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Questions tagged [scattering-cross-section]

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.

A cross-section is the name given to a hypothetical unit of area for measuring the probability of scattering events in particles collisions. See Beer-Lambert Law. should be used for questions about particle collision probabilities. DO NOT USE THIS TAG for a physical non-probabilistic cross-section of a macroscopic object.

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How do photons affect each other gravitationally?

Photons are energy. According to general relativity they should bend space. Assuming two photons pass one another in a large void of empty space how would they gravitationaly affect each other exactly? Would there be a change in their path, a…
Derek Seabrooke
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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: $$ \sigma = \frac {2\pi} {\hbar\,v_i} \left| M_{fi}\right|^2\varrho\left(E_f\right)\,V $$ $$ M_{fi} =…
Chris
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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: $$ {1 \over E_{A} E_{B} |v_A - v_B|} $$ Where $E_i$ and $v_i$ are energies and…
Forever_a_Newcomer
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Why, in spin sums, we sum over final spin states and average over initial states?

I am reading Halzen's book about quarks and leptons and on page 120 he talks about spin sums. He says that in order to calculate the amplitude between unpolarized states we have to sum over FINAL spin states and average over INITIAL states. Why is…
Yossarian
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Understanding scattering cross section

I think I might have a serious misunderstanding of some concepts to do with scattering cross sections and would really appreciate any help. As far as I can tell the differential cross section is basically a measure of what fraction of particles get…
plzhelp
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Why does Gadolinium have the highest neutron cross section?

Gadolinium-157 has the highest thermal-neutron capture cross-section among any stable nuclide. Based on my layman's understanding of neutron capture – particularly the fact that (I assume) neutrons don't much care about electron shells – I would…
feetwet
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Arbitrary normalisation of a free particle wave function

$\newcommand{\vec}[1]{\mathbf{#1}} \newcommand{\dd}{\mathrm{d}}$I'm reading Landau and Lifshitz' book on non-relativistic quantum mechanics and I have some doubts about a passage in the chapter about elastic scattering. I have the French edition of…
yellon
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Cross Section Peskin vs Srednicki

in Peskin Schroeder after the derivation of the differential cross section there is a comment for the central mass system (CMS), which says: In the special case, where all four particles have identical masses (...), this [the general formula]…
dag
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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?
fgfgf
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If the probability of a point (photon) hitting another point (electron) is zero why do they interact?

If the probability of a point (photon) hitting another point (electron) is zero why do they interact? To have a probability greater than zero almost one of them should be not a point. Correct me, please if I am wrong.
Krešimir Bradvica
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What is cross section?

I am learning about unit Barn, it is a unit of cross section. I know it means how likely a particle is to interact with the material, it's like opacity or transparency in optics. What I don't understand is what cross section means. Let's say…
Soliton
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The Ward-Takahashi identity in Peskin and Schroeder (page 311)

I'm working on the Ward-Takahashi identity in Peskin (page 311), but I canʻt obtain Eq.(9.105) from Eq.(9.103) According to Eq.(9.103) \begin{align} &i \partial_{\mu}\left\langle 0\left|T j^{\mu}(x) \psi\left(x_{1}\right)…
sky
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What is the cross-section size of a photon?

How "wide" is a photon, if any, of its electromagnetic fields? Is there any physical length measurement of these two orthogonal fields, $E$ and $M$, from the axis of travel? When a photon hits a surface, and is absorbed by an electron orbital, this…
UM Desai
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QFT cross section: missing information?

So I'm having a hard time understanding how the (QM) cross section fits into the general picture, of e.g. collider experiments. So we can calculate cross sections (for one reaction) exactly in QFT with Feynman diagrams (perturbation theory...). When…
CFRedDemon
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Does the differential cross section curve correspond to a probability density function?

Quick question here. If I know the differential cross section function for a given phenomenon, and if I normalize this function such as its integral over its domain is 1, can I interpret this normalized function as a probability density…
Jasmeru
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