What is Muons: Definition and 81 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. LuckyFox

    B Strange cosmic particles in my detector

    Hello! This is my first post on this forum. I am writing because I would be very interested to know the opinion of the forum participants on this issue. Almost ten years ago, I wrote a program Cosmic Ray Finder to record particle traces on a webcam (analogue of the project DECO) (the webcam is...
  2. S

    A Saha Equation In Plasma for Muons

    I am currently working on the determining the viability of muon-catalyzed fusion in a dense but tepid plasma and the first question pertains to the formation of muonic atoms once muons are injected into the plasma. Suppose the plasma is sufficiently dense such that pressure ionization ensures...
  3. L_ucifer

    How does relativity affect the detection of atmospheric muons?

    TL;DR Summary: I got this question on a quiz for a Coursera course on special relativity, and I'm confused about the answer. I've detailed my thinking below any help on where I went wrong would be greatly appreciated. Question. Muons are unstable fundamental particles. In its own rest frame...
  4. Kosdon3200

    I What are these directional energetic particles?

    In addition to the usual alpha and beta particles visible in my condensation cloud chamber, I see occasional tracks that seem highly energetic -they easily penetrate the entire width of the cloud chamber (10-12 inches) going in one side and out the other. More mysteriously, their orientation is...
  5. 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...
  6. B

    I Muons Decaying on Mt Washington: Expert Answers

    Dear Experts, Currently I am reading up on Special Relativity. I struggle to understand how from the perspective of the Muon that the distance to the surface of the Earth is contracted and thus more Muons arrive at the surface based detector. How can this be? To me the physical space is real...
  7. G

    B Muons traveling to Earth, time dilation question

    Hello learned people, I've been looking at special relativity of muons formed in the upper atmosphere... If I can summarise what I do understand (i think)... A muon has 12km to travel to the Earth from the atmosphere at 0.994c. Alice records this as taking 40.2 micro seconds. Now a muon has a...
  8. M

    Form Factor for Scattering (like muons off of protons)

    Homework Statement Homework Equations N/A The Attempt at a Solution I am trying to complete the last part of this question, part 5(c). My professor has told me that the form factor $$F(q)\rightarrow1$$ as $$q\rightarrow0$$ but I am unsure how to show this. I believe that $$\lim_{{q...
  9. kodybatill

    B Muons, Positrons & IR Energy: A Muon Q&A

    If a Chlorine Positron - Lithium Positron - and Argon Positron - all left the same unit of infrared energy at once - would the equivalent of a Muon(s) be taken by the interaction?
  10. 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...
  11. 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...
  12. K

    I Muons magnetic field time dilation

    muons mean lifetime of 2.2 µs muons in a strong gravitational field or traveling at relativistic speeds experience time dilation would a muon in a strong magnetic field, say near a magnetar experience additional time dilation more than a muon in an non-magnetic field with the same...
  13. K

    I Eletrons muons tau in string theory

    in string theory, where strings are posited as fundamental entities, what is the relation between eletrons muons tau how does string theory explain the increasing masses of leptons how do these leptons other properties come about in string theory what about the antiparticles of each? i.e...
  14. R

    The minimum KE required for muons to travel a given distance

    Homework Statement Muons of Kinetic energy 'E' are produced in collision with a target in a laboratory. The mass of a muon is ##106MeV/c^2## and its half life in it's rest frame is ## 1.4 * 10^{-6}## in its rest frame. what should be the minimum KE such that more than half of the muons...
  15. Pouyan

    Distance and Time for a Moving Muon

    Homework Statement A muon is created in the atmosphere 3 km above Earth's surface, heading downward at speed 0.98c. It survives 2.2 * 10-6s in its own frame of reference before decaying. Relativistitically, according to the muon, what is the distance from the point in the atmosphere where the...
  16. 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
  17. Quandry

    I Time Dilation Explained: Muon Decay & Reaching Earth

    As I understand it muons have a half life of 2.2 microseconds, thus, at the speed of light cannot get to the earth. But based on exponential decay, of every billion muons which head or way, about 70 will actually get here. Using time dilation the full billion will get here. Do we need a billion...
  18. Blidaru Bogdan

    A Calculating Primary Ionizations of Cosmic Muons in a Detector

    I am currently studying the MicroMEGAS detector principle. Ionizing particles traverse the space of around 6 mm of Ar:Co2 mixture in the detector (10x10cm2 x 6mm) like in the picture below. A cosmic muon (4GeV) enters this space and ionizes along its path. I assume the longest path it can take...
  19. R

    B Cosmic Ray Muons: Finding Experimental Data for Special Relativity

    Hi everyone, I'm current working on a project about special relativity, and i was thinking writing about the cosmic ray muons. But where do i, as a high school student get raw data of cosmic ray muons? I have searched quite a bit, but it doesn't seems like data like that is public and easy...
  20. 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...
  21. J

    Electrons, Muons and Pauli Exclusion

    Lepton Universality and Pauli Exclusion Put in a possibly oversimplified way, lepton universality says that electrons, muons, and taus all behave in the same way except for mass effects. The question is “Does this apply to Pauli exclusion?” Due to the Pauli exclusion principle, only two...
  22. L

    Muons hitting Earth half-life explanation in SR

    Muons time dilation from the Earth's frame (and length contraction of Earth's atmosphere from muon's frame) is the usual explanation of the fact that muons reach the Earth when they shouldn't just by their rest half-life. My question is if the explanation based on differential aging(different...
  23. Jess H. Brewer

    Who is Jess Brewer and What is Her Fascinating Field of Study?

    Hi, I'm a retired (since 2011) Physics prof from the University of British Columbia. I originally set out to get a PhD in Physics to increase my credibility as a science fiction writer, but I discovered a field* that was so cool it was like being a character in my own SF novel. In short, I got...
  24. ChrisVer

    Probability of measuring muons is a particular setup

    Homework Statement You want to measure the momentum of muons with the help of a proportional chamber, that is a chamber that applies an electric field inside its cavity and produces a signal current when a charged particle passes through it. The probability of generation such a signal for a...
  25. 1

    Calculating range of muons in a detector?

    Homework Statement If one can approximate NOvA detectors being built out of hundreds of "sandwiches" or PVC plastic of 1cm thickness and a "plane" of oil of 5.6 cm, what is the range of muon of energy 200MeV, 500MeV, 1GeV, and 1.8GeV in the detector? Homework Equations \frac{dE}{dρ*x} =...
  26. 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?
  27. R

    Speed of Muons, calculate KE and Momentum

    Homework Statement The average lifetime of muons at rest is 2.20 μs. A laboratory measurement on muons traveling in a beam emerging from a particle accelerator yields an average muon lifetime of 14.718 μs. a) What is the speed of the muons in the laboratory? b) What is their kinetic energy...
  28. F

    Muons reaching Earth's surface problem

    Question: Muons created in the upper atmosphere are sometimes able to reach the Earth's surface. Imagine that one such muon travels the 60km from the upper atmosphere to the ground (in the Earth's frame) in one muon half-life of 1.52us (in the muon's frame). How thick is that part of the Earth's...
  29. F

    What is the Mean Lifetime of Muons?

    Homework Statement I am doing an experiment where I try to the determine the mean lifetime of muons. I collected enough data and I put it in a histogram (attached file), but I have no idea how to calculate the mean lifetime with this. Homework Equations y(t)=Ne^(-t/τ), where τ is the mean...
  30. E

    How Does a Muon's Travel Illustrate Relativity Principles?

    Homework Statement A muon has a lifetime of 2.0x10^-6 seconds when at rest, after which time it decays into other particles a) Ignore any effects of relativity discussed in this section. If the muon was moving at 0.99c, how far would it travel before decaying into other particles, according to...
  31. N

    Do atmospheric muons accelerate?

    <<Moderator note: This discussion was originally posted in another thread. It has been moved as it did not concern the OP of that thread.>> The muons never accelerate from A->B?
  32. A

    Muons result from cosmic rays, but cosmic rays are protons that decay?

    I am wondering how Muons are manufactured. Wikipedia says they're the decay products of cosmic rays, and that cosmic rays are usually high energy protons. So a high energy proton (cosmic ray) decays into a muon after colliding with matter on earth. How is consistent with the fact that...
  33. ChrisVer

    Muon Interaction at ATLAS Hadron Calorimeter: Investigating Energy Dependence

    Can actually muons interact and give a signal while they go through the Hadron Calorimeter of the ATLAS? I think in general this isn't impossible, but it should depend on the muon energy... I would like to see that energy dependence, even quantitatively.
  34. I

    Muon Time Dilation: Exploring Earth's Perspective and Resolving the Muon Paradox

    when muons are created in the atmosphere and fall to Earth the Earth clock runs faster. Thus, the "slower" muon clock allows more of them to reach the Earth's surface. But from the muons' perspective, the Earth is moving towards the muon. Shouldn't the muon's clock run "faster" and there should...
  35. B

    Fermilab Muon g-2: How Do Muons Form?

    I was reading about Fermilab moving their new storage ring to the Muon Campus for the Muon g-2 experiment. I was curious about how the produce the Muons. I understand that protons hit a graphite target producing pions that quickly decay into Muons. How much energy are is required? How much...
  36. R

    Muons: Why time dilation takes precedence?

    I was browsing through old threads and a user named universal_101 kept asking about why we can use muons as a direct measurement of time dilation but only an indirect measurement of length contraction. It was pointed out that the two go together and cannot be separated, but it got me thinking...
  37. P

    Why is the zenith angle distribution of the muons cos2(x) ?

    Hello, Empirically, the flux distribution of cosmic ray muons follow cos^2(θ) where θ is angle of incidence. Looking up the papers, I did not find any clue as to why is this the case. All sources simply consider this an experimental fact. Is their any real explanation for this?
  38. M

    Are Muons and Tauons Higher-Dimensional KK Modes?

    Muons and tauons as KK modes?? Hello, everybody: I have (what I think is) a silly question. We all know that μ and τ particles are just as electrons, but with larger mass. Could it be that they are heavier Kaluza-Klein modes of the e in a higher dimensional theory, where the extra dimension...
  39. M

    Muon Lifespan: How We Measure Decaying of Muons

    Hello, I know that muons have an average lifespan of 2.2µs. What I'm curious about is given that we do not yet know of relativity and time dilation how were they able to know that in a frame at rest with the muons that's their life span. Or is it that we only knew of their actual life span after...
  40. Doofy

    Pair-production - how come it's always e+e-, never muons or tauons?

    Everyone is familiar with photons pair-producing electrons and positrons, but how come it never seems to be a mu+ / mu- or tau+/tau- pair that gets produced, even when the photon is at a sufficient energy to produce any of these?
  41. A

    Exploring the Danger of Muons and Tauons on Human Cells

    Are muons created in the atmosphere of Earth through nucleosynthesis a danger. I am not asking how probable it would be for one to get down the the surface of Earth but if one did could they be a dangerous to human cells? And also, would tauons be a danger to the human system if they would...
  42. N

    Detecting Muons w/ an Oscilloscope

    I'm trying to detect muons. I have two big scintillators, roughly 2900 cm^2 surface area. We also have sensitive PMTs and oscilloscopes. Right now, we are just trying to pick up a signal that a muon passed through, but there is too much noise and we have not had any consitency. I guess my...
  43. P

    Calculating the velocity of muons as they leave an accelerator. (Info is given)

    Please refer to the link below for the problem statement and known data. http://imgur.com/1CQPk Calculate the velocity of the muons as they leave the accelerator. From my understanding, I must manipulate the Time Dilation equation in such a way so as to make velocity 'v' the subject of the...
  44. U

    Time dilation of Muons and a Paradox

    Hello Friends, Consider a Linear accelerator, at the one end there is a Muon Generator, and it produces a certain amount of Mouns, let's say 'x'. These Muons are accelerated to the other End of the accelerator, where the number of Muons reached are detected and displayed on a Digital display...
  45. M

    Measuring the velocity of cosmic ray muons

    Homework Statement I'm participating in a worldwide undergraduate-level experiment to measure cosmic ray muons. I've got the data, and am in the process of writing a paper (called a poster for some reason), which details the experiment, procedure, and results. Right now I'm trying to...
  46. V

    Are muons elementary particles?

    Hi I've been reading that muons are supposedly leptons (elementary particles), in the past confused for mesons (hadronic particles). They are clearly not mesons, which are composed of a quark and an antiquark. But I've also read that muons decay to an electron and two neutrinos of different...
  47. T

    Muons experiment, strange logic

    In the muons experiment the flow is measured at top of a mountain and at the base of the mountain. The velocity of the muons was calculated http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muonex.html The velocity is 5 times the speed of light, which is of course against the relativity...
  48. J

    Bethe Bloch: Calculating ionisation energy losses for protons, alpha and muons

    Hi, this is my first post here. The forum seems like a great idea! I've got finals coming up in a few days and can't seem to get my head around this example and my tutor seems unreachable at the moment. Anyway, here it is: Homework Statement " A beam of particles contains protons, α particles...
  49. H

    Relativity Question Regarding Muons in movement

    Homework Statement A muon has a lifetime of 2.2x10^-6 s when at rest, after which time it decays into other particles. a)ignore any effects of relativity discussed in this lesson, if the muon was moving at 0.99c how far would it travel before decaying into other particles, according to...
  50. M

    Muons: Uses, Detection, & Volcanoes

    I recently saw on an episode of NOVA yesterday, a machine made to detect muons ... I haven't heard of them before this. What it was used for was too see inside a volcano, Successful ? ... Yes. How did it work I have no idea. What exactly is this and does anyone else know of any other projects...