We consider interjet observables in hard QCD processes given by the energy flow E out in a region away from all hard jets. Here the QCD radiation is depleted (E out ≪ Q), and therefore these observables provide ideal means to study non-perturbative effects. We derive an evolution equation (in the large N c limit) which resums, for large Q/E out , all leading terms arising from large angle soft emission (double logarithms are absent). We discuss the analytical features of the result and identify universal and geometry-dependent contributions. Our analysis confirms features found using numerical methods by Dasgupta and Salam.
We present the QCD analysis of the cumulative out-of-event-plane momentum distribution in the process pp into Z 0 and a hard jet (event plane defined by the pp and Z 0 momenta). Particular attention is placed on the near-to-planar events for which we derive the all-order resummed result to next-to-leading accuracy. We consider also the leading power correction originating from the fact that, even in hard processes, the resummed QCD coupling runs into the infrared region. We aim at the same level of accuracy which, in e + e − annihilation, seems to be sufficient for making predictions. Contributions from a "soft underlying event" due to beam remnant interactions are discussed. Experimental data (not yet available) are needed to cast light on the predictive level of standard QCD analysis in hard hadron-hadron collisions.We plot examples of the predicted distribution at Tevatron energies. The techniques here developed can be extended to other hard hadron-hadron and hadron-lepton processes.
We provide an exact analytical calculation at the two-loop level in the abelian limit of the leading power correction for the C parameter in e + e − annihilation. We compare our results to the numerical value obtained employing the soft approximation, the abelian part of the Milan factor. We demonstrate that a simple proportionality holds between the leading power corrections to the C parameter and to the longitudinal cross section in the soft region, and we verify that this proportionality holds for the full two-loop abelian contribution computed here. We comment on the possibility of extending this technique to other event shape variables and distributions, as well as to the non-abelian contributions.
We present a QCD analysis of the cumulative out-of-event-plane momentum distribution in DIS process with emission of high p t jets. We derive the all-order resummed result to next-to-leading accuracy and estimate the leading power correction. We aim at the same level of accuracy which, in e + e − annihilation, seems to be sufficient for making predictions. As is typical of multi-jet observables, the distribution depends on the geometry of the event and the underlying colour structure. This result should provide a powerful method to study QCD dynamics, in particular to constrain the parton distribution functions, to measure the running coupling and to search for genuine non-perturbative effects.
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