# 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.

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### Electron capture cross-section at qualitative level

I would like to compute the cross-section of electron capture but, as I understand, it is impossible in terms of usual QED due to the hadronic structure of nucleus. But it seems that there is a ...
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The differential scattering cross-section is the modulus square of scattering amplitude, so it has to be a real function. But the expression for differential scattering cross-section is $\frac {d\... 1answer 21 views ### Cross sections in Geant4 [on hold] Does anyone know where I can find the information about cross sections in Geant4? I would like to use my own file with cross section (exported from another code to MC simulations), but I cannot find ... 0answers 63 views ###$\tau \rightarrow \nu_{\tau} e^- \bar{\nu}_e$decay. Where is my mistake? I want to calculate$\tau \rightarrow \nu_{\tau} e^- \bar{\nu}_e$decay rate$\Gamma$, with the effective four fermion interaction to leading order. $$\mathcal{L}_{eff} = -\frac{G_F}{\sqrt{2}} [e^+\... 0answers 22 views ### Cross section for 2 particles that decay separately This maybe is a naive basic question but I want to be sure. If I want to calculate the cross section of the process$$pp \rightarrow W^+HX \rightarrow e^+\nu_e b\bar{b} X$$(H is a Higgs particle, ... 0answers 29 views ### Why is a diagonal scattering matrix preferable? Maybe it is a trivial question, but it is not so clear to me why (if it is so) I would rather want a diagonal S-Matrix. Thanks 0answers 26 views ### electron free mean path understanding I am having difficulties to grasp the idea that the probability a particle is absorbed between x and x + dx is given by$$dP(x) = \frac{I(x) - I(x+dx)}{I_0} = \frac{1}{l} e^{-\frac{x}{l}}dx$$... 1answer 24 views ### How do one find the first correction order of \lambda for scattering cross section? I have a lagrangian \mathcal{L}=\mathcal{L_0+\mathcal{L_1}}, where \mathcal{L_1} is a perturbation given by:$$\mathcal{L_1}=-(1/3!) \lambda \phi^3-(1/4!) \lambda \phi^4 $$and$$\mathcal{L_0}=-\... 0answers 95 views ### Non-relativistic limit of particle decay Let us consider the theory with scalar coupling$g\bar{\psi}\phi\psi$. For the decay process$\phi\rightarrow \bar{\psi}\psi$one can write down the following amplitude: $$\mathcal{M}=ig\bar{u}(p_{-})... 2answers 106 views ### Faster ways of computing feynman diagrams Obviously the machinery of QFT allows us to calculate processes, such as QED diagrams, to great precision, and whilst it is effective, it seems there are many processes that make calculations (say by ... 0answers 32 views ### Skobelev graviton-photon cross section diverges Skobelev calculated in 1975 the cross-section of graviton+photon to graviton +photon and the graviton+graviton to photon+photon. For the latter, he gave the integrated cross-section, but for the first,... 0answers 33 views ### e^+e^- \longrightarrow \mu^+\mu^- probability density function of \theta strange trend I'm considering the process:$$ e^+e^- \longrightarrow \mu^+\mu^-$$The cross section in the center-of-mass frame: \begin{equation} \left( \frac{d \sigma}{d \Omega} \right)_{CoM}= \frac{\alpha^2}{4 s}... 1answer 54 views ### What is the relationship between Mie scattering amplitudes, incident intensity and outgoing intensity? Wikipedia's Mie scattering Mathematics discusses the scattering amplitudes S_1(\theta), \ S_2(\theta) for each outgoing polarization of an incident EM plane wave on a uniform sphere. It defines the ... 1answer 18 views ### Motivation behind the representation of differential cross sections using histograms From my lecture notes: In most cases a cross section is represented in a differential way with respect to one or more observables. While it is possible to make a theoretical prediction for a ... 1answer 22 views ### Rate of reaction of collision in relation to the geometric cross-section I am reading "Particles and nuclei : an introduction to the physical concepts / Bogdan Povh" and on page 44 of the book there is a section about the geometric cross section in a idealised scattering ... 1answer 103 views ### Mass dimension of an n-particle scattering amplitude in 4D For the 4-dimensional case, and using the cross-section formula, how can we show that the mass dimensions of an n-particle amplitude must be$$[A_n] = 4-n~?\tag{2.99}$$My understanding is that the ... 0answers 37 views ### Elementary particles & their reactions: literature I would like to find a book which contains lot of examples of different reactions with elementary particles (for instance, electron-electron scattering, electron-positron annihilation, electron ... 0answers 5 views ### Why is number density of atoms taken in reaction cross-section? When reaction cross-section area corresponding to one target nuclei is given, then to calculate total scattering cross-section that area is simply multiplied by the number of atoms in that slab to ... 0answers 53 views ### QFT cross section: missing information? So I'm having a hard time understanding how the (QM) cross section fits into the general picture, of e.g. collider experiments. So we can calculate cross sections (for one reaction) exactly in QFT ... 0answers 56 views ### Why the nuclear fusion 6Li+D and 7Li+P reactions happens 10 time less than H+11B? The first two reactions generates 2 alphas and the boron one generates 3, but boron has 2 more protons than lithium so should repels more to hydrogen. I suppose is a question of nuclear states, but ... 0answers 17 views ### Ratio between neutrino scattering cross-sections I would like to calculate the ratio between the cross-section of the processes:$$\frac{\nu_\mu+e^- \rightarrow \nu_e+\mu^-}{\bar{\nu}_e+e^- \rightarrow \bar{\nu}_\mu + \mu^-}$$I found this set of ... 2answers 73 views ### Theoretical definition and pratical mesurement of differential cross section In Sakurai's book, the definition of differential cross section is:$$d\sigma/d\Omega= transition \;rate / probability\; flux $$However this def doesn't contain any information about the thickness ... 1answer 69 views ### How can I calculate scattering cross section of Yukawa potential classically? https://en.wikipedia.org/wiki/Yukawa_interaction#Classical_potential Here is classical form of Yukawa potential. I want to calculate classical scattering cross section of this potential ... 1answer 115 views ### Why is the laboratory frame energy always greater than the center of mass frame energy for collisions? [duplicate] I looked through lots of sources to answer the question, 'Why is lab frame energy (total energy) always greater than the center of mass frame energy?' Many of them provided lots of mathematical ... 3answers 719 views ### Why is the laboratory frame energy always greater than the center of mass frame energy? I have been looking for an answer to 'Why is the laboratory frame energy always greater than the center of mass frame energy during collisions?'. A lot of resources provided mathematical explanations.... 1answer 32 views ### Mass vs cross-section studies Let's assume we have a event generator like "Pythia", and from that I have collected four momentum of a certain lepton production. the leptons are from excited gamma state. And the excited ... 0answers 49 views ### exchanged momentum in Compton scattering I am trying to resolve a confusion regarding scattering kinematics. I am considering Compton scattering, i.e. a photon with four-momentum k scatters on an electron with four-momentum p, the final ... 1answer 169 views ### At what stage is it necessary to introduce a field theory in the regeon-pomeron-odderon model of hadron interactions? I've been reading some papers from G.F. Chew and S. C. Frautschi and they do not even bother to introduce the concept of "Field" when they describe hadron interactions. My impression is that they do ... 0answers 67 views ### What is \gamma$$\rho$ mixing?

In a previous question, I asked about the apparent universality behaviour in hadron elastic scattering. I was particularly shocked to see that even $\gamma p$ showed that universal behaviour with ...
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### Do Reggeons-Pomerons-Odderons offer an Universal picture of hadron interactions?

As far as I know, the total cross-sections of the following hadron interactions are well described by a single Reggeon trajectory and a single Pomeron (soft Pomeron) trajectory. It seems to work for ...
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### What is the Relative Radiation Absorbtion per unit Mass of the various states of matter?

I am trying to find information on the relative merits of using a gas, liquid, solid or even a plasma as a radiation shield. Examples Ice, water and water vapour. Iron, molten Iron, Iron ...
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### How is the cross section related to the probability of a process?

The question is in the title: How is the cross section related to the probability of a process? If I have the total cross section $\sigma$ of a process how is this related to the probability of this ...
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### Proton-proton and proton-antiproton elastic scattering symmetry

Is $A_{pp}(s,t)=A_{p\bar p}(t,s)$ true based on crossing symmetry? Consider $pp$ and $p\bar p$ elastic colissions ($p + p \rightarrow p + p$ and $p + \bar p \rightarrow p + \bar p$). The scattering ...
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### Computing hadronic cross sections with PDFs

I am trying to estimate the cross section for a BSM process at the LHC, and I would like to ask if anyone knows what is the simplest way to integrate over the PDFs, for example with Mathematica. I ...
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### Scattering angle for induced ion-dipole interaction (inverse-5th power force)

I've been trying to work out the relationship between impact parameter and scattering angle for the case where an ion travels near an uncharged atom at non-relativistic speed, near enough such that ...
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### How to derive the Klein-Nishina formula from the Dirac equation?

I'm looking for the simplest demonstration of the Klein-Nishina formula, from the Dirac equation without the field described as a quantum operator: https://en.wikipedia.org/wiki/Klein%E2%80%...
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### Møller scattering amplitudes

In order to compute the scattering cross section for Møller scattering, one needs the amplitudes for both the $t$- and the $u$-channel. Since the cross section is proportional to $|\mathcal{M}|^2$, ...
Consider the following reaction of strong interaction (in a scattering process) $$n+\pi^+\to \Lambda_0+K^+\tag{1}$$ Then the particle $\Lambda_0$ formed decays with weak interaction $$\Lambda_0\to ... 2answers 122 views ### Probability density in Fermi golden rule Consider Fermi golden rule$$\Gamma _{{i\rightarrow f}}={\frac {2\pi }{\hbar }}\left|\langle f|H'|i\rangle \right|^{{2}}\rho $$I don't understand why \left|\langle f|H'|i\rangle \right|^{{2}} is ... 0answers 21 views ### Measuring characteristic time of strong and weak interaction using cross section Consider a scattering between two particles a and b that produces two particles c and d: d is stable, while c decays in two other different particles e and f. The first interaction is by strong ... 0answers 67 views ### What are the higher order Feynman diagrams I have to consider in muon neutrino-electron scattering? I think in a \nu_\mu + e^{-} scattering can happen: \nu_\mu + e^{-} \rightarrow \mu^{-} + \nu_e and \nu_\mu + e^{-} \rightarrow \nu_\mu + e^{-} With two Feynman diagrams (CC and NC). My ... 0answers 30 views ### Shape of partons from differential cross section as function of Q^2: is it valid, despite the \theta dependence? For deep inelastic scattering of electron on a nucleon the following graph represent the ratio$$\frac{\frac{d^2 \sigma}{d \Omega d E'}}{(\frac{d \sigma}{d \Omega})|_{Mott}} $$as a function of Q^2,... 0answers 37 views ### Parton model: relation between F_2(x) at fixed Q^2 and differential cross section as function of x Consider deep inelastic scattering of electron on proton and parton model: F_2(x) as a function of Bjorken x at fixed Q^2 goes as in the following graph. The differential cross section is:$$\...
Griffiths defines Feynman amplitude for the CC process $\nu_\mu + e \rightarrow \mu + \nu_e$ as \mathscr{M} = \frac{ g_w^2}{8M_W^2} \left[\bar \nu_e \gamma^\mu (\mathbb{1} -\gamma^5) e\right] \...