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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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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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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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, 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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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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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 derive quark-antiquark parton distribution relation?
This is kind of similar to this post here How to define the parton distribution function of the antiquark? with no response.
I basically want to derive the following; $f_q(x) = -f_{\bar{q}}(-x)$ where
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Collinear factorisation in QCD: why can we multiply probabilities?
In the collinear factorisation equation for a QCD cross-section, schematically
$$
\sigma_{AB\to X}
=
f^A_a \otimes \hat{\sigma}_{ab\to X} \otimes f^B_b
,
$$
we essentially convolute the probability ...
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What are the differences between FFN, VFN, GMVFN and ZMVFN PDF schemes in QCD?
What are the differences between the fixed flavour number (FFN), variable flavour number (VFN), general-mass variable flavour number (GMVFN) and zero-mass variable flavour number (ZMVFN) schemes for ...
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What are extrinsic and intrinsic flavour production?
In terms of Feynman diagrams, what are extrinsic and intrinsic flavour production?
See for example this paper this paper (p.2).
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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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Is $\mu$ the renormalization or factorization scale in the DGLAP equations?
The DGLAP equations read
$$\frac{\partial f_i(x,\mu^2)}{\partial\ln\mu^2}=\sum_j\int^1_x\frac{dz}{z}P_{ij}(z,\alpha_s(\mu^2))f_j\left(\frac{x}{z},\mu^2\right),$$
where the $f_i$ are the parton ...
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Why are sea quarks dominant only at low value of the Bjorken $x$ variable?
In electron proton deep inelastic scatterings, the sea quarks or gluon PDFs are only dominant at low value of $x$. Thomson explained this in his book Modern Particle Physics (see page 194) by arguing
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Textbook for parton distributions?
Are there any textbooks, or good pedagogical review articles, on the subject of parton distributions? I'm looking for such sources that cover all the standard topics, such as:
Generalized parton ...
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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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How are DGLAP splitting kernels probabilites for parton branchings?
In the literature on parton evolution one often reads that the DGLAP splitting kernels $P_{ij}$ represent the probabilities for a parton of type $j$ to split into a parton of type $i$ and another ...
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Is the starting distribution in the solution of DGLAP IR-bare?
On p.27 of this paper by John Collins, he says that when defining PDFs in terms of partonic number operators, one acquires an IR-divergent bare PDF (eq. 52). The residue of the IR-divergent term is ...
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Why is the convolution between hadron structure functions and PDFs defined this way?
Say you have the distribution function $\rho_i$ of a quark $i$ (depending on the momentum fraction of that quark), and a structure function $\hat{F}_i$ (depending on the "Bjorken variable" $...
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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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Proton Structure and Parton Distribution Function
I recently read a question about whether photons, electrons, neutrinos... are a part of the proton since there are these sea-quarks he learned about. And the answers were confusing to me because the ...
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Does the path of a Wilson line in a quark-correlator matter?
Consider a gauge-invariant quark correlation function nested inside an arbitrary state $|p\rangle$
$$\langle p |\bar \psi(z)_{\alpha,a}\left( W_{\Gamma}(z,0)\right)_{ab}\psi(0)_{\beta,b}|p\rangle \...
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Deriving Callan-Gross from Parton Model
I want to derive the Callan-Gross relation from the parton model, not fom the Rosenbluth and Mott cross sections, but I am having some problems obtaining the textbook result. I am following M.D. ...
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Transverse momentum in partonic process $\gamma^\ast q\rightarrow qg$
Let $\hat{s}:=(q+p)^2$, $\hat{t}:=(k-p)^2$, $\hat{u}:=(p-p^\prime)^2$ be the Mandelstam variables of the partonic scattering process $\gamma^\ast(q) +q(p)\rightarrow q(p^\prime)+g(k)$, where the ...
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Transverse momentum in the parton model
Why is it so important that the partons in the parton model have low transverse momenta? And transverse to what anyway? I mean, basically one looks to justify breaking the hadronic subgraph in hadron-...
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How are the structure functions in Deep inelastic scattering measured?
I've been reading lots of different textbooks on the parton model and deep inelastic scattering and the discovery of quarks, and most of the time whenever I see a plot, it's about the measurement of ...
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Why is it that the Callan-Gross relation predicts that quark has spin 1/2?
I'm studying deep inelastic scattering, and currently at the part where they say the Callan-Gross relation:
$$F_1 (x) = \frac{1}{2x} F_x (x)$$
where $F_1$ and $F_2$ are the dimensionless structure ...
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