# Tagged Questions

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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### 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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### 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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### cteq5 mathematica [on hold]

Trying to compute the total cross-section for gg -> ttbar via cteq5 with Mathematica. So I know to use set 3, parton 0, but for q, do I use 7TeV for both pdf's, which would correspond to a total cms ...
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### $2\to3$ 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### Energy dependent cross sections for neutrons

Do you know where I can find a table with energy dependent cross sections for neutrons? Thanks!
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### Conversion of QCD cross section formula

I'm writing a program to calculate NLO cross sections for semi-inclusive high-$p_T$ pion production in proton-proton-collisions for my bachelor thesis. I've got a paper describing the production ...
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### Internuclear Binding Force: Experimental geometric detail

I am looking for the most precise currently available deuterium potential energy curve (generated purely by experimental data) on the nucleon-nucleon scale. This is crucial. I need a radial ...
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### Do molecular bounded systems shield or reduce neutron cross-sections?

When talking about neutron cross-sections, literature is usually investigating isolated cases of Neutron + Atom. Here, the abundance of hydrogen is dominating neutron fluxes through material. I ...
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### Rutherford Experiment - practical and theoretical questions

I performed the Rutherford experiment the other day, using Au thin foil of $2\,\mathrm{\mu{}m}$, a source/gun of α particles (241Am) and a detector/counter. α particles were shot from the source ...
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### How to prove the equivalence of two definitions of the scattering cross section

I have noticed that there are two definitions of differential scattering cross section in non-relativistic quantum mechanics. One of them is the most popular, particularly it is used in the book of ...
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### Integral in Peskin and Schroeder

I'm having a bit of a slow day, and can't see how to do the following integral in Peskin and Schroeder (page 107 for anyone with the book). We've derived in the centre of mass frame the integral over ...
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### SUSY, ways to boost Chargino/Neutralino production?

Does anybody know a good reference that works out the equations for the Chargino/Neutralino production cross section in SUSY? I'm trying to understand if there are any tricks for boosting the ...
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### Definition of scattered particle?

Compare the number of scattered particles: $N_s=Fa\int\sigma(\theta)d\Omega$ With the total number of incident particles: $N_{in}=Fa$ Here, F is the flux of incoming beam, a the area. sigma the ...
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### What is the spectrum of the Earth's albedo?

I was recently discussing climate change with a friend and was surprised (and embarrassed) to learn that the heat capacity of CO${}_2$ is not higher than that of nitrogen contrary to my assertions. ...
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### How do particle scattering cross sections scale with energy in colliders?

How do particle scattering cross sections scale with energy in colliders? Particularly photons, electrons, protons, and gold or lead nucleii? (If necessary, break this into four separate questions.) ...
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### What statistical test should I use?

I have two differential cross sections $d\sigma_{1,2}/dM$ ($M$ is some invariant mass) corresponding to different hypothesis. What I want is to calculate how well the appropriate experiment would do ...
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### Where to find cross section data for e- + p -> p + e-?

Where to find cross section data for e- + p -> p + e-? PDG's cross section data listing does not include it.
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### Physical interpretation of infinite total cross section

What does it tell us about a process, say A+B->C+D, if the calculated total cross section is infinite?
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### Inelastic nucleon-nucleon cross section at LHC energies

I am trying to reproduce the number of participants $N_{part}$ in Pb-Pb Collisions at LHC using a Glauber Monte Carlo simulation, specifically aiming to reproduce the values given in Phys. Rev. Lett. ...
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### Cross-section in relativistic limit: Fermi's golden rule still valid?

In order to calculate the cross-section of an interaction process the following formula is often used for first approximations:  \sigma = \frac {2\pi} {\hbar\,v_i} \left| ...
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### Cross section fon non-collinear beams

If I have two collinear beams with opposite velocities the cross section is defined by the formula: $\frac{dN}{dtdV}=\sigma \rho_1 \rho_2 |\underline{v}_1-\underline{v}_2|$ where $\sigma$ is the ...
Suppose you have a distribution function $f_{\alpha}( \vec{r} , \vec{p} , t)$ obtained from Vlasov equations for a certain $\alpha$ species, say some ions. Is there a rigorous way (in the domain of ...