Publications by Giulia Zanderighi


Electroweak W<sup>+</sup>W<sup>-</sup> jj prodution at NLO in QCD matched with parton shower in the POWHEG-BOX

Journal of High Energy Physics 2013 (2013)

B Jäger, G Zanderighi

We present an implementation of electroweak W + W - jj production at hadron colliders in the POWHEG framework, a method that allows the interfacing of a next-to-leading order QCD calculation with parton shower Monte Carlo programs. We provide results for both, fully and semi-leptonic decay modes of the weak bosons, taking resonant and non-resonant contributions and spin correlations of the final-state particles into account. To illustrate the versatility of our implementation, we provide phenomenological results for two representative scenarios with a light and with a heavy Higgs boson, respectively, and in a kinematic regime of highly boosted gauge bosons. The impact of the parton shower is found to depend on the setup and the observable under investigation. In particular, distributions related to a central-jet veto are more sensitive to these effects. Therefore the impact of radiation by the parton shower on next-to-leading order predictions should be assessed carefully on a case-by-case basis. © 2013 SISSA, Trieste, Italy.


MINLO: Multi-scale improved NLO

Journal of High Energy Physics 2012 (2012)

K Hamilton, P Nason, G Zanderighi

In the present work we consider the assignment of the factorization and renormalization scales in hadron collider processes with associated jet production, at next-toleading order (NLO) in perturbation theory. We propose a simple, definite prescription to this end, including Sudakov form factors to consistently account for the distinct kinematic scales occuring in such collisions. The scheme yields results that are accurate at NLO and, for a large class of observables, it resums to all orders the large logarithms that arise from kinematic configurations involving disparate scales. In practical terms the method is most simply understood as an NLO extension of the matrix element reweighting procedure employed in tree level matrix element-parton shower merging algorithms. By way of a proof-of-concept, we apply the method to Higgs and Z boson production in association with up to two jets.


Gauge boson production at colliders - Predictions for precision studies

Pramana - Journal of Physics 79 (2012) 603-616

G Zanderighi

The status of today's theoretical description of Standard Model (SM) processes involving gauge bosons at the Tevatron and the LHC, and of the tools that are used in their phenomenological studies are reviewed. A few recent ideas to further improve on the way technically challenging calculations can be performed also are discussed. © Indian Academy of Sciences.


One-loop calculations in quantum field theory: From Feynman diagrams to unitarity cuts

Physics Reports (2012)

RK Ellis, Z Kunszt, K Melnikov, G Zanderighi


NLL plus NNLO predictions for jet-veto efficiencies in Higgs-boson and Drell-Yan production

JOURNAL OF HIGH ENERGY PHYSICS (2012) ARTN 159

A Banfi, GP Salam, G Zanderighi


Next-to-leading order QCD corrections to electroweak Zjj production in the POWHEG box

Journal of High Energy Physics 2012 (2012)

B Jager, S Schneider, G Zanderighi

We present an implementation of electroweak Z-boson production in association with two jets at hadron colliders in the POWHEG framework, a method that allows the interfacing of NLO-QCD calculations with parton-shower Monte Carlo programs. We focus on the leptonic decays of the weak gauge boson, and take photonic and non-resonant contributions to the matrix elements fully into account. We provide results for observables of particular importance for the suppression of QCD backgrounds to vector-boson fusion processes by means of central-jet-veto techniques. While parton-shower effects are small for most observables associated with the two hardest jets, they can be more pronounced for distributions that are employed in central-jet-veto studies. © SISSA 2012.


One-loop calculations in quantum field theory: From Feynman diagrams to unitarity cuts

Physics Reports 518 (2012) 141-250

RK Ellis, Z Kunszt, K Melnikov, G Zanderighi

The success of the experimental program at the Tevatron re-inforced the idea that precision physics at hadron colliders is desirable and, indeed, possible. The Tevatron data strongly suggests that one-loop computations in QCD describe hard scattering well. Extrapolating this observation to the LHC, we conclude that knowledge of many short-distance processes at next-to-leading order may be required to describe the physics of hard scattering. While the field of one-loop computations is quite mature, parton multiplicities in hard LHC events are so high that traditional computational techniques become inefficient. Recently, new approaches based on unitarity have been developed for calculating one-loop scattering amplitudes in quantum field theory. These methods are especially suitable for the description of multi-particle processes in QCD and are amenable to numerical implementations. We present a systematic pedagogical description of both conceptual and technical aspects of the new methods. © 2012 Elsevier B.V.


Gluon fusion contribution to W <sup>+</sup>W <sup>-</sup> + jet production

Journal of High Energy Physics 2012 (2012)

T Melia, K Melnikov, R Röntsch, M Schulze, G Zanderighi

We describe the computation of the gg → W + W - g process that contributes to the production of two W-bosons and a jet at the CERN Large Hadron Collider (LHC). While formally of next-to-next-to-leading order (NNLO) in QCD, this process can be evaluated separately from the bulk of NNLO QCD corrections because it is finite and gauge-invariant. It is also enhanced by the large gluon flux and by selection cuts employed in the Higgs boson searches in the decay channel H → W + W - , as was first pointed out by Binoth et al. in the context of gg → W + W - production. For cuts employed by the ATLAS collaboration, we find that the gluon fusion contribution to pp → W + W - j enhances the background by about ten percent and can lead to moderate distortions of kinematic distributions which are instrumental for the ongoing Higgs boson searches at the LHC. We also release a public code to compute the NLO QCD corrections to this process, in the form of an add-on to the package MCFM. © 2012 SISSA.


Higgs- and Z-boson production with a jet veto

Physical Review Letters 109 (2012)

A Banfi, PF Monni, GP Salam, G Zanderighi

We derive first next-to-next-to-leading logarithmic resummations for jet-veto efficiencies in Higgs and Z-boson production at hadron colliders. Matching with next-to-next-to-leading order results allows us to provide a range of phenomenological predictions for the LHC, including cross-section results, detailed uncertainty estimates, and comparisons to current widely used tools. © 2012 American Physical Society.


NLL+NNLO predictions for jet-veto efficiencies in Higgs-boson and Drell-Yan production

Journal of High Energy Physics 2012 (2012)

A Banfi, GP Salam, G Zanderighi

Using the technology of the CAESAR approach to resummation, we examine the jet-veto efficiency in Higgs-boson and Drell-Yan production at hadron colliders and show that at next-to-leading logarithmic (NLL) accuracy the resummation reduces to just a Sudakov form factor. Matching with NNLO calculations results in stable predictions for the case of Drell-Yan production, but reveals substantial uncertainties in gluon-fusion Higgs production, connected in part with the poor behaviour of the perturbative series for the total cross section. We compare our results to those from powheg with and without reweighting by HqT, as used experimentally, and observe acceptable agreement. In an appendix we derive the part of the NNLL resummation corrections associated with the radius dependence of the jet algorithm.


NLO corrections to electroweak and QCD production of W+W+ plus two jets in the POWHEG BOX

JOURNAL OF HIGH ENERGY PHYSICS (2011) ARTN 055

B Jaeger, G Zanderighi


W+W-, W Z and ZZ production in the POWHEG BOX

JOURNAL OF HIGH ENERGY PHYSICS (2011) ARTN 078

T Melia, P Nason, R Roentsch, G Zanderighi


Next-to-leading order QCD corrections for W<sup>+</sup>W<sup>-</sup> pair production in association with two jets at hadron colliders

Physical Review D - Particles, Fields, Gravitation and Cosmology 83 (2011)

T Melia, K Melnikov, R Röntsch, G Zanderighi

We compute the NLO QCD corrections to the pair production of W-bosons in association with two jets at the Tevatron and the LHC. This process is an important background to heavy Higgs-boson production in association with two jets, either in gluon or weak boson fusion. We consider leptonic decays of W-bosons and include all the spin correlations exactly. For natural choices of the renormalization scale, the NLO QCD corrections to pp(p̄)→W + W - jj are moderate but different for various values of the center-of-mass collision energy at the LHC and the Tevatron, emphasizing the need to compute them explicitly. © 2011 American Physical Society.


W+W+ plus dijet production in the POWHEG BOX

EUROPEAN PHYSICAL JOURNAL C 71 (2011) ARTN 1670

T Melia, P Nason, R Rontsch, G Zanderighi


W<sup>+</sup>W<sup>-</sup>, WZ and ZZ production in the POWHEG BOX

Journal of High Energy Physics 2011 (2011)

T Melia, P Nason, R Röntsch, G Zanderighi

We present an implementation of the vector boson pair production processes ZZ, W + W - and WZ within the POWHEG framework, which is a method that allows the interfacing of NLO calculations to shower Monte Carlo programs. The implementation is built within the POWHEG BOX package. The Z/γ * interference, as well as singly resonant contributions, are properly included. We also considered interference terms arising from identical leptons in the final state. As a result, all contributions leading to the desired four-lepton system have been included in the calculation, with the sole exception of the interference between ZZ and W + W - in the production of a pair of same-flavour, oppositely charged fermions and a pair of neutrinos, which we show to be fully negligible. Anomalous trilinear couplings can be also set in the program, and we give some examples of their effect at the LHC. We have made the relevant code available at the POWHEG BOX web site. © SISSA 2011.


A proposal for a standard interface between Monte Carlo tools and one-loop programs

Computer Physics Communications 181 (2010) 1612-1622

T Binoth, F Boudjema, G Dissertori, A Lazopoulos, A Denner, S Dittmaier, R Frederix, N Greiner, S Höche, W Giele, P Skands, J Winter, T Gleisberg, J Archibald, G Heinrich, F Krauss, D Maître, M Huber, J Huston, N Kauer, F Maltoni, C Oleari, G Passarino, R Pittau, S Pozzorini, T Reiter, S Schumann, G Zanderighi

Many highly developed Monte Carlo tools for the evaluation of cross sections based on tree matrix elements exist and are used by experimental collaborations in high energy physics. As the evaluation of one-loop matrix elements has recently been undergoing enormous progress, the combination of one-loop matrix elements with existing Monte Carlo tools is on the horizon. This would lead to phenomenological predictions at the next-to-leading order level. This note summarises the discussion of the next-to-leading order multi-leg (NLM) working group on this issue which has been taking place during the workshop on Physics at TeV Colliders at Les Houches, France, in June 2009. The result is a proposal for a standard interface between Monte Carlo tools and one-loop matrix element programs. Dedicated to the memory of, and in tribute to, Thomas Binoth, who led the effort to develop this proposal for Les Houches 2009. Thomas led the discussions, set up the subgroups, collected the contributions, and wrote and edited this paper. He made a promise that the paper would be on the arXiv the first week of January, and we are faithfully fulfilling his promise. In his honour, we would like to call this the Binoth Les Houches Accord. © 2010 Elsevier B.V.


W+3 jet production at the LHC as a signal or background

Physical Review D - Particles, Fields, Gravitation and Cosmology 81 (2010)

K Melnikov, G Zanderighi

We discuss the production of W bosons in association with three jets at the LHC. We investigate how next-to-leading order QCD corrections modify basic kinematic distributions of jets and leptons. We also address the magnitude of next-to-leading QCD effects in W+3 jet observables, relevant for supersymmetry searches at the LHC. © 2010 The American Physical Society.


NLO QCD corrections to five-jet production at LEP and the extraction of alpha(s)(M-Z)

JOURNAL OF HIGH ENERGY PHYSICS (2010) ARTN 050

R Frederix, S Frixione, K Melnikov, G Zanderighi


Phenomenology of event shapes at hadron colliders

JOURNAL OF HIGH ENERGY PHYSICS (2010) ARTN 038

A Banfi, GP Salam, G Zanderighi


Next-to-leading order QCD predictions for W(+)W(+)jj production at the LHC

JOURNAL OF HIGH ENERGY PHYSICS (2010) ARTN 053

T Melia, K Melnikov, R Roentsch, G Zanderighi

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