All Questions
28
questions
1
vote
0
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52
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What is the difference between the center of mass energy of partons, and the invariant mass of the particles after a collision?
In a paper about the Atlas experiment (https://arxiv.org/abs/2103.01918) differential cross sections of $pp→ZZ→4\ell$
are being presented. However these cross-sections are functions of the invariant ...
- 172
5
votes
0
answers
230
views
Another "real vs virtual particle" one: calculate the full diagram or $\sigma \times \mathrm{BR}$?
I have recently been forced to think about something I always thought that I understood but that, in reality, I could not be more confused about.
Suppose I want to study the LHC prospects for ...
- 1,742
1
vote
1
answer
124
views
How to derive the modified Mott formula (with target recoil) using quantum field theory?
The differential cross-section of relativistic point electron off a static Coulomb potential provided by a point charge with density $\rho(\vec x)=e\delta^{(3)}(\vec x)$ is given by the Mott formula (...
- 11.8k
1
vote
0
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148
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QFT Scattering Cross Section Integral
I came across this integral studying QFT regarding what I think it may be the calculation of a 2$\rightarrow$2 particle scattering cross section.
$$I = \int \frac{dp_3}{(2\pi)^32E_3} \frac{d p_4}{(2\...
- 11
3
votes
1
answer
495
views
Phase space factor for a two-body decay
I was trying to understand how pion decays to muons and not electrons because of helicity suppression. So I was trying to figure out the ratio of the decay widths.
PDG review for kinematics (...
- 131
1
vote
1
answer
101
views
Muon pair production
Does muon pair production ($e^+ + e^- \rightarrow \mu^+ + \mu^-$) not have a $t$-channel at the lowest order (at the tree level)? All sources like Schwartz, etc. seem to only solve for $s$-channel, ...
- 433
0
votes
0
answers
268
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Addition of four-momenta in scattering amplitude of nucleon-anti-nucleon pair in scalar Yakuwa theory
Intro
I'm studying QFT using David Tong's lecture notes. In section 3.5 on examples of scattering amplitudes in scalar Yukawa theory, the scattering amplitude $A$ of a nucleon-anti-nucleon scattering ...
0
votes
1
answer
115
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Relation between Decay Rate and Annihilation Cross Section
In particle kinematics and realistic observable, one typically works with scattering cross sections and decay rates.
If one has an expression for a decay rate for a particle of a certain type to decay ...
- 1,410
5
votes
1
answer
801
views
Trouble deriving expression for differential scattering cross section from $S$-matrix
I am following the derivation of the scattering cross-section from Peskin and Schroeder textbook. On page 105, we get an expression for the differential cross-section:
$$d\sigma = \left(\prod_f \frac{...
- 316
2
votes
2
answers
396
views
Suppression of $W$ boson propagator by its mass
In my experimental particle physics introductory class it was often said that quantum electrodynamics (QED) is very predictive for sufficiently small center of mass energys since the $W^\pm$-...
- 2,196
0
votes
0
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97
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Spin Four-vector of a polarized top-quark in its center-of-mass frame in a weak decay
I am very confused about how the spin-four-vector of a polarized top-quark in its center-of-mass frame should look like in a weak decay. Could you help me, please?
The definition of the spin four-...
- 45
2
votes
1
answer
131
views
Why does the term $i\epsilon^{\alpha\mu\beta\nu}p_{\alpha}q_{\beta}$ vanish in the squared amplitude of the top decay?
I would like to calculate the squared of the amplitude of a top-decay $t-> Wb$. I know already the solution, but I can't get there: I get stuck with the Levi-Civita-Tensor on my way. Can you help ...
- 45
2
votes
0
answers
140
views
For which values of $n$ and $n'$ are $n \to n'$ particle scattering cross-sections well-defined?
When studying particle interaction events in QFT, we usually consider either (a) $2 \to 2$ particle "scattering" events, whose probabilities are quantified by scattering cross-sections, or (b) $1 \to ...
- 48.4k
0
votes
1
answer
138
views
Photo pair production: differential cross section
In a scientific paper, I need for my Bachelor thesis, the differential cross section for photo pair production
$\gamma\gamma\to e^{+}e^{-}$
is given as follow:
$\mathrm{d}\sigma = \frac{r_{0}^{2}\...
- 854
1
vote
3
answers
2k
views
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 $|\mathcal{M}|^2$, ...
- 723