The asymptotic freedom is known to split the leading-$\log$ BFKL pomeron into a series of isolated poles in the complex angular momentum plane. One of our earlier findings was that the subleading hard BFKL exchanges decouple from such experimentally important observables as small-$x$ charm, $F_2^c$, and the longitudinal, $F_L$, structure functions of the proton at moderately large $Q^2$. For instance, we predicted precocious BFKL asymptotics of $F_2^c(x,Q^2)$ with intercept of the rightmost BFKL pole $α_{\Pom}(0)-1=Δ_{\Pom}\approx 0.4$. On the other hand, the small-$x$ open beauty photo- and electro-production probes the vacuum exchange for much smaller color dipoles which entails significant subleading vacuum pole corrections to the small-$x$ behavior. In view of the accumulation of the experimental data on small-$x$ $F_{2}^{c}$, $F_{2}^{b}$ and $F_{L}$ we extend our early predictions to the kinematical domain covered by new HERA measurements. Our parameter-free results agree well with the determination of $F_2^c$, $F_L$ and published H1 results on $F_2^b$ but slightly overshoot the very recent (2008, preliminary) H1 results on $F_2^b$.
We calculate the Regge trajectories of the subleading BFKL singularities and eigenfunctions for the running BFKL pomeron in the color dipole representation. We obtain a viable BFKL-Regge expansion of the proton structure function $F_{2p}(x,Q^2)$ in terms of several rightmost BFKL singularities. We find large subleading contributions to $F_{2p}(x,Q^2)$ in the HERA kinematical region which explains the lack of a predictive power of GLDAP-extrapolations of $F_{2p}(x,Q^2)$ to a domain of small $x$. We point out the relation of our early finding of the precocious BFKL asymptotics to the nodal struc…
We report an evaluation of subleading eigenvalues and eigenfunctions of the BFKL equation in the color dipole representation with a running gauge coupling. We present an expansion of the small-$x$ proton structure function $F_{2p}(x,Q^2)$ in terms of the rightmost BFKL-singularities. The BFKL-Regge phenomenology of DIS structure functions is developed which is shown to provide remarkably good description of the data on $F_{2p}(x,Q^2)$ from E665 to HERA.
We propose a phenomenological study of the next-to-leading Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach applied to the data on the proton structure function $F_2$ measured at HERA in the small-$x_{Bj}$ region.
We perform a BFKL-NLL analysis of forward jet production at HERA which leads to a good description of data over the full kinematical domain. We also predict the azimuthal angle dependence of Mueller-Navelet jet production at the Tevatron and the LHC using the BFKL NLL formalism.
We show that the next-to-leading-order renormalization-group-improved asymptotically-free BFKL Pomeron provides a good fit to HERA data on virtual photoproduction at small x and large Q^2. The leading discrete Pomeron pole reproduces qualitatively the Q^2 dependence of the HERA data for x ~10^{-3}, and a fit using the three leading discrete singularities reproduces quantitatively the Q^2 and x dependence of the HERA data for x < 10^{-2}. This fit fixes the phase for all the BFKL wavefunctions at a chosen infrared scale.
In the framework of semihard QCD approach, with the emphasis on the BFKL evolution of gluon distributions, we calculate the differential cross sections of inclusive $D^{*\pm}$ mesons electroproduction at HERA and confront our results with available ZEUS experimental data.
The general properties of the Lipatov or BFKL equation are reviewed. Modifications to the infrared region are proposed. Numerical predictions for the deep-inelastic electron-proton structure functions at small $x$ are presented and confronted with recent HERA measurements.
As noticed by Fadin, Kuraev and Lipatov in 1975 incorporation of asymptotic freedom into the BFKL equation splits the QCD pomeron into a series of isolated poles in complex angular momentum plane. Following our earlier work on the proton structure function we explore the phenomenological consequences of the emerging BFKL-Regge factorized expansion for the small-$x$ structure function of the pion $F_{2π}(x,Q^2)$. We calculate $F_{2π}$ in a small-$x$ region and find good agreement with the recent H1 determination of $F_{2π}(x,Q^2)$. We also present the BFKL-Regge factorization based evaluation o…
The BFKL equation and the kT-factorization theorem are used to obtain predictions for F2 in the small Bjorken-x region over a wide range of Q**2. The dependence on the parameters, especially on those concerning the infrared region, is discussed. After a background fit to recent experimental data obtained at HERA and at Fermilab (E665 experiment), we find that the predicted, almost Q**2 independent BFKL slope lambda >= 0.5 appears to be too steep at lower Q**2 values. Thus there seems to be a chance that future HERA data can distinguish between pure BFKL and conventional field theoretic renorma…
We present a BFKL phenomenology of structure functions in the framework of the generalized BFKL equation for the dipole cross section proposed by us recently. We show that the HERA measurements of excitation of charm at $Q^{2} \lsim $10 GeV$^{2}$ allow determination of the intercept of the BFKL pomeron. A comparison with the experimental data suggests a large contribution from the nonperturbative cross section for colour dipoles of large size $r$.
We show that next-leading logarithmic (NLL) Balitsky-Fadin-Kuraev-Lipatov (BFKL) effects can be tested by the forward-jet cross sections recently measured at HERA. For dσ/dx, the NLL corrections are small which confirms the stability of the BFKL description. The triple differential cross section dσ/dxdk_T^2dQ^2 is sensitive to NLL effects and opens the way for an experimental test of the full BFKL theoretical framework at NLL accuracy.
In the framework of semihard (k$_T$ factorization) QCD approach, we consider the differential cross sections of $D^{*\pm}$ meson production at HERA. The consideration is based on BFKL and CCFM gluon distributions. We find that in the case of BFKL LO gluon distribution the theoretical results are sensitive to the Pomeron intercept parameter $Δ$. We present a comparison of the theoretical results with available ZEUS experimental data.
In the framework of the semi-hard ($k_t-$factorization) approach, we analyze the various charm production processes in the kinematic region covered by the HERA experiments
A study of differential cross sections for the production of four jets in multi-Regge kinematics is presented, the main focus lying on azimuthal angle dependences. The theoretical setup consists in the jet production from a single BFKL ladder with a convolution of three BFKL Green functions, where two forward/backward jets are always tagged in the final state. Furthermore, the tagging of two further jets in more central regions of the detectors with a relative separation in rapidity from each other is requested. It is found, as result, that the dependence on the transverse momenta and the rapi…
Starting from the multi-Regge effective action for high-energy scattering in QCD a $t$-channel approach can be developed which is similar to the approach by White based on general Regge arguments. The BFKL kernel of reggeized gluon interaction, contributions to the $2 \rightarrow 4 $ reggeized gluon vertex function and the one-loop correction to the BFKL kernel are considered. The conditions are discussed under which this approach can provide a simple estimante of the next-to-leading logarithmic corrections to the BFKL perturbative pomeron intercept.
We consider scattering amplitudes in string models in the Regge limit of high energies and fixed momentum transfers with the use of the unitarity in direct channels. Intermediate states are taken in the multi-Regge kinematics corresponding to the production of resonances with fixed invariant masses and large relative rapidities. In QCD such kinematics leads to the BFKL equation for the Pomeron wave function in the leading logarithmic approximation. We derive a similar equation in the string theory and discuss its properties. The purpose of this investigation is to find a generalization of the …
Recently the H1 and ZEUS collaborations have presented cross sections for DIS events with a forward jet. The BFKL formalism is able to produce an excellent fit to these data. The extracted intercept of the hard pomeron suggests that when all higher order corrections are taken into account the cross section will still rise very rapidly as expected for low $x$ dynamics.
Elastic production of vector mesons $γ^{*} N\to V N$ is the pomeron-exchange dominated diffractive reaction with much potential of probing the BFKL pomeron. The BFKL pomeron can conveniently be described in terms of the dipole cross section which is a solution of the generalized BFKL equation. In this paper we discuss, how the energy and $Q^{2}$ dependence of elastic production of vector mesons at HERA will allow scanning the dipole cross section as a function of dipole size $r$. We show that determinaton of the intercept of the BFKL pomeron requires measuring the $ρ^{0}$ and $J/Ψ$ production …
We suggest a formula interpolating between the known asymptotic regimes of the BFKL equation as the approximate solution of that equation. The parameters appearing in this interpolation are fitted to the data on deep inelastic scattering in a wide range of the kinematical variables. Care is taken of the large-$x$ domain as well, outside the HERA kinematical region. The boundaries and the interface between various dynamical regimes are also studied.
We investigate the impact of so called kinematic constraint on gluon evolution at small $x$. Implanting the constraint on the real emission term of gluon ladder diagram, we obtain an integro-differential form of BFKL equation. Later we solve the equation analytically using the method of characteristics. We sketch the Bjorken x and transverse momentum $k_t^2$ dependence of our solution of unintegrated gluon distributions $f(x,k_t^2)$ in kinematic constraint supplemented BFKL equation and contrasted the same with original BFKL equation. Then we extract the collinear gluon density $xg(x,Q^2)$ fro…
We calculate the rate for the deep-inelastic electroproduction of dijets at HERA. We study the weakening of the azimuthal (back-to-back) correlation between the jets, as $x$ decreases, to see whether it can be used to identify BFKL dynamics from conventional fixed-order QCD effects. We show how this may give information on the transverse momentum ($k_T)$ dependence of the gluon distribution of the proton.
We show that the forward-jet measurements performed at HERA allow for a detailed study of corrections due to next-to-leading logarithms (NLL) in the Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach. While the description of the dσ/dx data shows small sensitivity to NLL-BFKL corrections, these can be tested by the triple differential cross section dσ/dxdk_T^2dQ^2 recently measured. These data can be successfully described using a renormalization-group improved NLL kernel while the standard next-to-leading-order QCD or leading-logarithm BFKL approaches fail to describe the same data in the whole ki…
We suggest a modified form of a unitarized BFKL equation imposing the so-called kinematic constraint on the gluon evolution in multi-Regge kinematics. The underlying nonlinear effects on the gluon evolution are investigated by solving the unitarized BFKL equation analytically. We obtain an equation of the critical boundary between dilute and dense partonic system, following a new differential geometric approach and sketch a phenomenological insight on geometrical scaling. Later we illustrate the phenomenological implication of our solution for unintegrated gluon distribution $f(x,k_T^2)$ towar…
Determination of the intercept of the BFKL pomeron is one of the pressing issues in the high energy physics. Earlier we have shown that, at the dipole size $r=r_Δ=(0.1-0.2)$f, the dipole cross section $σ(x,r)$ which is a solution of the generalized BFKL equation, exhibits a precocious asymptotic behavior $σ(x,r)\propto \left({1\over x}\right)^{Δ_{\Pom}}$. In this paper we discuss how measuring $F_{L}(x,Q^{2})$ and $\partial F_{T}(x,Q^{2})/\partial \log Q^{2}$ at $Q^{2}= (10-40)$GeV$^{2}$ and $Q^{2}=(2-10)$GeV$^{2}$, respectively, one can probe $σ(x,r_Δ)$ and directly determine the intercept $Δ…
We determine the infrared behaviour of the BFKL forward amplitude for gluon-gluon scattering. Our approach, based on the discrete pomeron solution, leads to an excellent description of the new combined inclusive HERA data at low values of x (<0.01) and at the same time determines the unintegrated gluon density inside the proton, for squared transverse momenta of the gluon less than 100 GeV^2. The phases of this amplitude are sensitive to the non-perturbative gluonic dynamics and could be sensitive to the presence of Beyond-the-Standard-Model particles at very high energies.
We analyse, in NLO, the physical properties of the discrete eigenvalue solution for the BFKL equation. We show that a set of eigenfunctions with positive eigenvalues, ω, together with a small contribution from a continuum of eigenfunctions with negative ω, provide an excellent description of high-precision HERA F_2 data in the region, x<0.001, Q^2 > 6 GeV^2. The phases of the eigenfunctions can be obtained from a simple parametrisation of the pomeron spectrum, which has a natural motivation within BFKL. The data analysis shows that the first eigenfunction decouples completely or almost complet…
We compare the BFKL prediction for the associated production of forward jets at HERA with fixed-order matrix element calculations taking into account the kinematical cuts imposed by experimental conditions. Comparison with H1 data of the 1993 run favours the BFKL prediction. As a further signal of BFKL dynamics, we propose to look for the azimuthal dependence of the forward jets.
In this paper we developed approach based on the BFKL evolution in $\ln\Lb Q^2\Rb$. We show that the simplest diffusion approximation with running QCD coupling is able to describe the HERA experimental data on the deep inelastic structure function with good $χ^2/d.o.f. \approx 1.3$. From our description of the experimental data we learned several lessons; (i) the non-perturbative physics at long distances started to show up at $Q^2 = 0.25\,GeV^2$; (ii) the scattering amplitude at $Q^2 = 0.25\,GeV^2$ cannot be written as sum of soft Pomeron and the secondary Reggeon but the Pomeron interactions…
To find the region of applicability of the leading log(1/x) approximation for parton distributions in the small x region and to fix the argument of the QCD running coupling it is necessary to know radiative corrections to the kernel of the BFKL equation. The next-to-leading corrections to the BFKL kernel are expressed in terms of the two-loop correction to the gluon Regge trajectory, one-loop correction to the Reggeon-Reggeon-gluon vertex, and contributions from two-gluon and quark-antiquark production in the quasi-multi-Regge kinematics. We calculate differential and total cross sections of t…
Using the QCD dipole picture of the hard BFKL pomeron, we derive the general expressions of the elastic and inelastic components of the proton diffractive structure functions. We obtain a good 7 parameter fit (including a secondary reggeon contribution) to data taken at HERA by the H1 and ZEUS collaborations. The main characteristic features of the model in reproducing the data are discussed, namely the effective pomeron intercept, the scaling violations and the beta dependence. A difference obtained in the separate H1 and ZEUS fits leads us to analyse directly the differences between both mea…
Progress in the understanding of the BFKL approach in the NLL approximation is reported. The study based on the iteration of the kernel using the exponentiation of the gluon Regge trajectory is reviewed in QCD and N=4 super Yang-Mills theories. Properties of the gluon Green's function in the high energy Regge limit for forward and non-forward scattering are considered. A novel representation of collinearly improved kernels is also presented.
We examine the effect of suppressing the emission of gluons which are close by in rapidity in the BFKL framework. We show that, after removing the unphysical collinear logarithms which typically arise in formally higher orders of the perturbative expansion, the effect of the rapidity veto is greatly reduced. This is an important result, since it supports the use of multi-Regge and quasi-multi-Regge kinematics which are implemented in the leading and next-to-leading order BFKL formalism.
We present microscopic QCD calculation of the cross section of diffractive DIS and of the partonic structure of the pomeron from the dipole approach to the generalized BFKL pomeron. We show that the pomeron can not be treated as a particle with uniquely defined structure function and flux in the proton. We find strong factorization breaking which can approximately be described by the two-component structure function of the pomeron, each component endowed with the different flux of pomerons in the proton. We predict very weak $Q^{2}$ dependence of the diffractive contribution to the proton stru…
After a brief review of the BFKL approach to Regge processes in QCD and in supersymmetric (SUSY) gauge theories we propose a strategy for calculating the next-to-next-to-leading order corrections to the BFKL kernel. They can be obtained in terms of various cross-sections for Reggeized gluon interactions. The corresponding amplitudes can be calculated in the framework of the effective action for high energy scattering. In the case of N=4 SUSY it is also possible to use the Bern-Dixon-Smirnov (BDS) ansatz. For this purpose the analytic properties of the BDS amplitudes at high energies are invest…
We show that the HERA data for the inclusive structure function F_2(x,Q^2) for x < 0.01 and 0.045 < Q^2 < 45 GeV^2 can be well described within the color dipole picture, with a simple analytic expression for the dipole-proton scattering amplitude, which is an approximate solution to the non-linear evolution equations in QCD. For dipole sizes less than the inverse saturation momentum 1/Q_s(x), the scattering amplitude is the solution to the BFKL equation in the vicinity of the saturation line. It exhibits geometric scaling and scaling violations by the diffusion term. For dipole sizes larger th…
The contribution of subleading reggeons to the diffractive structure function ${dF_{2}^D / dx_{\funp} dt}$ is estimated from the soft physics data. This contribution leads in a natural way to the violation of the factorization property of the diffractive structure function.
High-energy virtual photon-virtual photon scattering can be viewed as interaction of small size color dipoles from the beam and target photons, which makes $γ^{*}γ^{*}, γ^{*}γ$ scattering at high energies (LEP, LEP200 & NLC) an indispensable probe of short distance properties of the QCD pomeron exchange. Based on the color dipole representation, we investigate consequences for the $γ^{*}γ^{*},γ^{*}γ$ scattering of the incorporation of asymptotic freedom into the BFKL equation which makes the QCD pomeron a series of isolated poles in the angular momentum plane. The emerging color dipole BFKL-Re…
We evaluate differential cross sections for production of four jets in multi-Regge kinematics at a hadron collider. The main focus lies on azimuthal angle dependences. As in previous studies, the ratios of correlation functions of products of cosines of azimuthal angle differences among the tagged jets offer us the cleanest quantities to compare with experimental data. The calculations are based on the jet production from a single BFKL ladder with a convolution of three BFKL Green functions where we always have two forward/backward jets tagged in the final state. We also demand the tagging of …
We use the BFKL equation to calculate the rate of deep inelastic scattering events containing two forward jets (adjacent to the proton remnants) at HERA. We compare the production of two forward jets with that of only one forward jet (the "Mueller" process). We obtain a stable prediction for this two to one jet ratio, which may serve as a measure of the BFKL vertex function.
The "triple-Regge" analysis of subleading Reggeon contributions to the diffractive structure function in DIS at HERA is presented. The recently published data allow to estimate the only free parameter of the analysis related to the ratio of the RRP and PPP couplings. The large value of this ratio is prefered which is in agreement with analyses of soft hadronic interactions. The role of the subleading Reggeons as well as pions for the fast forward neutron production in diffractive processes is estimated. The forward piN state production is also discussed.
Aspects of small x physics at HERA are discussed in honor of the work of Lev Lipatov, who influenced and motivated a whole generation of physicists to investigate this new region of phase space. The introduction of transverse momentum dependent parton densities is one of the essential aspects of small x and BFKL physics, and its extension to all flavors with application to various processes marks a new milestone.
We investigate the relation between the eigenvalues and eigenfunctions of the BFKL and JIMWLK/KLWMIJ Hamiltonians. We show that the eigenvalues of the BFKL Hamiltonians are also {\it exact} eigenvalues of the KLWMIJ (and JIMWLK) Hamiltonian, albeit corresponding to possibly non normalizable eigenfunctions. The question whether a given eigenfunction of BFKL corresponds to a normalizable eigenfunction of KLWMIJ is rather complicated, except in some obvious cases, and requires independent investigation. As an example to illustrate this relation we concentrate on the color octet exchange in the fr…
One of the well known effects of the asymptotic freedom is splitting of the leading-$\log$ BFKL pomeron into a series of isolated poles in complex angular momentum plane. Following our earlier works we explore the phenomenological consequences of the emerging BFKL-Regge factorized expansion for the small-$x$ charm ($F_2^c$) and beauty ($F_{2}^{b}$) structure functions of the proton. As we found earlier,the color dipole approach to the BFKL dynamics predicts uniquely decoupling of subleading hard BFKL exchanges from $F_2^c$ at moderately large $Q^{2}$. We predicted precocious BFKL asymptotics o…
The structure constants of twist-two operators with spin $j$ in the BFKL limit $g^2\rightarrow 0, j\rightarrow 1$ but ${g^2\over j-1}\sim 1$ are determined from the calculation of the three-point correlator of twist-two light-ray operators in the triple Regge limit. It is well known that the anomalous dimensions of twist-two operators in this limit are determined by the BFKL intercept. Similarly, the obtained structure constants are determined by an analytic function of three BFKL intercepts.
This is a personal recollection of several results involving the phenomenological study of the multi-Regge limit of scattering amplitudes. None of them would have been possible without the encouragement and constant support from Lev Nikolaevich Lipatov.
Recent $HERA$ data on the photoproduction of vector mesons are analysed within a "soft", dipole pomeron model. We argued that the data on $σ^{γ\rightarrow J/ψ}_{el}$ is consistent with a soft pomeron, the apparent rapid increase resulting from the non-asymptotic effects due to the delayed asymptotics of $σ_{el}$ with respect to $σ_{tot}$.
The gluon and quark production in the quasi-multi-Regge kinematics is considered. The differential cross section for different helicity states is calculated. The dimensional regularization is used to remove the infrared divergencies in the corresponding contributions to the BFKL-equation. The other next-to-leading corrections are discussed.
Lev Lipatov was a giant in the field of strong interactions and a dominant force in high-energy QCD for many decades. His work deeply influenced both how we think about QCD and how we perform calculations in the theory. Below we describe the work in two related research directions: the physics of parton saturation and proton spin at small $x$. Both developments would have been impossible without Lipatov's groundbreaking work. Saturation physics would not have happened without the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation. The recent progress in our theoretical understanding of the proton s…
In this paper we encode the perturbative BFKL leading logarithmic resummation, relevant for the Regge limit behavior of QCD scattering amplitudes, in the IR-regulated effective action which satisfies exact functional renormalization group equations. This is obtained using a truncation with a specific infinite set of non local vertices describing the multi-Regge kinematics (MRK). The goal is to use this framework to study, in the high energy limit and at larger transverse distances the transition to a much simpler effective local reggeon field theory, whose critical properties were recently inv…
We review the parton model and the Regge approach to the QCD description of the deep-inelastic $ep$ scattering at the small Bjorken variable $x$ and demonstrate their relation with the DGLAP and BFKL evolution equations. It is shown, that in the leading logarithmic approximation the gluon is reggeized and the pomeron is a compound state of two reggeized gluons. The conformal invariance of the BFKL pomeron in the impact parameter space is used to investigate the scattering amplitudes at high energies and fixed momentum transfers. The remarkable properties of the Schrödinger equation for compoun…
A Reggeometric (Regge+Geometry) model, based on the observed proportionality between the forward slope of the differential cross section and the interaction radius, the latter depending on virtuality Q2 of the incoming virtual photon and on the mass M 2 of the produced particle, is constructed. The objective of this study is the dependence of the Regge-pole amplitude on the virtuality Q2 and masses of the external particles, which remains an open problem for the theory. The present analysis is based on the HERA data on Deeply Virtual Compton Scattering (DVCS) and exclusive diffractive Vector M…
The production of forward jets of transverse momentum $p_T(j)\approx Q$ and large momentum fraction $x_{jet}\gg x$ probes the onset of BFKL dynamics at HERA. A full ${\cal O}(α_s^2)$ calculation of the inclusive forward jet cross section is presented and compared to the expected BFKL cross section. The kinematical region populated by these events and the scale dependence of the fixed order perturbative QCD cross sections are discussed.
To study diffractive photon production at HERA, we compute the projection of the virtual photon-photon impact-factor on the BFKL leading-order eigenfunctions E(n,nu) for non-zero transfer. This calculation supplements former ones performed for n=0. We provide an expression for n=+/-2 and check that all the other components are zero.
We discuss the high energy asymptotics in the next-to-leading (NLO) BFKL equation. We find a general solution for Green functions and consider two properties of the NLO BFKL kernel: running QCD coupling and large NLO corrections to the conformal part of the kernel. Both of these effects lead to Regge-BFKL asymptotics only in the limited range of energy ($y = \ln(s/q q_0) \leq (\as)^{- {5/3}}$) and change the energy behaviour of the amplitude for higher values of energy. We confirm the oscillation in the total cross section found in Ref. \cite{ROSS} in the NLO BFKL asymptotics, which shows that…
In color dipole gBFKL dynamics, we describe the emerging gBFKL phenomenology of a subasymptotic energy dependence of the diffraction slope and discuss possibilities of testing the gBFKL predictions in exclusive photo- and electroproduction of vector mesons $V$ at HERA. A substantial shrinkage of the diffraction cone $γ^{*}p\rightarrow Vp$ processes from the CERN/FNAL to HERA range of energy $W$ is predicted. This subasymptotic shrinkage is faster than expected from the small slope of pomeron's Regge trajectory $α_{\Pom}'$. We point out that the diffraction slope is a scaling function of $(m_{V…
We compute the longitudinal proton structure function F_L from the k_T factorization scheme, using the unified DGLAP/BFKL resummation approach at small x for the unintegrated gluon density. The differences between the k_T factorization, collinear factorization and dipole approaches are analyzed and discussed. The comparisons with the HERA data are made and predictions for the proposed Large Hadron-Electron Collider are also provided.
Recently, new observables in LHC inclusive events with three tagged jets were proposed. Here, we extend that proposal to events with four tagged jets. The events are characterised by one jet in the forward direction, one in the backward direction with a large rapidity distance $Y$ from the first one and two more jets tagged in more central regions of the detector. In our setup, non-tagged associated mini-jet multiplicity is present and needs to be accounted for by the inclusion of BFKL gluon Green functions. The projection of the cross section on azimuthal-angle components opens up the opportu…
We discuss the BFKL approach to processes with large momentum transferred through a rapidity gap. The Mueller and Tang scheme to the BFKL non-forward parton-parton elastic scattering amplitude at large $t$, is extended to include higher conformal spins. The new contributions are found to decrease with increasing energy, as follows from the gluon reggeisation phenomenon, and to vanish for asymptotically high energies. However, at moderate energies and high $|t|$, the higher conformal spins dominate the amplitude. We illustrate the effects by studying the production of two high $E_T$ jets separa…
The HERA data on the proton structure function, $F_2(x,Q^2)$, at very small $x$ and $Q^2$ show the dramatic departure of the logarithmic slope, $\partial F_2/\partial\log Q^2$, from theoretical predictions based on the DGLAP evolution. We show that the running BFKL approach provides the quantitative explanation for the observed $x$ and/or $Q^2$ -dependence of $\partial F_2/\partial\log Q^2$.
In this talk, I will argue that the HERA experimental data show that the typical parameter ($κ$) responsible for the value of the shadowing corrections (SC) in DIS is so large that the BFKL Pomeron is hidden under SC. The SC turn out to be large enough but mostly for the gluon structure function which is not well determined by the available experimental data and by the current theoretical procedure.
