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Questions tagged [leptons]

Leptons are elementary fermions that do not experience the strong interaction: electrons, muons, tauons, and neutrinos.

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Can a neutron decay into a proton + muon (+ muon-neutrino)

Can a neutron, if it has enough kinetic energy, decay like: $ \hspace{0.3cm} n \rightarrow p + \mu^- + \bar{\nu}_\mu $ I assume it's not allowed since it's not on the possible decay modes on the ...
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Naive question about lepton/quark energy states

I understand there are 3 energy states for quarks and leptons (electron, muon, tauon... Up, charm, top etc.) And we have 3 forces (not including gravity, em, strong and weak). This naively seems ...
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Why do we have constraints on the baryon asymmetry of the universe and not the lepton asymmetry?

What is it about baryons that means that CMB observations can determine their asymmetry without also including a charged leptonic component?
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Gamma Photons vs. Muons; Which is more expensive [closed]

Which one takes more energy to produce? I ask as I theorize that keeping the plasma in a fusion reactor is very expensive. Muons, while useful, are too short lived. Maybe... Keeping the plasma at ...
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Leptons during Electroweak Epoch

Prior to the electroweak force splitting, did charged leptons still carry a charge of $e$? I was under the impression that, since electromagnetism didn't exist in its current state prior to ...
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Black hole and lepton number conservation [duplicate]

Can falling of an electron into a black be treated as a process in which energy, charge, spin (angular momentum) and lepton number of the system are conserved? Imagine a small volume of space that at ...
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Muon decay - Type of interaction

Why does weak interaction occur when a muon decays? Why can't electromagnetic interaction occur when a muon decays?
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117 views

Is this Feynman diagram possible?

I have been introduced to Feynman diagrams in a particle physics University module and I just created this diagram to practice checking conservation laws: I have been told that charge, baryon and ...
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69 views

How does Bhabha scattering imply the existence of quark/lepton substructure?

In the 1983 journal article New Tests for Quark and Lepton Substructure which covers some science and mathematics behind quark and lepton composition (theoretical). It says: Bhabha-scattering ...
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Flavour violating muon decay

Why is a muon decay into gamma and electron not possible? Where/how does it violate the lepton flavour as muon and electron both have -1? Reference: https://en.wikipedia.org/wiki/Lepton_number
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What, specifically, creates tauons?

It is hard for me to find a site/book/article explaining how, exactly, tau particles are created.
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Gauging $U(1)_{B-L}$ in the absence of right-handed neutrinos

If we gauge the baryon minus lepton number symmetry $U(1)_{B-L}$, the mixed lepton-gravity-anomalies cancel in the presence of right-handed neutrinos (see e.g. this paper). However, if right-handed ...
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Why do we regard ($e^{-}, \nu_{e}$) as a doublet?

To my understanding, particles in a multiplet have similar properties (similar masses and so on) and slight or symmetric differences (in mass, electric charge, spin, and so on). They can be regarded ...
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Antimuon and electron annihilation to 2 photons [closed]

An antimuon and electron may bind together via Coulombic attraction and then decay, but is the following process possible? $$(\mu^++e^-) → \gamma + \gamma$$ $\mu^+$ : antimuon $\gamma$ : ...
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Can quark-lepton mass be partially generated by Higgs?

In the Standard Model, quark-lepton masses are also generated by their couplings with the Higgs particle as the W, Z vector bosons are. Their masses are different because the Yukawwa couplings are ...
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Can we tell something about rest mass from this plot of differential cross-section? [closed]

What we can interpret from the plots below? My aim is to find any resonance peak for di-leptons considering the the produced gamma from quarks and antiquarks can annihilate to lepton and anti ...
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Is it at least theoretically possible for an electron and an antimuon or antitauon to annihilate?

In other words, can mismatched particles and antiparticles react with each other? What about an up quark and anti-down quark?
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Why is $\mu\to e \gamma$ forbidden in the SM w/o neutrino masses?

I have some questions about the next problem: The process µ → eγ does not occur in the Standard Model in the absence of neutrino masses. a) The muon is identical to the electron except for ...
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Is this an acceptable formula for charged lepton masses?

Looking for a formula which gives good values for the charged lepton masses and which satisfy the Koide relationship, I derived this formula (note the square): $$\{m_e, m_\mu, m_\tau\} \propto ...
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Is it possible to create anti-muons in a particle accelerator?

I love particle and nuclear physics and I'm starting to search some things about it even though I'm only a high school student. So, my doubt is: is it possible to create antimuons (positive charged ...
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How does one categorize antiparticles in flavor, family and generation?

$$\newcommand{\A}{\text{A}}\newcommand{\B}{\text{B}}\newcommand{\C}{\text{C}}\newcommand{\D}{\text{D}} \begin{array}{|c|ccc|} \hline { } & \text{1st} & \text{2nd} & \text{3rd} \\ \hline \...
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Why the $\beta^-$ decay releases $e^-+\nu_e$ and not $\tau$ or $\mu$ generations?

The $\beta^-$ decay is \begin{equation} n \rightarrow p + e^- + \bar\nu_e \tag{1} \end{equation} It can be broken down into \begin{align} d \rightarrow & \ u + W^- \tag{2}\\ W^- \rightarrow &...
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Looking for info on the average decay energy of the Tauon

I am interested in finding the average decay energy of the Tauon. I am interested in the average net decay energy as a function of the known branching ratios of the tauon decay as well as the average ...
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How is the electron depicted in simplest string theory and how the muon and tau? Are intermediate masses excluded by the model?

I am curious to understand can string theory give the masses of electron, muon and tau. I suppose they are closed strings and vibration wavelength must be the length of the string divided by a digit $...
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How can energy in Ev of particles e.g. muons be measured in a cloud chamber?

I have a Wilson thermoelectric cloud chamber and would like to obtaine the energy of cosmic particles e.g. muons. I would greatly appreciate your answer.
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Feynman Diagram with antineutrinos and neutrinos

I just recently learned how to draw feynman diagrams by looking at an equation such as one for $\beta-$ Decay: $$n = p + e^- + \bar{v}_e$$ I was wondering in $\beta-$ why an electron-antineutrino was ...
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What is MIP hypothesis?

While reading about muon analysis I read that finding calorimetry segments along with the tracks in the silicon tracker for muons helps us find a subset of tracks compatible with the MIP hypothesis. I ...
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3answers
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What's the difference between muons and electrons in experiment?

In the lecture note Track Reconstruction and Pattern Recongnition in High-Energy Physics written by Prof. Ivan Kisel, there is a figure (in page 7), which describes the different pieces of modern ...
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Current experimental evidence of lepton flavour violation other than neutrino oscillation

Is Lepton Flavour Violation (LFV) experimentally established in processes other than neutrino oscillation? This answer by Luboš Motl points out that Interestingly, CMS has detected a 2.5 sigma ...
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Are pointlike massive particles naked singularities?

If elementary particles (specifically, those with mass, such as the electron or other leptons) are pointlike particles, wouldn't that mean they are naked singularities? But these particles have spin-...
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Why might $B$ meson decays violate lepton universality?

Scientists from various institutions have recently discovered that there might be a break in the application of the Standard Model, particularly with a fundamental principle called the lepton ...
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2answers
114 views

Which came first: leptons or baryons?

If you had a big collection of neutrons, they could decay into protons, electrons, and neutrinos through beta decay since protons are the only stable baryons. After a while, you should get hydrogen ...
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Why do we need MICE in order to build muon accelerators?

I heard that the MICE team (International Muon Ionization Cooling Experiment) have made great progress towards the realization of a high-energy leptonic synchrotron. Why is the MICE experiment an ...
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255 views

Why is lepton flavour violation suppressed in the standard model?

I know neutrinos cant oscillate in the SM due to lack of mass but why are other processes forbidden? Ie. $\mu\rightarrow e\gamma$
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What are quarks and leptons in Quantum Field Theory?

Are the different quarks and leptons different kinds of oscillations of the same underlying quark field and lepton field, or same kinds of oscillations of different up, down and so on quark fields, ...
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About the reason why the change of a muon into an electron plus a photon is not seen

Let me state first that I don't think this is a duplicate of the mentioned question, though the basic thought is the same. Nevertheless, I come up with the prequark rishon theory of Harari, which ...
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The decay of $\chi_c$ into $l \bar l$?

I know that the states $\chi_c$ cannot decay into $l\bar l$ and therefore cannot be made in a lepton-anti lepton collider. I can see why such a decay is not allowed via a virtual photon. Since (...
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Is there data available comparing neutrinos of different flavor scattering on hadrons?

I'm looking for data (ideally in the form of visually striking plots) comparing the scattering of neutrinos of different mass eigenstates (flavors) (or perhaps also, or instead, of different weak ...
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Why can't leptons interact with the strong nuclear force?

So if I understand correctly the strong nuclear force is mediated in the following way: Around nucleons, there exists a potential probability cloud of pions that can be fired by the nucleons. For two ...
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Are there any experimental bounds on the ratio of neutrinos to antineutrinos in the universe?

In the Standard Model, both baryon number and lepton number are conserved quantities (excluding the theoretical possibility of sphaleron processes which are exceeding rare, at least at non-"near in ...
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Compositeness and bounds on “preon” mass

Since the discovery of Higgs particle, compositeness models are not so popular despite the fact they have interesting features. Peskin, in the article "Compositeness of quarks and leptons" (pdf), ...
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Is It necessary, in the standard model, that the number of quark generations equals the number of lepton generations, i.e. 3?

This question showed up in my particle physics exam and I'm not sure of the answer. I said no, since I can't see any reason why they must be equal. But I my answer is right, I find it odd that it's ...
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Will three generations of particles exist if massless?

It seems there would be nothing to tell them apart if they were all massless. But can a symmetry breaking mechanism (if that were the generations' origin) make three where there was only one? If the ...
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1answer
51 views

Are quarks in a doublet weak analogues to strong color states?

Quarks and gluons interact so frequently that it makes little sense to regard each color state as a unique fundamental particle. These interactions also do not change any of the quarks' other ...
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Muon decay mode

In the particle data group booklet on page 14, it's written that muon decays into electron, electron antineutrino and muon neutrino at about hundred percent fraction. But it seems the booklet also ...
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Why can't weak interaction bind neutrino and electron together? [duplicate]

According to wiki, unlike the other three interactions, weak interaction does not produce bound states. However, according to this and this, the weak force should be attractive between particles with ...
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120 views

Is weak interaction the only interaction capable of changing the flavor of leptons?

I see this sentence in wiki about weak interaction: It is the only interaction capable of changing the flavor of quarks. So why only quarks? Why not leptons? Is there another interaction which can ...
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1answer
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Lagrangian of Yukawa Interaction and Quark Mixing

I'm trying to understand the original of quark and lepton mass. Here's a paragraph from the book: "Massive neutrinos in physics and astrophysics" by R. N. Mohapatra and P. B. Pal : The gauge ...
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Representation in $SU(2)_{L}\times U(1)_{Y}$

I'm reading the book "Massive neutrinos in physics and astrophysics" by R. N. Mohapatra and P. B. Pal, and have a question about its notation. The Equation 2.10, it says: $$ q_{L}=\binom{u_{L}}{d_{L}}...
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Does string theory explain the existence of 3 generations of quarks/leptons?

I am wondering whether string theory explains the existence of 3 families of quarks/leptons or not. I have a very limited understanding of string theory, as of now, and I have a mathematical ...