arXiv subjects
Publications and source records attributed to Javier Mazzitelli.
We summarize the current status and near future prospects for next-to-next-to-leading order calculations matched to parton shower based on the MiNNLO$_{\rm PS}$ method. We give a theoretical overview, illustrate selected results for $ZZ\to 4\ell$ and top-pair production processes at the LHC, and provide an outlook of the future challenges.
The production of top-quark pairs in hadronic collisions is among the most important reactions in modern particle physics phenomenology and constitutes an instrumental avenue to study the properties of the heaviest quark observed in nature. The analysis of this process at the Large Hadron Collider relies heavily on Monte Carlo simulations of the final state events, whose accuracy is challenged by the outstanding precision of experimental measurements. In this letter we present the first matched computation of top-quark pair production at next-to-next-to-leading order in QCD with all-order radiative corrections as implemented via parton-shower simulations. Besides its intrinsic relevance for LHC phenomenology, this work also establishes an important step towards the simulation of other hadronic processes with colour charges in the final state.
We consider the production of a pair of heavy quarks and illustrate the derivation of the MiNNLO method to match next-to-next-to-leading order calculations with parton showers (NNLO+PS) for this class of processes. As a first application, we construct an event generator for the fully differential simulation of hadronic top-quark pair production at NNLO+PS and discuss all details of its implementation in a parton shower Monte Carlo framework. We present new phenomenological results for the Large Hadron Collider obtained by including the tree-level decays of the top quarks, while accounting for spin-correlation effects. A comprehensive comparison to LHC measurements shows an excellent description of experimental data across multiple hadronic and leptonic particle-level observables. The computer code is available for download within the POWHEG-BOX.
We combine NLO predictions with full top-quark mass dependence with approximate NNLO predictions for Higgs-boson pair production in gluon fusion, including the possibility to vary coupling parameters within a non-linear Effective Field Theory framework containing five anomalous couplings for this process. We study the impact of the anomalous couplings on various observables, and present Higgs-pair invariant-mass distributions at seven benchmark points characterising different $m_{hh}$ shape types. We also provide numerical coefficients for the approximate NNLO cross section as a function of the anomalous couplings at $\sqrt{s}=14$ TeV.
We report on the first fully differential calculation of the next-to-next-to-leading-order (NNLO) QCD radiative corrections to the production of bottom-quark pairs at hadron colliders. The calculation is performed by using the $q_T$ subtraction formalism to handle and cancel infrared singularities in real and virtual contributions. The computation is implemented in the Matrix framework, thereby allowing us to efficiently compute arbitrary infrared-safe observables in the four-flavour scheme. We present selected predictions for bottom-quark production at the Tevatron and at the LHC at different collider energies, and we perform some comparisons with available experimental results. We find that the NNLO corrections are sizeable, typically of the order of $25$-$35\%$, and they lead to a significant reduction of the perturbative uncertainties. Therefore, their inclusion is crucial for an accurate theoretical description of this process.
We consider top-quark pair production at the LHC within the MSbar scheme for the renormalisation of the top-quark mass, and we present predictions for total and differential cross sections at next-to-next-to-leading order (NNLO) in QCD. Our state-of-the-art calculation extends the available differential results by one order in the perturbative expansion, and it is relevant for a precise determination of the top-quark mass, including possible effects of the running mass in the MSbar scheme. We consider variations of the scale at which the MSbar mass of the top quark is evaluated, extending the usual 7-point to a 15-point scale variation. This additional variation is crucial for a reliable estimate of the theoretical uncertainties, especially at low perturbative orders and close to the production threshold of the top-quark pair. We also compute, for the first time, the invariant-mass distribution of the top-quark pair by using a running mass, evaluated at a dynamic scale. Our predictions for the invariant-mass distribution in the MSbar scheme are compared with a recent measurement performed by the CMS Collaboration. We observe that the inclusion of the NNLO corrections improves the agreement with the data, and we discuss effects due to the QCD running of the MSbar mass of the top quark.
In this work we extend the $q_T$-subtraction formalism, originally developed for QCD corrections, to the case of mixed QCD$\otimes$QED corrections, and apply it to the fully exclusive calculation of the ${\cal{O}}(α_sα)$ contribution to the production of an off-shell $Z$ boson in hadronic collisions. We present explicit results for the subtraction term and the hard factor, therefore providing all the ingredients needed for the application of the formalism up to ${\cal{O}}(α_sα)$. To study the phenomenological impact we consider the decay of the off-shell $Z$ boson into a pair of neutrinos, and present kinematical distributions for the final-state leptons at LHC energies.
In this work we analyse the triple Higgs boson production cross section at hadron colliders via gluon fusion, and present for the first time the full set of QCD NNLO corrections in the heavy top limit. In order to account for finite top mass effects we perform two different reweighting procedures, and study the dependence of the result on the choice of the approximation. Combining the most accurate predictions available to date, we present the following result for the total NNLO cross section for triple Higgs boson production at a 100 TeV collider: $σ_\text{NNLO}=5.56^{+5\%}_{-6\%} \pm 20\%$ fb, where the first uncertainty is an estimate for higher order effects from scale variations, while the last one is an estimate for the missing finite top mass effects.
We report on a new fully differential calculation of the next-to-next-to-leading-order (NNLO) QCD radiative corrections to the production of top-quark pairs at hadron colliders. The calculation is performed by using the $q_T$ subtraction formalism to handle and cancel infrared singularities in real and virtual contributions. The computation is implemented in the Matrix framework, thereby allowing us to efficiently compute arbitrary infrared-safe observables for stable top quarks. We present NNLO predictions for several single- and double-differential kinematical distributions in $pp$ collisions at the centre-of-mass energy $\sqrt{s}=13$ TeV, and we compare them with recent LHC data by the CMS collaboration.
We report on a new calculation of the next-to-next-to-leading order (NNLO) QCD radiative corrections to the inclusive production of top-quark pairs at hadron colliders. The calculation is performed by using the $q_T$ subtraction formalism to handle and cancel infrared singular contributions at intermediate stages of the computation. We present numerical results for the total cross section in $pp$ collisions at $\sqrt{s}=8$ TeV and $13$ TeV, and we compare them with those obtained by using the publicly available numerical program Top++. Our computation represents the first complete application of the $q_T$ subtraction formalism to the hadroproduction of a colourful high-mass system at NNLO.
We perform the all orders resummation of threshold enhanced contributions for the Higgs boson pair production cross section via gluon fusion, including finite top quark mass ($M_t$) effects. We present results for the total cross section and Higgs pair invariant mass ($M_{hh}$) distribution. We obtain results at next-to-leading logarithmic accuracy (NLL) which retain the full $M_t$ dependence, and are matched to the full next-to-leading order (NLO) prediction. Our NLL+NLO results represent the most advanced prediction with full $M_t$ dependence for this process, and produce an increase of about 4% in the total cross section with respect to the NLO result for LHC energies, and for a central scale $μ_0 = M_{hh}/2$. We also consistently combine the full NLL with the next-to-next-to-leading logarithmically (NNLL) accurate resummation computed in the Born-improved large-$M_t$ limit, and match it to the next-to-next-to-leading order approximation of Ref. \cite{Grazzini:2018bsd}, so called NNLO_FTa. We find that the resummation effects are very small at NNLL for $μ_0 = M_{hh}/2$, in particular below 1% at 13 TeV, indicating that the perturbative expansion is under control. In all cases the resummation effects are found to be substantially larger for the central scale $μ_0 = M_{hh}$, resulting in a more stable cross section with respect to scale variations than the fixed order calculation.
We consider QCD radiative corrections to Higgs boson pair production through gluon fusion in proton collisions. We combine the exact next-to-leading order (NLO) contribution, which features two-loop virtual amplitudes with the full dependence on the top quark mass $M_t$, with the next-to-next-to-leading order (NNLO) corrections computed in the large-$M_t$ approximation. The latter are improved with different reweighting techniques in order to account for finite-$M_t$ effects beyond NLO. Our reference NNLO result is obtained by combining one-loop double-real corrections with full $M_t$ dependence with suitably reweighted real--virtual and double-virtual contributions evaluated in the large-$M_t$ approximation. We present predictions for inclusive cross sections in $pp$ collisions at $\sqrt{s}$=13, 14, 27 and 100TeV and we discuss their uncertainties due to missing $M_t$ effects. Our approximated NNLO corrections increase the NLO result by an amount ranging from +12% at $\sqrt{s}$=13TeV to +7% at $\sqrt{s}$=100TeV, and the residual uncertainty from missing $M_t$ effects is estimated to be at the few percent level. Our calculation is fully differential in the Higgs boson pair and the associated jet activity: we also present predictions for various differential distributions at $\sqrt{s}$=14 and 100TeV. Our results represent the most advanced perturbative prediction available to date for this process.
In this paper, we present the computation of the Higgs boson pair production cross section, both inclusive as well as differential on the invariant mass distribution, at next-to-next-to-leading order (NNLO) in QCD including effects of new physics beyond the standard model. We parametrize the effects of new physics with the relevant dimension 6 operators in a standard model effective field theory (EFT) approach and examine their phenomenology. The dependence of the NNLO $K$-factor on the EFT couplings is analysed, finding that, while rather flat for a number of EFT coefficients, it can considerably differ from the standard model value in some particular regions of the parameter space. We present explicit examples of (almost) degeneracy in the NNLO cross-section with respect to the anomalous couplings, showing that the invariant mass distribution has a much larger sensitivity to phenomena beyond the standard model and can be used as a tool to discriminate their effect.
In this paper we compute the QCD corrections for the triple Higgs boson production cross section via gluon fusion, within the heavy-top approximation. We present, for the first time, analytical results for the next-to-leading order corrections, and also compute the soft and virtual contributions of the next-to-next-to-leading order cross section. We provide predictions for the total cross section and the triple Higgs invariant mass distribution. We find that the QCD corrections are large at both perturbative orders, and that the scale uncertainty is substantially reduced when the second order perturbative corrections are included.
We present an effective description of a spin two massive state and a pseudo Nambu-Goldstone boson Higgs in a two site model. Using this framework we model the spin two state as a massive graviton and we study its phenomenology at the LHC. We find that a reduced set of parameters can describe the most important features of this scenario. We address the question of which channel is the most sensitive to detect this graviton. Instead of designing search strategies to estimate the significance in each channel, we compare the ratio of our theoretical predictions to the limits set by available experimental searches for all the decay channels and as a function of the free parameters in the model. We discuss the phenomenological details contained in the outcome of this simple procedure. The results indicate that, for the studied masses between 0.5 and 3 TeV, the channels to look for such a graviton resonance are mainly $ZZ$, $WW$ and $γγ$. This is the case even though top and bottom quarks dominate the branching ratios, since their experimental sensitivity is not as good as the one of the electro-weak gauge bosons. We find that as the graviton mass increases, the $ZZ$ and $WW$ channels become more important because of its relatively better enhancement over background, mainly due to fat jet techniques. We determine the region of the parameter space that has already been excluded and the reach for the LHC next stages. We also estimate the size of the loop-induced contributions to the production and decay of the graviton, and show in which region of the parameter space their effects are relevant for our analysis.
We report on the first fully differential calculation for double Higgs boson production through gluon fusion in hadron collisions up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. The calculation is performed in the heavy-top limit of the Standard Model, and in the phenomenological results we focus on pp collisions at 14 TeV. We present differential distributions through NNLO for various observables including the transverse-momentum and rapidity distributions of the two Higgs bosons. NNLO corrections are at the level of 10%-25% with respect to the next-to-leading order (NLO) prediction with a residual scale uncertainty of 5%-15% and an overall mild phase-space dependence. Only at NNLO the perturbative expansion starts to converge yielding overlapping scale uncertainty bands between NNLO and NLO in most of the phase-space. The calculation includes NLO predictions for pp -> HH+jet+X. Corrections to the corresponding distributions exceed 50% with a residual scale dependence of 20%-30%.
We study the diphoton excess at 750 GeV reported by ATLAS and CMS, by assuming that it corresponds to a new spin-two resonant state. We model this state as a massive graviton in a two-site model. We show that the very stringent bounds from $VV$ final states can be evaded naturally by considering that the Higgs is a pseudo Nambu-Goldstone boson. In this case the couplings of the graviton to the longitudinal electroweak gauge bosons can be parametrically suppressed. On the other hand, partial compositeness allows to suppress the leptonic channels. We compute loop-induced contributions to the graviton couplings by the presence of the SM third generation of quarks and composite partners of the SM fermions and obtain that they are not important. We find that the diphoton signal and the experimental constraints from other decay channels can be reproduced in a large and natural region of the parameter space of the theory.
We perform the threshold resummation for Higgs pair production in the dominant gluon fusion channel to next-to-next-to-leading logarithmic (NNLL) accuracy. The calculation includes the matching to the next-to-next-to-leading order (NNLO) cross section obtained in the heavy top-quark limit, and results in an increase of the inclusive cross section up to 7% at the LHC with centre-of-mass energy Ecm=14TeV, for the choice of factorization and renormalization scales $μ_F=μ_R=Q$, being Q the invariant mass of the Higgs pair system. After the resummation is implemented, we estimate the theoretical uncertainty from the perturbative expansion to be reduced to about +-5.5%, plus ~10% from finite top-mass effects. The resummed cross section turns out to be rather independent of the value chosen for the central factorization and renormalization scales in the usual range (Q/2,Q).