What is Muon: Definition and 175 Discussions

The muon (; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton. As with other leptons, the muon is not known to have any sub-structure – that is, it is not thought to be composed of any simpler particles.
The muon is an unstable subatomic particle with a mean lifetime of 2.2 μs, much longer than many other subatomic particles. As with the decay of the non-elementary neutron (with a lifetime around 15 minutes), muon decay is slow (by subatomic standards) because the decay is mediated only by the weak interaction (rather than the more powerful strong interaction or electromagnetic interaction), and because the mass difference between the muon and the set of its decay products is small, providing few kinetic degrees of freedom for decay. Muon decay almost always produces at least three particles, which must include an electron of the same charge as the muon and two types of neutrinos.
Like all elementary particles, the muon has a corresponding antiparticle of opposite charge (+1 e) but equal mass and spin: the antimuon (also called a positive muon). Muons are denoted by μ− and antimuons by μ+. Formerly, muons were called "mu mesons", but are not classified as mesons by modern particle physicists (see § History), and that name is no longer used by the physics community.
Muons have a mass of 105.66 MeV/c2, which is approximately 207 times that of the electron, me. More precisely, it is 206.7682830(46) me.Due to their greater mass, muons accelerate more slowly than electrons in electromagnetic fields, and emit less bremsstrahlung (deceleration radiation). This allows muons of a given energy to penetrate far deeper into matter because the deceleration of electrons and muons is primarily due to energy loss by the bremsstrahlung mechanism. For example, so-called "secondary muons", created by cosmic rays hitting the atmosphere, can penetrate the atmosphere and reach Earth's land surface and even into deep mines.
Because muons have a greater mass and energy than the decay energy of radioactivity, they are not produced by radioactive decay. However they are produced in great amounts in high-energy interactions in normal matter, in certain particle accelerator experiments with hadrons, and in cosmic ray interactions with matter. These interactions usually produce pi mesons initially, which almost always decay to muons.
As with the other charged leptons, the muon has an associated muon neutrino, denoted by νμ, which differs from the electron neutrino and participates in different nuclear reactions.

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  1. Jonathan Scott

    I Is the Near Integer Muon to Electron Mass Ratio a Coincidence or Significant?

    I've known for a long time that the muon mass is approximately 3∕2×137 times that of the electron, as in Nambu's empirical mass formula from 1952. I recently wondered what the difference was as a multiple of the electron mass, using current CODATA figures for the muon to electron mass ratio and...
  2. R

    I Muon Decay Example from Morin's Book: Issues Explained

    From the Lorentz transformation equations we know that $$t = \gamma(t^{'} - x^{'} v/c^2)$$ but for the Muon decay example where the setup is as follows : "Assume for simplicity that a certain muon is created at a height of 50 km, moves straight downward, has a speed v = .99998 c, decays in...
  3. racerunner

    B Muon Tomography Evidence for Special Relativity?

    Muons are a popular way to provide evidence for Special Relativity. But, does Muon Tomography provide evidence for SR? Can you calibrate your muon detectors without reference to SR? Is there any need to refer to SR when interpreting the data? I tutored a high school student who argued the...
  4. Sciencemaster

    I Incorrect units when calculating cosmic ray muon flux

    I recently performed an experiment that involved using a cylindrical scintillator to detect cosmic ray muons by observing the amount of particles that decayed within 20 microseconds over a long period of time. I'd like to use this to find the flux of muons at my scintillator so that I can...
  5. atyy

    B ETMC lattice results are closer to the measured muon g-2

    Jester points out a new lattice result https://arxiv.org/abs/2206.15084 from the Extended Twisted Mass Collaboration (ETMC) that is closer to the measured muon g-2. Davide Castelvecchi has a news item in Nature summarizing various results about the possibility of a muon g-2 anomaly.
  6. B

    B Time Dilation & Muon De Broglie Wavelength: Explained

    I understand it's experimentally verified muons traveling at relativistic speeds relative to an observer will be observed to have longer half-life than would be observed in the rest frame of the muons, which is explained theoretically by a relativistic time dilation effect. Does this correspond...
  7. X

    B A muon enters a lithium battery....

    Just wondering what would happen if a muon entered the LiH dense environment of a lithium battery. Could it explain the instances of spontaneous combustion of the battery in electric vehicles? Li + H => He
  8. Diracobama2181

    Special Relativity Muon problem

    i) The muon reaches the ground ii) To a ground observer, the decay time is dilated $$\Delta t_d=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}\Delta\tau_d>\Delta \tau_d$$ The time for the muon to reach the ground is $$\Delta t_g=\frac{10 km}{0.999c}< \Delta t_d$$ which is why it reaches the ground...
  9. R

    B Where can I buy a muon detector?

    Hi, Can you please help find where I can buy a muon detector, or someone who will build a muon detector for me? Nothing fancy just a detector that flashes and beeps when a muon is detected. I do not have the skill or knowledge to accomplish this task. Any help with this endeavor would be greatly...
  10. Andreas S-H

    B Calculating Energy Loss of Muon Moving Through a Medium

    Hello everyone. I have just complete an experiment calculating the speed of a muon. I got it to 2.6E8 m/s, however I know that they are created at close to speed of light to be able to get down to Earth's surface in their short lifespan. This speed could not have been its initial speed, as it...
  11. bbbl67

    I A large normal atom, but with a muon in its outer shell?

    So let's say we have a large neutral atom, e.g. gold with 79 electrons around it. Let's say we replace its outermost electron with a muon. Muons orbit closer to the nucleus than electrons, much closer. Will the outermost muon be closer into the nucleus than even its innermost ground-state...
  12. T

    Calculating Fermi Coupling Constant (muon)

    I am trying to determine the Fermi Coupling Constant which is measured to be ##1.1663787 *10^{-5}\text{Ge}V^{-2}##. The formula for Fermi is ##\frac{G_F}{(\hbar c)^3}=\sqrt{\frac{\hbar}{\tau_\mu}\cdot\frac{192\pi^3}{(m_\mu c^2)^5}},## where ##m_\mu## is the mass of a muon which is ##\approx...
  13. T

    Which threshold value provides the most accurate results for muon decay time?

    I am trying to understand my results for my muon experiment. I conducted the experiment using a plastic scintillator photomultiplier detector. I have four different data sets, with different discriminator thresholds: 148 mV, 190 mV, 260 mV and 550 mV. I made a histogram of the counts of all four...
  14. T

    What is the purpose of the decay time distribution equation?

    I know for muons that the the probability that a muon decays in some small time interval ##dt## is ##\lambda dt##, where ##\lambda## is a decay rate. Thus the change in the population of muons is just ##dN/N(t) = −\lambda dt##. Integrating gives ##N(t) = N_0 \exp(−\lambda t)##. This makes sense...
  15. ohwilleke

    B When Will Fermilab Release Its Initial Muon g-2 Measurement? [new update on August 10]

    Fermilab's E989 experiment is conducting the first precision measurement of the anomalous magnetic moment of the muon (muon g-2) since the Brookhaven lab did so fifteen years ago. It is currently collecting Run-3 data for this experiment, and said that it would be releasing preliminary Run-1...
  16. E

    I Uncertainties of the hadronic corrections for electron and muon

    The pie chart in this link shows that about 99.95% of the total error of g-2 of the muon in the theoretical prediction is due to the uncertainties in the hadronic corrections. What is this number for g-2 of the electron? Maybe this number exists also for tau particles? The new value of fine...
  17. M

    I Positron decay direction from muon

    Hello! I read that in the rest frame of a positive muon, decay positrons are preferentially emitted in the direction of the muon spin. Why is that the case? The decay is ##\mu^+\to e^+\nu_e\bar{\nu_\mu}##. Assuming that the positron is emitted at almost the speed of light, it will be a left...
  18. faca

    B Curvature radius question for my muon beam experiment

    Hello, I've a particle beam moving along the z-axis. The beam goes through a dipole magnet. I studied the hit position in a tracker after the magnet and I noticed that there are hits at 2 different x coordinate (the x asix is transverse to the z one). Let's call Delta x the shift between the 2...
  19. A

    I Building a muon Cherenkov detector

    So far I have an R928 Hamamatsu pmt from ebay, that I believe will be good since it has UV glass, and the majority of the photons should be in the UV range. I also have an old Brandenburg pmt HV power supply but need a BNC connector to use it. I already have a good rigol oscilloscope. Soon I...
  20. eedftt

    What is the orbital radius of a muon captured in the n=1 ground state of Carbon?

    The muon is a subatomic particle with the same charge as an electron but with a mass that is 207 times greater: mμ=207me. Physicists think of muons as "heavy electrons." However, the muon is not a stable particle; it decays with a half-life of 1.5 μs into an electron plus two neutrinos. Muons...
  21. F

    A Exploring the D0 Experiment: Proportional vs. Mini Drift Tubes

    Hi all, I'm reading an article describing the D0 experiment at Fermilab during Run II. Proportional drift tubes and mini drift tubes were used to detect muons: can someone explain me the difference between these two kinds of drift tubes? Thanks Federica
  22. A

    I Muon lifetime measurement experiment

    Hello everybody! I have a question regarding my physics laboratory at the university. I am performing the measure of muon lifetime. The setup is quite standard (coincidence measurement with plastic scintillators). My question is about the time resolution. I have tried to see if the time...
  23. A

    What are some ways net positive muon catalyzed fusion can be realized?

    Minute physics made an interesting video for laymen describing the feasibility of muon catalyzed fusion, specifically stating that the current state of technology would lead to an endothermic process. I was wondering if it would be possible to use muons in different fusion configurations, for...
  24. K

    Calculating Muon Decay Rate using Delta Function Identity

    Homework Statement I need to calculate the muon decay rate, ignoring the mass of the outgoing particles. Homework Equations ##d\Gamma = \frac{1}{2E_1}|M|^2d\Pi_{LIPS}## The Attempt at a Solution I am actually having problem with the math at a point. I reached this...
  25. QuarkDecay

    A Velocity Drifts of proton-muon gas

    When do we use the equations of curvature drift ( ΔΒ⊥Β) V∇B= ±1/2u⊥rL (B x ∇B)/B2 and the general VF= c/q (F x B)/B2? For particles like muons and protons, do they need different equations to calculate a gas' drift velocity, when the gas is made of protons or muons instead of electrons? Am I...
  26. QuarkDecay

    When is the Boltzmann equation applicable in a Fermi plasma?

    When do we use the Boltzmann equation for density in a Fermi plasma? n in [cm-3] and when do we use the ρ=m/V, ρ in [Kg/m3 ] (this is not an example, I just added the equations to make my question more understandable) Is the ideal gas only when we have electron and ions? Is the Boltzmann...
  27. QuarkDecay

    Electron Plasma to Muon/Proton

    Homework Statement Cylinder electron gas with density of ne= 1010 and radius or r=1cm is inside magnetic field of B=104 Gauss. If we change the electron gas with (i) muon gas (ii) proton gas does the Drift Velocity change? Homework Equations [/B] Boltzmann equation of density...
  28. caitphys

    Muon production and decay from relativistic annihilation

    Homework Statement An antiproton of energy 35 ##GeV## from a source outside the solar system interacts with a proton in the upper atmosphere traveling on a trajectory which is radial with respect to the centre of the Earth. The antiproton annihilates the proton with the final outcome that two...
  29. Ahmed Abdalla

    Negative absorption coefficient in muon absorption?

    Homework Statement I am conducting an experiment where I am interested in finding the absorption coefficient of different materials as muons pass through them. My data was all well until I realized more muons were measured AFTER they passed through one of the materials, which makes no sense...
  30. mfb

    A Possible explanation for muon g-2 anomaly: Gravity?

    For many years, the measurements of the Landé g-factor of the muon have been puzzling, as the experimental value and the theoretical predictions showed some disagreement - 3.6 standard deviations for the last years. Experimental and theoretical uncertainties have a similar size, so work on both...
  31. A

    I Why Does π+ Decay to Muon and Muonic Neutrino?

    I am having a question in mind that why π+ decays to muon and muonic neutrino ,why no electron and electronic neutrino?
  32. ohwilleke

    I Muon g-2 as a constraint on new physics

    I. Background The magnetic moment of the muon, g, is predicted by the Standard Model, to be equal to 2 and a bit more, with the quantity that we look at being g-2. We have both experimental measurements and theoretical predictions that are close to each other to many significant digits, but...
  33. ORF

    Misc. DIY muon detector -- Is it really working?

    Hello I found this video on YouTube, It seems that most of the counts are noise of the PMT... Thank you for your time. Regards.
  34. ohwilleke

    I Is this thesis a plausible explanation for muon weirdness?

    Background and Motivation In the Standard Model, a muon is simply an electron with a bigger mass. But, measurements of the radius of muonic hydrogen and the muon magnetic dipole moment (muon g-2), show a fairly significant discrepancy between theory an experiment in that respect, at the five...
  35. A

    B Muon Time Dilation: Earth vs Muon Perspective

    From the reference frame of the earth, the distance between the surface of the Earth and the muon is longer, but the muon survives because time for the muon is slowed down. From the reference frame of the muon, the time experienced by the muon is not slowed down but the muon survives because...
  36. Jr_Particle_Hunters

    B Can Water and Hydrocarbon Materials Effectively Shield Muons at Sea-Level?

    Hi! If water and hydrocarbon rich materials are good at absorbing cosmic radiation, would they also work for shielding muons at sea-level? What about gamma rays and electrons created by muon decay at sea-level...what would be good shields against those? Thanks!
  37. J

    Speed, momentum and total energy of a muon (SR)

    Homework Statement A muon has a mass of 106MeV/c2. Calculate the speed, momentum and total energy of a 200MeV muon(a muon with a kinetic energy of 200MeV). Homework Equations E=γmc K+mc2=E γ=1/(1-β)1/2 β=(v/c)2 The Attempt at a Solution To solve for the speed I plugged E=γmc into K+mc2=E to...
  38. R

    Pulsing an LED during muon detection

    Homework Statement For my lab physics class I was in a group doing the classic muon detection assignment. We ran the equipment for about two days and during the time we had a pulsing (100 Hz) LED inside the scintillator chamber. This gave some measurements that were extremely low (about 0.6 μs)...
  39. K

    I Any theories muon and tau are just electrons

    the current SM states that electrons, muons and tau are all different fundamental particles. are there any theories that suggest there is only 1 fundamental charged lepton, the electron, and that muons and tau are either electrons that are in a higher energy quantum state, and therefore mass...
  40. V

    Muon decay in flight - distribution of distance

    Homework Statement The average lifetime of muons at rest is τμ0 = 2.2 μs. A laboratory measurement on the decay in flight of muons in a beam emerging from a particle accelerator yields an average lifetime of τμ = 6.6 μs, as measured in the lab frame Σ. (g) [3 points] Given a large ensemble of...
  41. Quandry

    I What happens to the mass of a muon when it decays

    a muon has a mass about 207 times that of an electron. When the muon decays it produces an electron and two neutrinos (simplest form). Neutrinos have minimal mass, so what happens to the rest of the mass?
  42. min_oh

    I Where are the four muons in this picture

    Hi all.It is picture of simulation for higgs decays into four muons. Im wondering which track line is four muon. My guess is four thick yellow line at right-bottom side of the picture cuase it looks energetic. Am i right? Or any other opinion? Thanks alot Min
  43. Kara386

    Special relativity muon example

    Homework Statement Here's a standard example of special relativity in action: The mean lifetime of the muon as measured in a laboratory is about 2µs (rounded to 1 s.f.). Thus, the typical distance traveled by a muon should be about ##3\times 10^8ms^{-1}\times 2\times 10^6s = 600m##. The...
  44. H

    I Is a Muon/Anti-Muon Multiplier Possible?

    Hello every one, I was looking through my physics dictionary for a machine that multiplies the effect of muons and anti muons but couldn't find anything. I'm aware of the photomultiplier for photons but can't seem to find anything similar. Does anyone on this forum know of any such machine or...
  45. S

    Calculating Muon's Time Dilation and Travel Distance in a Particle Accelerator

    Homework Statement The muon has been measured to have a mass of ##0.106\ \text{GeV}## and a rest frame lifetime of ##2.19 \times 10^{-6}## seconds. Imagine that such a muon is moving in the circular storage ring of a particle accelerator, ##1## kilometer in diameter, such that the muon's total...
  46. C

    Velocity of a muon if observed travel distance is 800 m?

    Homework Statement For a modern physics class, has to do with relativity In a lab experiment a muon is observed to travel 800 m before disintegrating. The mean lifetime of a muon is Tau = 2E-6 s A muon's travel distance at the speed of light is x = tc = 0.66 km Earth's atmosphere is x = 100 km...
  47. Garlic

    Muon-Enhanced Atoms: Fusion Efficiencies Explored

    Hello everyone, I know that electrons in heavy atoms move at relativistic speeds, resulting in heavier electrons and smaller radius. If we replace an electron in a heavy atom with a muon, the muon would move to the center (occupying the lowest energy state possible), and making the radius of the...
  48. Anchovy

    What is the meaning of the term 'prompt muon'?

    In the context of cosmic rays?
  49. D

    What time dilation do muon observers experience?

    Re. time dilation muons, CERN. Given the accelerated muons were observed to have a lifetime increased by approximately x 29, What happens to the observers life span? Thank you.
  50. Fb.Researcher

    Compute decay rate of muon according to given equation

    Homework Statement A muon decays to an electron, an electron neutrino and a muon neutrino. ## \mu \rightarrow e \ \nu_\mu \ \nu_e## .The matrix element of the process is ## |\mathcal{M}|^2 = G^2_F (m^2-2mE)mE## with ##m## being the mass of the muon and ##E## the energy of the resulting...