Questions tagged [leptons]

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

21 questions with no upvoted or accepted answers
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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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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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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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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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The stunning footage of neutral currents, first observation of a neutrino: Knowledge needed

First of all, this question is purely motivated by curiosity. I call upon the community's knowledge on the matter. Following the link below, you can see the image of "A lepton event - a neutrino ...
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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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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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52 views

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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1answer
57 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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61 views

QCD condensate and lepton mass

I read that the QCD U(1) anomaly is caused by the QCD condensate giving rise to quark masses. Does the QCD condensate also give masses to leptons (electron, mu, tau, neutrinos), or are these masses ...
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1answer
99 views

$\beta^+$ decay question

I read that all baryons apart from the proton itself decay into protons (why though?) and that mesons do not decay into protons due to having less mass than protons. Thus it makes sense for the $\...
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45 views

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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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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1answer
56 views

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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23 views

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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28 views

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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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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29 views

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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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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53 views

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 ...