Fate of k_perp-factorization for hard processes in nuclear environment

Large thickness of heavy nuclei brings in a new scale into the pQCD description of hard processes in nuclear environment. The familiar linear $k_{\perp}$-factorization breaks down and must be replaced by a new concept of the nonlinear $k_{\perp}$-factorization introduced in \cite{Nonlinear}. I demonstrate the salient features of nonlinear $k_{\perp}$-factorization on an example of hard dijet production in DIS off heavy nuclei. I also discuss briefly the non-linear BFKL evolution for gluon density of nuclei.Comment: 5 papges, 3 figures, Invited talk at DIFFRACTION 2004 International Workshop on Diffraction in High-Energy Physics, Cala Gonone, Sardinia, ITALY, September 18 - 23, 200

How to measure the intercept of the BFKL pomeron at HERA

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 $r=r_{\Delta}=(0.1-0.2)$f, the dipole cross section $\sigma(x,r)$ which is a solution of the generalized BFKL equation, exhibits a precocious asymptotic behavior \sigma(x,r)\propto \left({1\over x}\right)^{\Delta_{\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 $\sigma(x,r_{\Delta})$ and directly determine the intercept \Delta_{\Pom} of the BFKL pomeron in the HERA experiments.Comment: 10 pages, 2 figures upon the request from [email protected], Juelich preprint KFA-IKP(Th)-1994-10, 28 February 199

On determination of the large-1x{1\over x} gluon distribution at HERA

We discuss corrections to the Leading-Log$Q^{2}$ relationships between the gluon density $g(x,Q^{2})$ and $F_{L}(x,Q^{2}),\,\partial F_{T}(x,Q^{2}) /\partial \log Q^{2}$ in the HERA range of large ${1\over x}$. We find that the above quantities probe the gluon density $g(x,Q_{T,L}^{2})$ at $Q_{T,L}^{2}=C_{T,L}Q^{2}$, with the $Q^{2}$-rescaling factors $C_{T}\approx 2.2$ and $C_{L}\approx 0.42$. The possibility of treating charm as an active flavour is critically re-examined.Comment: 12 pages, 4 figures upon the request from [email protected], J\"ulich preprint KFA-IKP(TH)-1994-12. Some misprints and ordering of references correcte

Splitting the pomeron into two jets: a novel process at HERA

We study a novel property of large rapidity-gap events in deep inelastic scattering at HERA: splitting the pomeron into two jets in the photon-pomeron fusion reaction \gamma^{*}\Pom \rightarrow q\bar{q}. It gives rise to the diffraction dissociation of virtual photons into the back-to-back jets. We find that at large invariant mass $M$ of two jets, $M^{2}\gg Q^{2}$, the transverse momentum of jets comes from the intrinsic transverse momentum of gluons in the pomeron, and the photon-pomeron fusion direcly probes the diffrential gluon structure function of the proton $\partial G(x,q^{2})/\partial \log q^{2}$ at the virtuality $q^{2}\sim k^{2}$. We present estimates for the jet production cross section, which show the process is easily measurable at HERA.Comment: 11 pages, 4 figures on request from [email protected], Juelich preprint KFA-IKP(Th)-1994-16, 10 March 199

Excitation of open charm and factorization breaking in rapidity gap events at HERA

We develop the pQCD description of diffraction excitation of heavy flavours in DIS and we derive the analytic formulas for the mass spectrum in leading log$m_f^{2}$. The result illustrates nicely non-factorization properties of the QCD pomeron. We predict a very steep rise of the charm content of diffraction dissociation of photons at small x_{\Pom}. We evaluate the contribution of open charm to scaling violations in the structure function of the pomeron.Comment: 13 pages. Accepted for publication on march 10th 1996 by Phys. Lett.

The color dipole BFKL-Regge expansion: from DIS on protons to pions to rise of hadronic cross sections

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 $F_{2\pi}(x,Q^2)$. We calculate $F_{2\pi}$ in a small-$x$ region and find good agreement with the recent H1 determination of $F_{2\pi}(x,Q^2)$. We also present the BFKL-Regge factorization based evaluation of the contribution from hard scattering to the observed rise of the $NN$, $\pi N$ and real photo-absorption $\gamma N$ and $\gamma \pi$ total cross sections.Comment: 12 pages Latex 2 PS figures, Revised version accepted for publication in Physics Letters

Factorization properties of the diffraction dissociation of longitudinal photons

We develop the pQCD description of the diffraction dissociation (DD) of longitudinal photons. We demonstrate that the longitudinal diffractive structure function does not factor into the flux of pomerons and the partonic structure function of the pomeron, thus defying the usually assumed Regge factorization. In contrast to DD of the transverse photons, DD of the longitudinal photons is strongly peaked at $\beta =1$. We comment on duality properties of DD in deep inelastic scattering.Comment: 11 page

The spectrum and solutions of the generalized BFKL equation for total cross section

The colour dipole cross section is the principal quantity in the lightcone $s$-channel description of the diffractive scattering. Recently we have shown that the dipole cross section satisfies the generalized BFKL equation. In this paper we discuss properties and solutions of our generalized BFKL equation with allowance for the finite gluon correlation radius $R_{c}$. The latter is introduced in a gauge invariant manner. We present estimates of the intercept of the pomeron and find the asymptotic form of the dipole cross section.Comment: 18 pages, 3 figures upon request from [email protected]

BFKL evolution and universal structure function at very small xx

The Balitskii-Fadin-Kuraev-Lipatov (BFKL) and the Gribov-Lipatov- Dokshitzer-Altarelli-Parisi (GLDAP) evolution equations for the diffractive deep inelastic scattering at ${1\over x} \gg 1$ are shown to have a common solution in the weak coupling limit: F_{2}(x,Q^{2})\propto [\alpha_{S}(Q^{2})]^{-\gamma} \left({1\over x}\right)^{\Delta_{\Pom}}. The exponent $\gamma$ and the pomeron intercept \Delta_{\Pom} are related by \gamma\Delta_{\Pom}={4\over 3} for the $N_{f}=3$ active flavors. The existence of this solution implies that there is no real clash between the BFKL and GLDAP descriptions at very small $x$. We present derivation of this solution in the framework of our generalized BFKL equation for the dipole cross section, discuss conditions for the onset of the universal scaling violations and analyse the pattern of transition from the conventional Double-Leading-Logarithm approximation for the GLDAP evolution to the BFKL evolution at large ${1\over x}$.Comment: 14 pages, 3 figures on request from [email protected]

Exploratory study of shrinkage of the diffraction cone for the generalized BFKL pomeron

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 $\gamma^{*}p\rightarrow Vp$ 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 \alpha_{\Pom}'. We point out that the diffraction slope is a scaling function of $(m_{V}^{2}+Q^{2})$, what relates production of different vector mesons.Comment: plain LaTeX, 4 figures upon the request from [email protected]