We consider propagation of heavy quarks in QCD matter. Because of large quark mass, the radiative quark energy loss appears to be qualitatively different from that of light quarks at all energies of practical importance. Finite quark mass effects lead to an in-medium enhancement of the heavy-to-light D/π ratio at moderately large (5-10 GeV) transverse momenta. For hot QCD matter a large enhancement is expected, whose magnitude and shape are exponentially sensitive to the density of colour charges in the medium.

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E the !& decade jet physics h s bee. i&~sive!y .?-.died zt ete-afid hadro~ic colliders. With the start of LEP activity a wealth of new data has become available (see, for example, [l]). They show that the global features of hadronic jets systems (multiplicities, angular patterns of particle flows, inclusive energy spectra etc), calcnlated at the parton level, agree very well with the measured ones. This convincingly demonstrates the dominant role of the perturbative (PT) phase of jet evolution and strongly supports the hypothesis of local parton-hadron duality (LPHD) [Zj 31; Such a local duality is naturally connected with the 'preconfinement' properties [4] of the QCD cascades. Together with the modified leading logarithmic approximation (MLLA)

We compute power corrections to hadronic event shapes in e + e − annihilation, assuming an infrared regular behaviour of the effective coupling α S . With the integral of α S over the infrared region as the only non-perturbative parameter, also measured in heavy quark physics, we can account for the empirical features of 1/Q corrections to the mean values of various event shapes.

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This remark is part of an ongoing project to simplify the structure of the multi-loop anomalous dimensions for parton distributions and fragmentation functions. It answers the call for a "structural explanation" of a "very suggestive" relation found by Moch, Vermaseren and Vogt in the context of the x->1 behaviour of three-loop DIS anomalous dimensions. It also highlights further structure that remains to be fully explained.Comment: 6 pages, v2 corrects misprints and contains an additional referenc

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.

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