Azimuthal decorrelation of forward and backward jets at the Tevatron

We analyse the azimuthal decorrelation of Mueller-Navelet dijets produced in the collisions at Tevatron energies using a BFKL framework which incorporates dominant subleading effects. We show that these effects significantly reduce the decorrelation yet they are still insufficient to give satisfactory description of experimental data. However a good description of the data is obtained after incorporating within formalism the effective rapidity defined by Del Duca and Schmidt.Comment: 1+9 pages, 6 eps figures; the final version to appear in Phys. Lett. B; one reference added, the use of effective rapidity and the need for BFKL resummmation for small azimuthal angles better motivate

The non-forward BFKL amplitude and rapidity gap physics

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 separated by a rapidity gap at HERA energies. In a simplified framework, we find excellent agreement with the HERA photoproduction data once we incorporate the rapidity gap survival probability against soft rescattering effects. We emphasize that measurements of the analogous process in electroproduction may probe different summations over conformal spins.Comment: Latex, 14 pages, 3 figures; the final version to appear in Phys. Lett. B; a short discussion of the Tevatron data added; a previously missing factor of i^n introduced in eq. (13

NLO corrections to ultra-high energy neutrino-nucleon scattering, shadowing and small x

We reconsider the Standard Model interactions of ultra-high energy neutrinos with matter. The next to leading order QCD corrections are presented for charged-current and neutral-current processes. Contrary to popular expectations, these corrections are found to be quite substantial, especially for very large (anti-) neutrino energies. Hence, they need to be taken into account in any search for new physics effects in high-energy neutrino interactions. In our extrapolation of the parton densities to kinematical regions as yet unexplored directly in terrestrial accelerators, we are guided by double asymptotic scaling in the large Q^2 and small Bjorken x region and to models of saturation in the low Q^2 and low x regime. The sizes of the consequent uncertainties are commented upon. We also briefly discuss some variables which are insensitive to higher order QCD corrections and are hence suitable in any search for new physics.Comment: 21 pages, LaTeX2e, uses JHEP3.cls (included), 8 ps files for figures published versio

Deep inelastic events containing a forward photon as a probe of small xx dynamics

We calculate the rate of producing deep inelastic events containing an energetic isolated forward photon at HERA. We quantify the enhancement arising from the leading $\log 1/x$ gluon emissions with a view to using such events to identify the underlying dynamics.Comment: 11 pages, Latex, 7 ps figure

A unified BFKL and GLAP description of F2F_2 data

We argue that the use of the universal unintegrated gluon distribution and the $k_T$ (or high energy) factorization theorem provides the natural framework for describing observables at small x. We introduce a coupled pair of evolution equations for the unintegrated gluon distribution and the sea quark distribution which incorporate both the resummed leading $ln (1/x)$ BFKL contributions and the resummed leading $ln (Q^2)$ GLAP contributions. We solve these unified equations in the perturbative QCD domain using simple parametic forms of the nonperturbative part of the integrated distributions. With only two (physically motivated) input parameters we find that this $k_T$ factorization approach gives an excellent description of the measurements of $F_2 (x,Q^2)$ at HERA. In this way the unified evolution equations allow us to determine the gluon and sea quark distributions and, moreover, to see the x domain where the resummed $ln (1/x)$ effects become significant. We use $k_T$ factorization to predict the longitudinal structure function $F_L (x,Q^2)$ and the charm component of $F_2 (x,Q^2)$.Comment: 25 pages, LaTeX, 9 figure

Theoretical issues of small xx physics

The perturbative QCD predictions concerning deep inelastic scattering at low $x$ are summarized. The theoretical framework based on the leading log $1/x$ resummation and $k_t$ factorization theorem is described and some recent developments concerning the BFKL equation and its generalization are discussed. The QCD expectations concerning the small $x$ behaviour of the spin dependent structure function $g_1(x,Q^2)$ are briefly summarized and the importance of the double logarithmic terms which sum contributions containing the leading powers of $\alpha_s ln^2(1/x)$ is emphasised. The role of studying final states in deep inelastic scattering for revealing the details of the underlying dynamics at low $x$ is pointed out and some dedicated measurements, like deep inelastic scattering accompanied by an energetic jet, the measurement of the transverse energy flow etc., are briefly discussed.Comment: 17 pages, LATEX, 7 uuencoded eps figures include

Hard pomeron enhancement of ultrahigh-energy neutrino-nucleon cross-sections

An unknown small-x behavior of nucleon structure functions gives appreciable uncertainties to high-energy neutrino-nucleon cross-sections. We construct structure functions using at small x Regge inspired description by A. Donnachie and P. V. Landshoff with soft and hard pomerons, and employing at larger x the perturbative QCD expressions. The smooth interpolation between two regimes for each Q^2 is provided with the help of simple polynomial functions. To obtain low-x neutrino-nucleon structure functions $F_2^{\nu N, \bar \nu N}(x,Q^2)$ and singlet part of $F_{3}^{\nu N,\bar \nu N}(x,Q^2)$ from Donnachie-Landshoff function $F_2^{ep}(x,Q^2)$, we use the Q^2-dependent ratios R_2(Q^2) and R_3(Q^2) derived from perturbative QCD calculations. Non-singlet part of F_3 at low x, which is very small, is taken as power-law extrapolation of perturbative function at larger x. This procedure gives a full set of smooth neutrino-nucleon structure functions in the whole range of x and Q^2 at interest. Using these structure functions, we have calculated the neutrino-nucleon cross-sections and compared them with some other cross-sections known in literature. Our cross-sections turn out to be the highest among them at the highest energies, which is explained by contribution of the hard pomeron.Comment: Final revised version, accepted by Phys. Rev. D; 18 pages, 7 figure

Possible probe of the QCD odderon singularity through the quasidiffractive eta_c production in gamma-gamma collisions

The reactions gamma-gamma to eta_c eta_c and gamma gamma to eta_c + X are discussed within the three gluon exchange model. We give predictions for the differential cross-sections and discuss feasibility of measuring these processes at LEP2 and TESLA. The total cross-sections were estimated to be approximately equal to 40 fb and 120 fb for gamma-gamma to eta_c eta_c and gamma-gamma to eta_c + X respectively assuming exchange of elementary gluons that corresponds to the odderon with intercept equal to unity. These values can be enhanced by a factor equal to 1.9 and 2.1 for LEP2 and TESLA energies if the odderon intercept is equal to 1.07. The estimate of cross-sections sigma(e^+ e^- to e^+ e^- eta_c eta_c) and sigma (e^+ e^- to e^+ e^- eta_c + X) for untagged e^+ and e^- is also given.Comment: 11 pages, Latex, epsf, 5 eps figures include