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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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Why the frequency component is not included when the energy of a wave is described?

Energy of a wave is directly proportional to its Amplitude squared. There is no inclusion of frequency in it. But by intuition if one thinks about it, isn't it obvious that a wave with higher ...
Vibhav shivadeker's user avatar
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1 answer
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Could a single gamma ray photon break the Schwinger limit? If so, at what energy?

Is it possible for a ray of light, or even a single photon, to 'break' the vacuum of space? If so, at what energies (in eV, e.g.) would this happen?
Kurt Hikes's user avatar
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BTZ black hole as a quotient of AdS space

I am trying to understand this paper 1 and trying to reproduce some calculations and had some questions about that. In section 3.2, page 12, eq. 3.9, the authors are writing normal geodesics of an ...
Goodfellow's user avatar
3 votes
0 answers
67 views

How feasible is a DIY neutrino detector in this day and age? [duplicate]

*This question is similar to: Is a DIY neutrino detector feasible?. The difference between my question, and the old one is that the question is from over 8 years ago. Naturally, some of the answers ...
Justyn's user avatar
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-1 votes
0 answers
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What is dielectric constant of conductor if it is connected to battery as the electric field will generate in conductor does it still be infinite? [closed]

as we calculate dielectric constant of conductor saying Eext/Eext-Einduced = 0 but as inside conductor electric field net would be not equal to zero. `
Mayur Namdev's user avatar
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0 answers
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Is there a theory that treats particles as just the shape of an interaction emergent from a more fundamental substance? [closed]

I'm certainly not a physicist but just curious. The more I hear about quantum physics, the more I'm becoming convinced that particles don't actually exist outside of interactions with other particles. ...
user81993's user avatar
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-3 votes
1 answer
95 views

Parity transformation of the $\pi^{0}\rightarrow\gamma\gamma$ process

I want to prove that the amplitude $$\mathcal{M}^{\mu\nu}=\epsilon^{\mu\nu\alpha\beta}q_{1\alpha}q_{2\beta}$$ is violating parity. Here $q_{i=1,2}$ are the external momenta of the photons. The total ...
Filippo's user avatar
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1 answer
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Square of the Feynman amplitude for $a +b\to c+d$ and its reverse

In quantum field theory, if a process $a +b\to c+d$ is allowed by a certain interaction Lagrangian (hermitian), the reverse process, $c+d\to a+b$, must also be allowed (as far as I understand) by the ...
Solidification's user avatar
0 votes
0 answers
73 views

Mandelstam variables sign

I am self-studying the book "Quantum Field Theory and the Standard Model" by Schwartz, on page 99 (paragraph "Mandelstam variables"), the context is the $2\rightarrow 2$ scattering ...
Andrea's user avatar
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-5 votes
1 answer
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I don't understand how energy is conserved when an electron-positron pair decay into a muon-antimuon pair [closed]

I'm trying to self-study particle physics using Griffiths Introduction to Elementary Particles, and when doing exercise 2.7 I'm getting this portion of the question wrong. Given that the problem doesn'...
user412811's user avatar
11 votes
3 answers
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Can a big mass defect make the mass negative?

Can two particles with small masses and a strong attractive interaction have a total negative mass when brought together? Let $m_1, m_2$ be the (rest) masses of two particles when infinitely distant. ...
HomoVafer's user avatar
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The other quarks also have some different properties or strange is the only one?

Particles that contain a strange quark decay more slowly, because of what we see in this answer. The other quarks, besides up and down, also have some particularity? E.g. according to Brumfiel, Geoff (...
Nicolas Induzzi's user avatar
2 votes
0 answers
89 views

Gravitational halos made of neutrinos...?

I have been recently interested in how halos made of standard model particles could be formed and behave. After asking some questions in this site, I was told about how neutrinos could form such halos....
vengaq's user avatar
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Action of charge conjugation on bispinors

I'm following an introductory course to particle physics. We have introduced Klein-Gordon's equation for spinless particles and Dirac's equation for spin $1/2$ particles. Klein-Gordon's equation works ...
HomoVafer's user avatar
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1 answer
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What is charge on a fundamental level and what is it caused by?

On bigger bodies, I've learnt so far that charge is caused by a lack or excess of electrons or protons but when you look at an electron or proton, how are they charged? what is the cause of their ...
shriekspeare's user avatar
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0 answers
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What is fragmentation scale in particle physics?

This is a quick guestion. What is used as the fragmentation scale in cross section calculations? If I have a quark which hadronizes, is the fragmentation scale (at which the fragmentation function is ...
Ville Alanko's user avatar
1 vote
0 answers
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Implementation of fragmentation functions into a cross section calculation

I'm trying to understand how fragmentation is put into a cross section calculation. I have learned that the full cross section can look something like \begin{equation} \sigma=\int_0^1d\xi\int_0^1dzf(\...
Ville Alanko's user avatar
-1 votes
0 answers
13 views

Jet events and Deeep Inelastic Scattering (Scaling Behavior) at the same time?

I am a philosopher of physics, so I already apologize for potential ignorance. I have also graduated in physics, but I now analyze problems on another level and also forgot some of the mathematical ...
Dontwastetime's user avatar
-1 votes
2 answers
77 views

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
3 votes
0 answers
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Is there a sigma for unexplained hypothetical discoveries?

I recently read that the Koide formula relating electronic leptons rest masses is often considered to be numerologic, since unexplained, even though recent years experiment data tend to narrow the ...
olivierlambert's user avatar
0 votes
1 answer
78 views

Could cosmic rays induce a vacuum decay in the future?

I've been told that very energetic cosmic rays could cause a vacuum phase transition or vacuum decay (and even could cause a true vacuum level to go "uphill" to a false vacuum) due to their ...
vengaq's user avatar
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2 votes
1 answer
85 views

Could there be states of matter that could avoid "matter decay"?

Regular structures of matter may decay over extremely long periods of time (especially if proton decay occurs, which is not proven but it remains a possibility) Even if that happens, are there any ...
vengaq's user avatar
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1 vote
0 answers
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How do I calculate the significance level (in Gaussian Sigma) of a particle classification's classier results/

I'm doing a high school project for which I'm training a Neural Network to classify signal and background events with this dataset: https://www.kaggle.com/datasets/janus137/supersymmetry-dataset/data ...
SidKT's user avatar
  • 21
0 votes
2 answers
116 views

Why does the up and anti-up quark combine into a pion and not a photon?

im currently studying a level particle physics and im confused about this. Particle annihilation occours when a particle meets its corresponding particle, converting their mass energy into two photons,...
liv.ysf's user avatar
12 votes
4 answers
2k views

What will happen if we keep bringing two protons closer and closer to each other, starting from a large distance?

I am asking this question for theoretical understanding of the topic: What will happen if we keep bringing two protons closer and closer to each other, starting from a large distance? I understand ...
Devansh Mittal's user avatar
0 votes
1 answer
67 views

How are quantum states of particles represented in particle processes?

For example, lets say we have an electron-positron annihilation scenario. What will be the density matrix representing the quantum state of the electron and the positron? What will be the density ...
cdebanil's user avatar
1 vote
0 answers
83 views

Doubt in $e^{+}e^{-}\rightarrow W^{+}W^{-}$ scattering

I am trying to understand how to compute the scattering amplitude for the process $e^{+}e^{-}\rightarrow W^{+}W^{-}$, as a reference one could look at Peskin chapter 21. What I do not understand is ...
Filippo's user avatar
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0 votes
0 answers
36 views

Receipt for writing down the Boltzmann-equation for a given interaction

Suppose one has a gas consisting of two particles, which are known to primarily interact with each other through a specific interaction. To describe the behavior of the particle densities, I would ...
Luca D's user avatar
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0 answers
31 views

QCD parton shower hard scale

Currently I'm studying parton showers from QCD and I'm having trouble with understanding how the hard scale $Q$ is related to the virtuality and energy of the parent parton. The Sudakov factor $\Delta(...
Jesse's user avatar
  • 291
3 votes
2 answers
143 views

How can we model the primordial Universe while the interior of a neutron star and comparable states of matter are still mostly unknown?

There is something I never quite understood about the physics of the primordial Universe. There are states of matter at high temperature/high pressure that are still, today, poorly understood. The ...
Vincent's user avatar
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0 votes
0 answers
36 views

Difference between jets and inclusive hadron production

I know both jets and inclusive hadron production are measured in high energy collisions. Is the difference just the way you measure it, or are there differences in the process behind them? If you ...
rafa's user avatar
  • 13
1 vote
0 answers
50 views

Do particle physics experiments need to take a possible gravitational wave background into account?

As I understand gravitational waves, we can barely detect them, because their strength is so small. On the other hand, they are presumably able to move individual particles like electrons. Does this ...
Allure's user avatar
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-1 votes
2 answers
69 views

Why does binding energy of particles, which constitutes most of macroscopic mass, make them harder to accelerate?

I've seen a lot of questions on this topic so please don't misunderstand, I understand E = mc^2 and SEMF and so on. I specifically want to know how internal forces within lets say a nucleus make it ...
Rok M.Vahtar's user avatar
1 vote
1 answer
27 views

What is the standard reference medium in which positron ranges data are obtained in property tables, specifically for isotopes used in PET?

What is the standard reference medium in which positron ranges data are obtained in property tables, specifically for isotopes used in (Positron Emission Tomography (PET)? I can't find any valuable ...
0 votes
0 answers
34 views

Relation bitween Mandelstam Variables in three-body final state

What is the relation between Mandelstam variables in the three body final state? There are 5 independent Mandelstam variables. What is the relationship between them?
Andrea's user avatar
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0 votes
2 answers
45 views

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
0 votes
2 answers
27 views

Problem when deriving formula of the momentum of photons in photoelectric emission

Now I know this might be a small error on my part or some wrong assumption taken, but for some reason when I tried deriving the momentum, I ended up with a different value. The momentum is given as: $$...
Aaron's user avatar
  • 3
-1 votes
1 answer
22 views

Can impact offset of an electron on an ion affect the resulting particle velocities?

A free electron, of mass $m_e$ and velocity $v_e$ collides with an ion of mass $m_i$ and velocity $v_i$. When they recombine, a photon of exactly the ionization energy $E_i$ will be emitted, moving in ...
Hugh Perkins's user avatar
0 votes
0 answers
21 views

Magnetic parity and electric parity parts of solutions?

I'm currently reading the paper Conserved charges of the extended Bondi-Metzner-Sachs algebra by Flanagan and Nichols. In equation (2.15), the solution $$Y^A = D^A\chi + \epsilon^{AB}D_B\kappa$$ is ...
CactusSnow's user avatar
3 votes
0 answers
46 views

Literature on intense field QED

Does anyone happen to know a good book or notes on intense field QED, for example about Volkov states and the Furry picture? To give you an idea of my pre-knowledge: I am a physics graduate student ...
2 votes
0 answers
30 views

Why does oxygen green (S1) emission in aurorae only occur at lower altitudes? [duplicate]

Aurorae have a red color at high altitudes caused by the excitation of atomic oxygen and the subsequent emission at about $630 \,\text{nm}$. This happens at high altitudes because at that height there ...
jack_O'Dim's user avatar
0 votes
0 answers
37 views

When two neutral atoms collide, and one atom ionizes, how does the speed of the ejected electron compare to that of the atoms?

When two neutral atoms collide, and one atom ionizes, how does the speed of the ejected electron compare to that of the atoms? Context is, I was trying to do the calculations for the velocity of the ...
Hugh Perkins's user avatar
0 votes
0 answers
64 views

Are there any recorded time-of-flight (ToF) measurement data for the $H\to\gamma\gamma$ collision products at the LHC Atlas detector?

Especially, I am interested in the time-of-flight (ToF) measured recorded values of the two $\gamma$-photons (diphotons) during $H \to\gamma\gamma$ Higgs boson detection events at the LHC Atlas ...
Markoul11's user avatar
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3 votes
1 answer
285 views

How to be sure that when a muon passes a detector it is actually a muon?

The question is as follows: when you have any kind of detector for muons you just take measurements and you say, for example, the number for the muon flux but how you're sure that all particles ...
Francisco Santiago's user avatar
5 votes
1 answer
130 views

Estimating particle mass from bubble chamber

In an example of a book, it shows how to estimate the $\pi^-$ rest mass 139MeV$/c^2$ from the trajectory of $\pi^-$ in a bubble chamber. It starts from the charge-to-mass ratio formula $$ \tag{1} \...
chichi's user avatar
  • 546
2 votes
1 answer
88 views

Why does the mass term not violate particle number conservation in a free theory?

The Lagrangian of a free real scalar field theory is $$ \mathcal{L} = \frac{1}{2} \partial_{\mu} \phi\; \partial^{\mu} \phi \; - \frac{1}{2} m^2 \phi^2. $$ If we decompose $\phi$ in terms of the ...
ratchet411's user avatar
1 vote
0 answers
45 views

How to calculate mean energy of fluorine-18 positron?

I know that Fluorine-18 becomes stable when a neutron takes the place of a proton and becomes Oxygen-18 where a positron and nutrino are emitted. Using Einstein formula, I can find the maximum energy (...
Gabriel L.'s user avatar
1 vote
0 answers
61 views

Semi-Inclusive Deep Inelastic Scattering (SIDIS) kinematics

I'm having some trouble understanding the kinematics in SIDIS. For example take the reaction $l+N\to l'+h+X$, where $l$ is a lepton, $N$ is the target Nucleon and $h$ is a hadron. The kinematic ...
rafa's user avatar
  • 13
0 votes
1 answer
70 views

Where is antineutrino in standard model Lagrangian?

I'm somewhat confused by the content I studied in Srednicki's work, where the neutrino is described as a Majorana field. In this framework, there shouldn't technically be antineutrinos, given the ...
Bababeluma's user avatar
0 votes
0 answers
24 views

How to find nuclear color transparency in following reaction?

I am doing my project on Nuclear Color transparency which involves calculating color transparency for nuclear reaction $h+A\rightarrow h+N+(A-1)$. In a nuclear reaction, the nuclear Color transparency ...
isnet's user avatar
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