A cross-section is the name given to a hypothetical unit of area (often in units of Barns) for measuring the probability of scattering events in particles collisions. DO NOT USE THIS TAG for a physical non-probabilistic cross-section of a macroscopic object.

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Bound state of $\mu^- \mu^+$ . Why non-relativistic muon states?

Peskin & Schroeber page 148 discuss the creation of a $ \mu^+ \mu^-$ resonance state . Equation (5.44) describes the creation of a Spin Up bound $ \mu^+ \mu^-$: $$ \mathcal{M} = \sqrt{2M} \int ...
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26 views

Is this possible to determine exactly the scattering angle for inverse-cube force?

I am trying to determine the scattering cross section for the potential $$ V= \frac{a}{r} + \frac{b}{r^2}$$ As I am completely stuck while determining the scattering angle (I don't see a way to ...
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47 views

Rate of interaction of free electron with photons from sunlight

How many photons does a free electron (in sunlight say) interact with per second? I did a rough calculation assuming the electron interacts with any photon that enters through an area the size of ...
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91 views

Is this statement correct or incorrect: Moving objects undergo length contraction because they appear in space-time cross-section

Why or why not? This is closely related to another question I posited here, Does it make sense to say that objects moving at relativistic velocities appear in space-time cross-section? What I mean ...
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84 views

Does it make sense to say that objects moving at relativistic velocities appear in space-time cross-section?

Let object A move at relativistic velocity relative to a frame O. In 4D space-time (Minkowski diagram) the space view of O at any given moment of its own time is a space-like hypersurface (hyperplane, ...
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59 views

Form factor for Proton

To find the charge distribution of proton , we study electron proton scattering and compute the form factor to find the cross section. The form factor comes out to be Fourier transform of charge ...
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24 views

Do exotic states of matter have high fusion cross-sections?

The Lawson criterion suggests that a chain fusion reaction will only occur in a confined plasma. Since it's a product of temperature and pressure (or density) a chain reaction would be virtually ...
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164 views

What determines the probability of creating a particular particle in a collision?

When discussing events at the quantum level, we deal in probabilities and not absolutes. Articles I've read on particle physics state that a particle has a probability of being created in a collision. ...
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20 views

Inelastic cross section derivation

I am trying to derive the inelastic cross section (the mass changes). I looked up the elastic derivation on Peskin's book (are there any alternatives?): $$d \sigma = \frac{1}{2 E_a 2 E_b \left| ...
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43 views

Differential cross section $d\sigma/dp^{\gamma}_{T}$?

Why we care about $d\sigma/dp^{\gamma}_{T}$? What the physical meaning of it? Why not plot $\sigma$ follow $p^{\gamma}_{T}$?. As in this picture.
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39 views

Total cross section of particle decay

Suppose a particle A travelling along the $z$-axis and decays into particles B and C. The cross section is given by $$\frac{d\sigma}{d\cos\theta^*} = k(1+\cos\theta^*)^2$$ where $k$ is a constant ...
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106 views

Scattering amplitude, link between quantum mechanics and QFT

In quantum mechanics, we can define the scattering amplitude $f_k(\theta)$ for two particles as the magnitude of an outgoing spherical wave. More precisely, the asymptotic behaviour (when ...
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32 views

colliding point particles

when I draw e.g. the diagram of compton scattering I assume that the electron of given momentum gets 'hit' by a photon and interacts with it. How close does the photon have to get to the electron that ...
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31 views

Gamma matrices in Decay Calculations [closed]

I am trying to calculate the transition amplitude, $\lvert M^2\rvert$, for the process where a top quark (momentum p) decays to a bottom quark (momentum q) and a $W^+$ boson (momentum k). I am ...
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39 views

Why IR divergences cancel by cross sections of next-to-leading diagrams?

I was reading QFT & Standard Model by Schwartz, Chapter 20 which is about IR divergences. He says that IR divergences only cancel cross sections for processes involving different initial or ...
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47 views

Database of experimental cross sections for atomic collisions

Does the atomic-physics community keep a comprehensive database of experimental data (cross sections) for atomic collisions? I am looking for data about Bremsstrahlung, ionization, elastic and ...
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45 views

Differential Cross Section

I would like to know what exactly the term differential cross section means. It comes from electron scattering experiments which are used to deduce the charge distribution of a nucleus and the cross ...
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24 views

Interaction rates from cross sections in a thermalized gas

Consider a target particle embedded in a gas with a thermal distribution of velocities. If we know the cross section $\sigma$ for interactions between the target particle and a gas particle, how do we ...
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82 views

One dimensional scattering cross section

My quantum mechanics book (http://www-thphys.physics.ox.ac.uk/people/JamesBinney/qb.pdf, pages 94-95 of the pdf, or 86-87 of the book) considers the one dimensional step potential ...
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25 views

Why average incoming spins and sum over outgoing spins? [duplicate]

The book by Griffith on elementary particles reads: A typical experiment starts out with beam of particles whose spin orientations are random, and simple counts the number of particles in a given ...
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63 views

Differential Cross sections from amplitude scattering matrix

How can I get the differential cross sections from the amplitude scattering matrix, $S$ (2x2 matrix)? I've seen this in a Mie solution solver: Parallel Polarized Light: dCsdOp = $\frac{2}{\pi k} ...
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54 views

Units of rutherford singly differentiated cross section for secondary electron production

I have an equation that I have found in several papers which I am currently using for a project, including Waligorski (1986) and this book page 32. 4.2 BUTTS AND KATZ MODEL Butts and Katz ...
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39 views

2-body differential cross section in CM frame discrepancy

The standard equation for the 2-body differential cross section in the CM frame (from several references) seems to be: $$\frac{d\sigma}{d\Omega} = \frac{1}{64\pi^2s}\frac{q}{k}|\mathcal{M}|^2,$$ where ...
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37 views

How to write down the Lippmann-Schwinger equation for such a problem? [closed]

Suppose there are three particles, 1, 2, 3. Initially, particle 2 and particle 3 form a bound state. Particle 1 is free. Now we want to study the scattering of particle 1 against the 2-3 bound system. ...
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1answer
40 views

How to get rid of Dirac deltas in a phase space integration of one final particle procecess?

I was trying to compute a cross section of a process $AB\to{}C$ using formula (4.79) from Peskin $d\sigma=\frac{1}{2E_A2E_B|v_A-v_B|}\frac{d^3p}{2E(2\pi)^3}|M|^2\delta^4(p_A+p_B-p) $ The problem is ...
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87 views

Going from width to cross section

Given the decay width of a process, $\Gamma(A\to B+C)$, is it possible to turn this around to find the production cross section, $\sigma(B+C\to A)$? Edit: In particular I have been thinking of ...
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23 views

Relation between Compton Wavelength and Bound States

In their paper, "A Theory of Dark Matter" (http://arxiv.org/pdf/0810.0713v3.pdf), the authors in a section argue that if there is a massive dark matter particle $\chi$ which interacts via a force ...
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81 views

Finding scattering cross section for a sphere

I am trying to determine the scattering cross-section for a sphere ($\sigma_s$). I have filled a scattering matrix $F(\phi,\theta)$ for all $\theta$ from $0$ to $180$ degrees and all $\phi$ from $0$ ...
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94 views

Phase space measure in positron-electron annihilation calculation

I'm still trying to calculate the cross-section of the $e^- e^+ \rightarrow \mu^- \mu^+$ interaction in first order. This time I'm struggling with the phase space measure. Note that I have two ...
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150 views

Measurement of cross section

When we measure the cross section of an interaction what is it that we actually measure in a real experiment? I know what cross section is and how to derive an expression for a given process but I ...
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23 views

Using couple channel plus imaginary potential as against only imaginary potential in nuclear reactions

In some situations coupled channel calculation incorporating inelastic scattering and imaginary potential produces results comparable to experiments for elastic scattering rather than using an ...
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101 views

A conceptual question about scattering theory in quantum mechanics

When defining the cross section, we use this formula $$ \psi_S = \frac{f(\theta,\phi)}{r} e^{ikr},$$ to prove this one $$ j_{out} = \frac{|f(\theta,\phi)|^2}{r^2} \frac{\hbar k}{\mu},$$ and then ...
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Differential cross section for photon scattering on fixed magnetic dipole

Photon with energy $\hbar\omega$ scattering on a fixed particle with magnetic momentum $\vec{\mu} = \mu \vec s$. How to calculate a differential and total cross section for the photon. I've found in ...
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200 views

Photon polarization sum prescription in $e^-e^+\to{}2\gamma$

In calculating the amplitude for the process $e^-\gamma\to{}e^-\gamma$ the substitution $\sum\epsilon_{\mu}\epsilon^*_{\nu}\to-\eta_{\mu\nu}$ is useful to sum over photon polarizations. If we ...
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110 views

Why is cross section inversely proportional to wavelength for interstellar scattering?

The following problem was part of a homework for my Cosmology class: Compare the probability of interstellar scattering of photons of yellow light (5000 angstroms) and 50 micron infra-red light. ...
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63 views

$2\to3$ Phase space Integration

I have a $2\to3$ process ($P=p_1+p_2 \to p_3+p_4+p_5$) where all particles in the initial state and one of the particles in the final state ($p_3$) are massless. The other two ($p_4$ and $p_5$) have ...
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1answer
108 views

Calculating $\alpha$-Particles Detected During Rutherford Scattering (Cross Sections)

I am currently studying nuclear cross sections and this question considers the classic Rutherford scattering experiment. Here is a diagram of the experiment: The detector is at right-angles to the ...
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62 views

Constant Rayleigh Scattering Cross Section

in the Review of Particle Physics - Interactions of Particles with Matter, there is a plot that gives the cross sections for different interactions of photons with matter. One of them is Rayleigh ...
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71 views

Is scattering cross section determined by mass?

This is just for visible light/photon scattering. Let's say I have small spherical particles in water, if I keep the weight concentration of glass the same but change the diameter of glass sphere from ...
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374 views

How to calculate the differential scattering cross section?

I am doing some simulations with the Meep code to study some properties of a metal nanoparticle. The situation is this: an incident electromagnetic wave on a metal nanoparticle. By now I know how to ...
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125 views

For which temperatures are the ENDF cross-sections given?

In ENDF there are cross-sections given for different types of nuclear interactions. For example, this file gives the cross-sections for different neutron energies. However, it is not clear, which ...
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Cross-Section Compendium?

Are there any books or references that exhaustively list cross-sections for various processes in QED or particle physics? I think such a book would make for a very useful reference, and in particular ...
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92 views

What is the phase space for outgoing photons?

For a scattering process for which $n$ fermions are scattered, (by some conventions) the cross section acquires a phase space factor of: $$d\sigma \sim \prod_{i=1}^n\frac{d^3p_i}{(2\pi)^3 2E_i}$$ ...
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28 views

regarding vertex function and proton scattering

I am currently going through electromagnetic form factor. I came across the fact that since the proton is not an elementary particle its scattering(elastic) with electron can be modeled using general ...
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68 views

total cross section and contribution

Since in electron electron scattering if initial energy is quite large then muon antimuon production process can also take place which also contributes thus increases the total cross section. What ...
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108 views

Different cross section for W and Z boson

At hadron colliders the cross section for W production is about ten times larger than the production cross section for Z bosons (e.g. Figure 2 in this review article). I guess the dominant ...
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Form Factor in Rutherford Scattering

My question relates to Rutherford Scattering of particles. When we calculate the "differential cross-section" expression for a nucleus with finite size, it is said that the expression is almost the ...
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441 views

Is the total cross section a Lorentz Invariant?

In Peskin and Schroeder's book (P&S), on the botton of page 106, the authors say that the total cross section transforms as its only non-invariant factor, namely: $$ {1 \over E_{A} E_{B} |v_A - ...
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Why is number of collisions equal to number of scattered particles times number of scatterers?

In Landau, Lifshitz "The Classical Theory of Fields" $\S12$ "Invariant cross-section" the following is said1: ... according to the usual definition of the cross-section $\sigma$, the number of ...
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Understanding the concept of cross section

The cross section is a tiny area, measured in barns ($10^{-28} \mathrm{m^2}$), which relates to the probability of a reaction. But I have trouble interpreting that number. For example how can I ...