Questions tagged [leptons]
Leptons are elementary fermions that do not experience the strong interaction: electrons, muons, tauons, and neutrinos.
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Electrons decaying into heavier particles
Suppose we have a system of electrons a very tightly confined space (like a tiny magnetic trap).
Let's say we continually increase the degree of confinement such that the electrons are confined into ...
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The muometric positioning system, how does it work exactly?
While GPS uses light signals to determine the location of a device, I just learned that something similar can be done using cosmic muons rather than light, see e.g. this paper.
The idea, as I ...
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Cloud Chamber Help Needed! [closed]
I was inspired by this video to attempt to create a cloud chamber without dry ice (it's very challenging to get where I live) and I have had limited success so far. This is what the design looks like:
...
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Time dilation - Example of Muon [duplicate]
A very common example of time dilation is given for muons i.e. how presence of large number of muons reaching earth (which were created in upper atmosphere) can be explained using time dilation.
The ...
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Could you use Muons as electricity (or rather mutricity)?
Muons and electrons are both leptons that carry charge, so could you build a circuit that uses muons instead of electrons? Do substances like copper that conduct electrons also conduct muons?
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Why is the branching fraction of strange $D$ mesons to tau leptons so high?
From the PDG (https://pdg.lbl.gov/2008/listings/s031.pdf & https://pdg.lbl.gov/2010/listings/rpp2010-list-Ds-plus-minus.pdf) the branching rate for strange D mesons to tau leptons is about 3 ...
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Does substituting electrons with muons change the atomic shell configuration?
Suppose we take an example of $\text{Be}^{2+}$ and we add two muons to it. Will they go into L shell or there will be two K shells - one each for muons and electrons?
If so, the system should have ...
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Can tau decay into a pair of charm and strange quarks?
I found on wikipedia that tau can decay to hadrons made of quarks and it seems like a tau can only decay to a pair of down and anti-up quarks. I understand that tau (1.8GeV) doesn't have enough mass ...
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Wilson Coefficients in the Standard Model
I'm not particularly knowledgeable in this area of physics. From my understanding as an undergraduate, Wilson coefficients are sets of parameters that arise from an effective field theory which ...
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How is the $SU(2)_L$ conjugation applied?
I'm reading a paper where they introduce the lepton doublets $L$ and "their $SU(2)_L$ conjugations" $\tilde{L}$, which I'm guessing means
$$
\tilde{L} = i\sigma_2L^*.
$$
After $\textit{vev}$,...
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What's the difference between Lorentz transformation properties of Hermitian and Dirac adjoint lepton doublets?
If the lepton doublet transforms like a left-handed Weyl spinor under Lorentz transformations,
$$
L \longrightarrow exp\left[\frac{1}{2}(i\theta_j\sigma^j - \beta_j\sigma^j)\right]L = \Lambda_{sL}L,
$$...
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What charge does muon have? [closed]
I have a simple $\mu$-meso atom model. Kernel is just one proton and on orbit there's one muon, which is 210 times heavier than electron. What charge does it have? I checked some tables about muons ...
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Are all elementary particles consequential?
Apologies if the title is misleading. Really what I'm curious about is if every elementary has a point, at least in what we know. I know the different types of quarks are important of course, as they ...
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Can a positive $W$ boson and negative $W$ boson exchange a lepton, and release a charged lepton antilepton pair or neutrino antineutrino pair?
Would it be possible for two passing $W$ bosons with opposing charge to either release a neutrino and become the corresponding charged lepton and charged antilepton, or release a charged lepton, and ...
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Do the different generations of fermions correspond with the epochs of the very early universe?
Up and down quarks as well as electrons and electron neutrinos currently dominate. Is it possible, that during the electroweak epoch, charm and strange quarks dominated? and that during the gut epoch, ...
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Chirality in muon decay
Consider the muon decay process:
We assign the chirality according to the $W$ boson current: (i.e. P&S eq.(20.80))
$$J_W^{\mu+}=\frac{1}{\sqrt{2}}\bar{\nu}_{\mu L}\gamma^{\mu}\mu_L \quad J_W^{\mu-...
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Clarification about the question of whether neutrinos are their own antineutrinos
There are various pages that say we can distinguish between neutrinos and antineutrinos.
Why do we not know whether or not neutrinos are their own antiparticles?
Why are neutrino and antineutrino ...
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Flavor Oscillations, the case of leptons
In the neutrino sector neutral particle oscillation occurs which gives rise to neutrino oscillation. From my currrent understanding , the observation of the neutrino oscillation occurred because the ...
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What particles existed in the Planck, GUT, and electroweak epochs, respectively?
What quarks, leptons, and bosons existed in each of the individual epochs of the early universe (Planck, GUT, electroweak)? Did the quantum zoo gain or lose species during these times? Or did some of ...
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Why LNV for 0νββ process has odd dimensions?
I am studying a couple of papers on the subject of neutrinoless double beta decay problem, somewhere in one of these papers, they emphasize that $ΔL=2$ operators have odd dimensions. What is the ...
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The Dirac equation predicted the positron. Does the Dirac equation also suggest the existence of muons?
The Dirac equation is given by:
$$ (i\partial \!\!\!/ - m) \psi(x) = 0$$
It famously predicted positrons by suggesting negative energy solutions. First it was solved with the 'Dirac sea' and positrons ...
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Is the muon superfluous?
When the muon was discovered, it was so unexpected that Rabi's reaction was, "What? Who ordered that?" The muon doesn't play any obvious role in the behavior of protons, neutrons, and ...
rob♦
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Is Lepton Flavour Universality an accidental symmetry of the Standatd Model?
Is Lepton Flavour Universality an accidental symmetry of the Standatd Model? If it is, why? How does it emerge from the Standard Model?
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Could the equal amounts of positive and electric charge point to equal amounts of matter and anti-matter?
The universe is electrically neutral because the electric charges of all quarks and leptons cancel.
If particles are electrically charged, then there are equal amounts of positive and negative ...
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Anomalous magnetic moment form factor of $e^-,\mu^-$ and $\tau^-$ in QED
The anomalous magnetic moment form factor $F(q^2)$ of an elementary fermion at $q^2=0$, calculated at one-loop, is $$F_2(0)=\frac{\alpha}{2\pi}.$$ At least at this order (order-$\alpha$), $F_2(0)$ ...
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Is leptons annihilation one process of 4 particles simultaneously or two independent processes of 3 particles? [duplicate]
Why leptons annihilation is not 4-particles, and it is represented in the form of two 3-particles? If the pair of an electron and a positron has formed a positronium particle, then what is virtual ...
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Fundamental reason for the color and flavor group to be the same?
The answer to this question might just be a straight-up "no, it's just a coincidence", but since coincidences are rarely a thing in physics, I thought I'd ask.
Is there a fundamental reason ...
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Does Lepton flavour universality arise natural in the SM
I always thought LFU is stated by the SM , but I recently read that it was just assumed because measurements suggested this universality. If thats true, proving LFU violation would not automatically ...
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Is the electromagnetic coupling constant of the muon exactly the same value with the electron $α \approx1/137$?
I am asking because I want to know If I can use the Schwinger equation:
$$a_{e}=\frac{\alpha}{2 \pi} \approx 0.0011614$$
to calculate the one-loop QED contribution to the anomalous magnetic moment of ...
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Why do we say lepton flavour violation is against the standard model if no symmetries are associated with lepton flavour?
Or if a symmetry does exist what is it?
If possible could you compare this to a symmetry that leads to a conservation?
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The effect of the fifth force of nature being detected?
The article
https://www.sciencealert.com/physicists-may-have-discovered-new-force-of-nature-in-lhc-experiment
speculates that possibly the effect of the fifth (so far unknown) force of nature has been ...
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Explanation for exact amounts ratio between up,down quarks and electrons in a universe
As I've understood in the quark era $\approx (10^{-12} - 10^{-6}) \,\text{s}$ unified interaction has decoupled into Leptons and Quarks. Given that now Hydrogen+Helium atoms accounts for $97.9\%$ of ...
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Why is the hadronic $\tau$ branching ratio into 2 pions prefered?
In the PDG the $\tau$ branching ratios are listed and Br$(\tau^- \rightarrow \pi^-\pi^0 \nu_\tau)\approx 25$ %, while Br$(\tau^- \rightarrow \pi^-\nu_\tau)\approx 11$ %.
How can this be since the ...
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Higgs Mechanism Confusion
I find myself confused about the Higgs mechanism, but more specifically about how the leptons get their mass.
The intuitive picture I have in my head is that since the leptons are interacting with the ...
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If neutrinos were Majorana fermions, then what would be the lepton number of the neutrino?
Majorana particles are their own antiparticles and the lepton number of antimatter is -1 whereas for matter is +1, so if neutrinos were Majorana fermions, then what would be the lepton number of the ...
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How could Leptoquarks explain Lepton Flavour universality (LFU) violation?
I recently read about the possibility of Leptoquarks and that this new particle could also explain a possible LFU violation.
Why would introducing a new particle explain LFU violation?
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Lepton Universality
Does universality of lepton also mean that two lepton families have the same renormalized coupling if they interact with a particular particle?
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Conservation of lepton number in neutrino oscillation
I was wondering how neutrino oscillations are possible and lepton number is conserved, as for example in the decay of an anti-muon: $$\mu^+ = e^+ \nu_e \bar{\nu_{\mu}}$$ all lepton numbers are ...
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How is this Yukawa coupling term invariant?
I have the seen the following term used to describe Yukawa coupling for the lepton and Higgs field:
$$ \epsilon_{ij}\phi^{i}\bar{e}_{R}f_{L}^{j} $$
Under $SU(2) \otimes U(1)$ and so expected the ...
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Feynman diagram for the decay $\tau \rightarrow \nu_{\tau}\pi^+\pi^-\pi^-$
$$\tau \rightarrow \nu_{\tau}\pi^+\pi^-\pi^-$$
This is a possible decay mode of the $\tau$ lepton (see Wikipedia). Given that a neutrino is present this must be the weak interaction and therefore we ...
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Is There A Reason lepton flavor violation (LFV) In $B^+$ Meson Decays Can't Be Explained By $K+πº$ Decays?
Physicists at Moriond 2021 reported New results on theoretically clean observables in rare $B$-meson decays from LHCb 3.1 sigma away from the SM prediction of lepton universality in the $B+→K+μ+μ- $vs....
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What is $a_\mu$ in particle physics? In terms of a muon; and its magnetic moment? What is, '$a_\mu$ × $10^9$ - 1165900 '?
What does $a_\mu × 10^9 - 1165900$ mean in the muon $g-2$ experiment at Fermilab?
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Is it possible that rescuing the Idea of a Baryo/lepto-dynamic Field had some Relevance in the FermiLab Result?
We know that Fermilab, Brookhaven, and other laboratories have found discrepancies with the SM.
One option that almost immediately comes to mind is that the so-far exact conservation law of baryon and ...
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Review of experiment $g-2$ of the muon
This week a new development was announced to measure the pressure of the muon magnetic moment and the variation of its result on the theoretical value. The question is: what is the meaning of this ...
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Could the muon's shape be attributing to our measurements of the $g$ term for the magnetic moment?
I read that the $g$ term in the magnetic moment is being studied carefully these days in muons. I was wondering if the $L$ term was also being studied? I know that electrons have been found to be ...
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Does the Higgs field interact differently with muons compared to electrons?
Muons decay into other particles. Does the Higgs field know that muons will decay and does it interact with them differently compared to how it interacts with electrons?
user294587
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Measure cosmic ray pions and protons below surface of the Earth?
In my particle physics lecture, the prof asserted that apparently cosmic ray muons can still be measured 1km below the surface of the earth (e.g. in a mine). This led me to ask the following two ...
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Is it accidental or deeply meaningful that the Higgs and the left-handed lepton have the same quantum numbers?
Is it accidental or deeply meaningful that the Higgs and the left-handed lepton have the same quantum numbers?
Precisely, under $SU(3) \times SU(2) \times U(1)$:
the Higgs has the quantum numbers: ...
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Why is the conservation of lepton number a thing?
Since there is no way to tell neutrinos and antineutrinos apart, does conservation of lepton number make any sense?
As far as we can tell, the neutrinos and antineutrinos are indistinguishable so from ...
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Why is this decay of the neutral pion suppressed?
I got given a homework problem to check various particle decays, whether they're allowed under the different conversation laws (Baryon, Lepton, charge etc.)
Currently im stuck at the following one:
$$
...
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