Questions tagged [partons]
A parton is a gluon, quark or antiquark in the eponymous model of scattering involving hadrons. In the hadron's infinite-momentum frame, incoming particles will be scattered instantaneously and incoherently, reducing the problem to a simple kernel convolved with parton distributions, at a particular physical scale (as probed by the inverse of the momentum transfer).
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Derivation of the Equivalent Photon Approximation in Peskin and Schroeder
I am trying to reproduce the equivalent photon approximation as discussed in chapter 17.5 in Peskin and Schroeder but cannot justify equation (17.93).
The process we are considering is the scattering ...
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QCD parton shower hard scale
Currently I'm studying parton showers from QCD and I'm having trouble with understanding how the hard scale $Q$ is related to the virtuality and energy of the parent parton. The Sudakov factor $\Delta(...
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OPE leading twist = collinear factorisation?
The operator product expansion systematically expands QFT interactions in terms of a sum of local operators.
Is the leading twist of this expansion identifiable with collinear factorisation and, if so,...
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Quark charges - parton-distribution function - factor 5/18
I got the following from Thomson’s Modern Particle Physics and some other sources.
The factor 5/18 distinguishing electron-DIS and neutrino scattering experiments is a basic proof for quarks and their ...
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Why is it that the Callan-Gross relation predicts that quark has spin 1/2?
I'm studying deep inelastic scattering, and currently at the part where they say the Callan-Gross relation:
$$F_1 (x) = \frac{1}{2x} F_x (x)$$
where $F_1$ and $F_2$ are the dimensionless structure ...
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What is a polarized/unpolarized parton?
In QCD physics, certain partonic distributions like Generalized Parton Distributions (GPDs) and Transverse Momentum Distributions (TMDs) are defined for the case where the parton is either unpolarized,...
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Polarized structure functions and Bjorken sum rule
I'm trying to understand what the Bjorken sum rule and the polarized structure functions entering it are. I will use equation (2.3) here as a reference for asking the question.
In Peskin, I've only ...
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Are parton distribution functions non-negative?
Let $f_i(x)$ be a parton distribution function as known from QCD factorisation theorems. Is $f_i(x)$ non-negative for $0<x<1$? If so, how can this be seen from the definition of PDFs in terms of ...
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Is the pion valence PDF symmetric?
The positive-pion $\pi^+$ is comprised of 1 valence up-quark and 1 valence anti-down-quark. Assuming isospin symmetry, the parton distribution functions (PDFs) for these two valence quarks should be ...
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Parton Distribution Functions - Antiquarks?
In all the PDF plots that I have seen so far (e.g. https://arxiv.org/abs/1111.5452 Fig. $3$ and $4$) the PDFs for sea or charm quarks contained only the strange or charm quark, but not the $\bar{s}$ ...
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Parton, detector and particle level at LHC [closed]
What is the difference between parton, detector and particle level in high energy physics?
I found a similar question but I couldn't understand the explanation for detector and particle level given ...
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Paper showing evidence for Callan-Gross Relation
I am getting ready for a presentation and want to show a plot showing experimental evidence for the Callan-Gross relation. Are there any papers plotting this beyond 1970 across different $Q^2$ or ...
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Physical interpretation of hadron distribution amplitudes
A parton fragmentation function can be interpreted as the probability that a final state hadron originated from that particular hadron.
A parton distribution function can be interpreted as the ...
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Meaning of $\gamma^\pm$ in Parton Fragmentation Functions
I was just working through the paper Parton fragmentation functions and came across equation 12.
What do $\gamma^{+}$ and $\gamma^{-}$ mean? The text doesn't explain this at all.
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How to define the parton distribution function of the antiquark?
So I can define the quark distribution function within a hadron as
$$
f_{\psi/h}(x)=\frac{1}{2}\int\frac{dz^-}{2\pi}e^{ixP^+z^-}
\langle h(p)|\bar{\psi}(0)\gamma^+\psi(z^-)|h(p)\rangle|_{z^2=0}
$$
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