Oreste Nicrosini

Precision electroweak calculation of the production of a high transverse-momentum lepton pair at hadron colliders

We present a detailed study of the production of a high transverse-momentum lepton pair at hadron colliders, which includes the exact (α) electroweak corrections properly matched with leading logarithmic effects due to multiple photon emission, as required by the experiments at the Fermilab Tevatron and the CERN LHC. Numerical results for the relevant observables of single Z-boson production at hadron colliders are presented. The impact of the radiative corrections is discussed in detail. The presence in the proton of a photon density is considered and the effects of the photon-induced partonic subprocesses are analyzed. The calculation has been implemented in the new version of the event generator HORACE, which is available for precision simulations of the neutral and charged current Drell-Yan processes.

Precision electroweak calculation of the charged current Drell-Yan process

We present a detailed study of the charged current Drell-Yan process, which includes the exact (α) electroweak corrections properly matched with leading-log effects due to multiple-photon emission, as required by the experiments at the Tevatron and the LHC. Numerical results for the relevant observables of single W boson production at hadron colliders are presented. The impact of the radiative corrections and of some sources of theoretical uncertainty is discussed in detail. The calculation has been implemented in the new version of the event generator HORACE, which is available for precision simulations of the charged current Drell-Yan process.

Higgs Boson production in e+e− → μ+μ−bb

The production of the Standard Model Higgs boson in the four-fermion reaction

TOPAZ0 - a program for computing observables and for fitting cross sections and forward-backward asymmetries around the Z0 peak

e^+ e^- \to \mu^+ \mu^- b \bar b

On a semi-analytical and realistic approach to e+e− annihilation into fermion pairs and to Bhabha scattering within the minimal standard model at LEP energies

is studied. The complete tree-level matrix element, including signal and backgrounds in the standard electroweak theory, is computed and initial state radiation is taken into account in the leading-log approximation. A Monte Carlo event generator has been built and numerical results for some distributions of experimental interest for the search of the Higgs particle at future electron-positron colliders are shown, compared with those existing in the literature and commented.

Neutral-current Drell–Yan with combined QCD and electroweak corrections in the POWHEG BOX

Abstract The program TOPAZ0, which is designed for computing and fitting cross sections and forward-backward asymmetries of e + e - annihilation into fermion pairs and of Bhabha scattering around the Z 0 peak, is described. The various observables are computed over both a completely inclusive experimental set-up and a realistic one, i.e. with cuts on acollinearity, energy or invariant mass and angular acceptance of the outgoing fermions. Pure weak corrections at the one-loop level are included and leading higher-order corrections due to a potentially large top quark mass are taken into account. Depending on the experimental set-up initial state QED corrections are included by a convolution of the weakly corrected kernel distribution with a radiator function or with structure functions, where resummation of soft-photon effects and hard-photon emission up to O (α 2 ) are taken into account. Final state QED radiation, even in the presence of kinematical cuts, is treated analytically and exactly at O (α) and higher-order contributions are taken into account. QCD effects for the parameters of the Z 0 resonance and for s -dependent quantities are included. Recently proposed higher-order corrections, as initial state leptonic and hadronic pair production or O ( G 2 F m 4 t ), O (α s G F m 2 t ), O (α 3 s ), are taken into account as well. The program structure is highly modular and particular care has been devoted to computing efficiency and speed, both for annihilation and Bhabha channels.

Implementation of electroweak corrections in the POWHEG BOX: single W production

Abstract Theoretical predictions for the annihilation of e + e − into fermion pairs as well as for e + e − → e + e − around the Z 0 peak are reported. Different observables are considered, including the possibility of a realistic set-up for LEP physics, i.e. with cuts on acollinearity angle, energies or invariant mass and angular acceptance for the outgoing fermions. Pure weak corrections at the one-loop level are included in the formulation and leading higher order corrections due to a potentially large top quark mass are taken into account. Depending on the experimental set-up the initial state QED corrections are included by a convolution of the weakly corrected kernel distributions with a radiator function or with structure functions, where resummation of soft photon effects and hard photon emission up to O( α 2 ) are taken into account. Final state QED radiation, even in the presence of kinematical cuts, is treated analytically and exactly at O(α), and higher order contributions are taken into account. QCD effects are discussed for the parameters of the Z 0 resonance and for s -dependent quantities. Results and considerations for quantities which are physically observable at LEP are presented and discussed. The interplay with the experimental results is shown through an analysis of the LEP data, both at the level of the Z 0 parameters are given by the four LEP collaborations and at the level of the published results for the lineshape and asymmetry data. As a consequence constraints on the unknown parameters of the minimal standard model are deduced and analyzed. The features of a new semi-analytical computer program (TOPAZ0), which includes all the physical effects previously discussed, are briefly introduced. The numerical relevance of recently proposed higher order corrections, as initial state leptonic and hadronic pair production or O( G F 2 m t 4 ), O( α S G F m 2 ), O( α S 3 ), is analyzed in detail. A careful comparison with the existing programs is shown, indicating the overall agreement in the light of the present experimental errors and within the same choice of parameters, kinematical cuts and correction factor.

Combination of electroweak and QCD corrections to single W production at the Fermilab Tevatron and the CERN LHC

Following recent work on the combination of electroweak and strong radiative corrections to single W-boson hadroproduction in the POWHEG BOX framework, we generalize the above treatment to cover the neutral-current Drell–Yan process. According to the POWHEG method, we combine both the next-to-leading order (NLO) electroweak and the QED multiple photon corrections with the native NLO and Parton Shower QCD contributions. We show comparisons with the predictions of the electroweak generator HORACE, to validate the reliability and accuracy of the approach. We also present phenomenological results obtained with the new tool for physics studies at the LHC.

TOPAZO 2.0 - A program for computing de-convoluted and realistic observables around the Z0 peak

A bstractWe present a fully consistent implementation of electroweak and strong radiative corrections to single W hadroproduction in the POWHEG BOX framework, treating soft and collinear photon emissions on the same ground as coloured parton emissions. This framework can be easily extended to more complex electroweak processes. We describe how next-to-leading order (NLO) electroweak corrections are combined with the NLO QCD calculation, and show how they are interfaced to QCD and QED shower Monte Carlo. The resulting tool fills a gap in the literature and allows to study comprehensively the interplay of QCD and electroweak effects to W production using a single computational framework. Numerical comparisons with the predictions of the electroweak generator HORACE, as well as with existing results on the combination of electroweak and QCD corrections to W production, are shown for the LHC energies, to validate the reliability and accuracy of the approach.

WWGENPV — A Monte Carlo event generator for four-fermion production in e+e− → W+W− → 4f

Precision studies of the production of a high-transverse momentum lepton in association with missing energy at hadron colliders require that electroweak and QCD higher-order contributions are simultaneously taken into account in theoretical predictions and data analysis. Here we present a detailed phenomenological study of the impact of electroweak and strong contributions, as well as of their combination, to all the observables relevant for the various facets of the