Out-of-plane QCD radiation in DIS with high p_t jets

Abstract

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.

Event shapes in e+e annihilation and deep inelastic scattering

“…In contrast, any observable involving momenta in the remnant hemisphere must take care to limit its sensitivity to the proton remnant, whose fragmentation cannot be reliably handled within perturbation theory. A possible alternative to studying just the current hemisphere, is to take all particles except those in a small cone around the proton direction [32].…”

“…For DIS to 1 + 1 jets the current-hemisphere observables are resummed in refs. [33,67,68] and the jet rates in [35] (though only to NLL R accuracy) while the 2 + 1 jet observables, K out and azimuthal correlations, have been resummed in [32,34]. Methods for automated resummation of arbitrary observables are currently in development for a range of processes [38], and techniques have also being developed for dealing with arbitrary processes [69].…”

“…The 1/ √ α s enhancement for the power correction to the mean broadening (tables 1 and 2) comes about simply because the average value of ln 1 v , after integration over v with the resummed distribution, is of order 1 √ α s . The full form for D 1 (v) and analogous results for the total e + e − and DIS broadenings have been given in [68,135], with results existing also for the thrust minor [18], and the DIS and Drell-Yan out-of plane momenta [32,36]. Yet subtler instances of perturbative, non-perturbative interplay arise for observables like the EEC [64] and DIS azimuthal correlation [34], with the appearance of fractional powers of Q in the power correction, as mentioned before.…”

Semi-numerical resummation of event shapes

“…In processes with three hard partons the resummation of the simple variable also proves straightforward, with R s just involving a sum over dipoles [8][9][10][11]. On the other hand, with 4 or more hard partons subtleties will arise from the large angle region as can be seen from [24].…”

“…One class of observables that has been extensively studied in this context is that of event shapes [1][2][3][4][5][6][7][8][9][10][11][12] and jet rates [13][14][15]. These measure geometrical properties of the hadronic energy flow in the final state of a given reaction, e.g.…”