Scattering is a general term for several physical processes in which radiation of some sort changes direction due to an interaction with a particle. Scattering can be classified by the type of radiation (ie, electromagnetic, x-ray, neutron), or by the relative sizes of the wave and the particle (ie, ...
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27 views
Concerning Scattering Intensity and Particle Concentration
I am trying to determine what governs my sensor output. I have an optical sensor that emits infrared radiation on a sample volume and gives me a voltage output from the scattering of (1 to 10 micron) ...
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0answers
25 views
Color of sky scattering by sky dust [duplicate]
Why does we see sky like blue in maximum time?
We know violet has less wavelength, so we should see sky like violet.
My assumption is that, violet is not primary color and not sufficient in the ...
6
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1answer
87 views
Some more questions about the BCFW reduction
This question is a continuation of this previous question of mine and I am continuing with the same notation.
One claims that one can actually split this $n$-gluon amplitude such that there is just ...
1
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1answer
74 views
Why can I add the Atomic form factors in the calculation of the Diamond Structure factor
When trying to calculate the structur factor for diamond I came across the calculation on the wikipedia. In the calculation they just add up the atomic form factors of alle the atoms in the unit cell ...
2
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1answer
778 views
Does the Breit Wigner formula apply to intermediate virtual particles?
Breit Wigner Formula describes the cross section for interactions that proceed dominantly via a intermediate particle (O*) A+B → O* → C + D:
$$σ = \frac{2\Pi}{k^{2}}\frac{Γ_{i}Γ_{f}}{(E-E_{o})^{2} + ...
5
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0answers
77 views
Setting of renormalization scale in field theory calculations
In dimensional regularization an arbitrary mass parameter $\mu$ must be introduced in going to $4-\epsilon$ dimensions. I am trying to understand to what extent this parameter can be eliminated from ...
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0answers
22 views
Best code for Mie Scattering? [closed]
I'm looking for a good code for Mie scattering. What is most generally used out there (free and commercial)?
Do you know of any "recent" code written for Mathematica?
0
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1answer
172 views
Expansion in solid spherical harmonics on the lattice
I'm interested in calculating scattering processes (e.g. Coulomb scattering of an electron beam by a single ion) in the context of lattice quantum field theory, and wonder if there is something like ...
4
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1answer
74 views
Mie scattering intensity and spherical particles on
I am running an experiment where I shine infrared light on (almost) spherical particles on the micron scale (PM2.5 - PM10). I then look at the (90 deg) scattering properties to try and size the ...
0
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1answer
45 views
Rutherford Scattering Spectra
I am using SimNRA to simulate the classical Rutherford Scattering. Playing around with it, I came across some spectra that I cannot explain...
First of all, if someone plots the spectrum of ...
2
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2answers
81 views
particles scattering on fluids: breakdown of the effective continuum description
When does the macroscopic continuum description of a medium like a fluid break down?
Say I'm interested in a scattering process of some particles with momentum p and energy E off a fluid of ...
1
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0answers
17 views
Impact parameter in scattering process
Let's consider classical two body scattering process. Is the impact parameter the same in the laboratory and inertial frame of references?
1
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1answer
76 views
Elementary question on pion-proton scattering cross-section
Is $E_k$ the energy of the outgoing or incoming pion?
The first peak is supposed to be a delta baryon.
What does the graph tell us, experimentally? A pion of kinetic energy x comes in, then we ...
5
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1answer
71 views
Significance of Poles of Correlation Function in QFT
In QFT, specifically in scattering processes, what is the physical significance of the poles / residues of the $N$-point correlation function? And why?
2
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1answer
23 views
Must neutron speed and diffusion speed be comparable for neutron scattering experiments to be probe atomic diffusion?
Neutron scattering experiments are sometimes used to study atomic diffusion in solid materials. My intuition is that the typical speeds of the atoms diffusing in the material--say, the diffusion ...
2
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1answer
68 views
Alternative methods to derive the static potential in the NR limit of QED
In QED, one can relate the two-particle scattering amplitude to a static potential in the non-relativistic limit using the Born approximation. E.g. in Peskin and Schroeder pg. 125, the tree-level ...
3
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1answer
73 views
Tunneling and transmission
Lets say we have a tunelling problem in the picture, where $W_p$ is a finite potential step:
If particle is comming from the left a general solutions to the Schrödinger equations for sepparate ...
2
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0answers
28 views
Do small-angle coherent scattering experiments really see coherent effects over arbitrarily large distances?
Short version
After integrating over all possible outgoing angles, the total cross-section of coherent elastic scattering from a fixed target of characteristic length $L$ scales like $L^4$. Does ...
4
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2answers
55 views
Attenuation mass-thickness for sunset light
We are able to look directly at the sun near sunset and sunrise, which clearly demonstrates the fact that our atmosphere attenuates visible light. Let's imagine it follows the typical attenuation ...
1
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0answers
30 views
Neutron scattering for a critical magnetic-ordering system : what about critical opalescence?
Liquid-gas transition critical point is believed to share the same universality class as the 3D Ising model.
We know that the liquid-gas transition is characterized by a phenomenon called critical ...
14
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2answers
461 views
Does the exact string theory $S$-matrix describe all physics there is?
Suppose someone manages to evaluate the string theory $S$-matrix to all orders for any and all vertex operator insertions including non-perturbative contributions from world-sheet instantons and ...
1
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1answer
63 views
Single photon's effect on conservation of momentum?
When your looking at basic Compton theory you find that if you shoot a stream of photons at a particle (usually atoms or electrons), then you have the basic laws of conservation of momentum. The ...
2
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0answers
47 views
Parton Distribution Functions, average cross section of the nucleon
Say we are given the scattering cross section for neutrinos from $d$ and $\bar{u}$ quarks as $\frac{d\sigma^{d}}{dQ^2}=\frac{G_F^2}{\pi}$, $\frac{d\sigma^{\bar{u}}}{dQ^2}=\frac{G_F^2}{\pi} (1-y)^2$, ...
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1answer
97 views
Potential step and its transmission / reflection
Lets say we have a potential step with regions 1 with zero potential $W_p\!=\!0$ (this is a free particle) and region 2 with potential $W_p$. Wave functions in this case are:
\begin{align}
...
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0answers
13 views
How to write down the detailed balance (microreversed) amplitude
I know that time-reversal of a reaction and the detailed balance (microreversed, or reciprocal) reaction are different. Textbooks on scattering theory explain how to relate the S-matrix elements of a ...
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0answers
92 views
Scattering and partial wave analysis for cross section [closed]
Problem
Given the central potential:
$V(r)=-\frac{\hbar^2}{m a^2}\frac{1}{\cosh({r\over a})}$
and given that we know the solution to the following ODE
$\frac{d^2 y}{dx^2}+k^2 ...
0
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1answer
60 views
Do particles in the solar core travel at the same speed as they would in vacuum?
I just read the Wikipedia article on the Sun. The section on Solar Core states
It has a density of up to 150 g/cm3[47][48] (about 150 times the density of water)
Do the particles (atomic, and ...
7
votes
3answers
813 views
Why is it necessary for an object to have a bigger size than the wavelength of light in order for us to see it?
I keep hearing this rule that an object must have a bigger size than the wavelength of light in order for us to see it, and though I don't have any professional relationship with physics, I want to ...
5
votes
2answers
218 views
Can scattering amplitudes be simplified with 1PI diagrams?
I have been teaching myself quantum field theory, and need a little help connecting different pieces together. Specifically, I'm rather unsure how to tie in renormalization, functional methods, and ...
0
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0answers
43 views
Wave equations for two intervals at Potential step
Lets say we have a potential step as in the picture:
In the region I there is a free particle with a wavefunction $\psi_I$ while in the region II the wave function will be $\psi_{II}$.
Let me ...
0
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0answers
60 views
Are EM waves scattered the most when the wavelength and the obstacle have a similar size?
I heard that when the wavelength and obstacle are similar in size, the scattering is the greatest. Is this true?
2
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0answers
67 views
Classical scattering of two particles by a Yukawa potential
A point-like particle $A$, coming from minus spatial infinity, heads at another one, $B$, with an impact parameter of $b$.
Initial momenta are $p_A$ and $p_B=0$.
They repel each other via a Yukawa ...
12
votes
3answers
13k views
Why does the moon sometimes appear giant and a orange red color near the horizon?
I've read various ideas about why the moon looks larger on the horizon. The most reasonable one in my opinion is that it is due to how our brain calculates (perceives) distance, with objects high ...
6
votes
1answer
131 views
Database of scattering amplitudes
I want to check whether my result for the invariant amplitude of the electron-electron scattering (to lowest order in $\alpha$; t+u channels) is correct or not.
I can't find any reference that has ...
3
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0answers
86 views
Why does scattering depend on spin?
I'm reading about giant magnetoresistance (GMR), and the most important feature of this phenomenon is the spin dependance of the electron scattering inside a magnetised lattice. However, I don't quite ...
8
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2answers
227 views
Optical theorem and conservation of particle current
The optical theorem
$$ \sigma_{tot} = \frac{4\pi}{k} \text{Im}(f(0)) $$
links the total cross section with the imaginary part of the scattering amplitude.
My lecture notes say that this is a ...
22
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3answers
1k views
Scattering of light by light: experimental status
Scattering of light by light does not occur in the solutions of Maxwell's equations (since they are linear and EM waves obey superposition), but it is a prediction of QED (the most significant Feynman ...
2
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1answer
56 views
In the expansion of the scattered wave function, why do these two functions have the same index?
See Griffiths Quantum Mechanics, eq. 11.21. Evidently,
$$\psi(r,\theta,\phi)=Ae^{ikz}+A\sum\limits_{l,m}^{\infty}C_{l,m}h_{l}(kr)Y_{l}^{m}(\theta,\phi).$$
But I don't see why the $l$th Hankel function ...
5
votes
3answers
306 views
Particle coming across a step potential barrier
My quantum mechanics textbook says that when a particle (in the classical case) comes across a potential-step barrier of finite height, if it has sufficient energy to surmount the barrier, it will ...
2
votes
2answers
80 views
Is there an upper limit to wavelength and particle size in the Mie Scattering solution?
I figure that Mie scattering is best for finding the scattering when the wavelengths are between 1/10th to 10x the particle diameter. However, is there an upper limit to this? If I send 2.8cm ...
3
votes
1answer
181 views
How did Lord Rayleigh derive/determine the phase function for his scattering model?
I've been researching the question for quite some time, as I understand it the phase function is actually an approximation due to the particle-wave duality inherent in participating media such as the ...
1
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0answers
21 views
Phase functions non-existent in original (J. Strutt) Lord Rayleigh's work?
This is related to my previous Phys.SE question on the derivation of the phase function - upon sifting and scanning through 600 pages of John Strutt's collected work, there is absolutely no mention of ...
4
votes
1answer
201 views
A certain gluon scattering amplitude
I am stuck with this process of calculating the tree-level scattering amplitude of two positive helicity (+) gluons of momentum say $p_1$ and $p_2$ scattering into two gluons of negative (-) helicity ...
6
votes
3answers
285 views
What is the capture cross-section of a black hole region for ultra-relativistic particles?
What is the capture cross-section of a black hole region for ultra-relativistic particles? I have read that it is
$$\sigma ~=~ \frac{27}{4}\pi R^{2}_{s}$$
for a Schwarzschild BH in the geometric ...
1
vote
1answer
104 views
Specific electron energy gap values $E_{i+1}-E_i$ vs. photons with arbitrary energy $\hbar \omega$
The energy levels of electrons in an atom are quantized $E_i$. A photon of a specific momentum $\vec p$ and energy $$\omega=(E_{i+1}-E_i)/\hbar$$ hits an atom and gets absorbed. Okay now say the ...
1
vote
1answer
91 views
Scattering from a box potential of width $L$ doesn't reproduce a step potential in the limit $L \rightarrow \infty$
Consider the scattering of a quantum particle in one dimension, caused by a step in the potential (this appears in many undergrad level QM books):
$$ V(x) = \begin{cases} V_1 & x<0 \\ V_2 ...
12
votes
4answers
452 views
Tree level QFT and classical fields/particles
It is well known that scattering cross-sections computed at tree level correspond to cross-sections in the classical theory. For example the tree level cross-section for electron-electron scaterring ...
0
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0answers
33 views
equation for the potential in terms of the phase shift for a rotational invariant potential
let be a potential in 3d invariant under rotations so $ V(r) $
in the WKB approximation the phase shifts are given by
$$ \delta _{l} (k)= \int_{a}^{\infty}dr ...
0
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1answer
33 views
What is pulsed neutron diffraction?
I have tried a google search and checked my condensed matter books but I can't find out what pulsed neutron diffraction is and how it differs from inelastic neutron scattering.
3
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0answers
124 views
Inclusion of information about external particles to calculate scattering amplitudes
In this (schematic) equation to calculate the scattering amplitude A by integrating over all possible world sheets and lifetimes of the bound states
$$ A = \int\limits_{\rm{life time}} d\tau ...
