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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the different settling speed of two solid particles in fluid

In a container full of fluid A, which can be water or oil, I have two solid particles, both of which are of the same material. These two particles are of different size. One is bigger than the other ...
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38 views

particle physics and the problem with understanding [on hold]

Imagine a world that is watching ours, theory is theory , what if theory was real, why do we breath, physics is all theory until proven otherwise
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12 views

What is the typical strength of the electric field in a particle accelerator?

I am working on a research project involving the closed orbits of hydrogen in the presence of an external electric field and I am curious what a reasonable approximation for the electric field ...
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17 views

Is a matter anti-matter collision comparable to Gamma Ray Burst (GRB) energy output?

Is a matter anti-matter collision (please assume two cosmological objects, neutron star sized say), the largest energy release method known? Would it be comparable in order of magnitude to gamma ray ...
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31 views

Can elementary particles be rightfully considered quasiparticles?

Can elementary particles rightfully considered quasiparticles? I have this association, because renormalization makes particle properties, like mass and couplings, energy-dependent quantities, even in ...
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1answer
37 views

Charged-current: Why does the neutrino interact with the down-quark?

I'm revising for an exam and looking at a few exercises, one of which starts with Consider the charged-current interaction between a muon neutrino with one of the valence quarks of the proton. ...
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28 views

What processes contribute to non-relativistic proton-antiproton collsions (annihilation)

I wonder what the dominant contributions of nuclear interaction to non-relativistic proton-antiproton annihilation are (I mean that the proton and antiproton are non-relativistic. The products might ...
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1answer
86 views

If the effects of gravity cannot travel faster than the “c”, does this mean we are only gravitationally bound by masses in our observable universe?

I'm 17 and fascinated by the differences and omissions Newton made in his equations of motion. However it makes sense that gravity can't travel faster than light because of the force-carrying ...
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2answers
239 views

Scalar field divergent mass correction interpretation question (hierarchy problem)

Simple power counting tells you that a scalar field coupled to some fermions at one-loop picks up a correction to the mass of the order $\Lambda^2$. Based on this people say things like "it's natural ...
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34 views

Electron-Positron Annihilation: How is charge conserved at the verticies?

How is reaction possible? The verticies do not conserve charge. Also, why is the arrow for the positron pointing downwards when as time increases, the positron should move towards its vertex? Sorry, ...
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1answer
35 views

Where does the Higgs Boson fit in the three generations of charged particle?

I am reading a book called "Gauge Fields, Knots and Gravity" by Baez et. al. In the first chapter, the authors explains that there are three generations of charged particles: First: electrons, ...
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2answers
88 views

Do shadows have mass?

It sounds like a joke but I just want to know if shadows have mass, since shadows are formed when there is blocking of light. It forms a black pattern with no energy therefore it has no mass.
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13 views

Chemical potentials of SM particles at high temperatures

Recently I've heard the statement that chemical potentials of SM particles on $T > 1 \text{ GeV}$ are very small, so that Gibbs potential reduces to free energy. How to prove this statement? Does ...
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3answers
647 views

Where does the majority of the mass of the usual matter come from? [duplicate]

I apologize in advance to experts for the naivety of the question. It should be a duplicate but I didn't find any satifying question or answer about that. The proton is composed by two up quarks ...
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1answer
45 views

Particle Physics Decay Question - Eta Prime Decay Parity/Angular Momentum Conservation

I was hoping someone could clarify why the following decay does not occur: $ \eta ^{'0} \rightarrow \pi ^{0} + \rho ^{0}$ The quark compositions and spin parity are as followed: $ \eta ^{'0} : ...
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2answers
29 views

Neutron antineutron reaction documentation

Has neutron-antinutron reaction been observed? If so, can you please provide a documentation (experimental observation) for neutron antineutron reaction?
69
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5answers
7k views

Gauge symmetry is not a symmetry?

I have read before in one of Seiberg's articles something like, that gauge symmetry is not a symmetry but a redundancy in our description, by introducing fake degrees of freedom to facilitate ...
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3answers
85 views

Does Time change over temperature? [duplicate]

I am not a physicist, I am just an engineer. But I dared to ask whether the temperature changes the perception of time. Let's consider a particle that "stops" at absolute zero. I was thinking as a ...
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1answer
2k views

What the heck is the sigma (f0) 600?

At one point, I decided to make friends with the low-lying spectrum of QCD. By this I do not mean the symmetry numbers (the "quark content"), but the actual dynamics, some insight. The pions are the ...
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28 views

What are the parity of particles? [duplicate]

When looking to see if particle collisions/decays are possible and what force they act through, how do you know the parity of particles to know whether they act through weak force? Is there a grouping ...
2
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1answer
51 views

How does radiation degrade mechanical parts and electronic devices?

I'm running out of places to look (lots of Googling, SE, [articles and books are too specific and never give a good overview]), and yet I am still unsure about how exactly radiation can degrade ...
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3answers
88 views

Do holes have physical existence?

We know that holes are created due to electrons hopping from one covalent bond to another. But does a hole have a physical existence or it's just a fictitious positive charge, an illusion created by ...
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3answers
2k views

What does it mean that the neutral pion is a mixture of quarks?

The quark composition of the neutral pion ($\pi^0$) is $\frac{u\bar{u} - d\bar{d}}{\sqrt{2}}$. What does this actually mean? I think it's bizarre that a particle doesn't have a definite composition. ...
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1answer
142 views

Can bosons have anti-particles?

Can bosons have anti-particles? In the past, I would have answered this question with a yes, primarily because I can imagine writing down a QFT for complex scalars that has a U(1) symmetry that ...
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1answer
51 views

Alpha particle in vacuum

Does the alpha particle travel in vacuum for ever and ever or can it undergo some transformation eg two protons get separated or the neutron decays etc.?
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1answer
251 views

Fierz identity for Weyl spinors in tensor currents

Using Fierz identity I found that certain four-fermion operator with left $l_i$ and right-chiral $r_i$ Weyl spinors vanish $\bar{l}_1\sigma_{\mu\nu} r_2 \bar{r}_3 \sigma^{\mu\nu} l_4 =$ $ ...
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440 views

Effective operator in four-fermion interaction

In one book, I have got the following lines which I found myself unable to understand what is effective operator? The paragraph is given below: The weak interaction describes nuclear beta decay, ...
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405 views

“Hard wall”/ “soft wall”

I have encountered those terms in various places. As I understand it, "soft wall" can correspond to a smooth cutoff of some spacetime, while "hard wall" can be a sharp one, which can be described in ...
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1answer
39 views

How would an atom behave (in terms of atomic particles) if the electrons were much heavier than the nucleus?

In other words, does the mass of electrically charged particles affect the electromagnetic forces that operate between them ? Is the electrons revolving around the nucleus simply a consequence of the ...
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1answer
21 views

Is there a major difference between neutron-neutron collisions compared to proton-proton collisions?

For the sake of argument, assume the LHC was able to accelerate / focus / collide neutron beams, with the same energy levels it runs at for p-p collision. Would the collisions produce any major ...
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11 views

Polarization in LCDs why the light need to be polorized twice? [closed]

In Lcd Screens there is a prcess called polarization. Two question about it: 1. Why is it needed to pass the light through two polarizers ? 2. How des a pixel devide the light to three sub pixel and ...
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14 views

Plasma wakefield acceleration for Protons

Laser plasma acceleration is a promising technology that could replace the current method of accelerating particles (which is via electric fields). It is somewhat cheaper also as it makes the ...
12
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2answers
696 views

Why can the Euler beta function be interpreted as a scattering amplitude?

The Wikipedia article on the Veneziano Amplitude claims that the Euler beta function can be interpretted as a scattering amplitude. Why is this? In another word, when the Euler beta function is ...
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2answers
79 views

Is electrons ability to produce mechanical motion considered the only reason for it to be material particle?

"Cathode rays (streams of electrons) produce mechanical motion of a small paddle wheel placed in their path indicating that they are material particles."$_1$ Isn't this statement wrong? Assuming ...
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Production of Inductively Coupled Plasma

I am working on an experiment hat requires the usage of inductively coupled plasma, but unfortunately, I do not have any equipment at the moment that can produce such plasma, and I really need your ...
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2answers
69 views

do the planes of electron orbits make an angle?

if we think as the electrons around the atoms classically, then as the two electrons in the first shell (1s) go around the nucleus; do the planes of orbit make an angle with each other (as an average) ...
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1answer
50 views

What happens when an electron collides with an atom?

I was solving this question: Here is part of the energy level diagram of hydrogen: n=4 --> -0.85eV n=3 --> -1.50eV n=2 --> -3.40eV n=1 --> -13.6eV When an electron of ...
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1answer
64 views

Is gauge invariance essential to a theory be renormalizable?

Let's consider a model of New Physics in which all operator have dimension smaller than four, but which breaks explicitly $SU(2)_L$ gauge symmetry. Is this model necessarily renormalizable? ...
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2answers
36 views

Energy transitions of 12.1eV electron?

Here is part of the energy level diagram of hydrogen: n=4 --> -0.85eV n=3 --> -1.50eV n=2 --> -3.40eV n=1 --> -13.6eV When an electron of energy 12.1eV collides with this ...
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0answers
44 views

Why are the particles called irreps of Poincare group? [duplicate]

Why are particle excitations called irreducible representation of the Poincare group? It will be very helpful if someone can illustrate with one concrete example of a particle. EDIT : But how does ...
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2answers
232 views

Question on particle decay process, conservation of energy

Why is $$\Sigma^0 \rightarrow \Lambda +\pi^0$$ not a possible process? Charge and baryon number both are conserved. There's no issue with strangeness that I can tell. The masses in $\frac{Mev}{c^2}$ ...
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31 views

How is an atom ionized by electron impact?

Can someone walk me through in detail what happens when an atom is ionized by colliding with an electron? I would prefer a solid example so I can understand it more concretely. What I think:- -The ...
0
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1answer
91 views

What is the smallest amount of neutrinos needed to create a black hole? [duplicate]

Is there some smallest amount of neutrinos needed to create a black hole? Note that this question is not at all the same as the question here If a 1kg mass was accelerated close to the speed of light ...
2
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3answers
73 views

Decay of matter

I was watching Stephen Hawking's documentary and in there he explained how he realized why black holes eventually disintegrate: There are ripples in space, an antiparticle and a particle get ...
2
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1answer
34 views

For Charmonium, why does the spin-spin interaction mostly affect the $L = 0$ states?

For Charmonium, why does the spin-spin interaction mostly affect the $L = 0$ states? My textbook states that this is because "only then is the wave function at the origin non-vanishing". Could anyone ...
2
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2answers
38 views

Ambiguity with reaction equations

I understand that if two particles are on the left hand side of a reaction equation they are said to "interact". For example, $p+e^{-}\rightarrow n+v_e$ is a proton and electron interacting (electron ...
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1answer
27 views

Similarity between particles and antiparticles

I was doing a past exam paper and there was this question: State the similarities between a particle and its antiparticle. The answer given was: Same mass and rest energy. I am not too bothered ...
4
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1answer
85 views

Where would the dark matter particle fit inside a picture of the standard model of particle physics?

Where would the dark matter particle fit inside a picture of the standard model of particle physics? While I am particularly fond of the Sterile Neutrino, I have not been able to find any example of ...
2
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1answer
337 views

Is the virtual photon a particle?

I just saw an exam question: Write down the antiparticle for the virtual photon. The answer was "virtual photon". Is the question even a meaningful one? If so please explain why?
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141 views

Is there a quark conservation law?

The section on particle interactions in my revision guide says that only the weak interaction can change quark types, e.g. when a neutron changes to a proton the down quarks in the neutron are changed ...