D_{0} \rightarrow K^{-} \pi^{+})}{\Gamma(D_{0} \rightarrow \pi^{+} \pi^{-})} Use the (Cabibbo–Kobayashi–Maskawa) CKM-matrix. Homework Equations The Attempt at a Solution D^{0} = |cu\rangle , D^{+} = |cd\rangle ...
  40. A

    Special Rel. 4 momenta, particle decay.

    Homework Statement A particle X with rest mass mx is traveling with speed vx = 0.8c along the x-axis in the lab frame. (a) Write down the four-vector momentum of the particle in the lab frame in terms of vx and mx. The particle decays to two particles, A and B, each with mass mx/4...
  41. J

    Why is the speed of light a constant in relativity?

    I'm not a physics person (did not take it in high school), but I was wondering why the speed of light is the constant (in relativity) and not the half life of an electron or positron. The name of a good introductory book to physics would be good too. Thanks in advance.
  42. K

    Why do particles decay and what processes are involved?

    why is that particles such as the tau muon have a short lifespan and why is it that particles decay into other partcles? furthermore, what are the process that occur in particle decay?
  43. Mordred

    Particle Decay Order for Beginners

    Ive searched in vain for a listing of what particles with which interactions decay into which particles. This is a subject I know very little on so any starting direction would be greatly appreciated
  44. P

    Multichannel particle decay survival probability

    Particle can decay through many channels with probabilities p_i, where in each channel its decay time is different \tau_i. It always decays through one of the channels. Particle decays according to exponential law where probability to decay in time t is...
  45. P

    Particle composition vs particle decay

    Ive read that elementary particles can decay. I am trying to understand how this can be with a particle that has no composition. So i have two questions: If elementary particle A decays into particles B and C, then why can't we say that A is composed of B and C? If an elementary particle can...
  46. G

    Particle Decay: Understanding Energies and Four-Momentum | Physics Homework

    Hello everybody, I'm assigned to do particle physics home, which I don't really understant because I'm a freshman and I have choosen it as a free subject. Obviously, that was a mistake. I have been reading a book, but I'm not sure if I understand everything. Homework Statement A particle of...
  47. F

    Energy and Momentum in Particle Decay

    If a particle decays via A →B + C, and A had some initial non-zero momentum, is it possible for either B or C to be stationary? I can't seem to find a restriction on this from energy conservation or momentum conservation. From energy conservation, the stationary particle B still contributes...
  48. jfy4

    Particle Decay Mode Percentages

    Hi everyone, I find the following table from WolframAlpha concerning the probability of various decay modes of the pion \pi^{+}. My question is: Are these probabilities calculated, or are they numbers from numerous experiments? Thanks,
  49. Islam Hassan

    What are the different forces that can contribute to particle decay processes?

    What drives particle decay? Is it an elementary, irreducible observation or can we model it based on a set of observable variables? Do all particle decay modes involve the weak force? Does one even need the intervention of a given force to have particle decay? Does string theory explain...
  50. K

    Particle decay using 4-momentum

    Homework Statement A particle of mass M, traveling horizontally through the laboratory, decays into two daughter particles, each of mass 0.4M. One of the daughters, A, is produced at rest in the Lab frame. Show that vcm , the speed with which the CM frame moves in the Lab frame, is equal...