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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What is the particle physics level description of corresponding optical diffraction of light?
At the particle physics level, what is responsible for the so called diffraction of light in optics thematic of general macroscopic physics ?
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Decay length and COM energy
Suppose you collide two particles and produce a new unstable one.
Does its decay length (i.e. the distance it will travel) depend on the COM energy at which it is produced? assuming that the COM ...
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How do you understand displaced vertices rigorously in quantum field theory?
When you produce a long-lived particle (like charged pions, muons), it enters your detector. When you produce a short-lived particle (like the higgs, tau), the production of the particle is only seen ...
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Help with Shell Model and Pauli Exclusion Principle
As I understand, the occupancy number in the nuclear shell model dictates the number of each type of nucleon that can occupy a specific sub-shell (angular momentum state l).
Note: s, p, d, f ...
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Beta decay experiments suggesting that neutrinos are massless
It's known that in the kinetic energy spectra of electrons from the negative beta decays that at the end of the spectra some electrons are found to have a maximum energy that is equal to the energy ...
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Why on the ATLAS Higgs discovery paper there are uncertanties on the expected cross section upper limits but not on the observed upper limits?
I was reading the ATLAS paper on the Higgs discovery and a question came to my mind. In the plot I attached, there are uncertainty bands on the background only hypothesis upper limits, and not on the ...
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Is it possible to collide two neutrons? [closed]
If it is possible to collide two neutrons, how is it so? What particle accelerator or pre-collision processes are necessary and what results can be expected? If the products of neutron-neutron ...
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Relation between (Anti-) Quark-Gluon-Quark Correlators
I'm having trouble in understanding the derivation for the realtion between Antiquark-Gluon-Quark and Quark-Gluon-Quark correlators given in a PhD thesis which I sadly can't find a link of to share ...
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Pile Ups in the particle accelerator
Can anyone explain what Pile ups are in a particle accelerator experiments? How can anyone know that an event is a pile-up interaction and how can anyone get rid of these events?
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What happens to protons AFTER deep inelastic scattering occurs?
As I understand in the deep inelastic scattering process, a collision of electron beams and protons occurs, resulting in a scattered electron. However, when the proton absorbs the virtual photon ...
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Don't seem to understand the behaviour standing waves
I have many confusions regarding standing waves. Firstly, will the frequency of standing waves be the same as the emitted waves that make up the standing wave?
What about wavelength? Will wavelength ...
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Dirac spinors vs. Wigner classification
As I understand, from Wigner's classification of particles it follows that for every $m > 0$ and $s \in \left\{ 0, \frac{1}{2}, 1, \frac{3}{2}, \dots \right\}$ there is an irreducible, unitary ...
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Quark structure of Baryons
I was studying Particle Physics then suddenly I came up with a question that why only Baryons are made up of three quarks, at first I thought to to conserve Baryon number which is $\frac{1}{3}$ for ...
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How does dual nature of matter affect collision at the quantum level?
I have a question suppose having two fundamental particles collide which each other at the quantum scale , then what will the collision behave as
Will the particle nature be dominant and make sure to ...
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Can quarks emit gluon waves?
Fundamentally, particles with a coupling constant to a gauge field interact with that force and can emit waves when accelerating. We observe this with particles with electric charge emitting EM waves ...
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What are active deformable particles? [closed]
Could anyone please clarify to me what are "active particles", in particular "active deformable particles"?
They are mentioned in a project in Statistical Mechanics, but I have ...
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Does an excitation of any quantum field extend forever through space?
For visualization purposes, let’s say I slam my hand into sheet metal and it vibrates. Will that vibration extend beyond the metal sheet into the space surrounding it, and would that energy wave ...
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Is weak hypercharge carried by $Z$ boson?
In the PBS spacetime video about charge (https://www.youtube.com/watch?v=esayi49OAk4), at 10:55 he said that weak hypercharge is carried by the $Z$ boson. Is this accurate?
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Background cuts [closed]
I am considering background events like, $p p \rightarrow t \bar{t}$ and QCD events where t is a top quark. I want also to reduced the QCD events such that QCD events will be less observed than that ...
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Can high energy photons be used to accelerate particles?
So I know that particle accelerators use electromagnets to accelerate particles. However, since photons can be used to recoil particles (such as in Compton scattering), is it possible to use high ...
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Electron-positron pair production cannot occur in empty space [closed]
I'm trying to prove that the electron-positron pair production cannot occur in empty space.
From the conservation of energy we have that
$$\hbar \omega = 2\gamma mc^2+E,$$
and from the conservation of ...
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Can someone explain this Feynman Diagram in the picture?
I don’t understand this diagram at all, and what is the meaning of the $g$?
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Is crossing symmetry violated in the difference between positron emission and electron capture?
As discussed in the relevant Wikipedia article, beta decay via electron capture is possible in circumstances when positron emission is not.
From a simple (and perhaps naive) point of view, the two ...
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Wilson Coefficients in the Standard Model
I'm not particularly knowledgeable in this area of physics. From my understanding as an undergraduate, Wilson coefficients are sets of parameters that arise from an effective field theory which ...
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Is an electron more stable than a proton/neutron?
Is an electron more stable than a proton/neutron under extreme temperature/pressure conditions, like several 100 millions K?
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Different kinds of energy Are they relative?
I'm not sure if this is a physics-based question. There are many kinds of energy in physics.
For example, kinetic energy, potential energy, thermal energy, electrical energy
Magnetic energy, radiant ...
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Stacking of magnetic moments in a polarised neutron beam
Neutrons are particles that have a half spin and a magnetic moment. if you polarise a beam of neutrons so that they all align with spin +1/2 will the combined neutron beam have an overall magnetic ...
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When performing a fast likelihood fit (flavio) why can we assume the uncertainties are weakly dependent on fit parameters?
In the angular analysis of the $B^{0} \rightarrow K^{*}\mu^{+} \mu^{-}$, Wilson coefficients can be determined from experimental data of angular observables through the following (flavio - a python ...
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QFT Books and Lectures notes [duplicate]
I am a passed college student. I have attended courses in QM (not advanced one), Particle Physics and Math Physics. Recently I became interested in Particle Physics. I want to learn QFT in great ...
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Why are accelerator beam neutrino experiments built an angle off the beam direction?
Was reading some papers and review articles on accelerator based neutrino experiments and this came up a few times. Most of what I could find mentions "shrinkage in neutrino energy spectra" ...
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Question on probability of alpha particle scattering at certain angle after hitting a gold atom
According to this video (roughly 20 minutes in), the angle at which an alpha particle is likely to scatter after entering a certain region of a gold atom is given by
$$\sigma(\theta)=\pi\left[\frac{...
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If the electromagnetic force did not exist before it froze out, how could there have been a meaningful distinction between matter and antimatter?
If electrons and positrons are identical except for their opposing charges, what was the nature of these particles before the EM force separated out?
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How can different representations of the same group correspond to different particles?
When I first learned group theory in the context of quantum mechanics, I got it into my head that a group was the unification of different "transformation actions" that ultimately have the ...
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Mass spectrum as a function of center-of-mass energy
I'm having some difficulty finding some clear data on the relationship of the average mass of emitted particles in collision experiments with respect to the center-of-mass energy. My understanding is ...
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Reconciling mass due to the Higgs mechanism with a particle being asymptotic
I have a basic understanding of how the Higgs mechanism works, and how it can be used to explain, or perhaps rather accommodate, masses of elementary particles like fermions, without breaking gauge ...
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What charge does muon have? [closed]
I have a simple $\mu$-meso atom model. Kernel is just one proton and on orbit there's one muon, which is 210 times heavier than electron. What charge does it have? I checked some tables about muons ...
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Experimental evidence that a particle experiences time?
It is a famous fact that massless particles don't experience time, i.e. have no well-defined proper time. Conversely, massive particles can meaningfully be assigned a proper time parameter; they do ...
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Too much photon energy required to excite an atom
Apologies if I have done this wrong, it's my first post.
To my understanding, atoms can be excited by a collision of an electron or photon with sufficient energy to excite the electron into a higher ...
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Numerators in LoopTools
I want to calculate the diagram
$$ \int \text{d}^D q \frac{q_\mu q_\nu q_\rho q_\eta}{(q^2-m_1^2)((q_1+p_1)^2-m_2^2)((q_1+p_1+p_2)^2-m_3^2)((q_1+p_1+p_2+p_3)^2-m_4^2)((q_1+p_1+p_2+p_3+p_4)^2-m_5^2)} $$...
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How do we know that the neutrino flavour states are the linear combination of mass states?
I am studying the neutrino oscillation phenomenom in which the flavour of a neutrino can change when it evolves in space-time.
What I understand is that this means that the 3 neutrino flavour states ...
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How do localized particles come out of QFT?
In my understanding of particle QM, the wavefunction of a free particle in a momentum eigenstate is a plane wave with the de Broglie wavelength but the particle itself is only ever measured to be at a ...
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Energy spectrum in Klein-Gordon equation in general relativity
I know that the Klein-Gordon equation in general relativity takes the form (a massless field)
$\nabla_\mu \nabla^\mu \phi=\sum_{a,b} \frac{1}{\sqrt{-g}}\partial_a(\sqrt{-g}g^{ab}\partial_b\phi) =0$
...
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Finite quotient of standard model group [closed]
In chapter three, p. 31, of this paper (https://arxiv.org/abs/0904.1556) Baez and Huerta show that the standard model's structure group contains, in a sense, superfluous parts.
They show that one can ...
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Wavefunction of a particle decay
Lets say we have a decay of $\rho^{0}$, in the following way. $$\rho^{0} \to \pi^{+} + \pi^{-}.$$
Is the following statement true?
$$|\rho^{0}\rangle = |\pi^{+}\rangle|\pi^{-}\rangle.$$
I don't think ...
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Physical Significance of Frequency of matter waves
So, in our book there was an additional exercise part and this question baffles me:-
Q. Answer the following questions:-
The energy and momentum of an electron are related to the frequency and ...
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Number of electrons and protons in an atom [closed]
Are the numbers of electrons and protons in an atom the same? I mean, is it not possible that they do are different, but the number so balance that the atom as a whole is neutral?
As far as I know, we ...
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Why the long lived Kaon can not decay into two pions?
The short-lived and long-lived states of kaon $|K_1>$ and $|K_2>$ respectively have the following compositions if they are the eigen states of CP parity:
$|K_1> = \frac{|K^0>\:-\:|\bar{K^0}...
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Deriving mathematical solutions from Feynman diagrams [duplicate]
So I know that we can represent mathematical expressions using Feynman diagrams, however, I wonder if we could derive mathematical solutions from a Feynman diagram.
For example, if we have the Feynman ...
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Formation of a hydrogen atom from delocalized electron and proton
From the initial state of an electron and a proton in a box. I would like to find a reasonable hamiltonian, or way to describe the interaction that leads to the formation of a Hydrogen atom.
Here is ...
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Why is the Charge parity eigenvalue of a photon -1?
I've seen in different references the following statement, for instance this comes from Perkins, Introduction to high energy physics:
"electromagnetic fields are produced by moving charges that ...
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