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Research paper thumbnail of Power corrections for jets at hadron colliders

We discuss non-perturbative QCD corrections to jet distributions in hadron collisions, focussing ... more We discuss non-perturbative QCD corrections to jet distributions in hadron collisions, focussing on hadronisation and underlying event contributions. Using soft gluon resummation and Monte-Carlo modelling we show that hadronisation dominates at small values of the jet radius R, behaving as 1/R, while underlying event corrections grow with the jet area. This provides a handle to disentangle them and parametrize them in terms of measurable QCD parameters, which might enjoy a degree of universality.

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Research paper thumbnail of Non-perturbative QCD effects in jets at hadron colliders

Journal of High Energy Physics, 2008

We discuss non-perturbative QCD contributions to jet observables, computing their dependence on t... more We discuss non-perturbative QCD contributions to jet observables, computing their dependence on the jet radius R, and on the colour and transverse momentum of the parton initiating the jet. We show, using analytic QCD models of power corrections as well as Monte Carlo simulations, that hadronisation corrections grow at small values of R, behaving as 1/R, while underlying event contributions grow with the jet area as R^2. We highlight the connection between hadronisation corrections to jets and those for event shapes in e^+e^- and DIS; we note the limited dependence of our results on the choice of jet algorithm; finally, we propose several measurements in the context of which to test or implement our predictions. The results presented here reinforce the motivation for the use of a range of R values, as well as a plurality of infrared-safe jet algorithms, in precision jet studies at hadron colliders.

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Research paper thumbnail of Resummed event-shape variables in DIS

Journal of High Energy Physics, 2002

We complete our study of resummed event-shape distributions in DIS by presenting results for the ... more We complete our study of resummed event-shape distributions in DIS by presenting results for the class of observables that includes the current jet mass, the C-parameter and the thrust with respect to the current-hemisphere thrust axis. We then compare our results to data for all observables for which data exist, fitting for alpha_s and testing the universality of non-perturbative 1/Q effects. A number of technical issues arise, including the extension of the concept of non-globalness to the case of discontinuous globalness; singularities and non-convergence of distributions other than in the Born limit; methods to speed up fixed-order Monte Carlo programs by up to an order of magnitude, relevant when dealing with many x and Q points; and the estimation of uncertainties on the predictions.

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Research paper thumbnail of On QCD resummation with kt clustering

Journal of High Energy Physics, 2006

We revisit the impact of the jet algorithm on predictions of energy flow into gaps between hard j... more We revisit the impact of the jet algorithm on predictions of energy flow into gaps between hard jets, defined using the kt clustering procedure. The resulting prediction has two distinct components: a primary emission piece that is related to independent emission of soft gluons by the hard jets and a correlated emission (non-global) piece known only in the large N_c limit. We analytically compute the dependence of the primary emission term on the jet algorithm, which gives significantly more insight than our previous numerical study of the same. We also point out that the non-global component of the answer is reduced even more significantly by the clustering than suggested previously in the literature. Lastly we provide improved predictions for the latest ZEUS photoproduction data, assessing the impact of our latest findings.

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Research paper thumbnail of Accounting for coherence in interjet E_t flow: a case study

Recently, interest has developed in the distribution of interjet energy flows, with for example t... more Recently, interest has developed in the distribution of interjet energy flows, with for example the leading-log calculation of the highly non-trivial colour structure of primary emissions in 4-jet systems. Here we point out however that at leading-log level it is insufficient to consider only multiple primary emission from the underlying hard antenna -- additionally, one must take into account the coherent structure of emission from arbitrarily complicated ensembles of large-angle soft gluons. Similar considerations apply to certain definitions of rapidity gaps based on energy flow. We examine this new class of terms in the simpler context of 2-jet events, and discover features that point at novel aspects of the QCD dynamics.

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Research paper thumbnail of TOPICAL REVIEW: Event shapes in e+e- annihilation and deep inelastic scattering

Journal of Physics G-nuclear and Particle Physics, 2004

This article reviews the status of event-shape studies in e+e- annihilation and DIS. It includes ... more This article reviews the status of event-shape studies in e+e- annihilation and DIS. It includes discussions of perturbative calculations, of various approaches to modelling hadronisation and of comparisons to data.

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Research paper thumbnail of Resummation of thrust distributions in DIS

Journal of High Energy Physics, 2000

We calculate the resummed distributions for the thrust in DIS in the limit T->1. Two variants of ... more We calculate the resummed distributions for the thrust in DIS in the limit T->1. Two variants of the thrust are considered: that normalised to Q/2, and that normalised to the energy in the current hemisphere. The results expanded to second order are compared to predictions from the Monte Carlo programs DISENT and DISASTER++. A prescription is given for matching the resummed expressions with the full fixed order calculation.

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Research paper thumbnail of Power corrections for jets at hadron colliders

We discuss non-perturbative QCD corrections to jet distributions in hadron collisions, focussing ... more We discuss non-perturbative QCD corrections to jet distributions in hadron collisions, focussing on hadronisation and underlying event contributions. Using soft gluon resummation and Monte-Carlo modelling we show that hadronisation dominates at small values of the jet radius R, behaving as 1/R, while underlying event corrections grow with the jet area. This provides a handle to disentangle them and parametrize them in terms of measurable QCD parameters, which might enjoy a degree of universality.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Non-perturbative QCD effects in jets at hadron colliders

Journal of High Energy Physics, 2008

We discuss non-perturbative QCD contributions to jet observables, computing their dependence on t... more We discuss non-perturbative QCD contributions to jet observables, computing their dependence on the jet radius R, and on the colour and transverse momentum of the parton initiating the jet. We show, using analytic QCD models of power corrections as well as Monte Carlo simulations, that hadronisation corrections grow at small values of R, behaving as 1/R, while underlying event contributions grow with the jet area as R^2. We highlight the connection between hadronisation corrections to jets and those for event shapes in e^+e^- and DIS; we note the limited dependence of our results on the choice of jet algorithm; finally, we propose several measurements in the context of which to test or implement our predictions. The results presented here reinforce the motivation for the use of a range of R values, as well as a plurality of infrared-safe jet algorithms, in precision jet studies at hadron colliders.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Resummed event-shape variables in DIS

Journal of High Energy Physics, 2002

We complete our study of resummed event-shape distributions in DIS by presenting results for the ... more We complete our study of resummed event-shape distributions in DIS by presenting results for the class of observables that includes the current jet mass, the C-parameter and the thrust with respect to the current-hemisphere thrust axis. We then compare our results to data for all observables for which data exist, fitting for alpha_s and testing the universality of non-perturbative 1/Q effects. A number of technical issues arise, including the extension of the concept of non-globalness to the case of discontinuous globalness; singularities and non-convergence of distributions other than in the Born limit; methods to speed up fixed-order Monte Carlo programs by up to an order of magnitude, relevant when dealing with many x and Q points; and the estimation of uncertainties on the predictions.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of On QCD resummation with kt clustering

Journal of High Energy Physics, 2006

We revisit the impact of the jet algorithm on predictions of energy flow into gaps between hard j... more We revisit the impact of the jet algorithm on predictions of energy flow into gaps between hard jets, defined using the kt clustering procedure. The resulting prediction has two distinct components: a primary emission piece that is related to independent emission of soft gluons by the hard jets and a correlated emission (non-global) piece known only in the large N_c limit. We analytically compute the dependence of the primary emission term on the jet algorithm, which gives significantly more insight than our previous numerical study of the same. We also point out that the non-global component of the answer is reduced even more significantly by the clustering than suggested previously in the literature. Lastly we provide improved predictions for the latest ZEUS photoproduction data, assessing the impact of our latest findings.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Accounting for coherence in interjet E_t flow: a case study

Recently, interest has developed in the distribution of interjet energy flows, with for example t... more Recently, interest has developed in the distribution of interjet energy flows, with for example the leading-log calculation of the highly non-trivial colour structure of primary emissions in 4-jet systems. Here we point out however that at leading-log level it is insufficient to consider only multiple primary emission from the underlying hard antenna -- additionally, one must take into account the coherent structure of emission from arbitrarily complicated ensembles of large-angle soft gluons. Similar considerations apply to certain definitions of rapidity gaps based on energy flow. We examine this new class of terms in the simpler context of 2-jet events, and discover features that point at novel aspects of the QCD dynamics.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of TOPICAL REVIEW: Event shapes in e+e- annihilation and deep inelastic scattering

Journal of Physics G-nuclear and Particle Physics, 2004

This article reviews the status of event-shape studies in e+e- annihilation and DIS. It includes ... more This article reviews the status of event-shape studies in e+e- annihilation and DIS. It includes discussions of perturbative calculations, of various approaches to modelling hadronisation and of comparisons to data.

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Research paper thumbnail of Resummation of thrust distributions in DIS

Journal of High Energy Physics, 2000

We calculate the resummed distributions for the thrust in DIS in the limit T->1. Two variants of ... more We calculate the resummed distributions for the thrust in DIS in the limit T->1. Two variants of the thrust are considered: that normalised to Q/2, and that normalised to the energy in the current hemisphere. The results expanded to second order are compared to predictions from the Monte Carlo programs DISENT and DISASTER++. A prescription is given for matching the resummed expressions with the full fixed order calculation.

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