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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Spin and isospin
Considering, for example, the baryon octet, we have then that for $L = 0$, $J = 1/2$, as it is made of spin-1/2 particles. Hence, the isospin $I = 1/2$ and so, some of the wavefunctions of the octet ...
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Antimuon-electron interaction
I was wondering if the following interaction is possible:
$\mu^++e^-\to \bar{\nu_{\mu}}+\nu_e$
Clearly every conservation law is satisfied, including each lepton number conservation, but I can’t seem ...
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How do radiation particles escape the atom unaffected in radiation?
Alpha radiation is the emission of two protons and two neutrons from the nucleus of an atom (helium nucleus). Beta radiation is the emission of a high-speed electron from the nucleus of an atom as a ...
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Can the particle reaction $a+b \rightarrow c+d$ occur in vacuum?
In particle physics, can the reaction $a+b \rightarrow c+d$ occur in vaccum from the point of view of energetic balance?
Both $a,b,c,d$ are generic and different particles.
It is true, for example, ...
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Do subatomic particles in atoms change shape? [closed]
Do protons, neutrons and electrons change shape?
If they don't:
What shape are they individually? Are they irregularly shaped? Are they 'regularly shaped'? Spherical (like in textbooks, diagrams)? ...
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What is the sequence of symmetry-breaking events in the very early universe?
My current understanding of the very early universe is that all particles were completely symmetrical at one instance, but a chain of symmetry breaking events split these perfectly symmetrical ...
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How to check whether particle interaction is allowed and how to classify interactions?
My question would be (as I couldn't find a website summarising it) to have a comprehensive list of how to check whether a particle interaction is allowed and if so, what interaction it is (or it would ...
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If mass is just energy, how does thermal or kinetic energy transfer happen? [closed]
If mass is just energy, as it's excitations on quantum fields that when they vibrate together a certain way, they end up a particle, then how does energy transfer work?
Specifically kinetic energy ...
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What are the dimensions of the proton's substructure?
I was looking over the "Visualizing the Proton" videos that MIT put out a few years ago, where the collision data from CEBAF, etc. was turned into a visual representation of quarks, gluons ...
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Do QFTs with a physical cut-off not respect the postulates of Quantum Mechanics?
Wilsonian renormalization says that it's fine to have a physical cut-off. But I am thinking that such theories do not respect the postulates of Quantum Mechanics. Is this true?
Theories with a ...
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Method of Neutral Particle Mass Calculations from Bubble Chamber Images
I am looking into events within bubble chamber images and have come across a stumbling block. It relates to finding masses of neutral particles within bubble chamber images, specifically the mass of ...
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Interplay between SUSY-spectrum generator and low energy sparticle masses
I'm trying to understand how to generate MC events for SUSY models at specific parameter points.
To be specific: I'd like to generate squark pair production : pp $\rightarrow \tilde{q} \bar{\tilde{q}} ...
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Double slit experiment
Engineering question: How does the electron gun shoot one electron at a time to the double slit target? How was this possible when the experiment was done 100 years ago? How is this done with photons? ...
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Why is particle creation and annihilation not observed on a macro scale?
I am new to QFT and the idea of particle creation/annihilation so this will likely be a soft question. I have read that due to special relativity, particles come in and out of existence (and some ...
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All possible QFTs from geometry? [closed]
Physicist Nima Arkani-Hamed has taken an approach to understand fundamental physics based on geometry (specifically, positive geometry). This started with his work with Jaroslav Trnka in the ...
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In what ways does quantum field theory (QFT) extend quantum mechanics (QM)?
The time evolution of any wave function is deterministically specified by the Schrödinger equation (unless measured).
However, particle creation is not allowed in quantum mechanics.
As I am unfamiliar ...
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Particle creation by inducing a set of values on the wavefunction? [closed]
The following 10 numbers:
completely specifies a self-propagating Schrodinger wavefunction:
If one is able to produce/induce these 10 excitation numbers directly onto a pre-existing wavefunction, is ...
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GIM mechanism and $K_L$ decay
I'm trying to solve the problem (14.5) of Introduction to Nuclear and Particle physics by A. Das and T. Ferbel.
What am I trying to do is to prove that $\langle Z^0|d\bar{s}\rangle = 0$ by ...
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Filtering combinatorial background in $B_0$ -> $\mu^+ \mu^- K^{*0}$ decay
We are looking to isolate a signal representing this decay from all possible background candidates produced in a pp collision in the LHCb. We have already dealt with all the peaking backgrounds (J/Psi ...
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Meaning of "coupling" in the context of Dark Matter decay?
I often hear the term "coupling" when people speak of a potentially decaying dark matter (DM) particle. I don't understand what a (hypothetical) DM particle should couple to when we consider ...
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How can a strong interaction in QFT give you a particle spectrum that's different from the free particle spectrum?
In quantum field theory, as long as the interaction is weak, one can use perturbation theory, i.e. Feynman diagrams and the virtual particle formalism. The particle spectrum of the interacting theory ...
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Can we say that for everything in our universe to exhibit a behaviour, it should have the capability to process information?v(details below) [closed]
Take the simple case of water molecules.. you freeze them, it turns into ice.. at around 100° it vaporizes.
For each and every reaction in this example, the molecule needs to react to heat, for it to ...
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How to use the quark model to explain that the $D^+$ won't be a strange particle?
For the system of $K^-,\pi^+,\pi^+$, with the invariant mass spectrum peaking about 1.87 GeV, call this resonant peak $D^+$; we find its spin to be zero by experiment.
Using the quark model, how ...
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How would one compute the heterotic amplitude for four gauginos using bosonization?
I'm reading through Polchinski's String Theory Volume II, and I was unsure of how to approach Problem 12.9. For posterity, the problem states:
Calculate the tree-level heterotic string amplitude with ...
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Do photons propagate in a single direction?
I’ve been researching this and can’t find a straight answer.
I’ve heard that the direction of a photon, when it’s emitted, is random. But I’ve also heard that if it’s emitted from point a to b, it ...
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Partially circular and partially linear particle accelerators
I know that circular accelerators, due to the radiation emitted by accelerated particles, are limited by their size in what energies they can reach. Linear accelerators (linacs) instead could reach ...
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Identifying electron and positron creation using bubble chamber tracks
Taken from a bubble chamber track image,
(http://hst-archive.web.cern.ch/archiv/HST2004/bubble_chambers/BCwebsite/media/lesson071.gif)
I have marked several single (unpaired) creation of what I ...
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Elementary question about charge of doublet
This is probably extremely elementary, but I am not sure how to look for an answer online. I'm reading a physics text that uses the following notation for a doublet of particles:
$$q_L \rightarrow (3,...
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Is it instantaneous for an unpolarized molecule to get polarized by a very fast particle & get unpolarized by emitting photon? Or is there a time gap?
The question is in the context of Cerenkov radiation, where a coherent wavefront is formed when a particle which is moving faster than speed of light in a dielectric medium, (v>c/n, where n is ...
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What is the effect of top quark on Flavor Changing Neutral Current (FCNC) suppression?
We know that the introduction of charm quark (GIM mechanism) suppresses Flavor Changing Neutral Current (FCNC) decays occuring via Electroweak box and penguin diagrams. But we have another doublet of ...
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Volume in a scattering process equal to 1?
I'm studying Fermi's golden rule, and in section 8.3.1 of "Braibant, Giacomelli, Spurio - Particles and Fundamental Interactions" there is an application to the decay of the neutron. While ...
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Experimental evidence for color charge via Electron-Positron-Annihilation experiments
In Electron-Positron-Annihilation R, the ratio of the hadronic cross section to the muon cross section, is calculated as the sum of charges squared, multiplied by 3 to factor in the 3 colors. I know ...
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How is the property of chirality used?
I was studying the book "Scattering and Structure" by Bogdan Povh; it mentions that this property is used as a criterion to decide whether one is dealing with a massless or a massive ...
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$K^{-} + p \rightarrow ...$ most likely outcome?
I'm supposed to find the most likely outcome for are negative kaon - proton collision. Is there any way to "calculate" this without resorting to measured values (PDG -particle data group)?
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Why photons have not magnetic moment? [closed]
Spin of a particle is a magnetic moment.
Photon have spin-1, so why photon have not a magnetic moment because only 0-spin particles can not have a magnetic moment?
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On the annihilation of a neutron with an antineutron
In my introductory to elementary particle physics course, I am asked to consider the process
\begin{equation}
n+\bar{n}\to\pi^++\pi^0+\pi^-
\end{equation}
and to determine whether it is possible or ...
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Do fields and particles have a one-to-one correspondence?
Do fields and particles have a one-to-one correspondence? That is can we have two different particle from same field (excitation) or can one unique particle gets created by different field (excitation)...
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Neutrino Cross-section approximation:
First, thank you for taking the time to read this question.
In section 5 of this paper the author explained that for energies between $1-20$ GeV the total Charged-Current Cross sections for $\nu_{\...
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When can spinless "particles" have dipole moments?
While fundamental point particles with zero spin cannot have a dipole moment because spin is their only directional property, this does not seem to be true for spinless composite "particles"....
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Doubt(s) about graviton + anti-graviton interaction
Britannica says this about the graviton:
graviton, postulated quantum that is thought to be the carrier of the gravitational field. It is analogous to the well-established photon of the ...
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Is there an experimental value for the magnetic moment of the Kaons?
I can't find (Google, PDG etc.) an experimental value for the magnetic moment of the Kaons $K^{⁺/-}$. They are u/s mesons so shouldn't there be a non-zero value even if total spin is zero? Lifetime is ...
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Hypercharge and photon definitions in $SU(5)$ GUT
So, a weak isospin and hypercharge in $SU(5)$ are defined as
$$ T_3 = \frac{1}{2}diag(0,0,0,1,-1) $$
$$ Y = \sqrt{\frac{3}{5}}diag(-1/3,-1/3,-1/3,1/2,1/2) $$
The hypercharge already has the $\sqrt{3/5}...
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If quarks and electrons are both 0-dimensional, how can they have different masses?
If they are zero-dimensional but have different masses, wouldn't that have to suggest they have different densities meaning they are composed of different things?
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Why would electron spin of 1 contradict Stern-Gerlach experiment?
in particle physics we know that electron have a spin of 1/2 (and Lande factor g with value 2).
Why can’t we for example conclude spin 1 and g also 1?
Thanks for any help! :)
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Physical coupling as a measurable quantity
I have a question about Preskill's quantum field theory note. He want to argue that the renormalized coupling is something measurable.
First let me introduce some backgroud. Suppose the Lagrangian can ...
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How do excitons move through a lattice?
If an exciton is a photoexcited electron attracted to the hole in the valence shell it left behind, how does the quasiparticle move around? The hole isn't an actual particle. The hole is an effective +...
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Anyone aware of a double, double slit experiment? [closed]
Is anyone aware of a double, double-slit experiment?
Where for example we can see that light and matter display characteristics of both classically defined waves and then classicly defined particles ...
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How to describe the physics process of scintillation? [closed]
I want to find some references on describing the physics of scintillation. As we know the lights generated by scintillator through atom activation and de-activation, and each material has a
spectrum ...
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What is the angle between two $b$-quarks when a Higgs boson decays to a $b$-quark pair, in the rest frame of Higgs boson?
I am generating events of $ep -> Xjv$, ($j$ is a jet, and $v$ shows a neutrino) where $X$ particle decays to a $b$-quark pair. I am going to calculate the angle between two b-quarks in the rest ...
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Associating correct Hessian mass-squared eigenvalues (masses) with correct particles
I am looking for the physical masses of two particles (call them $\sigma$ and $\pi$), described by a potential V. To do this, I compute the $2 \times 2$ Hessian mass-squared matrix $\frac{\partial^2 V}...
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