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Non-forward NLO BFKL Kernel

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 Added by Roberto Fiore prof
 Publication date 2005
  fields
and research's language is English




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Details of the calculation of the non-forward BFKL kernel at next-to-leading order (NLO) are offered. Specifically we show the calculation of the two-gluon production contribution. This contribution was the last missing part of the kernel. Together with the NLO gluon Regge trajectory, the NLO contribution of one-gluon production and the contribution of quark-antiquark production which were found before it defines the kernel completely for any colour state in the $t$-channel, in particular the Pomeron kernel presented recently.

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We investigate the infrared singularity structure of Feynman diagrams entering the next-to-leading-order (NLO) DGLAP kernel (non-singlet). We examine cancellations between diagrams for two gluon emission contributing to NLO kernels. We observe the crucial role of color coherence effects in cancellations of infra-red singularities. Numerical calculations are explained using analytical formulas for the singular contributions.
We derive the solution of the NLO BFKL equation by constructing its eigenfunctions perturbatively, using an expansion around the LO BFKL (conformal) eigenfunctions. This method can be used to construct a solution of the BFKL equation with the kernel calculated to an arbitrary order in the coupling constant.
60 - Florian Schwennsen 2007
We study jet physics in the high energy regime of QCD. Based on the NLO BFKL equation, we construct a vertex for the production of a jet at central rapidity in k_T-factorization. A jet algorithm is introduced, and we take special care of the separation of multi-Regge and quasi-multi-Regge kinematics. The connection with the energy scale of the evolution is investigated in detail. The result is discussed for two situations: scattering of highly virtual photons, which requires a symmetric energy scale to separate the impact factors from the gluon Greens function, and hadron-hadron collisions, where a non-symmetric scale choice is needed. For the second case we are able to define a NLO unintegrated gluon density, valid in the small-x regime, and give the evolution equation for this density as well. In the second part, we examine the angular decorrelation of Mueller-Navelet jets. Using an operator formalism in the space of anomalous dimension and conformal spin, we implement the NLO BFKL Greens function to study the rapidity dependence of angular decorrelations. We incorporate the necessary summation of collinearly enhanced corrections beyond NLO accuracy. We compare our results with data from the Tevatron ppbar-collider and provide predictions for the LHC as well. We also extend our study to the angular decorrelation between a forward jets and the electron in deep inelastic ep scattering. The angular decorrelation has not been measured in DIS so far, but we give theoretical results for this observable which already implement the experimental cuts.
On the basis of previous work by Fadin, Lipatov, and collaborators, and of our group, we extract the irreducible part of the next-to-leading (NL) BFKL kernel, we compute its (IR finite) eigenvalue function, and we discuss its implications for small-x structure functions. We find consistent running coupling effects and sizable NL corrections to the Pomeron intercept and to the gluon anomalous dimension. The qualitative effect of such corrections is to smooth out the small-x rise of structure functions at low values of Q2. A more quantitative analysis will be possible after the extraction of some additional, energy-scale dependent contributions to the kernel, which are not treated here.
The azimuthal angle correlation of Mueller-Navelet jets at hadron colliders is studied in the NLO BFKL formalism. We highlight the need of collinear improvements in the kernel to obtain good convergence properties and we obtain better fits for the Tevatron data than at LO accuracy. We also estimate these correlations for larger rapidity differences available at the LHC.
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