Article

On large angle multiple gluon radiation

(Impact Factor: 6.11). 03/2003; 2003(3). DOI: 10.1088/1126-6708/2003/03/040
Source: arXiv

ABSTRACT

Jet shape observables which involve measurements restricted to a part of phase space are sensitive to multiplication of soft gluon with large relative angles and give rise to specific single logarithmically enhanced (SL) terms (non-global logs). We consider associated distributions in two variables which combine measurement of a jet shape V in the whole phase space (global) and that of the transverse energy flow away from the jet direction, Eout (non-global). We show that associated distributions factorize into the global distribution in V and a factor that takes into account SL contributions from multi-gluon hedgehog'' configurations in all orders. The latter is the same that describes the single-variable Eout distribution, but evaluated at a rescaled energy VQ. Comment: 16 pages

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Available from: Yuri Dokshitzer, Sep 24, 2013
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• "Collinear singularities at the boundary of a small-R jet yields large logs in the radius parameter, which appear to all orders in α s [23] [28]. Note that the jet veto distribution, studied in the latter references, disentangles from the jet mass distribution to all orders [29] and has a non-global structure analogous to the E t distribution. That is, the coefficients of both 1 We speak of the logarithmic accuracy in the exponent of the distribution. "
Article: On the resummation of clustering logarithms for non-global observables
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ABSTRACT: Clustering logs have been the subject of much study in recent literature. They are a class of large logs which arise for non-global jet-shape observables where final-state particles are clustered by a non-cone--like jet algorithm. Their resummation to all orders is highly non--trivial due to the non-trivial role of clustering amongst soft gluons which results in the phase-space being non-factorisable. This may therefore significantly impact the accuracy of analytical estimations of many of such observables. Nonetheless, in this paper we address this very issue for jet shapes defined using the $k_t$ and C/A algorithms, taking the jet mass as our explicit example. We calculate the coefficients of the Abelian $\alpha_s^2 L^2$, $\alpha_s^3 L^3$ and $\alpha_s^4 L^4$ NLL terms in the exponent of the resummed distribution and show that the impact of these logs is small which gives confidence on the perturbative estimate without the neglected higher-order terms. Furthermore we numerically resum the non-global logs of the jet mass distribution in the $k_t$ algorithm in the large-$N_c$ limit.
Journal of High Energy Physics 07/2012; 2012(9). DOI:10.1007/JHEP09(2012)109 · 6.11 Impact Factor
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• "We formulate a factorization theorem for such jet shape distributions, and aim to resum logs of the jet shape which become large for collimated jets to NLL accuracy. Ref. [50] demonstrated the factorization of such a distribution into a " global " and " non-global " part, and our methods resum the logs in the global part, and at least a subset of those in the non-global part. We do not tackle the problem of ensuring full resummation of all non-global logs generated by phase space cuts, which would require an O(α 2 s ) analysis of jet and soft functions, beyond the scope of this work. "
Article: Jet shapes and jet algorithms in SCET
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ABSTRACT: Jet shapes are weighted sums over the four-momenta of the constituents of a jet and reveal details of its internal structure, potentially allowing discrimination of its partonic origin. In this work we make predictions for quark and gluon jet shape distributions in N-jet final states in e+e- collisions, defined with a cone or recombination algorithm, where we measure some jet shape observable on a subset of these jets. Using the framework of Soft-Collinear Effective Theory, we prove a factorization theorem for jet shape distributions and demonstrate the consistent renormalization-group running of the functions in the factorization theorem for any number of measured and unmeasured jets, any number of quark and gluon jets, and any angular size R of the jets, as long as R is much smaller than the angular separation between jets. We calculate the jet and soft functions for angularity jet shapes tau_a to next-to-leading order (NLO) in alpha_s and resum large logarithms of tau_a to next-to-leading logarithmic (NLL) accuracy for both cone and kT-type jets. We compare our predictions for the NLL resummed tau_a distribution of a quark or a gluon jet produced in a 3-jet final state in e+e- annihilation to the output of a Monte Carlo event generator and find that the dependence on a and R is very similar. Comment: 57 pages plus 20 pages of Appendices, 11 figures, uses JHEP3.cls. v2: corrections to finite parts of NLO jet functions, minor changes to plots, clarified discussion of power corrections
Journal of High Energy Physics 01/2010; 2010(11). DOI:10.1007/JHEP11(2010)101 · 6.11 Impact Factor
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