# 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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### How do funnels hinder (help?) detection of dark matter?

I came across some a new (to me) bit of terminology at a seminar recently. In the context of dark matter scattering off of atomic nuclei (but I think it may apply more generally for any particle ...
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### Exercise: Calculating Q-value for $D_0 \to \chi_s^-e^+\nu_e$

Question Is the following methodology correct in calculating the Q-value (change in kinetic energy) for the $D^0 \to \chi_s^-e^+\nu_e$ decay process? Steps The change in kinetic energy is ...
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### Semileptonic decay amplitude

I'm trying to do past exam papers and I am absolutely failing understand some things. I would very much appreciate any insights/intuition you have. The part I'm struggling is here: In the first ...
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### Momentum conserving delta-function in the transfer matrix of quantum-field-theoretic scattering theory

The $S$-matrix vanishes unless the initial and final states have the same total $4$-momentum, so it is helpful to factor an overall momentum-conserving $\delta$-function: ...
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### Issues of normalization & differential final state momenta in analysis of normalized differential quantum-field-theoretic probability of scattering

The normalized differential quantum-field-theoretic probability $dP$ of scattering is given by $$dP=\frac{|\langle f |S|i\rangle|^{2}}{\langle f|f\rangle\langle i|i\rangle}d\Pi,$$ where $|i\rangle$ ...
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### How do I calculate the differential cross section with respect to the transversal momentum?

First of all, sorry for my English, my first language is German. My problem is: I calculated the matrix element of the quark-gluon-Compton process (q+g -> gamma + q). With the kinematics of ...
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### Differential cross-section for a 2-particle process in the LAB frame

This should really be a straightforward calculation, but somehow, I keep confusing myself and failing over and over again. I did the calculation so many times that I don't even know what I'm looking ...
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### Decay rate and differential cross-section

If I have a $pp-$beam producing an on-shell particle $A$, which then decays into particle $B+C$, then I can find the total cross-section $pp \to A \to B+C+Y$ ($Y$ being inclusive particle which should ...
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### Resonant Scattering and the Breit-Wigner Formula

Most of what I ask relates to the derivation found here: https://farside.ph.utexas.edu/teaching/qm/lectures/node91.html The basic idea is that we first consider zero energy s wave scattering from a ...
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### Grazing angle in a nuclear collision

How is the grazing angle calculated theoretically? Also, experimentally, the quarter point angle of elastic scattering angular distribution is taken as the grazing angle in accordance with ...
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### Intensity of inelastic neutron scattering: analitycal expressions

I am currently working with experimental results of magnon spectrum (in antiferromagnet with many atoms per unit cell), which was obtained by inelastic neutron scattering method, but some spectral ...
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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 ...
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### Green's Function in the Lippmann Schwinger Equation

When deriving the scattering cross section using the Lippmann-Schwinger equation we need to calculate the Green's function defined by ...
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### Energy dependency of the total cross section for different species

Comparing the plots for the total (inelastic) cross sections as a function of the centre of mass energy for $pp$ and $e^+e^-$ collisions: one notes that the trend at high energy is opposite: the ...
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### Scattering Theory

In non-relativistic quantum mechanical scattering theory you can derive an expression for the differential scattering cross section under the first order Born approximation as ...
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### Neutron activation time for Boron, Silver, and possibly other materials

How do i justify/explain that the time needed to activate Boron is 2 hours and the time needed to activate Silver in water is 45 minutes? Response to comment: In a neutron cross section experiment, ...
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### Assigning values of angular momentum transfer

How do the shapes of the experimentally measured differential scattering or transfer cross sections help in assigning reliable angular momentum transfer values?
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### Relativistic Scattering

When we work out the relativistic general two-body scattering in the CM frame (like two elementary particles producing two other P1 +P2 -P3 -P4) , the cross section is proportional to absolute final ...
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### Scattering cross section in terms of current density

I was struggling to understand what a scattering cross section is (in a classical setting), and I found this document: ...
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### Analyzing electron-positron scattering cross section in detail

It can be found in any quantum electrodynamics book that the cross section for electron-positron scattering in the high energy limit is \dfrac{\mathrm{d} \sigma}{\sin \theta \, ...
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### 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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### 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 ...