In this paper we discuss a well known QCD result: the steep increase of Green's function for exchange of $n$ BFKL Pomerons $G_{n \pom}\Lb Y\Rb\propto \exp\Lb \frac{n^2}{N^2_c} Δ_{\mbox{\tiny BFKL}} Y\Rb$ where $N_c $ is the number of colours ,Y is the rapidity and $Δ_{\mbox{\tiny BFKL}}$ is the intercept of the BFKL Pomeron. We consider this problem in the framework of the simple Pomeon models in zero transverse dimensions, which have two advantages :(i) they allow to take into account all shadowing corrections, including the summation of the Pomeron loops and (ii) they have the same as in QCD striking increase of $G_{n \pom}\Lb Y\Rb $. We found that the strength of shadowing corrections is not enough to stop the increase of the scattering amplitude with energy in contradiction to the unitarity constraints. Hence, our answer to the question in the title is positive.We believe that we need to search an approach beyond of the BFKL Pomeron calculus to treat $1/N_c$ corrections in Colour Glass Condensate effective theory.
We evaluate the unintegrated gluon distribution of the proton starting from a parametrization of the color dipole cross section including DGLAP evolution and saturation effects. To this end, we perform the Fourier-Bessel transform of $σ(x,r)/α(r)$. At large transverse momentum of gluons we match the so-obtained distribution to the logarithmic derivative of the collinear gluon distribution. We check our approach by calculating the proton structure function $F_L(x,Q^2)$ finding good agreement with HERA data.
We investigate $ρ$ vector meson production in $ep$ collisions at HERA with leading neutrons in the dipole formalism. The interaction of the dipole and the pion is described in a mixed-space approach, in which the dipole-pion scattering amplitude is given by the Marquet-Peschanski-Soyez saturation model, which is based on the travelling wave solutions of the nonlinear Balitsky-Kovchegov equation. We estimate the magnitude of the absorption effects and compare our results with a previous analysis of the same process in full coordinate space. In contrast with this approach, the present study lead…
We show that the geometric scaling of the dipole cross section can be explained using standard DGLAP perturbative evolution. The DGLAP improved saturation model due to the Laplace transforms method is considered at LO and NNLO approximations from the experimental data by relying on a Froissart-bounded parametrization of $F_{2}(x,Q^{2})$. These results are comparable with Golec-Biernat-W$\ddot{\mathrm{u}}$sthoff (GBW) model in a wide kinematic region $rQ_{s}$ which takes into account charm mass. The successful description of $σ_{\mathrm{dip}}(x,r)/σ_{0}$ and $σ_{\mathrm{dip}}(rQ_{s})/σ_{0}$ are…
We present results from analytic solutions to the running coupling, full next-to-leading order, and collinearly improved next-to-leading order Balitsky-Kovchegov equations in the saturation region with the smallest dipole size QCD running coupling prescription. The analytic results of the $S$-matrix of the latter two equations show that the $\exp(-\mathcal{O}(Y^{3/2}))$ rapidity dependence of the solutions are replaced by $\exp(-\mathcal{O}(Y))$ dependence once the running coupling prescription is switched from parent dipole to the smallest dipole prescription, which indicate that the $S$-matr…
Constraining the Dipole Amplitude at NLO with HERA Data and Probing Gluon Saturation in SIDIS
Department of Physics, University of Jyv\"askyl\"a, P.O. Box 35, 40014 University of Jyv\"askyl\"a, Finland；Helsinki Institute of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
Gluon saturation and Feynman scaling in leading neutron production
在本文中，我们扩展的颜色偶极子形式主义的领导中子生产的研究在$e + p \rightarrow e + n + X$碰撞在高能量和估计相关的可观测量，这是在HERA测量，并可能在未来的电子-质子（$ep$）对撞机进行分析。特别地，我们计算了领先中子的Feynman $x_F$分布，它用π介子通量和光子-π介子总截面表示。在色偶极理论中，光子-π散射截面用偶极-π散射振幅来描述，它包含了高能QCD动力学和胶子饱和效应的信息。我们考虑不同的模型的散射振幅，这已被用来描述包容性和衍射$ep$ HERA数据。此外，我们的预测与描述的π通量的模型依赖性进行了详细的分析。我们发现最近公布的H1领先中子谱可以用色偶极形式再现，这些谱可以帮助我们更清楚地观察胶子饱和效应在未来的$ep$对撞机。
In this work we consider the QCD parton saturation models to describe soft interactions at the high energy limit. The total and elastic cross sections as well as the elastic slope parameter are obtained for proton-proton and pion-proton collisions and compared to recent experimental results. The analyses are done within the color dipole formalism taking into account saturation models which have been tested against DIS data. The main point is that the match between soft and hard interaction occurs in the saturation region which can be described by high density QCD approaches. Discussion is perf…
We investigate saturation effects in $ep$ scattering as well as in ultraperipheral $p$A and AA collisions at small $x$ with four variants of the impact parameter dependent color dipole model: with and without gluon saturation and with and without a novel mechanism that suppresses unphysical dipole radii above the confinement scale, a problem not addressed by most implementations. We show that $ep$ scattering at HERA can be very well described by any of the four variants. When going from $ep$ to $e$A scattering, saturation effects are expected to increase as $\sim$A$^{1/3}$. In lieu of an elect…
We present a modification of the DGLAP improved saturation model with respect to the nonlinear correction (NLC). The GLR-MQ improved saturation model is considered by employing the parametrization of proton structure function due to the Laplace transforms method, which preserves its behavior success in the low and high $Q^{2}$ regions. We show that the geometric scaling holds for the GLR-MQ improved model in a wide kinematic region $rQ_{s}$. These results are comparable with other models in a wide kinematic region $rQ_{s}$. The behavior of the dipole cross sections, with respect to the GLR-MQ …
We present an updated impact parameter dependent saturation model (IPsat) determined trough a fit to the combined HERA I and I+II reduced cross section data. The same HERA data are used to fit the linearized (IPnonsat) version of the applied dipole amplitude, which makes it possible to estimate the magnitude of the saturation effects in various experiments. We find that both parametrizations provide comparable descriptions of the considered data when an effective confinement scale dynamics is incorporated with quark masses. Moreover, it is possible to consistently determine the light and charm…
Forward production of Drell-Yan dileptons at high energies and low dilepton invariant masses in a $k_t$-factorization approach: Do we see onset of saturation?
We investigate events with very forward neutrons in $ep$ collisions at HERA using impact parameter dependent colour dipole models with and without saturation. This is the first study of the leading neutron process deploying these models. The model predictions are compared with the available HERA measurements for $6<Q^2<100$~GeV$^2$, $70<W<245$~GeV. Our analysis shows that the models exhibit Feynman scaling, independent of $Q^2$. Our results demonstrate that the $W$ and $Q^2$ dependence of the cross section is independent of the presence of a forward neutron as predicted by the limiting fragmen…
We explore possible extensions of the $t$-channel and $s$-channel unitary model of high energy evolution in zero transverse dimensions appropriate to very high energy/atomic number where the dipole density in a toy hadron is parametrically high.We suggest that the appropriate generalization is to allow emission of more than one dipole in a single step of energy evolution. We construct explicitly such a model that preserves the $t$-channel and s-channel unitarity and have the correct low density limit, and study the particle multiplicity distribution resulting from this evolution. We consider i…
