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.

learn more… | top users | synonyms (2)

2
votes
2answers
99 views

How to interpret the field configuration in quantum field theory?

We often use the Fock space as the start point for our quantum field theory. In the Fock space we have definite physical meanings for the state. For example, the state $$|k_1k_2...k_n\rangle$$ ...
0
votes
0answers
22 views

Why dark matter do not gather together? [duplicate]

Stars and planets were gathered together by gravity, thus emit light. Why dark matter doesn't behave that way? Why they won't be gathered together by gravity and form stars?
0
votes
0answers
53 views

$S$-matrix expansion and Feynman graphs for toy model

I have a toy model with three interacting particles $A$, $B$ and $C$ and $A$ can decay to $B$ and $C$. Looking at the process $AB\to BBC$ I just want to know which orders of the $S$-matrix expansion ...
7
votes
2answers
178 views

Yukawa interaction between Dirac particles is universally attractive?

Can anyone provide me a specific reference to (or supply themselves) the derivation of the fact that the Yukawa interaction$$\mathcal{L}_{\text{int}} = -g\overline{\psi} \psi \phi$$between Dirac ...
7
votes
0answers
155 views

In a universe with four spatial dimensions would there be elementary particles with intrinsic isoclinic spin?

Elementary particles have an intrinsic property called spin which is different from classical spin as it does not involve actual rotation and the magnitude of spin cannot be changed but particles with ...
0
votes
1answer
45 views

Electrons-muons through matter

Do electrons and muons behave differently while passing through matter?Why does this even happen even though both of them are leptons and they can be found in 2 different states due to their ...
2
votes
0answers
45 views

Would CP Violation happen in a universe with four spatial dimensions?

The weak force is the force that violates CP symmetry as the way it effects a particle depends on that particles handedness. Particles have a property known as spin although it is different from ...
3
votes
0answers
26 views

$\rho$-parameters for several Higgs multiplets

I'm studying the Higgs mechanism of the spontaneus symmetry breaking in the SM. The expression for the $\rho$-parameter is $$ \rho=\frac{M^2_W}{{\cos^2\theta_w}M^2_Z}, $$ that, in the case of a ...
0
votes
1answer
83 views

Gravity goes through everything?

I was thinking about it, the Earth has her gravitational field, but this field comes by the Earth right? Or he just exists around the Earth? If the "gravitons" comes by the Earth, can them goes ...
3
votes
2answers
74 views

Does quark confinement imply indivisibility of quarks?

I recently heard the statement$^1$ that quark confinement is evidence for the indivisibility of quarks (i.e. that they are indeed fundamental and have no substructure), but I don't see any reason why ...
0
votes
2answers
68 views

What subatomic particle is a blackhole composed of?

In a black hole, what is the "state" in which the mass that is present is in? Are they there as tightly packed neutron or soup of quark or are particles broken down into 10D strings and coiled as ...
1
vote
2answers
90 views

What does “charge” actually mean? [duplicate]

I know that a charged particle is defined as a particle that experiences a force in an electric field, as explained in this post: What does a subatomic charge actually mean? However, I still don't ...
0
votes
0answers
21 views

Does matter shrink due to energy radiation and does it have anything to do with dark matter and dark energy?

Is matter shrinking? Is shrinking the cause of concentrated dark matter that makes up matter moving from concentration to unconcentration. Does dark energy and expansion of the universe come from this ...
1
vote
1answer
41 views

Fire, catch and fire a particle

To be more specific, would it be possible to perform the stern Gerlach experiment on a single electron multiple times provided that none of the electrons paths were blocked.
0
votes
0answers
9 views

References on particle cooling

I am looking for references on the topic of particle and mechanical oscillators cooling, in particular: Doppler cooling Resolved sideband cooling and Lamb-Dicke regime Stokes and anti-stokes modes ...
6
votes
0answers
96 views

Real world applications of post-1950s High Energy Physics [closed]

Imagine a world where people knew everything we know today except for high energy physics, where their knowledge ends at our ~1950s level. Is there any real world application, any particular piece of ...
2
votes
0answers
69 views

how to analyze the collision of two photons with four-momentum vector? [closed]

Q: If two photons with energies $E_1$ and $E_2$ collide, with their trajectories making an angle $\theta$. Is the following right about individual initial 4-momentums and total initial 4-momentum? and ...
2
votes
1answer
59 views

Particles, quasiparticles, and “stability”?

So I'm studying Fermi Liquid Theory, which concerns itself with quasiparticle excitations made by superpositions of single-electron wavefunctions. We create particle-like wavepackets which exist for ...
1
vote
1answer
26 views

Positive free particle Dirac equation

I've been set the task of showing that: $$ \bar{\psi^{s}}\psi^{s}=2m $$ For s=0,1. Where: $$ \psi^{0,1}=\sqrt{|E|+m}\begin{pmatrix}\chi^{0,1}\\ ...
2
votes
1answer
34 views

Valence sea quarks parton distribution functions

There's somethin from Thomson (Modern Particle Physics) that I am a little mythed by. Section 8.4.3, eq. 8.3 is given as $$ ...
0
votes
1answer
29 views

colorless charge in a baryon

In a baryon there are 3 quarks and in a meson there are one quark + one anti-quark. So color charge is colorless ( a color singlet state ) in a meson. But how is it colorless in a baryon ?
1
vote
0answers
34 views

Help - calculation probabilities - new theory [closed]

I need help to calculate exact or approximated probabilities. I am interesting by the content of a new theory (view this link nokton theory for details). Currently, I studing the interactions of two ...
0
votes
0answers
56 views

How often do quarks annihilate?

How often do quarks annihilate? Quarks bond frequently with quarks, and antiquarks bond frequently with antiquarks. So why do quarks not annihilate antiquarks extremely quickly? More to the point, ...
1
vote
0answers
48 views

$SU(3)$ Tensor Methods in a Tetraquark

I am trying to understand the Georgi chapter of tensor methods in $SU(3)$ representations, and I don't know how to resolve the tensor product of 2 matrices in a 2 heavy quark + 2 light antiquark ...
1
vote
0answers
33 views

Quark axial-vector current in nucleion

In almost all direct detection articles (see for example Jungman, G., Kamionkowski, M. & Griest, K., 1996. Supersymmetric dark matter) I found the following parametrization for the matrix element ...
0
votes
1answer
41 views

How to measure the mass of an uncharged particle like a neutron?

How we can measure the mass of a neutral particles like neutron? To measure the mass of a charge particles like electron we use mass spectroscopy. What about uncharged particles?
0
votes
2answers
52 views

How do we determine total isospin when only third component of isospin is known?

Both $ \frac{1}{\sqrt{2}} (np - pn)$ and $\frac{1}{\sqrt{2}} (np + pn)$ has third component of isospin equal to 0. But the first combination has total isospin equal to 0 while the second combination ...
0
votes
1answer
34 views

FWHM increase with energy (gamma spectra)

Below I have two plots from a gamma spectrum which I've been analyzing. The first plot is between a low energy range, the second between a significantly higher energy range. It is clear that the FWHMs ...
2
votes
2answers
126 views

Has the Higgs boson always existed?

I am slow and need some help understanding this. So has the Higgs boson always existed? If not, than how did it come to exist? What would have excited it before matter or particles were created? So ...
3
votes
0answers
40 views

How does one determine chirality experimentally?

The Standard Model says that only left-handed electrons participate in weak interaction. A very natural question for novices like me is then: How can we tell, experimentally, if an electron is ...
0
votes
1answer
36 views

What is the physical meaning of $\alpha$ in this disintegration problem?

I am taking a course where I have to solve the following problem related to the disintegration of a baryon in a proton and a pion $(\Lambda \to p^+ + \pi^-)$: Assume that a $\Lambda$ particle with ...
0
votes
0answers
11 views

Kinematic equations of a cascading particle decay

This paper discusses different measurable quantities that can be used to search for unknown particles at particle accelartors. For the following decay it introduces the invariant mass $m_{XY}$: It ...
0
votes
1answer
47 views

Particle Physics: Weak Interaction

Consider the following decay equation:- A Kaon(+) decays into a muon(-) and an antineutrino(?) The question is as follows :- State and explain whether the anti-neutrino is an electron, muon or tau ...
0
votes
0answers
2 views

Parametrization of the medium change from solid to gas?

I am thinking the model where the parametrization of GEM (Gas Electron Multiplier) is open. I can reach a high sensitivity in similar systems where the medium is solid such as in solar cells (5 ...
1
vote
0answers
20 views

Speed of an antimuon in a pi meson decay [closed]

I'm trying to confirm the speed of an antimuon in the $ \pi^+ \rightarrow \mu^+ \nu_{\mu}$ decay through the laws of conservation but it doesn't add up. I'm using $m_{\pi} = 139.6 \ \frac{MeV}{c^2}$, ...
1
vote
0answers
26 views

Simple special relativity problem [closed]

A body at rest in a frame of reference $S$ disintegrates into two pieces moving in opposite directions. The masses of each fragment are $3.0 \ kg$ and $4.0 \ kg$ and their velocities $0.8 \ c$ ...
0
votes
1answer
32 views

Charge inducing electric field or electromagnetic fields?

I am thinking the therminology here which is about Gas Electron Multipliers (GEM). There is a continuous flow of the fill gas which is ionized so no particles created/destroyed: #1 By Gauss's ...
0
votes
0answers
27 views

Direct vs indirect detection of dark matter

Background There are two categories of searches for dark matter. Direct Detection via reproducible experiments Indirect detection Detection of e.g. annihilation signal from astrophysical sources ...
0
votes
0answers
45 views

A Magnetic Vortex in a Magnetic Vortex

This is not to scale. Can a magnetic vortex be compressed into a flat disk using magnetic entrapment? Can a magnetic vortex happen inside another magnetic vortex?
0
votes
0answers
31 views

Magnetic field of a circular particle accelerator

Suppose there's a $500 \ GeV$ proton beam ($q=1.6 \times 10^{-19} C$) inside a circular particle accelerator, what would be the magnetic field intensity $B$ in Teslas required to keep it stable at a ...
0
votes
1answer
42 views

Combined function magnet

I am searching how a combined function magnet for accelerator physics works, but on the books that i have and on the web i can find only patents for this thing, that suppose to know already how this ...
1
vote
0answers
16 views

Pre-, post- and analytical phases of physics data analysis? [closed]

I am writing a technical (physics) report about a GEM (Gas Electron Multiplier) system which has several weaknesses in several parts of the system: pre-analytic: wrong post-operative tool has been ...
0
votes
2answers
54 views

Energy forms of a charged particle in an electric field?

I am thinking an explicit list of all energy forms in a system of charged particle (take electron or proton, for instance). It has at least potential energy and kinetic energy by Newton. ...
1
vote
1answer
78 views

Angular Momentum of a Photon

Why is it that the angular momentum of a photon is $\hbar$, irrespective of its energy? I encountered such a claim in a text about Raman spectroscopy. Is there an explanation for this using basic ...
4
votes
0answers
108 views

How are bound states handled in QFT?

QFT seems very well suited to handle scattering amplitudes between particles represented by the fields in the Lagrangian. But what if you want to know something about a bound state without including ...
0
votes
0answers
17 views

Subnuclear reactions: combining quarks

When you try and pull two quarks apart, you don't get two separate quarks, but instead: the energy stored in the field between them gets high enough to create more quarks, and instead of two ...
0
votes
0answers
56 views

Propagator for fermion fields and Feynman diagrams

I need some help concerning the interpretation of propagators and Feynman diagrams. The free fermion propagator is given by the contraction of two fields $\psi(x),\bar\psi(y)$: ...
0
votes
0answers
13 views

Are GEMs parallel plate capacitors?

I am studying different forms of GEMs (Gas Electron Multiplier) and some literature uses the word parallel plate capacitor (Mansfield, Understanding Physics p. 457). However, I am not sure if this ...
1
vote
0answers
35 views

Why is this decay process allowed? [duplicate]

I have been given an assignment in which I have been asked to list some quantum numbers for some given allowed processes. One of them is $\Delta^+ \rightarrow p^+ + \pi^0$ I know that $\Delta^+$ ...
0
votes
1answer
28 views

momentum conservation in particle-antiparticle creation

It's understood that the PRESENCE of a heavy nucleus is necessary for conservation of linear momentum in pair creation. What I can't understand is why it must occur in ADJACENCY of the nucleus. Is ...