We calculate the contribution from the $q\bar{q}g$ component of a virtual photon state to the small-$x$ diffractive cross section in deep inelastic scattering in the saturation regime. The obtained cross section is finite by itself and a part of the full next-to-leading order result. We perform the calculation in exact kinematics in the eikonal limit, and show that the previously known high virtuality $Q^2$ and large invariant mass $M_X^2$ results for the structure functions can be extracted. We furthermore discuss the steps required to obtain the full next-to-leading order result.
We consider the diffractive photo-production of vector mesons on a proton, in the dipole model. We take into account the effect of the fluctuations of the the dipole size, whose magnitude is controlled by the overlap between the photon and the vector meson wave functions. Our predictions for the incoherent diffractive cross section, obtained within the Impact Parameter Saturation Model (IPSat), are shown to be in excellent agreement with the HERA data on $J/Ψ$ photo-production, down to very low momentum transfer, where the dipole size fluctuations are shown to play an essential role. This stud…
We discuss recent developments towards next-to-leading order (NLO) accuracy in the dipole picture. We review recent NLO results for exclusive vector meson production and diffractive structure functions, and discuss how it is becoming possible to describe both inclusive and exclusive DIS data simultaneously within the Color Glass Condensate framework at NLO accuracy. These developments will make it possible to probe the gluon saturation phenomena in detail especially when nuclear-DIS data from the EIC become available.
We calculate cross sections and transverse momentum distributions for the incoherent diffractive production of vector mesons $J/ψ$ and $Υ$ on heavy nuclei. In distinction to coherent diffraction, the nucleus is allowed to break up, but except for the vector meson no new particles are produced in the reaction. Within the color dipole approach, we derive the multiple scattering expansion of the incoherent diffractive cross section as an expansion over quasielastic scatterings of the color dipole. We also compare our results to the measurement of the ALICE collaboration for incoherent $J/ψ$ produ…
We calculate the contribution from the $q \bar q g$ state production to the diffractive cross sections in deep inelastic scattering at high energy. The obtained cross section is finite by itself and a part of the full next-to-leading order result for the diffractive structure functions. We perform the calculation in exact kinematics in the eikonal limit, and show that the previously known high-$Q^2$ and large $M_X^2$ results for the structure functions can be extracted from our results in the appropriate limits. We furthermore discuss the steps required to obtain the full next-to-leading order…
We present the first evaluation of the color dipole diffraction slope from the data on diffractive photo- and electroproduction of vector mesons. The energy and dipole size dependence of the found dipole diffraction slope are consistent with the color dipole gBFKL dynamics.
We analyse the newest diffractive deep inelastic scattering data from the DESY collider HERA with the help of dipole models. We find good agreement with the data on the diffractive structure functions provided the diffractive open charm contribution is taken into account. However, the region of large diffractive mass (small values of a parameter beta) needs some refinement with the help of an additional gluon radiation.
We present the first evaluation of color dipole cross section from experimental data on diffractive photo- and electroproduction of vector mesons. The dipole-size and energy dependence of the found dipole cross section is consistent with expectations from the BFKL dynamics.
We review the recent progress in the theory of diffractive DIS, focusing on predictions of strong breaking of the Ingelman-Schlein-Regge factorization and the related breaking of the GLDAP evolution for the diffractive structure function.
We determine the diffractive scattering amplitude of a color-dipole on a nucleon using a non-perturbative model of QCD which contains only parameters taken from low-energy physics. This allows to relate specific features of the confinement mechanisms with diffractive electro-production processes and structure functions. The agreement with phenomenological data is satisfactory.
We present a precise comparison of the results of the dipole models with the newest data from HERA on the diffractive open charm production. We found good agreement with the data on the diffractive open charm production both for the the gluon distributions from the considered dipole models and the DGLAP fits to HERA data from our earlier analysis for diffractive parton distributions with higher twist. We also show that exclusive diffractive charm production can practically be neglected
Starting from the phenomenologically successful color dipole representation of the diffractive structure function, we identify the dominant contribution to the diffractive cross section at small beta. The beta dependence is calculated taking advantage of the Regge factorization properties of the hard mechanism which drives the dependence on the diffractive mass. We impose the unitarity constraints on the $x_\Pom$-dependence and comment on the screening corrections to $F_{2p}$.
In this presentation, we obtain the corresponding universal function to the diffractive process and show the cross section exhibits the geometrical scaling. It is observed the diffractive theory according to the color dipole approach at small-$x$ is a convenient framework that reveals the color transparency and the saturation phenomena. Also we calculate the contribution of heavy quark productions in the diffractive cross section for high energy that is determined by the small size dipole configuration. The ratio of the diffractive cross section to the total cross section in the electron-proto…
We analyse the newest diffractive deep inelastic scattering data from HERA using the dipole model approach. We find a reasonable good agreement between the predictions and the data although the region of small values of a kinematic variable $β$ needs refinement. A way to do this is to consider an approach with diffractive parton distributions evolved with the DGLAP evolution equations.
It is argued that the QCD dipole picture allows to build an unified theoretical description -based on BFKL dynamics- of the total and diffractive nucleon structure functions. This description is in qualitative agreement with the present collection of data obtained by the H1 collaboration. More precise theoretical estimates, in particular the determination of the normalizations and proton transverse momentum behaviour of the diffractive components, are shown to be required in order to reach definite conclusions.
The diffractive t-slope, B_V, of elastic charmonia (V=J/psi, psi') photo- and leptoproductions off a nucleon is studied at low |t| (< 1 GeV^2) in the leading logarithmic approximation of perturbative QCD, with a special emphasis on the space-time evolution of the c\bar{c}-dipole. We obey a framework based on QCD factorization, which describes a certain Fermi motion effect due to the $c(\bar{c})$-quarks in the proper manner and includes appropriately kinematical corrections of the momentum transfer Delta_perp in the t-channel. Assuming the universal two-gluon form factor of the nucleon, we show…
The $F_{2}$, $F_{G}$, $R=F_{L}/F_{T}$ proton structure functions are derived in the QCD dipole picture of BFKL dynamics. We get a three parameter fit describing the 1994 H1 proton structure function $F_{2}$ data in the low $x$, moderate $Q^{2}$ range. Without any additional parameter, the gluon density and the longitudinal structure functions are predicted.The diffractive dissociation processes are also discussed, and a new prediction for the proton diffractive structure function is obtained.
Effects of coherence in neutrino-production of pions off nuclei are studied employing the color dipole representation and path integral technique. If the nucleus remains intact, the process is controlled by the interplay of two length scales. One is related to the pion mass and is quite long (at low Q^2), while the other, associated with heavy axial-vector states, is much shorter. The Adler relation is found to be broken at all energies, but especially strongly at ν> 10 GeV, where the cross section is suppressed by a factor ~A^{-1/3}. On the contrary, in a process where the recoil nucleus brea…
We study the hard color dipole-nucleon cross section within perturbative QCD and discuss its relation to observables in diffractive leptoproduction of heavy quarkonium. The dipole cross section calculated with the unintegrated gluon density of the nucleon substantially differs from the well-known perturbative form $σ_{dip} \sim b^2$ for $b > 0.3$fm, where $b$ is the transverse separation of the dipole. We show the measured ratio of $ψ'$ to $J / ψ$ photoproduction cross sections constrains the dipole cross section at intermediate $b$, and in fact excludes the simple $σ_{dip} \sim b^2$ behavior.…
We extract the S-matrix element for dipole-proton scattering using the data on diffractive electroproduction of vector mesons at HERA. By considering the full t dependence of this process we are able to reliably unfold the profile of the S-matrix for impact parameter values b>0.3 fm. We show that the results depend only weakly on the choice of the form for the vector meson wave function. We relate this result to the discussion about possible saturation effects at HERA.
The QCD dipole picture allows to build an unified theoretical description -based on BFKL dynamics- of the total and diffractive nucleon structure functions. We use a four parameter fit to describe the 1994 H1 proton structure function F2 data in the low x, moderate Q2 range. Without any additional parameter, the gluon density and the longitudinal structure functions are predicted. The diffractive dissociation processes are discussed within the same framework, and a new 6 parameter fit of the 1994 H1 data is performed which leads to a comprehensive description of F2D(3).
We study the diffractive photo- and leptoproductions of $J / ψ$ and $ψ'$ on the proton, and examine the validity of the small-size color dipole approximation to the production of radially excited heavy quarkonium. The dipole model predicts a small ratio of $ψ'$ to $J / ψ$ photoproduction cross sections, which does not agree with experimental data. We show that this discrepancy originates from a large transverse size of $ψ'$ which makes the convergence of the transverse size expansion questionable, and the calculation without the dipole approximation turns out to be consistent with the data. Pr…
Combining the QCD dipole model with the Good and Walker picture, we formulate diffractive dissociation of a photon of virtuality Q^2 off a hadronic target, in the kinematical regime in which Q is close to the saturation scale and much smaller than the invariant mass of the diffracted system. We show how the obtained formula compares to the HERA data and discuss what can be learnt from such a phenomenology. In particular, we argue that diffractive observables in these kinematics provide useful pieces of information on the saturation regime of QCD.
We further analyze the holographic dipole-dipole scattering amplitude developed in arXiv:1202.0831, 1205.3223. Gribov diffusion at strong coupling yields the scattering amplitude in a confining background. We compare the holographic result for the differential cross section to proton-proton and deeply virtual Compton scattering data.
Through a determination of the $S$-matrix element for the scattering of a localized colour dipole on a proton, we show that saturation effects can already be sizable at HERA. The saturation scale is found to be around 1-1.5 $GeV^2$ for the highest available energies and for central collisions, and is a decreasing function of the impact parameter.
We discuss two different models for the impact parameter dependent dipole cross section: one based on DGLAP evolution and the other inspired by the Balitsky-Kovchegov equation. The parameters are determined from fits to data on the total gamma* p cross section measured at HERA. The impact parameter dependent saturation scale is extracted. Predictions are then confronted with HERA data on exclusive diffractive vector meson production and deeply virtual Compton scattering. Finally, predictions are given for the cross sections of exclusive photoproduced J/psi and Upsilon mesons, and Z^0 bosons, e…
We develop the color dipole phenomenology of diffractive photo- and electroproduction $γ^{*}\,N\rightarrow V(V')\,N$ of light vector mesons ($V(1S) = ϕ^0, ω^0, ρ^0$) and their radial excitations ($V'(2S) = ϕ', ω', ρ'$). The node of the radial wave function of the $2S$ states in conjunction with the energy dependence of the color dipole cross section is shown to lead to a strikingly different $Q^2$ and $ν$ dependence of diffractive production of the $V(1S)$ and $V'(2S)$ vector mesons. We discuss the restoration of flavor symmetry and universality properties of production of different vector mes…
We predict the cross-section for diffractive $ϕ$ electroproduction within the dipole model, using a holographic meson wavefunction for the $ϕ$. For the dipole cross-section, we use the Color Glass Condensate dipole model whose parameters are fitted to the latest 2015 combined HERA data on Deep Inelastic Scattering. Choosing a strange quark mass of $0.14$ GeV, we find good agreement with the available data.
We present a simultaneous analysis, within an impact parameter dependent saturated dipole model, of exclusive diffractive vector meson (J/psi, phi and rho) production, deeply virtual Compton scattering and the total gamma* p cross section data measured at HERA. Various cross sections measured as a function of the kinematic variables Q^2, W and t are well described, with little sensitivity to the details of the vector meson wave functions. We determine the properties of the gluon density in the proton in both longitudinal and transverse dimensions, including the impact parameter dependent satur…
We present a partonic picture for diffractive onium-nucleus scattering in the large-number-of-color limit from which the distribution of rapidity gaps in a certain kinematic region can be deduced. This picture allows us to draw a parallel between diffractive dissociation and the genealogy of partonic evolution, the latter being essentially similar to a branching-diffusion process in which the branching is the parton splitting, and the diffusion occurs in the transverse momenta of the partons. In particular, we show that the rapidity gap distribution corresponds to the distribution of the split…
We study coherent diffractive dijet production in electron-hadron and electron-nucleus collisions within the dipole picture. We provide semi-analytic results for the differential cross section and elliptic anisotropy in the angle between dijet transverse momentum and hadron recoil momentum. We demonstrate the direct relation between angular moments of the dipole amplitude in coordinate space and angular moments of the diffractive dijet cross sections. To perform explicit calculations we employ two different saturation models, extended to include the target geometry. In the limit of large photo…
We calculate proton and nuclear diffractive structure functions in the IPsat (Kowalski-Teaney) dipole model. This parametrization has previously been shown to provide good agreement with inclusive F_2 measurements and exclusive vector meson measurements at HERA. We discuss how the impact parameter dependence crucially affects our analysis, in particular for small beta.
We have in earlier papers presented an extension of Mueller's dipole cascade model, which includes subleading effects from energy conservation and running coupling as well as colour suppressed effects from pomeron loops via a ``dipole swing''. The model was applied to describe the total cross sections in pp and gamma*p collisions. In this paper we present a number of improvements of the model, in particular related to the confinement mechanism. A consistent treatment of dipole evolution and dipole--dipole interactions is achieved by replacing the infinite range Coulomb potential by a screened …
We study exclusive dijet production in coherent diffractive processes in deep inelastic scattering and real (and virtual) photon-hadron ($γ^{(*)}$-h) collisions in the Color Glass Condensate formalism at leading order. We show that the diffractive dijet cross section is sensitive to the color-dipole orientation in the transverse plane, and is a good probe of possible correlations between the $q\bar{q}$-dipole transverse separation vector $\r$ and the dipole impact parameter $\b$. We also investigate the diffractive dijet azimuthal angle correlations and $t$-distributions in $γ^{(*)}$-h collisi…
Predictions for deep Virtual Compton Scattering are obtained in a two-component dipole model of diffraction. The model automatically includes hard and soft components and implicitly allows for ``hadronic'' contributions via large dipoles. It is also applicable to real Compton Scattering, which provides an important constraint.
Within the colour dipole picture for deep inelastic scattering at small Bjorken $x$, we study the production of a pair of relatively hard jets via coherent diffraction. By "relatively hard" we mean that the transverse momenta of the two jets -- the quark ($q$) and the antiquark ($\bar{q}$) generated by the decay of the virtual photon -- are much larger than the target saturation momentum $Q_s(Y_{\mathbb{P}})$ evaluated at the rapidity gap $Y_{\mathbb{P}}$. We argue that the typical final-state configurations are such that the hard $q\bar q$ dijets are accompanied by a semi-hard gluon jet, with…
Using the QCD dipole picture of the BFKL pomeron, the cross-section of single diffractive dissociation of virtual photons at high energy and large diffractively excited masses is calculated. The calculation takes into account the full impact-parameter phase-space and thus allows to obtain an exact value of the triple BFKL Pomeron vertex. It appears large enough to compensate the perturbative 6-gluon coupling factor (alpha/pi)^3 thus suggesting a rather appreciable diffractive cross-section.
We studied the $ep\rightarrow ep+2jets$ diffractive cross section with ZEUS phase space. Neglecting the $t$-channel momentum in the Born and gluon dipole impact factors, we calculated the corresponding contributions to the cross section differential in $β=\frac{Q^{2}}{Q^{2}+M_{2jets}^{2}}$ and the angle $ϕ$ between the leptonic and hadronic planes. The gluon dipole contribution was obtained in the exclusive $k_{t}$-algorithm with the exclusive cut $y_{cut}=0.15$ in the small $y_{cut}$ approximation. In the collinear approximation we canceled singularities between real and virtual contributions…
We discuss diffractive photon-production of vector mesons in holographic QCD. At large $\sqrt{s}$, the QCD scattering amplitudes are reduced to the scattering of pair of dipoles exchanging a closed string or a pomeron. We use the holographic construction in AdS$_5$ to describe both the intrinsic dipole distribution in each hadron, and the pomeron exchange. Our results for the heavy meson photon-production are made explicit and compared to some existing experiments.
We demonstrate that hard dijet production via coherent inelastic diffraction is a promising channel for probing gluon saturation at the Electron-Ion Collider. By $inelastic$ diffraction we mean a process in which the two hard jets - a quark-antiquark pair generated by the decay of the virtual photon - are accompanied by a softer gluon jet, emitted by the quark or the antiquark. This process can be described as the elastic scattering of an effective gluon-gluon dipole. The cross section takes a factorised form, between a hard factor and a unintegrated ("Pomeron") gluon distribution describing t…
The AdS/QCD holographic wave function of basis light-front quantization (BLFQ) for vector meson $J/ψ$ is applied in this manuscript. The exclusive production of $J/ψ$ in diffractive process is computed in dipole model with AdS/QCD holographic wave function. We use IP-Sat and IIM model in the calculation of the differential cross section of the dipole scattering off the proton. The prediction of AdS/QCD holographic wave function in BLFQ gives a good agreement to the experimental data.
Inspired by a recent study of Iancu, Mueller and Triantafyllopoulos [1] and earlier papers by Golec-Biernat and Wusthoff [2,3], we propose semi-inclusive diffractive deep inelastic scattering (SIDDIS) to investigate the gluon tomography in the nucleon and nuclei at small-$x$. The relevant diffractive quark and gluon parton distribution functions (DPDF) can be computed in terms of the color dipole S-matrices in the fundamental and adjoint representations, respectively. Novel correlations from the gluon tomography in the dipole S-matrix can be experimentally studied through the DPDFs in these pr…
In this work we study the diffractive photoproduction of $J/Ψ$ in proton-proton, proton - nucleus and nucleus - nucleus collisions at LHC energies using the color dipole formalism and different models for the forward dipole - target scattering amplitude. Our goal is to estimate the theoretical uncertainty present in the current predictions in the literature. Our results are compared with the experimental data and predictions for higher energies are presented.
Using the eikonal approximation, we show that inclusive gluon production is related to the scattering of a gluon-gluon dipole while diffractive gluon production in DIS is related to a two-$q\bar q$ dipole scattering amplitude. Hence diffractive photon dissociation cross-sections are observables that provide potential information on dipole correlations, which represent an open issue in high-energy QCD.
We present the color dipole phenomenology of diffractive photo- and electroproduction $γ^{*} N\to V(V') N$ of vector mesons ($V(1S) = ϕ^0, ω^0, ρ^0, J/Ψ, Υ$) and their radial excitations ($V'(2S) = ϕ', ω', ρ', Ψ', Υ'$). The main emphasis is related to light vector mesons. We discuss how the energy dependence of the color dipole cross section in conjuction with the node of the radial wave function of the $2S$ states can lead to an anomalous $Q^2$ and energy dependence of diffractive production of $V'(2S)$ vector mesons. The color dipole model predictions for $V(1S)$ light vector meson productio…
A Dyson-Schwinger-based model of pomeron exchange is employed to calculate diffractive rho-, phi- and J/psi-meson electroproduction cross sections. It is shown that the magnitude of the current-quark mass m_f of the quark and antiquark inside the produced vector meson determines the onset of the asymptotic-q^2 power-law behavior of the cross section, and how correlated quark-exchanges are included to provide a complete picture of the diffractive electroproduction of light vector mesons applicable over all energies and photon momenta q^2.
We compute cross sections for incoherent and coherent diffractive J/$Ψ$ and $Ψ(2S)$ production in ultraperipheral heavy ion collisions. The dipole models used in these calculations are obtained by fitting the HERA deep inelastic scattering data and compared with available electron-proton diffraction measurements. We obtain a reasonably good description of the available ALICE data. We find that the normalization of the ultraperipheral cross section has large model dependence, but the rapidity dependence is more tightly constrained.
We propose a new description of inclusive diffraction in deep inelastic scattering (DIS). The diffractive structure functions are expressed in the dipole picture and contain heavy-quark contributions. The dipole scattering amplitude, a saturation model fitted on inclusive DIS data, features a saturation scale Q_s(x) larger than 1 GeV for x=10^{-5}. The q\bar{q}g contribution to the diffractive final state is modeled in such a way that both the large-Q^2 and small-beta limits are implemented. In the regime xpom<0.01 in which saturation is expected to be relevant, we obtain a parameter-free desc…
The cross section of the diffractive Drell-Yan (DY) process, pp->(l-lbar X)p, where the system (l-lbar X) is separated by a large rapidity gap from the recoil proton, is calculated in the light-cone dipole approach. This process reveals unusual features, quite different from what is known for diffractive DIS and nonabelian radiation: (i) the diffractive radiation of a heavy dilepton by a quark vanishes in the forward direction; (ii) the diffractive production of a dilepton is controlled by the large hadronic radius; (iii) in contrast with DIS where diffraction is predominantly soft, the diffra…
Using the Good and Walker picture, we derive a simple formula for diffractive dissociation that can apply to recent data collected at HERA in the low Q2 regime.
In this thesis, we study the detailed partonic content of the quantum states of a quark-antiquark color dipole subject to high-energy evolution, which are represented by a set of dipoles generated by a stochastic binary branching process, in the scattering off a large nucleus, and produce predictions for diffractive dissociation in electron-ion collisions, based on the dipole picture of QCD. Our main results are as follows. First, the scattering events of a color dipole, when parameters are set in such a way that the total cross section is small, are triggered by rare partonic fluctuations, wh…
We suggest a simple physical picture for the diffractive parton distributions that appear in diffractive deeply inelastic scattering. In this picture, partons impinging on the proton can have any transverse separation, but only when the separation is small can they penetrate the proton without breaking it up. By comparing the predictions from this picture with the diffractive data from HERA, we determine rough values for the small separations that dominate the diffraction process.
We present a new technique to calculate the cross-section for diffractive vector meson production and DVCS in electron-ion collisions based on the dipole model. The measurement of these processes can provide valuable information on non-linear QCD phenomena, such as gluon saturation, and is the the only known way to gain insight into the spatial distribution of gluons in nuclei. We present predictions of differential cross-section distribution $dσ/dQ^2$ and $dσ/dt$ for $J/ψ$ and $ϕ$ meson production for diffractive processes of heavy nuclei and demonstrate the feasibility of extracting the gluo…
We demonstrate that study of large t vector meson photoproduction with rapidity gaps in ultraperipheral proton-ion and ion-ion collisions at LHC would allow to investigate the energy dependence of cross section of elastic scattering of a small dipole off the parton over a wide range of energies $10^3 < s_{dipole - parton} < 10^6 GeV^2$ where this cross section is expected to change by a factor $\ge 20$. The accessible energy range exceeds the one reached at HERA by a factor of 10 both in $γp$ and in $γA$ scattering. In addition, study of A-dependence of this process will allow to determine the…
We calculate azimuthal correlations between the exclusively produced vector meson and the scattered electron in Deep Inelastic Scattering processes at the future Electron-Ion Collider (EIC). We identify "kinematical" and "intrinsic" contributions to these correlations, and show that the correlations are sensitive to the non-trivial correlations in the gluon distribution of the target. Realistic predictions at the EIC kinematics are provided using two different approaches to describe the dipole-proton interaction at relatively small $x$.
Using the pre-LHC and LHC data for $πp$ and $pp$ diffractive collisions we study the ultrahigh energy asymptotic regime in the framework of the black disk picture. The black disk picture, being constrained by the s-channel unitarity condition and the $t$-channel analyticity, gives rather definite predictions for diffractive processes increasing with the energy. To deal with the data, we consider the Dakhno-Nikonov eikonal model which predicts a growth of the $\ln^2s$ type for total and elastic cross sections and $(τ={\bf q}_\perp^2\ln^2s)$-scaling for diffractive scattering and diffractive dis…
