Questions tagged [leptons]

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

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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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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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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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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 ...
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Why was the first discovered neutrino an anti-neutrino?

In the search for neutrinos, Cowan and Reines discovered the electron anti-neutrino and named it as such. Why is the particle they discovered the anti-variety? The reason we call electrons 'electrons'...
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Relationship between electrons (leptons) and quarks

I assert the following is true: Either: electrons are made up of (two) quarks Or: Quarks are made up of some kind of smaller particles, which also make up electrons. I think this must be the case ...
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Why do the different lepton generations have different masses?

I've been reading Mark Srednicki's book on Quantum Field Theory, and toward the end (Chapter 88), he describes how the different generations of leptons acquire mass via Yukawa interactions. However, I'...
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How is each neutrino associated with a specific charged lepton?

For instance, why is an electron neutrino called that and what is its relationship with an electron?
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Is there any property of a neutrino that prevents it from being considered the missing monopole that will make Maxwell's equations symetric

The zero in Gauss's magnetic law, is it an approximation? Could it be in reality be a really tiny number like the magnetic field strength of a neutrino? Neutrinos are members of the Lepton family ...
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Help me understand Lepton universality

I understand that we have three pairs of Leptons (generations). $(\nu_e , e^-), (\nu_{\mu}, \mu), (\nu_{\tau}, \tau^-)$ But what is this principle of Lepton universality? I have obviously tried ...
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Lepton Universality and Pauli Exclusion [duplicate]

Electrons, Muons 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 ...
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What exchange particles can change lepton flavor?

So I know that in the standard model $W^+$ and $W^-$ can change lepton flavors but $Z^0$ cannot. I don't think photons can (is this correct?) and gluons can't because they would not interact with ...
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Is there a name for leptons that are not neutrinos?

Is there a name for leptons that are not neutrinos? Not sure if its exists, its not particularly easy to search for. Is there a name for the set of charged leptons (or leptons that are not neutrinos)? ...
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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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Are there different colors of leptons? [closed]

Are there different colors of leptons? The Pauli Exclusion principal made it necessary for quarks to have 3 different colors. However, although leptons don't undergo the strong interaction they still ...
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How is mass conserved when a muon decays?

A small disclaimer: I am a layperson and not a formal student of physics so forgive any glaring stupidity betrayed in the nature of the question. A muon is supposed to always decay into an electron ...
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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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Ideal energy to study higgsstrahlung at a lepton collider

Referring to this diagram: I understand that any energy excess could be taken away as kinetic energy of the final $h$ and $Z$. If you are interested in this (kind of) process should you tune the ...
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Ratio of electrons and protons in Universe

What is the relation between amount of electrons and protons in Universe? I expect that the Universe should not be charged, so the estimation is 1:1. But then, why there should be the same amount of ...
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What is the difference between leptons and baryons?

I am learning about the formation of the first atoms and, from what I am reading, before heavy particles, like neutrons and protons could form, there were already other types of particles, called ...
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How do electrons get a charge?

Electrons belong to a group of elementary particles called leptons. There are charged and neutral leptons. And electron is the charged one. But how come it got charged? The negative or positive ...
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What is the Difference between a Lepton and a Fermion?

As the Title Says: I am Wondering what the Difference between a Lepton and A Fermion is. I know they both have an ½ integer spin number e.g. a electron, an atom with an odd mass number such as Helium-...
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$\beta^+$ 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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Lepton flavour violation

I was reading about the evidence of lepton flavour violation coming from the observation of neutrino oscillations, and was wondering whether this could also lead to LVF in weak interactions or not. ...
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Why is a “Semi-leptonic” Decay Mode called so?

Why is a semileptonic decay mode called so? I mean, if there is one lepton amongst the decay products, it should be leptonic, right? If there are two, that should be called bi-leptonic or something ...
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How to find Lepton Number? [closed]

is a Standard Model particle with (u, d, b) quark content. What are the electric charge, baryon number and lepton number of this particle? Is this the only particle expected to exist with this quark ...
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Lepton number conservation in standard model

Why is it said that in standard model lepton number is conserved? How do I know that Lepton number is an abelian charge? Why is this conservation not as sacred as electric charge conservation. How ...
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Could elementary particles join to create bound states?

I recently had question, can 2 elementary particles be "attached" together using Strong and weak nuclear forces to create a bound state. For example can Electron and some other stable elementary ...
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Advantages of $e^-e^-$ or $e^+e^+$ collisions over $e^+e^-$ collisions?

Is there any (interesting) HEP process whose study would take advantage from $e^-e^-$ or $e^+e^+$ collisions with respect to $e^+e^-$ collisions?
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Are there new states of matter at ultrahigh temperatures and densities?

Under extreme energetic conditions, matter undergoes a series of transitions, and atoms break down into their smallest constituent parts. Those parts are elementary particles called quarks and leptons,...
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Would it be consistent with QED to have leptons of different charges?

A recent question, Equality of electric charges of all leptons, made me wonder about a specific aspect of why exactly the charges of the different (free) fundamental particles are all the same. ...
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Are the second and third generations of matter required or optional?

If the second and third matter families (so-called generations: muon, muon neutrino, tau, tau neutrino, ...) didn't exist, would that affect how the universe runs? Are they optional or required?
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Mixing of quarks, neutrinos… and leptons?

This is a quite simple question: quarks do mix (through the CKM matrix), neutrinos do mix (through the PMNS matrix). Then why do charged leptons not mix?
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The physical meaning of electromagnetic waves

What, fundamentally, is an electromagnetic wave? As far as I know, all wave phenomena are derivations of an oscillating processes, e.g. particles vibrating in a medium. I can't imagine a wave process ...
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What is lepton number?

What exactly is a lepton number of a particle? With the charge (eg proton is just 1, not the exact charge), I can understand because it's a physical property, put a particle with charge + next to ...