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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.

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Estimating Accidental Coincidence

I am trying to measure muon's mean lifetime using 3 scintillators. The logic of the experiment is shown below: I know that accidental coincidences could happen because of unrelated muons that ...
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Is there a weak hypercharge : spin-3/2 analogy?

So I was not trained as a particle physicist, but I left a table of particles on a post on Hacker News based on what little I do understand about the conservation of weak hypercharge and weak isospin. ...
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Can we image the interior of the earth by shooting weakly interacting particles through it?

Could we image the various layers of the earth by shooting weakly interacting particles through it? Let's say we shot a very high amount of neutrinos in one side (say, the north pole) and then ...
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Clarification on isotope notation

I am a bit confused about the idea of isotope notation. I know that the top number is the mass number, equivalent to the number of neutrons + protons, while the bottom is the atomic number, equivalent ...
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Is there a physical difference between the colors of quarks?

Is there any physical difference to the way, say, red quarks behave compared to green or blue ones? Or is it just an intrinsic property that they have that doesn't provide any physical difference ...
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Can charged leptons undergo oscillation?

Neutrino oscillation is an observed fact while charged lepton oscillation is not. Unlike neutrinos, is it possible for the charged leptons to oscillate, theoretically? In other words, is there ...
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Is there any Feynman diagram for Baryon/Hyperon decay with missing energy?

I am reading the hyperon decays with missing energy this paper tells for the prospects of baryon decays with missing energy I want to know some of the Feynman diagrams for hyperon decays. Can anyone ...
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Why do we say that a photon is a particle if it is massless?

If light is made of photon particles and the photon doesn't have any mass but it is a form of energy (according to my thinking) then why do we call photons particles?
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Energy of the particles in the particle accelerator

Recently I came across something and I was surprised. I always thought that huge amount of energy is required to accelerate particles in the accelerator in the particle physics.But looks like no. The ...
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How do we know the LHC results are robust?

Nature article on reproducibility in science. According to that article, a (surprisingly) large number of experiments aren't reproducible, or at least there have been failed attempted reproductions. ...
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Difference between electron, muon and tau neutrinos [duplicate]

What is the difference between the neutrinos of electron, muon and tau leptons.? They all same to be neutral and carry a very small mass. Similarly what is the difference bewteen anti neutrinos of ...
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Effect of Lepton Flavor Universality (LFU) on Lepton Flavor Violation (LFV)

Does the search for Lepton Flavor Violation (LFV) get affected in any possible way when Lepton Flavor Universality (LFU) is used for background estimation? More specifically, because tau's show some ...
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Why do we need a two higgs doublet model? [duplicate]

Why do we need a two Higgs doublet model? What are the shortcomings in the standard model one Higgs doublet model? And is this 2HDM an independent approach or it is embedded in supersymmetric theory?
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Rydberg Blockade's experimental mechanism

This idea for an experiment is for a high school competition (bl4s). Utilizing a positron beam,can we knock out gas which has been energized to its Rydberg state.I plan to do this to verify when the ...
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Would manganese, iron, osmium,fluorine or nitrogen cations hold a higher linear energy transfer than carbon cations?

Is linear energy transfer in particle radiation therapy directly proportional to the particles' density? I.e directly proportional to the mass and inversely directly proportional to the volume? If ...
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Can neutronic emissions be used as a power source?

The free neutron will degrade to a proton electron and anti neutrino in about 15 minutes. Assuming you could slow a beam of free neutrons sufficiently to keep the size of the reactor manageable: Is ...
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How is it possible that unrolling scotch tape in a vacuum causes X-rays? [duplicate]

A fun kind of question... In 2008, researchers at the UCLA's Department of Physics and Astronomy found that unrolling of scotch tape in a vacuum caused X-rays to be created. First, energetic ...
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Thomson's Plum Pudding and Rutherford's scattering [duplicate]

Why did Rutherford's scattering experiment disprove the plum pudding? Assuming a gold-atom to be a large homogeneous ball and hitting it with small homogenuous $\alpha$-balls should lead to the ...
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Why do we always choose centre-of-mass frame to study particle physics problems (e.g. Feynman diagrams)? Even in non-relativistic regimes (v<0.3c)

Example: electron positron annihilation forbids a single photon production, and searching through this forum (Why can't a single photon produce an electron-positron pair?) and a few books, they ...
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Radiation emitted by collision of two photons

Using Lamor's formula, can someone tell me how much radiation is emitted by a particle accelerator or by the collision of two photons? It requires a 4 momentum vector which I'm not very acquainted ...
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Radiation pressure at a surface which is perfectly refracting

Radiation pressure at perfectly reflecting surface = 2I/c Radiation pressure at perfectly absorbing surface = I/c What will be the radiation pressure at a perfectly refracting surface? Will it be ...
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Is naturalness meaningful for non-fundamental theories?

Naturalness has been a guiding philosophy for particle physics for a long time, but a few years ago I heard a talk by Nima Arkani-Hamed where he pointed out that it seems to have failed us as it ...
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Particle accelerators and the amount of radiation they emit

Do particle accelerators emit a lot of radiation? If they do, can someone give me a rough estimate of how much? I'm also curious as to what kind of radiation they give off.
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Why can't a particle decay into a higher mass particle?

I mean, why can't the initial particle (decaying particle) give some of its initial energy to the final particle such that the particle in the end will have a greater mass?
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Why do we need the two higgs doublet model? [duplicate]

Why do we add an extra doublet to the two higgs doublet model?I mean what are the conditions due to which we had to add an extra doublet. What are the limitations with only one doublet and how 2HDM ...
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What paper experimentally ruled out the original Peccei-Quinn axion?

Could someone please refer me to the paper that ruled out Peccei-Quinn axions experimentally. Most literature mentions this happening but doesn't refer to the original paper where it was proven so.
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Drell-Yan Process notes

As the title suggests, I am looking for notes on the Drell-Yan procedure. Specifically, I want to understand how the convolutions with the parton distribution functions appear and the general ...
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Do positrons have electric dipole moments?

Is there experimental evidence checking to see if the positron has an electric dipole moment at rest? Or has an experiment measured it’s magnetic dipole moment at rest?
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Why are there infinitely many Feynman diagrams for any particular reaction?

In Griffith's Intro to Elementary Particles book, he wrote there are infinitely many Feynman diagrams for any particular reaction! Why is this true? Take for example Moller scattering that ...
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Do gluons interact with each other by the strong foce?

I learned that strong force between quarks are mediated by gluons. What does this say about interactions between gluons? Do they interact with each other by the strong force?
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Long-term fate of hydrogen atoms in a rogue planet

Imagine a rogue planet drifting in intergalactic space. For the sake of specificity, suppose that it is the size of Jupiter and composed of pure hydrogen. What will happen to it over the next $10^{...
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Plasma tubes and accelerators

to find a relation between acceleration produced by a plasma beam accelerator and the density of the plasma and length of the plasma tube. So what is the feasibility of this idea .
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Why does literature list the strong coupling at the scale of the Z-boson's mass?

In the 2004 edition of the book "QCD as a Theory of Hadrons" by S. Narison, the author provides a value for the strong coupling at a scale of the mass of the Z boson, $$ \alpha_s (M_Z) = 0.1181 \pm ...
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Neutrino energy density vs photon energy density

So I'm currently following a course in Cosmology and we're covering the densities of different species in the universe right now. Starting from the photon density $\rho_{\gamma}$ we need to derive the ...
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Energy conservation when exchanging meson

In Prob 1.2 of Griffith's "Introduction to Elementary Particles" 2nd ed., it says that: However, I don't understand why it states that "they must temporarily violate the conservation of energy by ...
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Thomson Exercise 2.12: Why is $p_i^2 = m_i^2$?

I'm just working on some problems from Thomsons Modern Particle Physics. I' having a hard time understanding the last step in this calculation: The relativistic energy-momentum relation is $E^2 = m^2 ...
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Are there theories that can predict the Yukawa couplings?

In the standard model, the Yukawa couplings, hence the masses of the fermions, are free parameters and are only determined by experiment. Are there beyond the SM theories that can "predict" the Yukawa ...
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Why is the proton (uud) lighter than the $Δ^0$ (uud) baryon?

Neutron has quark composition udd with spin $\frac 12$. $\Delta^0$ baryon has quark composition udd with spin $3 \over 2$. On Wikipedia it says that $\Delta$ baryons have mass of approximately $1232 ...
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Upper limits from Bayesian inference [closed]

While setting an upper exclusion limit for the new physics interaction with Bayesian inference, how do people decide on whether to claim 90% or 95% upper limit from the posterior marginalized pdf? ...
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Difference between 'anything' and 'X' in Particle Data Group publications' decay modes?

In the PDG publications, (like M. Tanabashi et al. (Particle Data Group) Phys. Rev. D 98, 010001 (2018) ) the decay modes of particles are listed. From the $B^0$ meson chapter, I took this ...
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Positron beams and crystallography

I wad mainly reading about impact and uses of positron beam to determine conductivity and the structure of material . Do can anyone just describe how positron beams can determine conductive of ...
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What are the Basic Properties of a Photon?

I want to grasp the idea of a photon. While researching, I have come upon many different ways of describing a photon, but have found "quantum of the electromagnetic field" to be most satisfying. ...
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Retrodiction of Particle Masses

While researching baryon asymmetry, I came across this article discussing problems with the Standard Model, where it is noted that: The Standard Model did not and cannot predict the masses of the ...
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Neutron Degeneracy Pressure Calculations

Today I was having a discussion with a colleague about what would happen if you took a 1 cm cube of neutron star matter and set it on the earth. He thought it would fall through and I was trying to ...
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Breit–Wheeler experimental evidence?

has there been any experimental evidence of the Breit–Wheeler process? Either in it's full or weak form, would you have some links to back this up? Can we say that all matter is merely energy ...
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Can space be considered as a grid of cubes of planck length, or is it continuous? [duplicate]

I don't know how to describe it exactly, please try to understand. The question is if space is continuous or gridded. Consider a particle of planck length (or whatever is the smallest possible ...
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Experimental justification for modelling electron as point instead of charged shell? [duplicate]

Down to what size is there experimental justification for modelling the electron as a point like particle without volume? Asked in another way, at what size scale would it be more correct to model the ...
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1answer
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What is a String Wall?

This question has nothing to do with sound waves, physical strings or walls... I am reading: https://arxiv.org/abs/1709.07091 It states "In the post-inflationary PQ symmetry breaking scenario, ...
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Lack of knowledge about ambient neutrinos below a certain energy?

A colleague and I were discussing the fact that beta decay can emit neutrinos with arbitrarily low energies. We have neutrino detectors that can detect solar neutrinos -- and maybe extrasolar ...
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Is the interaction $\gamma p \to \pi^+n$ allowed?

I'm doing an undergraduate lecture course in particle physics and I'm still getting to grips with the basics of interactions. One of the example interactions I've been given in an exercise is $\gamma ...