6
votes
2answers
572 views

How is antimatter made?

How is antimatter made in laboratory? Can anyone explain, at the particle level, specifically how anti-protons and anti-electrons are made?
3
votes
2answers
354 views

What is meant by the spin of a particle? [duplicate]

I have been studying that electrons have quantum number called spin quantum number(s), this number can have either +1/2 or -1/2 value. If s=+1/2, the spin is clockwise and if s=-1/2, the spin is anti ...
4
votes
1answer
136 views

Why is Planck's constant the same for all particles?

This question came to me while reading "Where does de Broglie wavelength $\lambda=h/p$ for massive particles come from?". This question has a nice answer that explains that wave number has be ...
1
vote
1answer
45 views

Tetrad choice for Pauli-Lubanski in the massless case

The Pauli-Lubanski pseudovector coincides with intrinsic spin in the rest frame of the particle. In a more general frame, one defines a tetrad and projects the PL vector on it to define intrinsic spin ...
9
votes
1answer
155 views

Why Lorentz group for fields and Poincaré group for particles?

Wigner treatment associates to particles the irreps of the universal covering of the Poincaré group $$\mathbb{R}(1,3)\rtimes SL(2,\mathbb{C}).$$ Why don't we consider finite dimensional ...
4
votes
1answer
74 views

Understanding the Particle Data Group review documents

Would someone mind outlining what each piece of semi-structured data means in these images taken of some PDG documents? As a newcomer it is very difficult to interpret the tables. tl;dr This ...
1
vote
0answers
57 views

What's the value of the coupling constant in interacting field theories?

Consider this Lagrangian : $L = \frac{1}{2}(\partial_\mu \Phi)^2 - \frac{M^2}{2}\Phi^2 +\frac{1}{2}(\partial_\mu \phi)^2 -\frac{m^2}{2} \phi^2 -\mu\Phi\phi^2$ Its interaction term is given by : ...
2
votes
2answers
81 views

Is negative mass for a bound system of two particles forbidden?

Is there any theorem that forbids the bound system of two massive particles to have negative mass?
0
votes
0answers
83 views

General definition of vector spinor and spin

I am looking for basic and exact definitions of fundamental physical consepts in graduate level. I reach this following definitions. Could you please help to improve these definitions. Spin: ...
2
votes
2answers
135 views

How to explain spin of electron? [duplicate]

How can we explain spin of electron, or the spin of other fundamental particles? If we think the spin of electron is similar to the spin of a ball or planet we make a mistake. We say it is an ...
0
votes
0answers
44 views

Size of an elementary particle [duplicate]

Do we have a well defined mathematical expression denoting the size of a fundamental particle with no internal structure (electron for example) ? If we do, how does it fit in with the uncertainty ...
6
votes
2answers
2k views

Where does the number “380,000 years for electrons to be trapped in orbits around nuclei” come from?

How does this number get calculated? About 380,000 years after the Big Bang the temperature of the universe fell to the point where nuclei could combine with electrons to create neutral atoms. ...
1
vote
1answer
50 views

Is there a standard resource that lists all understood particle-particle relationships?

I am just starting to dig a little deeper into particle interactions, and just have an introductory college physics background (no quantum mechanics). But I am interested in the conditions of the ...
2
votes
0answers
40 views

How do I calculate integer and half integer spin? [closed]

How do I calculate integer and half integer spin, and how do I use the calculations?
3
votes
1answer
111 views

Local number operators in quantum field theory

Redhead claims in his paper "More ado about nothing" (http://link.springer.com/article/10.1007%2FBF02054660) that number operators associated with different space points (at fixed time) fail to ...
1
vote
1answer
64 views

Does this photograph portray double muon impact with nanogold atoms?

1PHOTO 1: Macro-photograph of an NIH/FDA TEM of a nanogold dark stained biological sample projected onto Silver Halide (AgX) photographic gel paper. On June 10 I questioned if PHOTO 1 ...
0
votes
2answers
83 views

Does yukawa potential of two particles have effect on each other? [closed]

Okay,a novice here.Suppose two particle interact with Higgs field.Does The Yukawa potential created by each of them affect each other or the interaction in any way.If so,what is it physical ...
0
votes
1answer
37 views

Equation for Photon and Electron Propagation [closed]

What equation accurately describes the movement of a photon? Does this equation also apply to the movement of an electron?
2
votes
0answers
61 views

Quantum Boltzmann Equation

What is the Quantum Boltzmann equation and what does it describe? I think it describes the propagation of electrons and photons but I am not sure.
4
votes
3answers
201 views

Where does the electron get its high magnetic moment from?

I have always found the concept of spin a little weird. I had read somewhere that for the charge or size of electrons, their magnetic field is very high. In order to produce such fields, they must be ...
5
votes
1answer
93 views

Is there still mystery about spin crisis?

The gluon is a vector boson; like the photon, it has a spin of 1. If this is true and if we know the spin of protons and neutrons then why the news SPIN COMES FROM GLUONS? is telling that, we ...
0
votes
0answers
14 views

in an organic semiconductor, what is the average distance travelled by an exciton?

In an organic semiconductor, what is the average distance travelled by an exciton up to recombination? How is this value related to the morfology / structure of the organic semiconductor?
15
votes
4answers
2k views

Why do we need high energy to explore small dimensions?

I am taking a quantum physics class, and for the life of me, I can not remember why we would need a vast amount of energy to understand the microscopic universe.
2
votes
2answers
169 views

Can a photon move at another speed that's not the speed of light?

I was reading an article about the new collider photon-photon, and the writer says "the scientists accelerate photons in a very high speed". It's non sense to me, because as far I know a photon only ...
3
votes
3answers
82 views

Which side of wave-particle duality to choose in a given situation

How does one know whether, in treating a certain problem, one should consider particles as waves or as point-like objects? Are there certain guidelines regarding this?
1
vote
2answers
107 views

Which is the most fundamental constant between the Planck constant $h$ and the reduced Planck constant $\hbar$?

This question is related to Planck units (also called natural units, absolute units or God's units). I'm wondering which constant is the most fundamental and should be normalized to 1. I would like as ...
1
vote
2answers
108 views

How to determine a strong or weak interaction (Strange particles)?

As you know $\pi^-$ meson + proton ---> $K^+$ meson + $\Sigma^-$ particle. (AntiUp,down) + (up up down) --> (up antistrange) + (down down strange) I know that the quark number has be conserved in ...
1
vote
0answers
39 views

Subnuclear physics vs wave function

This question is more a philosophical question than a physics one. When we appreciate particle physics we study that in order to explain some experimental results we have to introduce a new particle ...
0
votes
1answer
128 views

Double slit experiment observation

In the double-slit experiment, if you shoot particles through the slits one by one and observe which slit they travel through, is there still an interference pattern on the screen behind the slits? If ...
1
vote
0answers
73 views

How to calculate relative branching fractions of the $Z$ boson to specific pairs of “neutral lepton and anti-lepton”?

The PDG is listing values of "$Z$ couplings to neutral leptons" as $$ \begin{eqnarray} g^{\nu_{\ell}} & = & 0.5008 \, \pm \, 0.0008 \\ g^{\nu_{e}} & = & 0.53 \, \pm \, 0.09 \\ ...
1
vote
0answers
21 views

Entropy of Reeh-Schlieder correlations

Any state analytic in energy (which includes most physical states since they have bounded energy) contains non-local correlations described by the Reeh-Schlieder theorem in AQFT. It is further shown ...
4
votes
1answer
261 views

Mandelstam variables 1 positive 2 negative

The three Mandelstam-variables are defined as: $$s=(p_A+p_B)^2=(p_C+p_D)^2,$$$$t=(p_A-p_C)^2=(p_B-p_D)^2$$$$u=(p_A-p_D)^2=(p_B-p_C)^2.$$ Where A and B are the incoming particles and C and D are the ...
1
vote
1answer
72 views

Multiparticle generalization of $\langle \vec k \vert E,l,m \rangle$ spherical harmonics.

From Sakurai eq. 6.4.21a we have that $$\langle {\bf k} \vert E,l,m \rangle=\frac{\hbar}{\sqrt{M k}}\delta\left(E-\frac{\hbar^2 k^2 }{2M}\right) Y_l^m({\bf\hat k}),$$ where $M$ is the mass of the ...
1
vote
2answers
80 views

Under what circumstances is observing a superposition possible?

According to Ian Stewart's 2013 Symmetry: A Very Short Introduction (pp. 119-120), Experiment and theory suggest that superposed states should not be observable as such; only individual ...
0
votes
1answer
123 views

How does an electron adjust itself to fit in an excited state that is completely filled?

According to quantum mechanics each state has a specific shape. So, how does the electron get into that shape of the orbital?
3
votes
3answers
165 views

Unitarity of PMNS matrix

Why should the neutrino mixing matrix (PMNS matrix) be unitary? Is the unitarity dictated by experiments or is it a theoretical demand?
3
votes
0answers
158 views

Entanglement entropy and area law

I am currently reading a review "Area law for the entanglement entropy" by Eisert, Cramer and Plenio (2010). From what I understand: In one dimension, for local gapped models, we have an area law ...
2
votes
2answers
456 views

Why does Matter occupies space? Matter and space are two things… If Space does not has mass, why should matter have space-ful nature?

This thought has completely changed my perspective towards matter. If the matter in a star can collapse to a point to form a Black hole, surely the true nature of matter should be able explain this ...
5
votes
3answers
479 views

How are anti-matter atoms created?

What is the reaction, or reactions that make anti-matter? I don't understand how anti-matter is created by CERN if interaction with normal matter causes annihilation.
2
votes
0answers
65 views

Electromagnetic force interaction

As far as I know, the electromagnetic force only interacts on particles with electrical charge, but I was told that the electromagnetic force was involved in the following reaction: ...
2
votes
1answer
69 views

Which types of particles are affected by the wave-particle duality?

If we take the double slit experiment as a way of demonstrating the wave-particle duality, which types of particles would show an interference pattern? For example, I know that electrons show such a ...
0
votes
0answers
11 views

multiple frequency trapped power signal

is there any possibility to generate a waveform that consists of multiple power signals with different frequencies such that these signals travel together like they constitute [to form a ...
2
votes
2answers
149 views

Increased likelihood of photon emission due to “nearby” absorber?

Is an excited atom more likely to emit a photon if there is a similar atom in the ground state nearby ready to absorb it? When I say "nearby" I guess I mean that the absorber has an approximately ...
0
votes
2answers
119 views

Do atoms have an outter shell or boundary?

Do atoms have boundaries or an outer shell? If so, how do photons react to it? Also, if not, then does the atom always have the same set of electrons or do the electrons keep on changing? What I mean ...
0
votes
1answer
168 views

Photons and proper time

Why is there no proper time without inertial frame? In question n°95054 I learned that there is no proper time zero and no proper distance zero for photons because they are no inertial frames. That ...
1
vote
2answers
211 views

Electron recoil after emitting virtual photon

Assume that a stationary electron $A$ emits a virtual photon with $4$-momentum $k$ and a stationary electron $B$ absorbs it. Let us assume a description in which time is moving forwards. At the ...
0
votes
1answer
222 views

Do particles ever touch each other during a collision? [duplicate]

Do particles ever touch each other during a collision? My understanding is that they can get really close to each other but never actually touch, is that true? Another thing I've read about is, the ...
0
votes
0answers
71 views

Born rule and Feynman propagators

Let us assume that we want to describe the full process of photon emission by electron A and absorption by electron B. Therefore electron B must be on the forward lightcone of electron A. In the ...
1
vote
0answers
45 views

What are the ways of finding the spin of a particle [duplicate]

How many ways are there for this mission? Any article about that on the internet. I heard about TODAI made a reprogrammable quantum computer. Any more ideas are welcome
5
votes
1answer
188 views

Photons traveling backwards in time?

Imagine that two widely separated charged particles $A$ and $B$ exchange a photon. Because they are far apart one can imagine that there is a major contribution to the photon propagator that travels ...