We present a calculation of t-channel single-top-quark production and decay in the five-flavor scheme at NNLO. Our results resolve a disagreement between two previous calculations of this process that found a difference in the inclusive cross section at the level of the NNLO coefficient itself. We compare in detail with the previous calculations at the inclusive, differential and fiducial level including b-quark tagging at a fixed scale $μ=m_t$. In addition, we advocate the use of double deep inelastic scattering (DDIS) scales ($μ^2=Q^2$ for the light-quark line and $μ^2=Q^2+m_t^2$ for the heavy-quark line) that maximize perturbative stability and allow for robust scale uncertainties. All NNLO and NLO$\,\otimes\,$NLO contributions for production and decay are included in the on-shell and vertex-function approximation. We present fiducial and differential results for a variety of observables used in Standard Model and Beyond Standard Model analyses, and find an important difference between the NLO and NNLO predictions of exclusive $t+n$-jet cross sections. Overall we find that NNLO corrections are crucial for a precise identification of the t-channel process.
We report on a fully differential next-to-next-to-leading order (NNLO) calculation of s-channel single top (anti-)quark production with a semi-leptonic decay at the LHC, neglecting the color correlation between the light and heavy quark lines and in the narrow width approximation. The NNLO corrections can increase the cross section by about 10% in the low transverse momentum region of the top quark and reduce scale variation uncertainty. In order to compare with experimental results without unfolding procedures, we also present theoretical predictions with fiducial cuts, including total cross …
We present a comprehensive study of differential distributions for Tevatron top-pair events at the level of stable top quarks. All calculations are performed in NNLO QCD with the help of a fully differential partonic Monte-Carlo and are exact at this order in perturbation theory. We present predictions for all kinematic distributions for which data exists. Particular attention is paid on the top-quark forward-backward asymmetry which we study in detail. We compare the NNLO results with existing approximate NNLO predictions as well as differential distributions computed with different parton di…
We calculate all main top-quark pair differential distributions at the Tevatron. For the first time Tevatron predictions for this process include all Standard Model corrections through NLO (referred to as complete-NLO) consistently combined with previously computed NNLO QCD corrections. We also assess, for the first time, the impact of dynamical scales on predictions for the latest Tevatron measurements.
We release fastNLO tables with NNLO QCD top-quark pair differential distributions corresponding to 8 TeV ATLAS [Eur. Phys. J. C 76 538 (2016)] and CMS [Eur. Phys. J. C 75 542 (2015)] measurements. This is the first time fastNLO tables with NNLO QCD accuracy have been made publicly available. The tables are indispensable in pdf fits and allow, for the first time, very fast calculation of differential distributions with any pdf set and for different values of $α_s$. The numerical accuracy of the resulting differential distributions is high and comparable to the accuracy of all publicly available…
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 $pp$ collision…
We present the inclusive transverse momentum distribution for Higgs bosons produced in bottom quark annihilation at the LHC. The results are obtained in the five-flavor scheme. The soft and collinear terms at small $p_T$ are resummed through NNLL accuracy and matched to the NNLO transverse momentum distribution at large $p_T$. We find that the theoretical uncertainty, derived from a variation of the unphysical scales entering the calculation, is significantly reduced with respect to lower orders.
We present numerical calculations of the partial width of the charged Higgs boson decay into a top quark, $H^- \rightarrow \bar{t} + b + X$, and the partial width of the top quark decay into a light charged Higgs boson $t \rightarrow H^+ + b + X$ at next-to-next-to-leading order (NNLO) in QCD, based on a factorization formula of the jet mass. The NNLO corrections significantly reduce the renormalization scale dependence of the partial decay width in both cases. We show relative size of the NNLO corrections for different charged Higgs boson masses and for different renormalization scales. The N…
We present phenomenological predictions at NNLO QCD and NLO EW accuracy for $t \bar t$ distributions at the LHC (8 and 13 TeV). We discuss the impact of the electroweak corrections and quantify the theory errors from scale and PDF uncertainties. Moreover, we show the relevance of a precise determination of the photon PDF for $t \bar t$ distributions.
We calculate a comprehensive set of spin correlations and differential distributions in top-quark pair production and decay to dilepton final states. This is the first time such a complete study is performed at next-to-next-to leading order in QCD. Both inclusive and fiducial distributions are presented and analyzed. Good agreement between NNLO QCD predictions and data is found. We demonstrate that it is possible to perform high-precision comparisons of fixed-order calculations with fiducial-level data. Subtleties of the top quark definition are raised and clarified. Some of those are found to…
We consider extensions of the Standard Model with a number of additional heavy quarks which couple to the Higgs boson via top-like Yukawa interactions. We construct an effective theory valid for a Higgs boson mass which is lighter than twice the lightest heavy quark mass and compute the corresponding Wilson coefficient through NNLO. We present numerical results for the gluon fusion cross-section at the Tevatron for an extension of the Standard Model with a fourth generation of heavy quarks. The gluon fusion cross-section is enhanced by a factor of roughly 9 with respect to the Standard Model v…
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…
Top-quark pair production at the LHC is directly sensitive to the gluon PDF at large x. While total cross-section data is already included in several PDF determinations, differential distributions are not, because the corresponding NNLO calculations have become available only recently. In this work we study the impact on the large-x gluon of top-quark pair differential distributions measured by ATLAS and CMS at $\sqrt{s}=8$ TeV. Our analysis, performed in the NNPDF3.0 framework at NNLO accuracy, allows us to identify the optimal combination of LHC top-quark pair measurements that maximize the …
We describe predictions for top-quark pair differential distributions at hadron colliders, which combine state-of-the-art NNLO QCD calculations and NLO electroweak corrections together with double resummation at NNLL$'$ accuracy of threshold logarithms and small-mass logarithms. This is the first time that such a combination has appeared in the literature. Numerical results are presented for the invariant-mass distribution, the transverse-momentum distribution as well as rapidity distributions.
We report on a complete calculation of electroweak production of top quark pairs in $e^+e^-$ annihilation at next-to-next-to-leading order in Quantum Chromodynamics. Our setup is fully differential and can be used to calculate any infrared-safe observable. Especially we calculated the next-to-next-to-leading order corrections to top-quark forward-backward asymmetry and found sizable effects. Our results show a large reduction of the theoretical uncertainties in predictions of the forward-backward asymmetry, and allow a precision determination of the top quark electroweak couplings at future $e…
We present a fully differential next-to-next-to-leading order calculation of charm quark production in charged-current deep-inelastic scattering, with full charm-quark mass dependence. The next-to-next-to-leading order corrections in perturbative quantum chromodynamics are found to be comparable in size to the next-to-leading order corrections in certain kinematic regions. We compare our predictions with data on dimuon production in (anti-)neutrino scattering from a heavy nucleus. Our results can be used to improve the extraction of the parton distribution function of a strange quark in the nu…
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 …
We present a fully differential next-to-next-to-leading order calculation of t-channel single top-quark production and decay at the LHC under narrow-width approximation and neglecting cross-talk between incoming protons. We focus on the fiducial cross sections at 13 TeV, finding that the next-to-next-to-leading order QCD corrections can reach the level of -6%. The scale variations are reduced to the level of a percent. Our results can be used to improve experimental acceptance estimates and the measurements of the single top-quark production cross section and the top-quark electroweak coupling…
We present the calculation of QCD radiative corrections to heavy-quark production at NNLO. The calculation is implemented in an updated version of \textsc{Matrix}, which allows us to obtain multidifferential predictions for stable top quarks. We also report on the NNLO calculation for $b{\bar b}$ production and comment on the inclusion of top-quark decays and of the extension of our results to $t\bar tH$.
We present the derivation of the NNLO two-parton final state contributions to top pair production in the quark-antiquark channel proportionnal to the leading colour factor $N_c^2$. Together with the three and four-parton NNLO contributions presented in a previous publication, this enables us to complete the phenomenologically most important NNLO corrections to top pair hadro-production in this channel. We derive this two-parton contribution using the massive extension of the NNLO antenna subtraction formalism and implement those corrections in a parton-level event generator providing full kine…
I present recent NNLO-NNLL results for top quark hadroproduction at the Tevatron. The total cross section as well as transverse momentum and rapidity distributions are shown.
We consider the decay of a neutral Higgs boson of arbitrary CP nature to a massive quark antiquark pair at next-to-next-to-leading order in perturbative QCD. Our analysis is made at the differential level using the antenna subtraction framework. We apply our general set-up to the decays of a CP-even and CP-odd heavy Higgs boson to a top-quark top-antiquark pair and to the decay of the 125 GeV Higgs boson to a massive bottom-quark bottom-antiquark pair. In the latter case we calculate, in particular, the two-jet, three-jet, and four-jet decay rates and, for two-jet events, the energy distributi…
We present results for top quark production at the Tevatron including next-to-next-to-leading order (NNLO) soft-gluon corrections. We show the stability of the cross section with respect to kinematics choice and scale when the NNLO corrections are taken into account.
We present the first results on the two-loop massless QCD corrections to the four-point amplitude $b+\overline{b} \rightarrow H+H$ in the five flavor scheme, treating bottom quarks as massless. This amplitude is sensitive to the trilinear Higgs boson coupling. Our two-loop result for this amplitude constitutes of purely virtual contributions to the next-to-next-to-leading order QCD predictions for the production of a pair of Higgs bosons at the Large Hadron Collider. Using these two loop amplitudes and exploiting the universality of the soft contributions in perturbative QCD, we obtain the NNL…
Using the recently derived NNLO cross sections \cite{Czakon:2013goa}, we provide NNLO+NNLL theoretical predictions for top quark pair production based on all the available NNLO PDF sets, and compare them with the most precise LHC and Tevatron data. In this comparison we study in detail the PDF uncertainty and the scale, $m_t$ and $α_s$ dependence of the theoretical predictions for each PDF set. Next, we observe that top quark pair production provides a powerful direct constraint on the gluon PDF at large $x$, and include Tevatron and LHC top pair data consistently into a global NNLO PDF fit. W…
We construct predictions for top quark pair differential distributions at hadron colliders that combine state-of-the-art NNLO QCD calculations with double resummation at NNLL' accuracy of threshold logarithms arising from soft gluon emissions and of small mass logarithms. This is the first time a resummed calculation at full NNLO+NNLL' accuracy in QCD for a process with non-trivial color structure has been completed at the differential level. Of main interest to us is the stability of the M_{tt} and top-quark p_T distributions in the boosted regime where fixed order calculations may become str…
We present partial results on NLO and NNLO QCD, and NLO electroweak corrections to polarized top quark decays. In parallel we derive positivity bounds for the polarized structure functions in polarized top quark decays and check them against the perturbative corrections to the structure functions.
We present the calculation of next-to-next-to-leading order (NNLO) corrections in perturbative QCD for the production of a Higgs boson decaying into a pair of bottom quarks in association with a leptonically decaying weak vector boson: $\mathrm{pp} \to V \mathrm{H} + X \to \ell\bar{\ell}\;\mathrm{b\bar{b}} + X$. We consider the corrections to both the production and decay sub-processes, retaining a fully differential description of the final state including off-shell propagators of the Higgs and vector boson. The calculation is carried out using the antenna subtraction formalism and is impleme…
At the next generation of linear colliders, forward-backward asymmetries will be involved again in the precise determination of the neutral current couplings of heavy quarks in inclusive heavy-quark production. The theoretical understanding of these observables at the level of NNLO radiative corrections is required. We review a recent calculation of the two-parton contribution to the heavy-quark A_FB at NNLO QCD in e+e- collisions. The results are valid for arbitrary values of the momentum transfer and non-vanishing heavy-quark mass m_Q.
We provide the most up-to-date predictions for the top-quark charge asymmetry A_C at the LHC with a centre-of-mass energy of 8 TeV. Our result is accurate at the NNLO level in the strong interactions and at the complete-NLO level in both the strong and electroweak interactions. We present results for the inclusive A_C, several differential asymmetries as well as the P_{T,tt} and M_{tt} cumulative asymmetries. Similarly to the Tevatron forward-backward asymmetry A_FB, both NNLO QCD and NLO EW corrections to A_C are found to be significant. The inclusion of higher-order corrections reduces the r…
The fully differential computation of the hadronic production cross section of a Higgs boson via bottom quarks is presented at NNLO in QCD. Several differential distributions with their corresponding scale uncertainties are presented for the 8 TeV LHC. This is the first application of the method of non-linear mappings for NNLO differential calculations at hadron colliders.
We compute the next-to-next-to-leading order QCD correction to the total inclusive top pair production cross-section in the reaction qg \to t\bar t + X. We find moderate O(1%) correction to central values at both Tevatron and LHC. The scale variation of the cross-section remains unchanged at the Tevatron and is significantly reduced at the LHC. We find that recently introduced approximation based on the high-energy limit of the top pair cross-section significantly deviates from the exact result. The results derived in the present work are included in version 1.4 of the program Top++. Work towa…
We present a fully differential description of a decay of a scalar Higgs boson into massive b-quarks valid at next-to-next-to-leading order (NNLO) in perturbative quantum chromodynamics (QCD). We work within the nested soft-collinear subtraction scheme extended to accommodate massive partons. We include the loop-induced contribution involving a Higgs coupling to a top quark. We test our calculation against results existing in the literature, comparing the predictions for the total decay width and jet rates.
We present a detailed phenomenological study of the next-to-next-to-leading order (NNLO) QCD corrections for $t$-channel single top (anti-)quark production and its semi-leptonic decay at the CERN Large Hadron Collider (LHC). We find the NNLO corrections for the total inclusive rates at the LHC with different center of mass energies are generally smaller than the NLO corrections, indicative of improved convergence. However, they can be large for differential distributions, reaching a level of $10\%$ or more in certain regions of the transverse momentum distributions of the top (anti-)quark and …
We compute the one-loop QCD amplitude for the process gg-->Q\bar{Q} in dimensional regularization through order ε^2 in the dimensional regulator and for arbitrary quark mass values. This result is an ingredient of the NNLO cross-section for heavy quark production at hadron colliders. The calculation is performed in conventional dimensional regularization, using well known reduction techniques as well as a method based on recent ideas for the functional form of one-loop integrands in four dimensions.
I present some results for the next-to-next-to-leading order expansions of the resummed cross sections for heavy quark and direct photon production near threshold in hadronic collisions.
We calculate the cross section of the process e^+e^- \to t\bar t near threshold by resumming Coulomb-like terms with next-to-next-to-leading (NNLO) accuracy. The nonrelativistic Green function formalism and the method of ``direct matching'' are used. The NNLO correction turns out to be large, of the same size as the NLO correction. It changes the position and the normalization of the 1S-peak. The obtained results are compared with results existing in the literature.
This contribution attempts to determine the $b$-quark pole mass $M_b$ and \MSbar running mass $\overline{m}_b$ with two different approaches at the next-to-next-to-leading order (NNLO) corrections. At the first approach, we derive a relation between the $b$-quark pole mass $M_b$ and its \MSbar running mass $\overline{m}_b$ at the NNLO corrections based on the perturbative Quantum Chromo Dynamics (pQCD) predictions. At the second approach, we extract numerical values of the $b$-quark pole and \MSbar running masses based on the NNLO phenomenology of H1 and ZEUS Collaborations combined beauty ver…
We present a next-to-next-to-leading order (NNLO) calculation of the quasi parton distribution functions (Quasi-PDFs) in the large momentum effective theory (LaMET). We focus on the flavor non-diagonal quark-quark channel and demonstrate the LaMET factorization at the NNLO accuracy in the modified minimal subtraction scheme. The matching coefficient between the quasi-PDF and the light-cone PDF is derived. This provides a first step towards a complete NNLO analysis of quasi-PDFs and to better understand the nucleon structures from the first principle of QCD.
We present the NNLO corrections to top pair production in the quark-antiquark channel proportional to the number of light quark flavors $N_l$. While the double real corrections were derived previously, here we compute the real-virtual and virtual-virtual contributions in this partonic channel. Using the antenna subtraction formalism, we show that the subtraction terms correctly approximate the real-virtual contributions in all their infrared limits. Combined with the integrated forms of the double real and real-virtual subtraction terms, we show analytically that the explicit infrared poles ca…
We compute the next-to-next-to-leading order (NNLO) QCD corrections to the decay $t(\uparrow) \to X_b +W^+$ of a polarized top quark. The spin-momentum correlation in this quasi two-body decay is described by the polar angle distribution $\mathrm{d}Γ/\mathrm{d}\cosθ_P=\fracΓ{2}(1+P_t\, α_P\, \cosθ_P)$ where $P_t$ is the polarization of the top quark and $α_P$ denotes the asymmetry parameter of the decay. For the latter we find $α^{\mathrm{NNLO}}_P=0.3792\pm 0.0037$.
We present the first calculation of a fully-unintegrated parton distribution (beam function) at next-to-next-to-leading order (NNLO). We obtain the fully-differential beam function for quark-initiated processes by matching it onto standard parton distribution functions (PDFs) at two loops. The fully-differential beam function is a universal ingredient in resummed predictions of observables probing both the virtuality as well as the transverse momentum of the incoming quark in addition to its usual longitudinal momentum fraction. For such double-differential observables our result provides the …
Decay rates of unpolarized top quarks into longitudinally and transversally polarized W bosons are calculated to second order in the strong coupling constant alpha_s. Including the finite bottom quark mass and electroweak effects, the Standard Model predictions for the W boson helicity fractions are F_L=0.687(5), F_+=0.0017(1), and F_-=0.311(5).
We present next-to-next-to-leading order corrections to the inclusive production of the Higgs bosons at the CERN Large Hadron Collider (LHC) including finite top quark mass effects. Expanding our analytic results for the partonic cross section around the soft limit we find agreement with a very recent publication by Harlander and Ozeren \cite{Harlander:2009mq}.
The resummed transverse-momentum distribution for Higgs bosons produced via bottom-quark annihilation at the LHC is presented. Our results are obtained in the five-flavor scheme to NNLO+NNLL accuracy. We present a theoretical prediction which consistently matches the cross section at small and large transverse momenta. Theoretical uncertainties are derived from a variation of the unphysical scales entering the calculation. Their size is significantly reduced with respect to lower orders.
We discuss the impact of the charm quark mass in the CTEQ NNLO global analysis of parton distribution functions of the proton. The $\bar{\rm MS}$ mass $m_c(m_c)$ of the charm quark is extracted in the S-ACOT-$χ$ heavy-quark factorization scheme at ${\cal O}(α_s^2)$ accuracy and found to be in agreement with the world-average value. Impact on $m_c(m_c)$ of combined HERA-1 data on semiinclusive charm production at HERA collider and contributing systematic uncertainties are reviewed.
We compute the relation between the quark mass defined in the minimal modified $\MSbar$ scheme and the mass defined in the ``Regularization Invariant" scheme (RI), up to the NNLO order. The RI scheme is conveniently adopted in lattice QCD calculations of the quark mass, since the relevant renormalization constants in this scheme can be evaluated in a non-perturbative way. The NNLO contribution to the conversion factor between the quark mass in the two schemes is found to be large, typically of the same order of the NLO correction at a scale $μ\sim 2$ GeV. We also give the NNLO relation between…
We construct a resummation at partial next-to-next-to-next-to-leading logarithmic accuracy for hadronic top-quark pair production near partonic threshold, including simultaneously soft-gluon and Coulomb corrections, and use this result to obtain approximate next-to-next-to-next-to-leading order predictions for the total top-quark pair-production cross section at the LHC. We generalize a required one-loop potential in non-relativistic QCD to the colour-octet case and estimate the remaining unknown two-loop potentials and three-loop anomalous dimensions. We obtain a moderate correction of $1.5\%…
We calculate, for the first time, the next-to-next-to leading order (NNLO) QCD corrections to spin correlations in top quark pair production at the LHC. The NNLO corrections play an important role in the description of the corresponding differential distributions. We observe that the Standard Model calculation describes the available delta-phi data in the fiducial region but does not agree with the delta-phi measurement extrapolated to full phase space. Most likely this discrepancy is due to the difference in precision between existing event generators and NNLO calculations for dilepton top-pa…
We present the O(as^4) virtual QCD corrections to unlike-quark and like-quark scattering due to the interference of one-loop amplitudes with one-loop amplitudes. The structure of the infrared divergences agrees with that predicted by Catani. The results are expressed in an analytic form so that the relevant expressions for crossed scattering processes can be obtained in a straightforward manner. The one-loop contributions presented here, together with the interference of tree with two-loop amplitudes given recently, complete the 2 to 2 virtual QCD corrections at NNLO for the massless quark sca…
We study the transition of a heavy quark pair from octet to singlet color configurations at next-to-next-to-leading order (NNLO) in heavy quarkonium production. We show that the infrared singularities in this process are consistent with NRQCD factorization to all orders in the heavy quark relative velocity v. This factorization requires the gauge-completed matrix elements that we introduced previously to prove NNLO factorization to order v ^2.
