REVIEW
Saturation Effects in Deep Inelastic Scattering at low $Q^2$ and its Implications on Diffraction
High Energy Physics - Phenomenology · Submitted 27 Jul 1998 · 25 references
Pith's verdict: The original GBW paper: a genuinely useful three-parameter saturation fit, with a diffractive-ratio claim that is an asymptotic estimate rather than a result.
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Referee report
The paper
The paper claims
A three-parameter saturation model reproduces all small-$x$ deep inelastic data and predicts a nearly constant diffractive-to-inclusive ratio.
The reading
What carries the argument
The load-bearing object is the $x$-dependent saturation radius $R_0(x)$, which turns the dipole cross section into a two-regime function of $r/R_0$ and thereby defines a critical line $Q^2=1/R_0^2(x)$ in the $(x,Q^2)$ plane. The authors compute the photon-convolution integrals by Mellin transform in the variable conjugate to $ln r^2$, which reduces the numerical work to a single integral over $nu$ and, more importantly, exposes the pole structure in the complex $nu$-plane: a double pole at $nu=-i/2$ in the hard regime generates the logarithmic $ln(Q^2/Q_0^2)$ behaviour, a double pole at $nu=+i/2$ generates the soft behaviour, and stitching the two gives the simplified formula $sigma_{gamma^*p}=sigma_0'left{ln[(x_0'/x)^{lambda'}Q_0^2/Q^2+1]+(x_0'/x)^{lambda'}Q_0^2/Q^2ln[(x/x_0')^{lambda'}Q^2/Q_0^2+1]right}$ that reproduces the model's qualitative shape. For diffraction, the function $G_D(nu)=(2-2^{1/2+inu})G(nu)$ carries the whole argument: its zero at $nu=-i/2$ cancels the leading double pole down to a single pole, which is why the transverse diffractive cross section keeps the same power behaviour in $x$ as the inclusive one, while the longitudinal piece loses its pole entirely and rises twice as fast.
Extended reading notes
Core claim
The paper proposes that the interaction of a quark–antiquark pair with the proton is governed by a single saturating dipole cross section, $hat{sigma}(x,r^2)=sigma_0left{1-exp[-r^2/(4R_0^2(x))]right}$, where the saturation radius scales as $R_0^2(x)=(x/x_0)^lambda/Q_0^2$ with $Q_0=1$ GeV. The exponential form gives colour transparency at short separations, $hat{sigma}propto r^2$, and a constant at large separations, which is what produces saturation of the total $gamma^*p$ cross section. Fitting only $sigma_0$, $lambda$ and $x_0$ to all available DIS data below $x=0.01$ yields $sigma_0=23.03$ mb, $lambda=0.288$, $x_0=3.04cdot10^{-4}$ for three light flavours with a common mass of 140 MeV ($chi^2=441$ for 372 data points), and $sigma_0=29.12$ mb, $lambda=0.277$, $x_0=0.41cdot10^{-4}$ when charm at 1.5 GeV is included without new parameters ($chi^2=558$ for 372 points). The same parameters extrapolate into photoproduction and give an effective slope $lambda_{rm eff}=partialln sigma_{gamma^*p}/partialln W^2$ that runs from about $0.08$, the soft-Pomeron value, at low $Q^2$, up to about $0.29$ in the deep region. Applying the identical wave-function convolution with $hat{sigma}$ replaced by $|hat{sigma}|^2$ gives a diffractive cross section whose leading singularity structure matches the inclusive one, so the ratio of diffractive to inclusive cross sections is roughly constant, with only mild logarithmic dependence on $x$ and $Q^2$.
Load-bearing premise
The central premise is that a single eikonal-like dipole cross section with a sharp-edged proton profile, and with the diffractive amplitude taken as the square of that same cross section, captures both the inclusive and the diffractive data without any additional gap-survival or resolved-Pomeron contribution.
Editorial extensions
If this is right
- The turnover of $sigma_{gamma^*p}$ towards low $Q^2$ should track the critical line $Q^2=1/R_0^2(x)$, so the position of the maximum in the logarithmic $Q^2$-slope of $F_2$ is a measurable map of where saturation sets in.
- The effective Pomeron intercept extracted from $W^2$ dependence should slide continuously from about 1.08 in photoproduction to about 1.29 in the deep inelastic region, with the low-$Q^2$ value following from the fit rather than being imposed.
- The longitudinal structure function $F_L$ is predicted to be roughly 20 percent of $F_2$ near $Q^2=10$ GeV$^2$, a number that can be checked once $F_L$ is measured.
- The diffractive-to-inclusive ratio should stay at the few-percent level from the quark contribution alone and near ten percent with gluon emission, with only logarithmic drift in $x$ and $Q^2$.
- Raising the collision energy moves the saturation scale up only modestly: from about 1 to 2 GeV$^2$ between $x=10^{-4}$ and $10^{-5}$, and perhaps to 3 GeV$^2$ at a 1 TeV electron–proton collider.
Reading between the lines
- The critical line is defined by the model rather than derived, and the authors themselves note that it sits slightly to the left of the maxima in the $Q^2$-slope plots; an alternative definition along the maxima would shift the quoted saturation scales by a modest but non-trivial amount, so the numerical values of $R_0$ should be read as convention-dependent.
- Because the diffractive prediction uses the same convolution with $hat{sigma}^2$ and no gap-survival factor, the constant-ratio result is really a statement about the $x$-dependence of the two leading singularities; a measurement that found the ratio falling with $Q^2$ faster than a logarithm would not necessarily kill the saturation idea, only the specific identification of the diffractive amplit
- The model has no explicit perturbative evolution, so its natural completion is to match the dipole cross section onto a DGLAP-resummed gluon density at large $Q^2$; the fact that a fixed power $lambda$ already fits down to $x=10^{-5}$ suggests the anomalous dimension is effectively frozen over the measured range, which is a testable statement once higher $Q^2$ precision data exist.
- Since the three fitted parameters absorb the proton's transverse profile into a sharp-edged disc, a realistic profile function would change the normalisation and possibly the low-$Q^2$ turnover while leaving the small-$x$ power intact; comparing the two would separate the genuinely nonperturbative profile from the dynamical saturation.
Original abstract
We present a model based on the concept of saturation for small $Q^2$ and small $x$. With only three parameters we achieve a good description of all Deep Inelastic Scattering data below $x=0.01$. This includes a consistent treatment of charm and a successful extrapolation into the photoproduction regime. The same model leads to a roughly constant ratio of diffractive and inclusive cross section.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
We present a model based on the concept of saturation for small $Q^2$ and small $x$. With only three parameters we achieve a good description of all Deep Inelastic Scattering data below $x=0.01$. This includes a consistent treatment of charm and a successful extrapolation into the photoproduction regime. The same model leads to a roughly constant ratio of diffractive and inclusive cross section.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We present a model based on the concept of saturation for small $Q^2$ and small $x$. | contribution 0.52 | 0.90 | 0.10 | asserted 0.98 |
| s1 | With only three parameters we achieve a good description of all Deep Inelastic Scattering data below $x=0.01$. | result 0.96 | 0.93 | 0.22 | asserted 1.00 |
| s2 | This includes a consistent treatment of charm and a successful extrapolation into the photoproduction regime. | result 0.93 | 0.89 | 0.11 | asserted 1.00 |
| s3 | The same model leads to a roughly constant ratio of diffractive and inclusive cross section. | result 0.95 | 0.89 | 0.35 | asserted 0.83 |
What was examined, and what was not
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- P abstract
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Figures
Figures reproduced from arXiv:hep-ph/9807513 by the authors.
References
How later papers used it
249 later papers cite it
20 later papers by other authors are listed below: 11 used its method or tool, 8 used its data or values and 1 compared its own results with it. 1 more paper by the same authors is listed: 1 used its data or values.
Uses its method or tool 11 of 50 papers with this label
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Used the approach of this paper to set the variable x-tilde with an effective light-quark mass of 140 MeV when computing F2.
Energy dependence of dissociative $\mathrm{J/}\psi$ photoproduction as a signature of gluon saturation at the LHC (2016) · 1.00 · paraphrased: the licence does not allow quoting
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We work at leading order in the number of colours and use the GW model for the target average of two Wilson lines [ref] .
Correlations between azimuthal asymmetries and multiplicity and mean transverse momentum in small collisions systems in the CGC (2021) · $v_2^2$ and correlations · 0.99
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We chose the form of $N(x,r)$ given by the model of Golec-Biernat and Wusthoff [ref] : [equation] with the saturation scale, $Q_s(x)$, given by the parameters $λ$, $x_0$ and $Q^2_0$.
Mass dependence of vector meson photoproduction off protons and nuclei within the energy-dependent hot-spot model (2018) · Review of the formalism · 0.98
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Used the well-known GBW parametrization as a model for the dipole scattering amplitude.
Low projectile density contributions in the dilute-dense CGC framework for two-particle correlations (2023) · 0.98 · paraphrased: the licence does not allow quoting
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Chose this paper's model for its purpose of calculating distributions from HERA data.
Ioffe Times in DIS from a Dipole Model Fit (2009) · 0.97 · paraphrased: the licence does not allow quoting
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Used this paper's saturation model to do its calculation, which assigns the neutrino a fixed fraction of the mother meson's momentum.
Prompt neutrino fluxes from atmospheric charm (2008) · 0.88 · paraphrased: the licence does not allow quoting
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Employed an s-dependent dipole cross section parametrization similar to this paper's x-dependent GBW parametrization at small Q squared.
Neutrino-production of single pions: dipole description (2011) · 0.84 · paraphrased: the licence does not allow quoting
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Used this paper's model together with geometrical scaling to parametrize the dipole gluon distribution.
Drell-Yan Lepton-Pair-Jet Correlation in pA collisions (2012) · 0.93 · paraphrased: the licence does not allow quoting
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The dipole amplitude $N(r⃗, x)$ is computed with the Golec-Biernat and Wusthoff model [ref] with the value of the parameters as in Ref. [ref] .
Diffractive photoproduction of dark photons (2024) · Brief overview of the formalism · 0.93
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Evaluated structure functions through an integral from this paper, with the dipole cross section as the imaginary part of the dipole-nucleon scattering amplitude.
Studying low-$x$ structure function models with astrophysical tau neutrinos: double bang, lollipop and sugardaddy topologies (2019) · 0.97 · paraphrased: the licence does not allow quoting
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Gave the dipole scattering amplitude by this paper's model, with the saturation scale defined by Q0 squared, x0 and lambda.
Incoherent ${\rm J}/\psi$ production at large $|t|$ identifies the onset of saturation at the LHC (2023) · 0.90 · paraphrased: the licence does not allow quoting
Uses its data or values 9 of 33 papers with this label · 1 by the same authors
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Used the numerical value of sigma0 of 29.12 mb, obtained from fitting HERA data in this paper.
Pseudo and quasi quark PDF in the BFKL approximation (2023) · 1.00 · paraphrased: the licence does not allow quoting
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Took its value of lambda from this paper's fits to deep-inelastic e-p data from HERA, which determined Q0 squared times x0 to the lambda of about 0.097 GeV squared together with lambda.
Relativistic diffusion model for hadron production in p-Pb collisions at the LHC (2024) · 1.00 · paraphrased: the licence does not allow quoting
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The values of the involved parameters are obtained from a fit to HERA data as $λ=0.277$, $x_0=0.41·10^-4$ and $Q_0=1 GeV$ [ref] .
The impact of glasma on heavy flavor azimuthal correlations and spectra (2024) · Numerical $R_AA$ (glasma simulations) · 1.00
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As for the light quarks, a massive case with $m_l=0.14$ GeV, the value used originally in Ref. [ref] , and the massless cases were studied.
Sudakov effects and the dipole amplitude (2022) · Fits of the Sudakov-improved saturation models · 0.99
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Obtained the parameters sigma0 of 29 mb, lambda of 0.28 and x0 of 4 times 10 to the minus 5 from a fit including charm quarks to inclusive deep-inelastic scattering data in this paper.
Impact parameter dependent colour glass condensate dipole model (2007) · 0.99 · paraphrased: the licence does not allow quoting
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Fixed its parameters Lambda of 0.6 GeV and lambda of 0.3 by DIS data from this paper.
Forward hadron production in high energy pA collisions: from RHIC to LHC (2007) · 0.98 · paraphrased: the licence does not allow quoting
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The free parameters in this model are chosen as $λ= 0.29$, $x_0 = 3 ×10^-4$ and $S_⊥=1/2 ×23 mb$ for proton targets following Ref. [ref] .
Transverse Energy-Energy Correlators in the Color-Glass Condensate at the Electron-Ion Collider (2023) · Quark distribution · 0.98
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Gave the parameters lambda, sigma0 and x0 in a table, citing this paper.
Charmed Meson Production in Deep Inelastic Scattering (2007) · 0.90 · paraphrased: the licence does not allow quoting
By the same authors
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Took the dipole cross section parameters sigma0 of 29 mb, x0 of 4 times 10 to the minus 5 and lambda of 0.28 from this paper's Fit 2 with charm.
Diffractive structure function F_L^D from fits with higher twist (2007) (same authors) · 1.00 · paraphrased: the licence does not allow quoting
Compares with it 1 of 12 papers with this label
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Compared its numerical results for the integrated diffractive gamma-p to V-p photoproduction cross section obtained with this paper's original GBW model and with an updated GBW fit accounting for heavy quarks.
Exclusive photoproduction of excited quarkonia in ultraperipheral collisions (2020) · 0.98 · paraphrased: the licence does not allow quoting
How the literature uses it
225 arXiv papers cite this in 374 sentences
Papers citing it · 225 sentences without a confident label
Contests it 1 paper
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We found that inserting popular parametrizations such as the GBW model [ref] into higher correlations of the dipole operator, <ref>, leads to inconsistencies for higher-order $N$-point functions, where e.g. the absence of cancellatiosn in the quadrupole correlation leads to a non-vanishing constant even for $||→∞$, resulting in divergent amplitudes.
Saturation effects in exclusive vector meson production in DIS · Proton hotspot model · contest 0.84
Builds on it 2 papers
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First of all, we made evaluations in the GBW model [ref] extended to the $b$-dependent partial amplitude $f_q̅q^N(r⃗,b⃗)$.
DVCS via color dipoles: Nonperturbative effects · GBW based partial dipole amplitude · 0.98
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In particular, we first study the Golec-Biernat Wusthoff (GBW) model [ref] , extended to include a spatially dependent target and angular correlations.
Diffractive dijet production in impact parameter dependent saturation models · Introduction · 0.96
Uses its method or tool 45 papers
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This calculation takes fragmentation into account by assigning the neutrino a fixed fraction of the momentum of the mother meson, and is done using the saturation model of Golec-Biernat and Wüstoff [ref] described above.
Prompt neutrino fluxes from atmospheric charm · Results and discussion · 0.88
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We use the $s$-dependent dipole cross section proposed in [ref] , which saturates at large separations in analogy to the $x$-dependent one proposed in [ref] .
Real Compton Scattering via Color Dipoles · Photoabsorption · 0.84
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At small $Q^2$ we employ the $s$-dependent parametrization of the dipole cross section [ref] , which is similar to the $x$-dependent GBW parametrization [ref] , but is more suitable for soft processes [equation] These parameters and the scale $s_0=1000$ GeV$^2$ are fitted to data on DIS, real photoproduction and $πp$ scattering.
Neutrino-production of single pions: dipole description · Numerical results · 0.84
Uses its data or values 31 papers
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The dipole cross section parameters, $σ_0=29 mb, x_0=4·10^-5$ and $λ=0.28$, are taken from [ref] (Fit 2 with charm).
Diffractive structure function F_L^D from fits with higher twist · Twist–4 contribution · 1.00
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The initial condition is given by a form motivated by the momentum space Golec-Biernat, Wusthoff (GBW) model [ref] , and the fit is performed to the reduced cross section data from HERA [ref] , and consistent description is achieved.
Revisiting gluon density from the BK equation with kinematical constraint and large x terms · Introduction · 0.86
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The parameters $λ, σ_0$ and $x_0$ are given in Table ([ref]) [ref] .
Charmed Meson Production in Deep Inelastic Scattering · $D$-Meson production in the color-dipole model · 0.90
Compares with it 12 papers
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The refitted parameters are close to the original values from [ref] with around $10 %$ decrease of the power $λ$ in the saturation scale ([ref]), see Table 1.
Saturation model of DIS : an update · Conclusions · 0.97
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First, data are compared with the energy-dependent hot-spot model by Cepila et al. [ref] , where the energy evolution is given by two sources: the Golec-Biernat Wüsthoff model [ref] and the growth in the number of hot spots inside a nucleon to mimic the growth of the gluon density with energy [ref] .
Evidence for J/$\psi$ suppression in incoherent photonuclear production · Introduction · 0.95
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In a separate dedicated analysis, we have compared the numerical results for the integrated diffractive $γp→V p$ photoproduction cross section obtained with the original GBW model [ref] discussed above and with the updated GBW fit accounting for heavy quarks [ref] .
Exclusive photoproduction of excited quarkonia in ultraperipheral collisions · Numerical results for $γp→V p$ cross sections · 0.98
Cites it as support 3 papers
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Such models successfully described all the data on deep inelastic scattering, including the behavior of inclusive and diffractive cross sections, at a low value of photon virtuality [ref] .
Soft processes at high energy without soft Pomeron: a QCD motivated model · Introduction · 0.97
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For example, in the small-$x$ region, we expect that $q̂$ depends on the gluon saturation scale, which exhibits a power-law behavior as $Q_s^2 ∝x^-1/3$ [ref] .
Probing the jet transport coefficient of cold nuclear matter in electron-ion collisions · Framework and previous results of the analysis · 0.98
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This result supports the numerous saturation models that describes well the experimental data [ref] .
Summing Pomeron loops in the dipole approach · Conclusions · 0.97
Cites it as background 36 papers
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Since the publication [ref] , numerous fits with the dipole picture of DIS were performed.
Saturation model of DIS : an update · Introduction · 0.93
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In Ref. [ref] , following Golec-Biernat–Wüsthoff (GBW) model [ref] , function $Q_s(x)$ – called saturation scale – was taken in the following form
Quantitative Study of Different Forms of Geometrical Scaling in Deep Inelastic Scattering at HERA · Introduction · 0.80
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Here [equation] is Bjorken $x$ variable, $M_p$ stands for the proton mass, and the saturation scale $Q_s$ takes the following form [ref] [equation] Here $Q_0$ and $x_0$ are free parameters which can be fitted to the data within some specific model of DIS, and exponent $λ$ is a dynamical quantity of the order of $λ∼0.3$.
Quantitative Study of Geometrical Scaling in Deep Inelastic Scattering at HERA · Introduction · 0.90
Discussion
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