Questions tagged [leptons]

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

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How to find theoretically the decay width of a particle-decay process? [closed]

The problem is devided into two parts: First part: There is an interaction Lagrangian for real scalar fields given by L=$\lambda_1 \phi_1 \phi_2\phi_3+\lambda_2\phi_1^2\phi_3$. I need to know how to ...
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Why is usual matter made up of $n,p$ and $e^-$?

We have six leptons and six quarks. Yet most of what we see around us is made of only neutrons, protons and electrons. For $\mu^-$ and $\tau^-$, I think the reason is that these are unstable particles ...
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Are the electron and positron doublets in any mathematical sense?

I know left handed electrons and electron neutrinos are isospin doublets. Is there any analogous way in which an electron and a positron are related? My first thought is some sort time-parity doublet.
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How $W^{\pm}$ bosons get their electric charge $\pm 1$ as opposed to $Z_0$ that have neutral electric charge?

In the 'Standard Model' book by Y. Grossman and Y. Nir, in chapter 7 (the leptonic standard model) on page 93 after defining the charge of the broken symmetry generator, i.e $Q=T_3+Y$ they say that ...
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What is the way to work out the running of lepton masses?

If we assume the GUT unification energy is some value E, (say $10^{16}GeV$). Can we work out the running of the particle masses for example the electon, muon and tau at various energies? And will ...
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How can pure leptonic interactions be mediated by the weak force?

$\mu^+ \rightarrow e^+ + \nu_e + \bar \nu_\mu$ Consider the above decay, it is given in my lecture notes as a weak force interaction. I thought the weak force was only involved when quarks change ...
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Conservation of lepton

I was reading a bit about nuclear/particle physics when I came up to Cours et problèmes corrigés de physique nucléaire et de physique des particules by Philippe Miné in 2016 ISBN 2340011566, which is ...
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Can muonic atoms exist?

Would it be possible in the standard model to have atom like systems in which muons (or tauons) take the place of electrons? Why don't we see more of them? For instance it could be related to some ...
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Can muons decay into quarks?

Muon decays are almost always written as $$\mu^- \rightarrow e^-+ \bar\nu_e +\nu_\mu.$$ The reason given on wikipedia is that one of the product neutrinos of muon decay must be a muon-type neutrino ...
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Mass splitting for leptons and down quarks in $SU(5)$ model?

In the minimal $SU(5)$ GUT model, the masses of the leptons and the corresponding down-type quarks must be equal. i.e. $m_e=m_d$, $m_\mu=m_s$, $m_\tau=m_b$. Whereas this is approximately correct for ...
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Fierz identities and Weinberg operator

I've been told that $$ (\bar{L_i^c}\widetilde{\phi}^{\ *})(\widetilde{\phi}^\dagger L_k) = -\frac{1}{2}(\bar{\widetilde{L}}_i \vec{\sigma}L_k)(\widetilde{\phi}^\dagger \vec{\sigma} \phi) \tag1 $$ by ...
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Decay width of the tau lepton

The total decay width of a particle, $\Gamma$, is proportional to the fifth power of its mass, $m$, $$ \Gamma \propto m^5$$ We also know that the dominant decays of the tau lepton are $$\tau^- \to \...
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Feynman diagram for semileptonic decay of neutral kaon

I am unsure how to draw a feynman diagram for a reaction that occurs as follows $$ K^0 --> l^+\nu_l\pi^- $$ Any tips would be helpful.
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Effect of Lepton Flavor Universality (LFU) on Lepton Flavor Violation (LFV)

Does the search for Lepton Flavor Violation (LFV) get affected in any possible way when Lepton Flavor Universality (LFU) is used for background estimation? More specifically, because tau's show some ...
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Possible decay modes of Pion

I am aware that the following decay mode may happen: $$\pi^- → e^-\overline\nu $$ My question is why is the following decay mode not possible $$\pi^- → e^-\nu $$
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Muons - how are we even able to detect them? [closed]

muons have a very small half life comparable to 2.5 μs or so. But we know that it has to cover a very large distance from upper atmospheric layers to reach the particle detectors installed at earth's ...
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Half-life and muon decay

Imagine that we have a single muon. It has a life span of 2.2 microseconds on average. So normally, after that amount of time, the muon will decay. Now imagine we have two groups of muons. Group A has ...
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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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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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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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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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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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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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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. $\mu\rightarrow e\gamma$