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Questions tagged [weak-interaction]

one of the four known fundamental forces of nature and the one responsible for beta-decay radioactivity. The weak interaction is very short-ranged and more weakly coupled than either the strong nuclear force or electromagnetism. At energy scales above the Z mass the weak and electromagnetic interactions are unified (that is subject to a unified mathematical treatment).

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What is the associated charge for the weak neutral current?

So for the strong force, there's color charge; for electromagnetism, there's electric charge; and for weak charged current, there's weak isospin. How about the weak neutral current? Is there an ...
Positron99's user avatar
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How can a virtual $W$ boson turn into an electron and electron antineutrino?

This is specifically with regard to beta decay. My current understanding is that in one type of beta decay, a neutron turns into a proton, an electron, and an electron antineutrino. In order to change ...
save environment's user avatar
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What does it mean for the electron to be absorbed in electron capture?

In electron capture, when looking at the Feynmann diagram, I'd interpret the interaction as the electron emitting a W boson which interacts with the proton and turning into a neutrino. However, as the ...
Flamethrower's user avatar
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Why do heavy bosons have less range?

Why is it that there's a precise relationship between the mass of a mediator particle and its range? Because mass shouldn't directly affect decay time, right?
Flamethrower's user avatar
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How does a $\mu_R^-/\mu_L^+$ decay?

While studying SM, I was taught that weak force bosons $V=\{W^\pm,Z^0\}$ do not interact with right/left-chiral fermions/antifermions. For this reason, we cannot observe right-handed neutrinos (if ...
A.M.M Elsayed 马克's user avatar
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Fermi theory cutoff from unitarity bound

Tree-level cross sections for processes described by Fermi theory behave like $\sigma $ $\sim$ $G_{F}^2 \cdot s$, where $G_{F}$ is the Fermi constant and $\sqrt s$ is the energy entering in the ...
onibaku's user avatar
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Elastic vs inelastic scattering in particle physics

Does elastic scattering occur via the Z boson and inelastic scattering via the W boson? If so, why? Does it have something to do with the fact that interactions via the Z boson don't change quark ...
user374355's user avatar
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$Z$ bosons coupling to other $Z$ bosons

I'm learning about Higgs boson production at the moment. One way that it's produced is by 'vector boson associated production' or VH, which has this Feynman diagram: What I'm wondering is: how can $Z$...
user374355's user avatar
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Average kinetic energy of a non-relativistic electron in beta decay

I am trying to show that (a bird told me), in a beta decay, the average kinetic energy carried off by a non-relativistic electron is $E_0 / 3$. I have derived that, for the states, a distribution $$dN ...
Jiashu Huang's user avatar
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How does crossing symmetry affect the value of an electroweak vertex (e.g. $u+W^-\to d$ vs. $W^-\to\pi^-$)?

Two of the weak charged current vertices I often encounter in my first foray into particle physics are $u+W^-\to d$ and $W^-\to\pi^-$, shown in the following Feynman diagrams: These feel like the ...
DanDan面's user avatar
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Can $W^\pm$ bosons act by changing the weak isospin state of particles?

From what I understand, the weak isospin part of the symmetry-unbroken electroweak interaction consists of the $\mathfrak{su}(2)$ valued gauge field $\hat W_\mu = \sum_i^3W^i_\mu \hat T^i$, where $\{\...
Er Jio's user avatar
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Is electron capture the exchange of a virtual $W$-boson?

Betaplus: an upquark emits a $W^+$-boson which turns it into a downquark and then decays into a positron and electron neutrino. Electron capture: an upquark emits a $W^+$-boson which is absorbed by a ...
Faalkar's user avatar
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Asimov's nuclear intensifiers

Well, it is fiction: in Isaac Asimov's stories there are "nuclear amplifiers" that magically (fiction without even an attempt of explanation) produce a beam of W-bosons, thus amplifying the (...
Gyro Gearloose's user avatar
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Kinematics in the pion decay

If a charged pion decays via a charged current $W$, the $W$ boson is much heavier than the pions. How is this not a problem? Could the processes be off-shell in such a drastic manner? It is tempting ...
JinH's user avatar
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Determining force of interaction from a decay equation

I have the decay equation $$p + π^− → n + K^− + π^+.$$ I have been told the force of interaction in this is the weak nuclear force, but I was looking for an explanation of how you can work that out ...
Techwizard's user avatar
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General matrix element in weak interaction

During my studies on weak interactions and $\beta$-decay, I've to study how theory and experimental results bring us to achieve the V-A structure of weak vertices. My doubts regard the theory. Suppose ...
Matteo Brini's user avatar
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Neutrinos and Weak interaction

As a beginner in particle physics I have a small doubt. Do we get neutrinos as a product in any process involving weak interaction? Is emission of a neutrino signature of weak interaction? OR there is ...
Sagar K. Biswal's user avatar
7 votes
2 answers
901 views

Does the kaon participate in the weak interaction?

I'm looking at a physics textbook for A-level and in the book it states that kaons are only affected by the strong force and the electromagnetic force. Isn't this incorrect? Aren't kaons affected by ...
S Paul's user avatar
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Do the WI coupling constants change sign under $C$?

I am trying to understand discrete symmetries in the SM, and I have some troubles in understanding why the CC interaction violates CP. In my (badly written) notes it's said that, taken two fermonic ...
Filippo's user avatar
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Interpretation of Gargamelle Experiment Photos

I have been trying to understand the Gargamelle experiment, but would like some clarification. I understand the apparatus is designed to cause charged particles to generate bubbles which are visible ...
user62783's user avatar
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Gauge invariance of simplified weak interaction

I am having difficulties with a homework set. We are given the following lagrangian for a simplified weak interaction between an electron $\psi$, neutrino $\chi$, and a massive (complex) vector-boson $...
Victor Voropaev's user avatar
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Mass of different isospin baryons

Why are the masses of baryons (of same quark content) with different isospin, different? - Is there a physical intuition/explanation to this? Does higher isospin baryons always higher mass than lower ...
ICOR's user avatar
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Why is the decay of the positive Kaon into two Pion more likely than decay of the positive Kaon into three Pion?

I was wondering if someone could explain me (or introduce me a reference) about my following question: Why is the decay of the positive Kaon into two Pion more likely than decay of the positive Kaon ...
Mahtab's user avatar
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Feynmann diagram for $W$ boson decay

So a $W^{-}$ boson decays into right-handed antineutrino and left-handed lepton with "wrong" helicity. I found that textbook explanation of that process involves lots of handwaving. I am ...
haael's user avatar
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Why is the fermionic sector of Standard Model the way it is? [closed]

"Because it works!" will be considered too broad an answer. I want to precisely know which experiments forced to consider the model construction the way it is. For example, I can see Wu's ...
Sanjana's user avatar
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Why is the vacuum state $|0\rangle$ invariant under parity?

I was studying the leptonic pion decay $\pi\rightarrow l\nu_{l}$, and usually the amplitude is computed by $$\mathcal{M}(\pi\rightarrow l\nu_{l})=-i\frac{G_{F}}{\sqrt{2}}V^{*}_{ud}\langle0|\bar{d}\...
Filippo's user avatar
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How Fast Can Toponium Form?

I understand that Toponium is only theoretical because the T quark decays too quickly. My question is this, would a right handed T quark live long enough to form a meson? If not, how long would it ...
Rick's user avatar
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How is the chirality for the weak interaction conserved for non-relativistic neutrinos?

In this article, one can read that the neutrinos in the cosmic neutrino background have a speed of about 1/50 of the speed of light, which is clearly non-relativistic. From the viewpoint of, say, ...
Il Guercio's user avatar
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Electroweak Interaction and SSB

I read that above unification energy, on the order of 100 GeV, electromagnetic force and weak force would merge into a single electroweak force. I do not really understand how and when exactly two ...
Alex's user avatar
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Gamma Ray Emission in the Wu Experiment

In the classic Wu experiment (https://doi.org/10.1103/PhysRev.105.1413) parity violation was discovered in the weak interaction through the asymmetry in the distribution of electrons in the beta decay ...
jkcwioqnkfdsoia's user avatar
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2 answers
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How does parity conservation follow from the Wu experiment?

The Wu experiment shows how parity symmetry does not hold for the weak force. However, how does this proof that parity conservation also doesn't hold? If my understanding is correct, the absence of ...
QuantumQuasar's user avatar
1 vote
2 answers
431 views

Why are there no particles that ONLY interact via the strong force?

The title speaks for itself really: I noted everywhere I learned about fundamental interactions that there are particles that interact ONLY via the Weak Force (and gravity, if it counts)(e.g. ...
Istvan Cziegler's user avatar
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1 answer
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Is this Why a Neutron can Decay Into a Proton, Electron and Electron Antineutrino?

A neutron is udd, then an u-anti-u starts to exist close to the neutron. Then the one d and u change places forming an uud (proton) and anti-ud which decays to an electron and electron-antineutrino. ...
Willem Esterhuyse's user avatar
3 votes
1 answer
427 views

Calculation of the decay rate of the $W$ boson

I am trying to calculate the decay rate of the $W^-$ boson to a charged lepton and the corresponding antineutrino. I denote the four momentum of the $W$ boson with $q = (M_W, \vec{0})$. The momenta of ...
JLS's user avatar
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1 answer
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Two Possible States for Weak Interactions?

Layperson trying to learn particle physics here. For strong interactions, there are three colors (and corresponding anti-colors) which define the possible states of a particle (i.e. quark) for the ...
18th Shard's user avatar
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Improved estimate of density of free neutrons in solar core

In an answer to this question: Free neutrons in the sun's core? I made a very rough attempt to estimate the density of free neutrons in the solar core. There is some non-zero rate for production ...
Andrew Steane's user avatar
-2 votes
1 answer
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Isn't weak interactions necessarily violate strangeness?

The electron-proton elastic scattering process $$e^-+p^+\to e^-+p^+$$ can take place either via a photon exchange (electromagnetic interaction) or via $Z^0$ exchange (weak interaction). But isn't weak ...
Solidification's user avatar
3 votes
1 answer
108 views

How is this equation about pion decay derived?

I'm reading Peskin's Concepts of Elementary Particle Physics and these equations confuse me. What are the $\pi^1$ and $\pi^2$ in (15.49) and why $\pi^-$ equals to this? I don't understand the ...
auntologist's user avatar
1 vote
1 answer
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How do we prove that hypercharge is different for singlets and doublets?

I am trying to teach myself about the standard model and I am stumped by this point. I understand that: When picking an U(1) generator for SU(2)xU(1), any multiple of the identity will do ($YI_n$) ...
SgtJohn74's user avatar
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1 answer
74 views

$\beta^{+}$ and $\beta^{-}$ decay processes

We know that electron cannot exist inside the nucleus for various reasons like its energy, angular momentum violation and etc. But these $\beta^{+}$ and $\beta^{-}$ processes occurs inside the nuclei ...
Anshul Sharma's user avatar
-2 votes
1 answer
104 views

Why is $\beta$ decay a weak force interaction?

In my graduation and also in post graduation, I was told that $\beta$ decay is a weak interaction. But till date I don't know the reason as if why it is a weak interaction process. In my classes some ...
Anshul Sharma's user avatar
1 vote
1 answer
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Non-leptonic weak decay with $|\Delta T=3/2|$ suppression (from "Inward bound" Pais' book)

In Abraham Pais' "Inward Bound" book at page 564 it is mentioned that if we describe the weak interactions with the usual current-current interaction (including Cabibbo angle) we still do ...
Arnaldo Maccarone's user avatar
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Has Anti-beta decay been observed?

I am looking for references or resources regarding the transition of an anti-neutron through weak decay, into an anti-proton, positron, and electron-neutrino. Have such studies been conducted or ...
1 vote
1 answer
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Is it possible to construct a realistic $SU(2)$ model for the weak interaction despite the failure to introduce full weak isospin symmetry?

In his chapter on the electroweak unification, Griffiths introduces the weak hypercharge explaining that his attempt at introducing full weak isospin symmetry with the Pauli spin matrices failed ...
Hrach's user avatar
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2 votes
1 answer
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Why were weak neutral currents considered evidence for electroweak theory?

For example, Wikipedia says: The existence of the electroweak interactions was experimentally established in two stages, the first being the discovery of neutral currents in neutrino scattering by ...
Brian Bi's user avatar
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2 answers
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Is there any something something force other than the electro magnetic force?

Far as I can tell, the force generated by electromagnetic field can be seen as an electrical force or as a magnetic force depending on the observer, i.e., these forces are actually the same phenomenon ...
João Mendes's user avatar
1 vote
1 answer
235 views

Is weak hypercharge carried by $Z$ boson?

In the PBS spacetime video about charge (https://www.youtube.com/watch?v=esayi49OAk4), at 10:55 he said that weak hypercharge is carried by the $Z$ boson. Is this accurate?
Crinoid's user avatar
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1 answer
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QFT symmetry breaking and CP violation

Since the weak interaction violates CP symmetry but electromagnetism doesnt,does it mean that the electroweak fields also violates CP symmetry?Can a field which violates some symmetry be the product ...
appliedSciences's user avatar
2 votes
1 answer
127 views

What is a CP number? In terms of CP-Symmetry and CP-Violation?

When researching the origins of CP-symmetry and CP-violation, and the Fitch-Cronin experiment demonstrating 'indirect' CP-violation, I came across these statements: https://www2.lbl.gov/abc/wallchart/...
Kurt Hikes's user avatar
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4 votes
1 answer
114 views

Is crossing symmetry violated in the difference between positron emission and electron capture?

As discussed in the relevant Wikipedia article, beta decay via electron capture is possible in circumstances when positron emission is not. From a simple (and perhaps naive) point of view, the two ...
Geoffrey's user avatar
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