We study production of two pairs of jets in hadron-hadron collisions in view of extracting contribution of double hard interactions of three and four partons (3 → 4, 4 → 4). Such interactions, in spite of being power suppressed at the level of the total cross section, become comparable with the standard hard collisions of two partons, 2 → 4, in the back-to-back kinematics when the transverse momentum imbalances of two pairing jets are relatively small.We express differential and total cross sections for two-dijet production in double parton collisions through the generalized two-parton distributions, 2GPDs [1], that contain large-distance two-parton correlations of non-perturbative origin as well as small-distance correlations due to parton evolution. We find that these large-and small-distance correlations participate in different manner in 4-jet production, and treat them in the leading logarithmic approximation of pQCD that resums collinear logarithms in all orders.A special emphasis is given to 3 → 4 double hard interaction processes that occur as an interplay between large-and short-distance parton correlations and were not taken into consideration by approaches inspired by the parton model picture. We demonstrate that the 3 → 4 mechanism, being of the same order in αs as the 4 → 4 process, turns out to be geometrically enhanced compared to the latter and should contribute significantly to 4-jet production.The framework developed here takes into systematic consideration perturbative Q 2 evolution of 2GPDs. It can be used as a basis for future analysis of NLO corrections to multi-parton interactions (MPI) at LHC and Tevatron colliders, in particular for improving evaluation of QCD backgrounds to new physics searches.

In the last few years considerable progress has been achieved in our understanding of the decays of heavy flavour hadrons. One can now calculate inclusive transition rates in QCD proper through an expansion in inverse powers of the heavy flavour quark mass without recourse to phenomenological assumptions. The non-perturbative contributions are treated systematically in this way; they are found to produce corrections of order a few percent in beauty decays, i.e. typically somewhat smaller than the perturbative corrections. One finds, among other things: (a) The lifetime of B − mesons is predicted to be longer than that of B 0 mesons by several percent. (b) The QCD prediction for the semileptonic branching ratio of B mesons appears to exceed present experimental values. We discuss the implications of this discrepancy. The phenomenological engineering that has been developed for the description of exclusive two-body modes of B mesons has reached a mature stage and awaits more precise and detailed experimental tests. First steps towards a genuine QCD treatment of these modes are being made. 'Anyone who keeps the ability to see beauty never grows old'Franz Kafka 1 To appear in the second edition of the book 'B Decays', S.Stone (ed.), World Scientific 2 Permanent address

We demonstrate that in the back-to-back kinematics the production of four jets in the collision of two partons is suppressed in the leading log approximation of pQCD, compared to the hard processes involving the collision of four partons. We derive the basic equation for four-jet production in QCD in terms of the convolution of generalized two-parton distributions of colliding hadrons in the momentum space representation. Our derivation leads to geometrical approach in the impact parameter space close to that suggested within the parton model and used before to describe the four-jet production. We develop the independent parton approximation to the light-cone wave function of the proton. Comparison with the CDF and D0 data shows that the independent parton approximation to the light-cone wave function of the proton is insufficient to explain the data. We argue that the data indicate the presence of significant multiparton correlations in the light-cone wave functions of colliding protons.

A generalization of the operator product expansion is used to find the differential distributions in the inclusive semileptonic weak decays of heavy flavors in QCD. In particular, the double distribution in electron energy and invariant mass of the lepton pair is calculated. We are able to calculate the distributions in an essentially model-independent way as a series in m~' where rnQ is the heavy quark mass. All effects up to r n~' are included.

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We examine the role played in double-parton interactions (DPI) by the parton-parton correlations originating from perturbative QCD parton splittings. Also presented are the results of the numerical analysis of the integrated DPI cross sections at Tevatron and LHC energies. To obtain the numerical results the knowledge of the single-parton GPDs gained by the HERA experiments was used to construct the non-perturbative input for generalized double-parton distributions. The perturbative two-parton correlations induced by three-parton interactions contribute significantly to a resolution of the longstanding puzzle of an excess of multi-jet production events in the back-to-back kinematics observed at the Tevatron.

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