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Giulia Zanderighi

Publications and source records attributed to Giulia Zanderighi.

105 records · Page 6Linked to original sources
arXiv2007

Hadronic Final States

In this summary we give a concise overview of the experimental and theoretical results, which were presented during the QCD and Hadronic Final State Working Group sessions at the DIS 2007 workshop.

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arXiv2007

Accurate predictions for heavy quark jets

Heavy-flavour jets enter many of today's collider studies, yet NLO predictions for these quantities are subject to large uncertainties, larger than the corresponding experimental errors. We propose a new, infrared safe definition of heavy-quark jets which allows one to reduce theoretical uncertainties by a factor of three.

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arXiv2007

Accurate QCD predictions for heavy-quark jets at the Tevatron and LHC

Heavy-quark jets are important in many of today's collider studies and searches, yet predictions for them are subject to much larger uncertainties than for light jets. This is because of strong enhancements in higher orders from large logarithms, ln(p_t/m_Q). We propose a new definition of heavy-quark jets, which is free of final-state logarithms to all orders and such that all initial-state collinear logarithms can be resummed into the heavy-quark parton distributions. Heavy-jet spectra can then be calculated in the massless approximation, which is simpler than a massive calculation and reduces the theoretical uncertainties by a factor of three. This provides the first ever accurate predictions for inclusive b- and c-jets, and the latter have significant discriminatory power for the intrinsic charm content of the proton. The techniques introduced here could be used to obtain heavy-flavour jet results from existing massless next-to-leading order calculations for a wide range of processes. We also discuss the experimental applicability of our flavoured jet definition.

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arXiv2006

The one-loop amplitude for six-gluon scattering

We present results for the six-gluon scattering amplitude at one-loop. Since our method is semi-numerical, it yields the result for arbitrary momenta and helicities of the external gluons. We evaluate the colour-ordered sub-amplitudes with gluons, fermions and scalars running in the internal loop. This is more than sufficient to give a complete description of six-gluon scattering at one-loop in QCD. Combination of these results into amplitudes with ${\cal{N}}=4$ and ${\cal{N}}=1$ multiplets of supersymmetric Yang-Mills or with a complex scalar in the internal loops allows comparison with analytic results in the literature. The numerical results for most of the helicity combinations with loops of complex scalars are new.

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arXiv2006

Infrared safe definition of jet flavour

It is common, in both theoretical and experimental studies, to separately discuss quark and gluon jets. However, even at parton level, widely-used jet algorithms fail to provide an infrared safe way of making this distinction. We examine the origin of the problem, and propose a solution in terms of a new "flavour-kt" algorithm. As well as being of conceptual interest this can be a powerful tool when combining fixed-order calculations with multi-jet resummations and parton showers. It also has applications to studies of heavy-quark jets.

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arXiv2005

Principles of general final-state resummation and automated implementation

Next-to-leading logarithmic final-state resummed predictions have traditionally been calculated, manually, separately for each observable. In this article we derive NLL resummed results for generic observables. We highlight and discuss the conditions that the observable should satisfy for the approach to be valid, in particular continuous globalness and recursive infrared and collinear safety. The resulting resummation formula is expressed in terms of certain well-defined characteristics of the observable. We have written a computer program, CAESAR, which, given a subroutine for an arbitrary observable, determines those characteristics, enabling full automation of a large class of final-state resummations, in a range of processes.

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arXiv2004

Resummed event shapes at hadron-hadron colliders

This article introduces definitions for a number of new event shapes and jet-rates in hadron-hadron dijet production. They are designed so as to be measurable in practice at the Tevatron and the LHC, and to be global so that they can be resummed with currently available techniques. We explain how to vary their sensitivity to beam fragmentation, limiting its impact for purely perturbative studies, or deliberately enhancing it so as to focus on non-perturbative effects. Explicit next-to-leading logarithmic resummed results are presented, as obtained with CAESAR.

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arXiv2004

Resummed event shapes at hadron colliders

We present recently defined jet-observables for hadron-hadron dijet production, which are designed to reconcile the seemingly conflicting theoretical requirement of globalness, which makes it possible to resum them (automatically) at NLL accuracy and the limited experimental reach of detectors, so that they are measurable at the Tevatron and at the LHC.

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arXiv2004

Effective theory approach to unstable particles

We present a novel treatment of resonant massive particles appearing as intermediate states in high energy collisions. The approach uses effective field theory methods to treat consistently the instability of the intermediate resonant state. As a result gauge invariance is respected in every step and calculations can in principle be extended to all orders in perturbation theory, the only practical limitation in going to higher orders being the standard difficulties related to multi-loop integrals. We believe that the longstanding problem related to the treatment of instability of particles is now solved.

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arXiv2003

Automated resummation of jet observables in QCD

We present a master formula, with applicability conditions, which allows us to automate the resummation of infrared and collinear logarithms appearing in distributions of jet observables in QCD at next-to-leading logarithmic accuracy.

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arXiv2003

Automated resummation of final state observables in QCD

We present an innovative method to resum infrared and collinear logarithms appearing in distributions of jet observables in QCD. The method, based on a general master formula with applicability conditions, allows resummations at next-to-leading logarithmic accuracy in an automated way. As a sample application we present resummed results in hadronic dijet events.

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arXiv2002

Seminumerical resummation of event shapes and jet rates

For many observables, the most difficult part of a single logarithmic resummation is the analytical treatment of the observable's dependence on multiple emissions. We present a general numerical method, which allows the resummation specifically of these single logarithms. Some first applications and new results for the thrust major, the oblateness and the two-jet rate in the Durham algorithm are also presented.

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arXiv2001

Interplay between perturbative and non-perturbative QCD in three-jet events

We present the perturbative (PT) and non-perturbative (NP) analysis of the cumulative out-of-event-plane momentum distribution in e+e- annihilation in the near-to-planar three-jet region. A physical interpretation based on simple QCD considerations and kinematical relations will be given, with the aim of extending the described techniques to other multi-jet processes and, possibly, to hadron-hadron collisions.

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