TOPICAL REVIEW: Event shapes in e+e- annihilation and deep inelastic scattering

CERN, Genève, Geneva, Switzerland
Journal of Physics G Nuclear and Particle Physics (Impact Factor: 2.78). 05/2004; 30(5). DOI: 10.1088/0954-3899/30/5/R01
Source: arXiv


This review examines the status of event-shape studies in e+e- annihilation and DIS. It includes discussions of perturbative calculations, of various approaches to modelling hadronization and of comparisons to data.

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    • "In the recent years the subject has attracted a lot of attention due to the very precise extraction of the strong coupling constant α s from fits to the tail of the thrust distribution [1] [2] [3] and moments of the thrust distribution [4] [5] 1 . Excellent reviews on event shapes are [7] [8], where the definition of the most commonly used can be found. "
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    ABSTRACT: We study the effect of hadron masses on the leading power correction of dijet event-shape distributions. We define the transverse velocity operator, that describes the effects of hadron masses. It depends on the "transverse velocity" r, which is different from one only for non-vanishing hadron masses. We find that hadron-mass effects in general break universality. However we provide a simple method to identify universality classes of event shapes with a common power correction. We also compute the anomalous dimension of the power correction and the structure of the corresponding Wilson coefficient, finding a nontrivial result.
    Preview · Article · Jan 2013
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    • "They have also been used to extract moments of the non-perturbative coupling, as reviewed in refs. [1] and [4] (and references therein). Despite the fact that the LEP collider was a clean environment to " measure " QCD using event/jet shapes, they will still be an important tool at the LHC, particularly jet shapes and jet substructure which are expected to be invaluable tools in the search for new physics due to the final state being dominantly jets [7] [9]. "
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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.
    Full-text · Article · Jul 2012 · Journal of High Energy Physics
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    • "Resummed results for jet rates have been also obtained [27] [28] [29] [30] [31]. High-quality data, primarily from LEP measurements at the Z-pole, open up an opportunity to perform very accurate studies in jet physics [32]. Since, by now, gross features of QCD are well understood, the interest shifts towards subtle details which can be revealed only through dealing with complicated final states and improving the accuracy of theoretical predictions. "
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    ABSTRACT: The highest exclusive jet multiplicity studied at LEP experiments is five. In this paper we compute the next-to-leading order QCD corrections to e + e − annihilation to five jets, essentially closing the (pure) perturbative QCD studies of exclusive jetty final states at LEP. We compare fixed-order perturbative results with ALEPH data. We estimate hadronization corrections to five-jet observables using the event generator SHERPA, which employs the CKKW procedure to combine a reliable perturbative treatment of high-multiplicity jet final states with parton showers. We show that a competitive value of the strong coupling constant can be extracted from the distribution of the five-jet resolution parameter and the five-jet rate at LEP1 and LEP2.
    Preview · Article · Nov 2010 · Journal of High Energy Physics
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