Questions tagged [particle-physics]
Particle physics is the study of the fundamental forces of nature as they are embodied in the interactions of elementary and composite particles at high energies and short time and distance scales. DO NOT USE THIS TAG for point particles in classical mechanics.
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Feynman Diagrams - Specific Questions
I have a very naive question concerning Feynman diagrams: If we consider the process $\pi^{+}\rightarrow \mu^{+}\nu_{\mu}$ via the weak interaction, then we get this Feynman Diagram according to ...
user248824
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Supersymmetry non-breaking $\iff$ no "Goldstone fermion"?
In Supersymmetry and Morse Theory (1982) by E Witten,
Concern whether the supersymmetry is broken by checking whether
$$
Q | 0 \rangle=0
$$
exists or not --- Witten said:
SUSY breaking: A solution ...
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Research in next decade on dark matter: sky surveys vs particle detectors
The next decade is very promising for cosmology as new surveys such as SPHEREx, Roman, Euclid, DESI which will shed light on inflation, dark matter/energy and more. At the same time there are particle ...
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Is the nucleus smaller than the electron?
In the classical incorrect 'billiard ball' model of the atom, electrons are often drawn as smaller balls than the protons and neutrons in the nucleus.
However from quantum mechanics we know the ...
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Number of $\pi ^+$ and $\pi^-$ in collision experiments
My first idea is that number of $\pi ^+$ and $\pi ^-$ mesons in collision of heavy ions with some target made of heavy nuclei should be close to 50/50. But after that I start to think that mass of $d$ ...
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Feynman diagram of Higgs production by $gg$-Fusion
I am slowly going to develop intuition for dealing with Feynman diagrams but
have a couple of problems understanding the following
Feynman diagrams representing the Higgs production via gluon-gluon
...
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$C$-conjugation of a gluon
In some explanations about the OZI rule ( for example at page 38 here), I found that gluons have definite eigenvalue of the charge conjugation operator $C$. The eigenvalue is $-1$. How can this result ...
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Feynman Diagrams understanding problems
I'm trying to understand the basics of the formalism of Feynman diagrams describing interactions in QED and below I present two examples where I still don’t understand the logic behind them:
Image 1 (...
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How to measure the mass of alpha particle?
I was reading the rutherford experiment of the $\alpha$ particles. where we conclude that the positive charge and mass are concentrated in the center of atoms. while concluding the above result we use ...
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Could a Λ or Σ baryon be stable inside a nucleus?
A common "cartoon model" of a nucleus is that there are a set of bound energy levels for the protons and a similar set of bound energy levels for the neutrons. The existence of these energy ...
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Can protons and neutrons be completely converted into Leptons?
In beta decay, a neutron releases an electron and turns into a proton. The inverse happens, though usually not naturally, in positron emission, where a proton emits a positron and becomes a neutron. ...
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What is the value of electromagnetic coupling at the energy where it merges into electroweak couplings?
It is known that its zero-energy value is the fine-structure constant α, about 1/137.036.
Various sources state that the running value is in the 1/129-1/127 range at the Z-boson energy (91 GeV). ...
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How to measure wavelength of gamma-rays
How can we experimentally measure the wavelength of gamma-rays, say for about 0.7MeV without knowing the exact energy and without measuring energy, i.e. sort of direct measurement.
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Do Clebsch Gordan Coefficients add to one when squared for adding 3 isospin states?
I've been calculating the possible isospin states for $\pi^0\pi^+\pi^-$ state and get this as my final answer after referencing the Clebsch Gordan Coefficients table:
$$\frac{1}{\sqrt{10}}|30\rangle+\...
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Interaction of quantum fields [closed]
Do quantum fields in QFT interact with each other constantly and continuously, or only from time to time?
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Can an alpha particle (or any charged particle) can penetrate through nucleus of gold atom?
Can an alpha particle (or any charged particle) can penetrate through nucleus of gold (or any other) atom ?
Today I was watching a lecture on the "Estimation of Size of Nucleus" which was a ...
user276626
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How do I determine the rest mass of a $J/\psi$ particle from CMS Dimuon Data?
Essentially, I'm using CMS Dimuon data, from the decay of a $J/\psi$ particle, to prove that momentum is 'conserved' in relativistic collisions. However, I'm unable to find how I can do this. I ...
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Why can’t gravitons distinguish gravity and inertial acceleration?
If gravitons mediate the gravitational force, couldn’t the detection of gravitons by an observer be used to distinguish whether they are experiencing gravitational acceleration vs. inertial ...
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How does the ionic radius influence the ion's interaction?
What can we deduce about an ion, its interaction or the structure it is in, based on the ionic radius?
My understanding of the concept of the ionic radius is that these are seen almost as having a ...
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$b$ mesons lifetime
I read about a technique called $b$-tagging in which one can check if a $b$ meson was produced in a collision by looking for a jet which has a secondary vertex within it. The reason is that b mesons ...
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Can a massless particle have both spin and charge?
Can a hypothetical elementary particle, at least in theory (according to the current science), have 0 mass and yet also have both spin and electrical charge (at the same time)?
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Has there been research done on the dependence of particle decay to its immediate surroundings?
The meson particle, Kaon, can decay into pions or leptons + neutrinos. Each decay has its own probabilities as measured and confirmed during experiments.
Has there been any research into the ...
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Protons and neutrons are subatomic particles that affect the mass of an atom. What would be a heavy particle and what would be a light particle? [closed]
An atom consists of 3 parts: Protons, neutrons, electrons. Protons and neutrons go to the center to make up the nucleus, while the electrons go to the outside in the electron cloud. Of the three ...
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Where does the extra energy come during superelastic collison
It is known that in superelastic collison the energy of particles after collison is more than the original particles but how is it possible . I barely could find suitable information on net for a high ...
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Negative Energy in the 4-momentum of an Antiparticle?
According to the Wikipedia article on Antiparticles:
Solutions of the Dirac equation contain negative energy quantum states. As a result, an electron could always radiate energy and fall into a ...
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What do sigma confidence levels mean in particle physics?
My level of understanding of Particle Physics is elementary.
Suppose say I have conducted an experiment (maybe a poll) with a sample size of $n$, then I can calculate the mean $\mu$ and the standard ...
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Muon $g\!-\!2$ experiment at Fermilab
At Fermilab the $g\!-\!2$ Muon experiment is going on which measures the magnetic dipole moment of the muon.
Can we explain the difference in prediction of theory and experiment if we introduce preons,...
user276797
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Why is the flavour space for flavour symmetry defined in terms of low mass quarks?
In the textbook, I am following it describes flavour space with basis up, down and strange quarks. I am not sure why we did not choose up, charm and top as the basis and why only three bases can ...
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How would quarks behave in the event of 'The Big Rip'?
I have always heard that you can't get a quark by itself because "the energy required to split them apart is enough to create another." But, in the case of The Big Rip, the idea is that ...
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Which one is more efficient in producing high energy gamma rays?
According to https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf the big pulsed power accelerator, HERMES III, generate electron beam with peak energy at 22 MeV and average electron energy at 16 MeV ...
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CKM matrix flavour vs mass eigenstate implication for decay of mesons
From reading the answer in Difference between the CKM and the PMNS matrix , I gather that the transition $W\to ub$ where $u$ and $b$ mean flavour eigenstates is not possible, but it is possible where $...
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Confusion on the proof of Goldstone’s theorem
I amd reading a proof Goldstone’s theorem in Zee's QFT book. On page $228$, Zee presents the proof as follows.
The conserved charge $Q$ is given by
\begin{equation}
Q=\int d^D\vec{x}J^0(t,\vec{x}).
\...
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Why does light hitting a charged particle cause it to oscillate?
I am trying to study the classical Physics interpretation of light hitting a charged particle.
Why does light hitting a charge particle, such as an electron, cause it to oscillate?
Is it because the ...
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Why can only the Higgs particle have a non-zero expected value in a vacuum? [duplicate]
What does the phrase “Due to Lorentz invariance, only the Higgs particle can have a non-zero expected value in a vacuum” mean?
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Calculating the residue as part of Matsubara summation
On page no. $166$ of "Many-body quantum theory in
condensed matter physics" by Henrik Bruus & Karsten Flensberg, while explaining the summation of Matsubara frequency, the following ...
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Deep inelastic scattering (DIS) and handbag diagram
Here, in page 11, you can see the so-called 'handbag' diagram that explains how a virtual photon emitted in a deep inelastic scattering (DIS) process interacts with a parton.
I'm going to use this ...
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Length of cloud of virtual particles [closed]
Every subatomic particle which interact with the 3 quantum interactions has a cloud of virtual particles.
How big is that cloud and where is its density bigger?
user276797
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Friction at atomic level
What is happening at atomic Level between two bodies when there is friction force acting between them?
user273923
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Is the wave packet of a relativistic quantum particle oblate (flattened) or prolate (elongated)?
A free, non-relativistic wave packet of a quantum particle is usually thought of as having spherical shape. What happens for a particle moving relativistically? For an outside observer, is the wave ...
user85598
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Are protons bigger than electrons?
In every text/ physics book that I've read, Protons are mentioned as particles that are bigger, way bigger 2000 times to be precise, than electrons...I believed that until a few minutes ago when I ...
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Antiproton synthesis
For a pion minus hitting a stationary proton, what are the other particles if an antiproton is to be created among them? A positive pion is possible but the total rest mass energy of the final state ...
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Decay of spin-1 particle into two 1/2 particles
If particle of spin 0 decays in rest frame decays in 2 particles the angular distribution will be uniform. How it will change for particle with spin 1 decaying in pair of $e^{-} e^{+}$ for example?
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Book on Representations and Group Theory in Particle Physics for Mathematicians
Is there a book for someone who already knows some group theory and theory of group representations on the mathematical side, and just wants something which explains the applications in particle ...
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Is it theoretically possible that electrons are made up of quarks just like protons and neutrons? [duplicate]
Before closing it as a dupe of this. Please go through the question once .
Is it theoretically possible that quarks make up an electron ( like you may get a particle with the same electronic charge $(-...
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Deep inelastic electron-proton scattering amplitude
In 'QCD and collider Physics' book by Ellis, Stirling and Webber, chapter 4.2 'The parton model from field theory' there is this equation for the amplitude of the process $e^- (k) P \rightarrow e^- (k^...
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Can only two electrons be in ground state? Are the energy levels the same thing as the energy shells? I can't find a straight answer
So for a model like this one, can there be two electrons in one energy level?
And I don't understand the Pauli principle that two electrons can't be on the same energy level when there are 2 electrons ...
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$\beta$ decay paths question
Can the $\beta^-$ decay proceed by the absorption of a $W^{+}$ boson or the $\beta^+$ by the absorption of a $W^-$ boson?
The $\beta^-$ decay is known as the decay of a $d$ quark into an $u$ quark and ...
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Can $Z$ bosons mediate short-range forces between electrons?
The flavor quantum numbers and charge of $Z$ bosons should allow it to mediate between electrons without violating any conservation rules. So at very short displacement scales do electrons actually ...
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Murray Gell-Mann's independent discovery of group theory [closed]
In this article I found an interesting remark on how group (representation) theory was introduced into the physical sciences :
Murray Gell-Mann developed the “eight-fold way” to explain the spectrum ...
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