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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).

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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Does the path of a Wilson line in a quark-correlator matter?

Consider a gauge-invariant quark correlation function nested inside an arbitrary state $|p\rangle$ $$\langle p |\bar \psi(z)_{\alpha,a}\left( W_{\Gamma}(z,0)\right)_{ab}\psi(0)_{\beta,b}|p\rangle \tag{1}$$ where $\alpha,\beta$ are spinor indices,…
Arturo don Juan
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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 functions, tests that quarks have spin…
Juan
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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 of producing a final-state $X$ given initial-state…
JCW
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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 ...in reality the proton is a dynamic system…
Hector
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Do electrons interact with gluons?

I know the straightforward answer to this question is no: electrons are leptons which by definition don't interact via the strong force, gluons are the mediators of the strong force and hence electrons don't interact with gluons. That said, in this…
Quantum spaghettification
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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 of an electron off of an unpolarized target $e^-X…
Lurianus
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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 parton. At leading order the kernels…
Thomas Wening
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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. Schwartz: Quantum Field Theory and the Standard Model…
Thomas Wening
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Parton model in experimental particle physics

In experimental particle physics, what does "parton-level" , "particle-level" and "detector-level" exactly mean ? PS : detailed explanations, links, etc .. would be deeply appreciated
M.A.B
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Spin-charge separation and Spin-Statistics relations

Usually, we associate the half-integer spin to fermion, and the integer spin to boson. And there are constraints like the Spin-Statistics relations. However, in Spin–charge separation or the parton-construction techniques (Schwinger/Abrikosov…
wonderich
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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 correlation functions distribution…
Arturo don Juan
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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 proportional to the DGLAP splitting…
Thomas Wening
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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 seen the first line of this equation, eq. (18.113).…
mavzolej
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Parton distribution function in terms of Fock space kets

To my understanding, I can (at least, formally) express the (unnormalized) PDF for a certain constituent of a composite state as $$ f(x)=f\left(\dfrac{k}{K}\right)=\sum_j m_j^{(k)}|\langle\psi_j^{(k)}|\Psi^{(K)}\rangle|^2…
mavzolej
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How to derive operator form of the parton distribution function

A similar question is found here in Stackexchange a year ago without any response. I am following the formulation of the parton densities from the handbag diagram in Collins Handbook of Perturbative QCD, Chapter 6. I know that the quark density can…
firest
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