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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Do the Casimir operators for $su(3)$ algebra of particle physics carry any physical meaning?
For the $su(2) $ algebra of angular momentum, the eigenvalues of the Casimir operator, $\hat{J^2}$, represents the square of the total angular momentum of a system. The $su(3)$ algebra has rank 2 and ...
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Flavor changing neutral current with photon
I'm trying to understand why the penguin diagram for photons takes its form.
$I$ here is the integral and some CKM elements.
The author (Ch1.6.1) says that for $b\rightarrow s\gamma$, we get a factor ...
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Why doesn't the lack of electromagnetic repulsion between dark matter particles result in the formation of black holes? [duplicate]
From what I've researched dark matter isn't subject to electromagnetic forces, which I'm assuming implies that there is a lack of electromagnetic repulsion between dark matter particles.
If there's ...
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How can it be "unfortunate" while this is what the experiments want?
In John Gribbin's Ten Tantalizing Truths, the author discusses the cyclotron:
for a particular mass as the particles spiral outward, the rotation frequency stays constant, because the particles are ...
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Comprehensive references to learn about the flavor $SU(3)$ model of hadron classification
What are some comprehensive references to learn about the flavor $SU(3)$ model of hadron classification based on group theory? Textbooks, Lecture notes, videos anything will do. I need to learn this. ...
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Main subatomic particles [closed]
I've come across a question that asks what the subatomic particles are. The answer being the proton, neutron and electron. However, from my understanding subatomic particles also include quarks etc. ...
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1
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Rayleigh law contradicting tyndall effect
Sir, we have been taught that according to Rayleigh, the amount of scattering of light is inversely proportional to the fourth power of its wavelength and this law only occurs when the size of a ...
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Why do atoms want to attain stability? [duplicate]
So, back in my school, our teacher was teaching structure of an atom. I had some doubts, like why do hot objects emit radiations and so many. I noticed that every question I had asked had an answer. ...
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84
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What is the minimum energy needed for the photodisintegration of U-238?
What is the minimum threshold energy needed for a photon to cause photodisintegration in Uranium 238, and how different (in terms of MeV) is this energy needed for photodisintegration from the energy ...
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Simplifying a Decay Process with Centre of Mass Frame
I am considering a process where a particle decays into a pair of particles, where the incoming particle has momentum $-p$ and the two outgoing particles have momenta $q$ and $r= -p - q$.
When ...
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Is $X\,X \rightarrow \overline{X} \,\overline{X} $ kind of baryon number violating reaction possible?
I am reading Daniel Baumann's "Cosmology" book. In the part of Sakharov conditions,the third condition he mentions is the 'Departure from equilibrium'. To show the necessity of this ...
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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 ...
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How Atlas differentiated that the di-photon produced was not by a graviton but instead by a Higgs Boson decay?
The Wikipedia article here, https://en.wikipedia.org/wiki/Higgs_boson#Confirmation_of_existence_and_current_status , confirms (see "zero spin requirement" table row test) that the graviton (...
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Is a qubit just a bit that hasn't been measured or observed?
A qubit is a superposition of a 0 and 1, apparently meaning that as long as the qubit isn't observed it is both 0 and 1, or a probability of being both. If this is the case, why don't regular bits ...
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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 ...
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Color vectors for antiquarks
For a single quark, the colour vectors are given by
$$r=\begin{pmatrix}
1 \\ 0 \\0
\end{pmatrix} \qquad
g=\begin{pmatrix} 0 \\ 1 \\ 0 \end{pmatrix}
\qquad b=\begin{pmatrix} 0 \\ 0 \\ 1 \end{pmatrix}$$
...
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Are non-virtual particles of QFT real?
Perhaps the question may seem a bit provocative, but it refers to several mathematical and, presently physical facts, pointed out a long time ago:
The Unruh effect suggests that an accelerated ...
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Can a massless virtual graviton decay into a Higgs Boson and two γ-photons in the LHC at CERN? [closed]
Τheoretically, is it possible?
G--> H--> γγ
And if not, why?
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Scatter angles at IceCube
Is it possible to have a scatter angle(in lab frame) to be greater than 90 degrees at IceCube, with this I mean the relative angle between the incoming (muon) neutrino and the outgoing (muon)lepton.
$$...
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Can Bernoulli's Principle be applied to subatomic particles or virtual particles or "the quantum foam"?
If we create a pair of rotary wings like those on a helicopter, and spin them in a vacuum, would it be possible for a virtual particle and anti particle pair to spawn, be split by an approaching wing, ...
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Lifetime of a WIMP [duplicate]
I have been watching videos of WIMP's and have a simple question..
The larger the particles, the shorter their lifetime. A top quark is so massive that it cannot form a "stable" bond with ...
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Are electrons immune to scattering in plasma accelerators?
Plasma accelerator is a promising new technology which may increase the acceleration gradient by orders of magnitude. Unlike conventional RF accelerators which operate in high vacuum, plasma ...
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How do the different Neutrino masses come about?
The determination of the Neutrino mass can be roughly divided in three strategies:
The neutrino mass from cosmological observations:
$$m_\nu = \sum_{i} m_i $$
The neutrino mass from the neutrinoless ...
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Can top quark decay into a top quark and a $W$ boson?
I have a question regarding Figure 1 from this paper:
https://cds.cern.ch/record/2859612/files/TOP-22-008-pas.pdf
How can a top quark decay into a top quark and a $W^{-}$ boson?
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Is there a software that computes simple particle decay kinematics?
I was trying to figure out some details about a specific decay channel for a generic particle accelerator experiment. For instance if I have a proton proton collider with fixed energy, I would like to ...
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Are there enough parameters in standard model to falsify SUSY?
I know that the search for Higgs would be quite pointless if there was no estimation of its mass.
Namely the perturbative violation of unitatity, gave us an upper bound on its mass.Unitarity ...
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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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Hey there I'm a beginner in particle physics trying to "selfstudy" from online resources. I want to ask how much of what I learned is correct? [closed]
The information I have gained thus far regarding the standard model is;
fermions and how their intrinsic nature.
they have half spin, non zero mass, a charge, a weak hypercharge (for leptons), a ...
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Can off-shell corrections to processes lead to corrections on number of jets distributions? (both for MC and Data)
I was looking at the modeling of ttW production (but the question is general) and came upon an off-shell corrections paper. As I am no expert on MC generators, I am not sure if these off-shell ...
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Are there equations for Parton Distribution Functions?
Are there actual equations for the Parton Distribution Functions for quarks and gluons? I've been looking high and low for theory-based papers about this and it seems like a wild goose chase at this ...
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Integrals and Sudakov decomposition
Suppose that an arbitrary vector $k^\mu$ is decomposed in the so-called Sudakov basis
$$
k^\mu = k_i \frac{n_j^\mu}{n_{ij}} + k_j \frac{n_i^\mu}{n_{ij}} + k_\perp^\mu
$$
where $n_{ij} \equiv n_i \cdot ...
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Neutrino oscillations imply neutrino mass — Does the usual argument really hold?
An argument that people put forth is that because neutrinos can undergo changes in lepton flavor midflight, they must "experience time." Since massless particles must travel at the speed of ...
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Is it possible to Compton scatter from delocalised pi-electrons in liquid scintillator?
I am wondering if an incident gamma could compton scatter from the delocalised pi-electrons in an aromatic compound (e.g. liquid scintillator).
I understand that compton scattering is valid for free ...
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Is an electron a point charge? [closed]
Doesn't electron capture imply an electron is not a point charge?
It needs to have a radius that overlaps with the proton. If it was a point charge, no matter how close it got to the proton, the ...
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Does strongly gravitating object travel along geodesic of a background field？ [closed]
That test particles travel along the geodesic is assumed in the context of GR. But does it apply to strongly gravitating object, such as black hole in an expanding universe, binary neutron star, etc.? ...
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What is vetoing in the context of experimental particle physics?
I saw in this paper by the CMS Collaboration that two of the selection requirements defining the signal regions are the requirements on $b$ jet veto and $\tau_h$ veto. What is, in this context, a veto ...
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Maximum energy of neutrino from decay of $W$ boson
Figure 2 of this paper suggests that neutrinos from the decay of on shell W bosons can have an energy as high as the W boson mass. However, in the $W^{-} \rightarrow e^{-} + \bar{\nu}_{e}$ process, ...
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Normal Force - What if I stepped on a molecularly frozen object? [closed]
I’ve been trying to understand normal force on a molecular level, and I’ve come across the idea that atoms are connected to each other by forces that act like springs. You step on the floor; the floor ...
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Massless electrons pre electroweak symmetry breaking observation
I recently heard that electrons are massless at energies above electroweak symmetry breaking, has this ever been observed experimentally? I looked for it but couldn’t find anything
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What is the difference between 7TeV and 13.6 TeV ? Why don't we just dump the low energy data and use the one with highest energy?
I saw some results from particle physics that combines 7 TeV and 13.6 TeV results but they are different. Why they are different? Why do we combine them? If we need them why did LHC stopped taking ...
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Why isn't there Bremsstrahlung Radiation for Energy less than 20 keV for Tungsten?
https://www.researchgate.net/figure/Bremsstrahlung-and-characteristic-radiation-spectra-are-shown-for-a-tungsten-anode-with_fig4_8365056
Fast electrons produce X-rays in the anode of an X-ray tube ...
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Does Thomson and Rayleigh Scattering cause any change in rotational and vibrational energy of an electron or atom?
We know from molecular spectroscopy that incoming light on a molecule can change a molecule's rotational, vibrational and electronic energy levels.
If the incoming light is,
on the far-infrared and ...
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Why doesn't KE of annihilation electrons necessarily have to be equal to each other?
We know that when a high energy gamma ray(E >= 1022 keV because the total energy of 1 electron at rest and 1 positron at rest is 511 keV) passes near a high Z(atomic weight) atomic nucleus ...
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When particles began interacting with the Higgs field, what determined the specific numbers for their masses?
All up quarks and antiup quarks have the exact same mass of 2.3 MeV/c³, just as every instance of each particle also has an exactly set quantum for their mass, according to their kind.
But if the ...
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Why there are no pseudoscalar mesons like $\eta_u = u\bar{u}$, $\eta_d = d\bar{d}$, etc?
Consulting the list of pseudoscalar mesons, we found that for charm and bottom quarks there are two mesons with quark content given by:
$$\eta_c=c\bar{c},\qquad \eta_b = b\bar{b}$$
on the other hand, ...
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Feynman diagram of muon pair production [duplicate]
Hi to everyone. I don't understand why the diagram in which final antimuon and muon are exchanged is not possible (so having in the upper part positron and muon, downwards electron and antimuon). It ...
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Redefinition of fields and interpretation of the particle content
Suppose I have some Lagrangian $\mathcal L_1$ involving multiple fields $\phi_i$ with interactions. I can reparametrize the Lagrangian in terms of new fields $\psi_i$ by inserting some ...
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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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Why are vector mesons heavier than pseudoscalar mesons?
From the hyperfine calculation we find that the mass of the vector mesons are heavier than pseudoscalar meson, as the following proves.
The magnetic moment is proportional to the spin and inversely ...
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Phase Space Contributions to Decays with Fixed Momentum
Neglecting helicity, consider the decays
$π^-\rightarrow e^-\bar{ν_e}$ and$π^-\rightarrow μ^-\bar{ν}_μ$. I understand that from Fermi's golden rule, the decay probability should be proportional to the ...
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