Massimiliano Grazzini

Vector Boson Production at Hadron Colliders: A Fully Exclusive QCD Calculation at Next-to-Next-to-Leading Order

We consider QCD radiative corrections to the production of W and Z bosons in hadron collisions. We present a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform this NNLO computation, we use a recently proposed version of the subtraction formalism. The calculation includes the gamma-Z interference, finite-width effects, the leptonic decay of the vector bosons, and the corresponding spin correlations. Our calculation is implemented in a parton level Monte Carlo program. The program allows the user to apply arbitrary kinematical cuts on the final-state leptons and the associated jet activity and to compute the corresponding distributions in the form of bin histograms. We show selected numerical results at the Fermilab Tevatron and the LHC.

Next-to-next-to-leading-order subtraction formalism in hadron collisions and its application to Higgs-boson production at the large hadron collider.

We consider higher-order QCD corrections to the production of colorless high-mass systems (lepton pairs, vector bosons, Higgs bosons, etc.) in hadron collisions. We propose a new formulation of the subtraction method to numerically compute arbitrary infrared-safe observables for this class of processes. To cancel the infrared divergences, we exploit the universal behavior of the associated transverse-momentum (qT) distributions in the small-qT region. The method is illustrated in general terms up to the next-to-next-to-leading order in QCD perturbation theory. As a first explicit application, we study Higgs-boson production through gluon fusion. Our calculation is implemented in a parton level Monte Carlo program that includes the decay of the Higgs boson into two photons. We present selected numerical results at the CERN Large Hadron Collider.

Soft-gluon resummation for Higgs boson production at hadron colliders

We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadron collisions. We compute the cross section, performing the all-order resummation of multiple soft-gluon emission at next-to-next-to-leading logarithmic level. Known fixed-order results (up to next-to-next-to-leading order) are consistently included in our calculation. We give phenomenological predictions for Higgs boson production at the Tevatron and at the LHC. We estimate the residual theoretical uncertainty from perturbative QCD contributions. We also quantify the differences obtained by using the presently available sets of parton distributions.

Transverse-momentum resummation and the spectrum of the Higgs boson at the LHC

Abstract We consider the transverse-momentum ( q T ) distribution of generic high-mass systems (lepton pairs, vector bosons, Higgs particles, …) produced in hadron collisions. At small q T , we concentrate on the all-order resummation of the logarithmically-enhanced contributions in QCD perturbation theory. We elaborate on the b-space resummation formalism and introduce some novel features: the large logarithmic contributions are systematically exponentiated in a process-independent form and, after integration over q T , they are constrained by perturbative unitarity to give a vanishing contribution to the total cross section. At intermediate and large q T , resummation is consistently combined with fixed-order perturbative results, to obtain predictions with uniform theoretical accuracy over the entire range of transverse momenta. The formalism is applied to Standard Model Higgs boson production at LHC energies. We combine the most advanced perturbative information available at present for this process: resummation up to next-to-next-to-leading logarithmic accuracy and fixed-order perturbation theory up to next-to-leading order. The results show a high stability with respect to perturbative QCD uncertainties.

ZZ production at hadron colliders in NNLO QCD

Charged gauge boson pair production at the Large Hadron Collider allows detailed probes of the fundamental structure of electroweak interactions. We present precise theoretical predictions for on-shell W+ W- production that include, for the first time, QCD effects up to next to next to leading order in perturbation theory. As compared to next to leading order, the inclusive W+ W- cross section is enhanced by 9% at 7 TeV and 12% at 14 TeV. The residual perturbative uncertainty is at the 3% level. The severe contamination of the W+ W- cross section due to top-quark resonances is discussed in detail. Comparing different definitions of top-free W+ W- production in the four and five flavor number schemes, we demonstrate that top-quark resonances can be separated from the inclusive W+ W- cross section without a significant loss of theoretical precision.

Higgs production in hadron collisions: soft and virtual QCD corrections at NNLO

We consider QCD corrections to Higgs boson production through gluon{gluon fusion in hadron collisions. Using the recently evaluated (14) two-loop amplitude forthisprocessandthecorresponding factorizationformulae(15){(18)de- scribingsoft-gluonbremsstrahlungatO( 2 ),wecomputethesoftandvirtualcontri- butionstothenext-to-next-to-leadingordercrosssection. Wealsodiscusssoft-gluon resummation at next-to-next-to-leading logarithmic accuracy. Numerical results for Higgs boson production at the LHC are presented.

Infrared factorization of tree-level QCD amplitudes at the next-to-next-to-leading order and beyond ☆

Abstract We study the infrared behaviour of tree-level QCD amplitudes and we derive infrared-factorization formulae that are valid at any perturbative order. We explicitly compute all the universal infrared factors that control the singularities in the various soft and/or collinear limits at O (α S 2 ) .

Diphoton production at hadron colliders: a fully-differential QCD calculation at NNLO

We consider direct diphoton production in hadron collisions, and we compute the next-to-next-to-leading order QCD radiative corrections at the fully differential level. Our calculation uses the q(T) subtraction formalism, and it is implemented in a parton-level Monte Carlo program. The program allows the user to apply arbitrary kinematical cuts on the final-state photons and the associated jet activity and to compute the corresponding distributions in the form of bin histograms. We present selected numerical results related to Higgs boson searches at the LHC and corresponding results at the Tevatron.

Higgs production through gluon fusion: Updated cross sections at the Tevatron and the LHC

Abstract We present updated predictions for the total cross section for Higgs boson production by gluon–gluon fusion in hadron collisions. Our calculation includes the most advanced theoretical information available at present for this observable: soft-gluon resummation up to next-to-next-to-leading logarithmic accuracy, the exact treatment of the bottom-quark contribution up to next-to-leading order, and two-loop electroweak effects. We adopt the most recent parametrization of parton distribution functions at next-to-next-to-leading order, and we evaluate the corresponding uncertainties. In comparison with our previous central predictions, at the Tevatron the difference ranges from +9% for m H = 115 GeV to −9% for m H = 200 GeV . At the LHC the cross section is instead significantly increased. The effect goes from +30% for m H = 115 GeV to +9% for m H = 300 GeV , and is mostly due to the new parton distribution functions. We also provide new predictions for the LHC at s = 10 TeV .

NNLO predictions for the Higgs boson signal in the H → WW → lνlν and H → ZZ → 4l decay channels

We consider Standard Model Higgs boson production by gluon-gluon fusion in hadron collisions. We present a calculation of the next-to-next-to-leading order QCD corrections to the cross section in the H ? WW ? l?l? and H ? ZZ ? 4l decay channels. The calculation is implemented in the parton level Monte Carlo program HNNLO and allows us to apply arbitrary cuts on the final state leptons and the associated jet activity. We present selected numerical results for the signal cross section at the LHC, by using all the nominal cuts proposed for the forthcoming Higgs boson search.