Top-antitop quark pairs belong to the most abundantly produced and precisely measurable heavy-particle signatures at hadron colliders and allow for crucial tests of the Standard Model and new-physics searches. Here we report on the calculation of the next-to-leading order (NLO) QCD corrections to hadronic WWbb production, which provides a complete NLO description of the production of top-antitop pairs and their subsequent decay into W bosons and bottom quarks, including interferences, off-shell effects, and non-resonant backgrounds. Numerical predictions for the Tevatron and the LHC are presented.
We present the NLO QCD corrections to the production of a W+W- pair and two b-jets, including the leptonic decays of the W bosons. Contributions from singly resonant and non-resonant top quarks are fully taken into account. We also discuss observables relevant for top quark mass measurements and top quark asymmetries.
We present an NLO simulation of WWbb production with massive b-quarks at the LHC. Off-shell and non-resonant contributions associated with top-pair and single-top channels and with leptonic W-boson decays are consistently taken into account using the complex-mass scheme. Thanks to the finite b-quark mass, WWbb predictions can be extended to the whole b-quark phase space, thereby including Wt-channel single-top contributions that originate from collinear g->bb splittings in the four-flavour scheme. This provides a consistent NLO description of tt and Wt production and decay, including quantum i…
We present the extension of two general algorithms for the treatment of infrared singularities arising in electroweak corrections to decay processes at next-to-leading order: the dipole subtraction formalism and the one-cutoff slicing method. The former is extended to the case of decay kinematics which has not been considered in the literature so far. The latter is generalized to production and decay processes with more than two charged particles, where new "surface" terms arise. Arbitrary patterns of massive and massless external particles are considered, including the treatment of infrared s…
We address the issue of single top production in association with a W boson at the Large Hadron Collider, in particular how to obtain an accurate description in the face of the top pair production background given that the two processes interfere with each other. We stress the advantages of an MC@NLO description, and find that for cuts used to isolate the signal, it makes sense to consider Wt as a well-defined production process in that the interference with top pair production is small, and the cross-section of the former is above the scale variation uncertainty associated with the latter. We…
We emphasize the role that the associated production of a Higgs boson with a pair of top-antitop quarks can play at present and future hadron colliders. Results of recent calculations of the NLO total cross section for the associated production of a Standard Model like Higgs boson with a pair of top-antitop quarks at the Tevatron (sqrt(s)=2 TeV) are presented.
Electroweak one-loop calculations for production of top-quark pairs at colliders are completed by providing the missing QED type contributions from real and virtual photons, where also effects from interference between QED and QCD contributions have to be taken into account. Moreover, photon-induced $t \bar{t}$ production is included as another partonic channel.
Production of the $B_c$ and $B_c^*$ mesons at $Z$-factory (an $e^+e^-$ collider running at energies around $Z$ pole) is calculated up-to the next-to-leading order (NLO) QCD corrections. The results show that the dependence of the total cross sections on the renormalization scale $μ$ is reduced by the corrections, and the NLO corrections enhance the production cross section by $52\%$($33\%$) when the renormalization scale is taken at $μ=2m_b$. For experimental observations of the $B_c$ and $B_c^*$ mesons, the differential cross sections for the production are also analyzed up-to the NLO accurac…
We calculate the full $\mathcal{O}(α_s^2α)$ corrections to the process of gluino pair production at hadron colliders in the framework of the real MSSM. We show that these contributions can be neglected at the LHC performing a scan over a wide region of the parameter space. The impact of these corrections in the parameter range investigated at the Tevatron is small.
We calculate the Next-to-Leading Order (NLO) QCD corrections to W-b-bbar production including full bottom-quark mass effects. We study the impact of NLO QCD corrections on the total cross section and invariant mass distribution of the bottom-quark jet pair at the Fermilab Tevatron p-pbar collider. We perform a detailed comparison with a calculation that considers massless bottom quarks. We find that neglecting bottom-quark mass effects overestimates the NLO total cross-section for W-b-bbar production at the Tevatron by about 8% independent of the choice of renormalization and factorization sca…
We present updated NLO predictions for the electroweak t-channel production of heavy quarks at the Tevatron and at the LHC. We consider production of single top and fourth generation t' starting from both 2 to 2 and 2 to 3 Born processes. Predictions for tb' and t'b' cross sections at NLO are also given for the first time. A thorough study of the theoretical uncertainties coming from parton distribution functions, renormalisation and factorisation scale dependence and heavy quark masses is performed.
We present results on NLO electroweak (EW) corrections to multiple massive boson production processes at a future muon collider. Inclusive cross sections with $\mathcal{O}(α)$ corrections for processes for up to four bosons in the final state as well as differential distributions for $HZ$ production are computed for $\sqrt{s}=3$, $10$ and $14$ TeV by using FKS subtraction in the NLO EW automated Monte-Carlo framework WHIZARD+RECOLA. Large logarithmic effects due to collinear ISR and EW virtual correction factors as well as the impacts of an energy cut on hard photons are discussed with an emph…
I review the present status of the automatic NLO tools MadLoop and aMC@NLO by presenting, as an example of their use, phenomenological studies of hadron collider processes. Perspectives on applications to linear collider Physics are also discussed
We calculate the next-to-leading order (NLO) quantum chromodynamics (QCD) correction to the exclusive process $γ+γ\to J/ψ+J/ψ$ in the framework of non-relativistic QCD (NRQCD) factorization formalism. The cross sections at the SuperKEKB electron-positron collider, as well as at the future colliders, like the Circular Electron Positron Collider (CEPC) and the International Linear Collider (ILC), are evaluated. Numerical result indicates that the process will be hopefully to be seen by the Belle II detector within the next decade.
We present the NLO electroweak radiative corrections to the eeγproduction in γγcollision, which is an ideal channel for calibrating the beam luminosity of a Photon Linear Collider. We analyze the dependence of the total cross section on the beam colliding energy, and then investigate the kinematic distributions of final particles at various initial photon beam polarizations at EW NLO accuracy. The numerical results indicate that the EW relative corrections to the total cross section are non-negligible and become increasingly significant as the increase of the beam colliding energy. Such EW cor…
We present results for the next-to-leading order QCD corrections to the production and semi-leptonic decays of a top quark pair in hadron collisions, retaining all spin correlations. To evaluate the virtual corrections, we employ generalized D-dimensional unitarity. The computation is implemented in a numerical program which allows detailed studies of ttbar-related observables at the Tevatron and the LHC.
We consider lepton pair production at a hadron collider in a class of effective theories with the relevant operators being four-fermion contact interaction. Despite the nonrenormalizable nature of the interaction, we explicitly demonstrate that calculating QCD corrections is both possible and meaningful. Calculating the corrections for various differential distributions, we show that these can be substantial and significantly different from those within the SM. Furthermore, the corrections have a very distinctive flavour dependence. And finally, the scale dependence of the cross sections are g…
We calculate the next-to-leading order (NLO) quantum chromodynamics (QCD) corrections to $γ+γ\to η_c+c+\bar{c}$, $γ+γ\to η_b+b+\bar{b}$ and $γ+γ\to B_c+b+\bar{c}$ processes in the framework of non-relativistic QCD (NRQCD) factorization formalism. The cross sections at the SuperKEKB electron-positron collider, as well as the future collider like the Circular Electron Positron Collider (CEPC), are evaluated. Numerical results indicate that the NLO corrections are significant, and the uncertainties in theoretical predictions with NLO corrections are reduced as expected. Due to the high luminosity…
We report on the calculation of the next-to-leading order QCD corrections to the production of top--anti-top quark pairs in association with a hard jet at the Tevatron and at the LHC. We present results for the t tbar + jet cross section and the forward--backward charge asymmetry. The corrections stabilize the leading-order prediction for the cross section. The charge asymmetry receives large corrections.
We use aMC@NLO to study the production of four charged leptons at the LHC, performing parton showers with both HERWIG and Pythia6. Our underlying matrix element calculation features the full next-to-leading order $O(α_S)$ result and the $O(α_S^2)$ contribution of the $gg$ channel, and it includes all off-shell, spin-correlation, virtual-photon-exchange, and interference effects. We present several key distributions together with the corresponding theoretical uncertainties. These are obtained through a process-independent technique that allows aMC@NLO to compute scale and PDF uncertainties in a…
We report on the calculation of the next-to-leading order QCD corrections to the production of W-boson pairs in association with a hard jet at the Tevatron and the LHC, which is an important source of background for Higgs and new-physics searches. The corrections stabilize the leading-order prediction for the cross section considerably, in particular if a veto against the emission of a second hard jet is applied.
We report on the next-to-leading order(NLO) QCD computation of top-quark pair production in association with a photon at the Fermilab Tevatron RUN II and CERN Large Hadron Collider(LHC). We describe the impact of the complete NLO QCD radiative corrections to this process, and provide the predictions of the leading order(LO) and NLO integrated cross sections, distributions of the transverse momenta of top-quark and photon for the LHC and Tevatron, and the LO and NLO forward-backward top-quark charge asymmetries for the Tevatron. We investigate the dependence of the LO and NLO cross sections on …
We study the process of the association production of chargino and neutralino including the NLO QCD and the complete one-loop electroweak corrections in the framework of the minimal supersymmetric standard model(MSSM) at the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). In both the NLO QCD and one-loop electroweak calculations we apply the algorithm of the phase-space slicing(PSS) method. We find that the NLO QCD corrections generally increase the Born cross sections, while the electroweak relative corrections decrease the Born cross section in most of the chosen parameter space.…
We describe a new method, based on an extension of the unitarity cutting rules proposed earlier, which is very efficient for the algorithmic evaluation of phase-space integrals for various differential distributions. As a first application, we compute the next-to-leading order normalized rapidity distribution of the CP-even and the CP-odd Higgs boson produced in hadron collisions through gluon fusion. We work in the heavy top-quark approximation; we find that the NLO corrections at the LHC are approximately 5% in the zero rapidity region.
A fully differential calculation of the next-to-leading order QCD corrections to the production of Z-boson pairs in association with a hard jet at the Tevatron and LHC is presented. This process is an important background for Higgs particle and new physics searches at hadron colliders. We find sizable corrections for cross sections and differential distributions, particularly at the LHC. Residual scale uncertainties are typically at the 10% level and can be further reduced by applying a veto against the emission of a second hard jet. Our results confirm that NLO corrections do not simply resca…
The phenomenology of Standard Model and New Physics at hadron colliders depends critically on results from global QCD analysis for parton distribution functions (PDFs). The accuracy of the standard next-to-leading-order (NLO) global analysis, nominally a few percent, is generally well matched to the expected experimental precision. However, serious questions have been raised recently about the stability of the NLO analysis with respect to certain inputs, including the choice of kinematic cuts on the data sets and the parametrization of the gluon distribution. In this paper, we investigate this…
Recent results from NLO QCD calculations for inclusive jet cross sections in gamma^*-gamma scattering at e+e- colliders, especially for LEP, are reported. The virtuality Q^2 of the virtual photon is non-zero and can be unlimited large. The virtuality of the second photon is zero and the spectrum is calculated with the Weizs"acker-Williams approximation. Four components of the cross sections have to be distinguished, involving direct and resolved real and virtual photon contributions. Since Q^2 is non-zero, the virtual photon structure function is needed to calculate the contributions involving…
We calculate NLO QCD corrections to the lightest neutral Higgs boson production associated with top quark pair at hadron colliders in the minimal supersymmetric standard model(MSSM). Our calculation shows that the total QCD correction significantly reduces its dependence on the renormalization/factorization scale. The relative correction from the SUSY QCD part approaches to be a constant, if either $M_S$ or $m_{\tilde{g}}$ is heavy enough. The corrections are generally moderate(in the range of few percent to 20%) and under control in most of the SUSY parameter space. The relative correction is…
We present the next-to-leading order (NLO) electroweak (EW) corrections to the top quark pair production associated with a hard photon at the current and future hadron colliders. The dependence of the leading order (LO) and NLO EW corrected cross sections on the photon transverse momentum cut are investigated. We also provide the LO and NLO EW corrected distributions of the transverse momentum of final top quark and photon and the invariant mass of top quark pair and top-antitop-photon system. The results show that the NLO EW corrections are significant in high energy regions due to the EW Sud…
Models with large extra dimensions predict the existence of Kaluza-Klein graviton resonances. We compute the next-to-leading order QCD corrections to graviton plus jet hadro-production, which is an important channel for graviton searches at the Tevatron and the LHC. The QCD corrections are sizable and lead to a significant reduction of the scale dependence. We present numerical results for cross sections and distributions, and discuss the uncertainty from parton distribution functions and the ultraviolet sensitivity of the theoretical prediction.
We present a theoretical framework for systematically calculating next-to-leading order (NLO) QCD effects to various experimental observables in models with massive COVB in a model independent way at hadron colliders. Specifically, we show the numerical results for the NLO QCD corrections to total cross sections, invariant mass distribution and AFB of top quark pairs production mediated by a massive COVB in both the fixed scale (top quark mass) scheme and the dynamical scale (top pair invariant mass) scheme. Our results show that the NLO QCD calculations in the dynamical scale scheme is more r…
We present the calculations of the complete next-to-leading order (NLO) QCD effects on the single top productions induced by model-independent $tqg$ flavor-changing neutral-current couplings at hadron colliders. Our results show that, for the $tcg$ coupling the NLO QCD corrections can enhance the total cross sections by about 60% and 30%, and for the $tug$ coupling by about 50% and 20% at the Tevatron and LHC, respectively, which means that the NLO corrections can increase the experimental sensitivity to the FCNC couplings by about 10%$-$30%. Moreover, the NLO corrections reduce the dependence…
We present the next-to-leading order QCD corrected total cross sections and the distributions of the transverse momenta of the final anti-bottom-quark, top-quark and charged Higgs-boson for the processes of $p\bar p/pp \to t\bar b H^-+X$ in the minimal supersymmetric standard model(MSSM) at the Tevatron and the LHC. We find that the NLO QCD corrections significantly modify the leading-order distributions of the transverse momenta of final particles($p_T^b$, $p_T^t$ and $p_T^{H^-}$), and the total NLO QCD corrections reduce the dependence of the cross section on the renormalization and factoriz…
We thoroughly investigate both transverse momentum and threshold resummation effects on scalar-pseudoscalar pair production via quark-antiquark annihilation at the $13~ \text{TeV}$ Large Hadron Collider at QCD NLO+NLL accuracy. A factorization method is introduced to properly supplement the soft-gluon (threshold) resummation contribution from parton distribution functions to the resummed results obtained by the Collins-Soper-Sterman resummation approach. We find that the impact of the threshold-resummation improved PDFs is comparable to the resummation effect of the partonic matrix element and…
In this talk we discuss recent progress concerning precise predictions for hadron colliders. We show results of two applications of tensor reduction using GOLEM methods: the next-to-leading order (NLO) corrections to $pp \to ZZ+$jet as an important background for Higgs particle and new physics searches at hadron colliders, and the NLO corrections to graviton plus jet hadro-production, which is an important channel for graviton searches at the Tevatron and the LHC.
We consider the next-to-leading order corrections, O(alpha_s), to forward-backward charge asymmetries for lepton-pair production in association with a large transverse momentum jet at large hadron colliders. We find that the leading order results are essentially confirmed. Although experimentally challenging and in practice with large backgrounds, these observables could provide a new determination of the weak mixing angle sin2 theta^lept_eff (M_Z^2) with a statistical precision for each lepton flavour of ~10^(-3) (7 x 10^{-3}) at LHC (Tevatron), and if b jets are identified, of the b quark Z …
$W^+W^-γ$ production in proton-proton collision provides a window to the mechanism of electroweak symmetry breaking and a direct accessment to triple and quartic gauge couplings. Precision study of gauge boson self-interactions may also provide evidence of existence of new physics beyond the Standard Model. In this paper, we study the $W^+W^-γ$ production at the LHC and future higher energy proton-proton colliders at the QCD+EW NLO including parton shower effects. We find that the contributions from the photon-induced (i.e., $qγ$- and $γγ$-initiated) channels are non-negligible since the photo…
mcsanc is a Monte-Carlo tool based on the SANC (Support for Analytic and Numeric Calculations for experiments at colliders) modules for higher order calculations in hadron collider physics. It allows to evaluate NLO QCD and EW cross sections for Drell-Yan processes (inclusive), associated Higgs and gauge boson production and single-top quark production in s- and t-channel. The paper contains theoretical description of the SANC approach, numerical validations and manual.
The complete next-to-leading order (NLO) QCD corrections to charged Higgs boson associated production with top quark through $b g \to tH^{-}$ at the CERN Large Hadron Collider are calculated in the minimal supersymmetric standard model (MSSM) and two-Higgs-doublet model in the $\bar{MS}$ scheme. The NLO QCD corrections can reduce the scale dependence of the leading order (LO) cross section. The K-factor (defined as the ratio of the NLO cross section to the LO one) does not depend on $\tanβ$ if the same quark running masses are used in the NLO and LO cross sections, and varies roughly from $\si…
We present a first and extensive study of threshold resummation effects for supersymmetric (SUSY) particle production at hadron colliders, focusing on Drell-Yan like slepton-pair and slepton-sneutrino associated production. After confirming the known next-to-leading order (NLO) QCD corrections and generalizing the NLO SUSY-QCD corrections to the case of mixing squarks in the virtual loop contributions, we employ the usual Mellin N-space resummation formalism with the minimal prescription for the inverse Mellin-transform and improve it by resumming 1/N-suppressed and a class of N-independent un…
We present the complete next-to-leading order (NLO) QCD corrections to the top quark associated with $γ$ production induced by model-independent $tqγ$ and $tqg$ flavor-changing neutral-current (FCNC) couplings at hadron colliders, respectively. We also consider the mixing effects between the $tqγ$ and $tqg$ FCNC couplings for this process. Our results show that, for the $tqγ$ couplings, the NLO QCD corrections can enhance the total cross sections by about 50% and 40% at the Tevatron and LHC, respectively. Including the contributions from the $tqγ$, $tqg$ FCNC couplings and their mixing effects…
We calculated the next-to-leading order (NLO) QCD corrections to the cross sections for direct top quark productions induced by model--independent flavour changing neutral current couplings at hadron colliders. The NLO results increase the experimental sensitivity to the anomalous couplings. Our results show that the NLO QCD corrections enhance the leading order (LO) total cross sections at the Tevatron Run 2 about 60% for both of $κ_{tc}^g$ and $κ_{tu}^g$ couplings, and enhance the LO total cross sections at the LHC about 40% for $κ_{tc}^g$ couplings and 50% for $κ_{tu}^g$ couplings, respecti…
We present the complete next-to-leading order (NLO) QCD corrections to $tZ$ associated production induced by the model-independent $tqg$ and $tqZ$ flavor-changing neutral-current couplings at hadron colliders, respectively. Our results show that, for the $tuZ$ coupling the NLO QCD corrections can enhance the total cross sections by about 60% and 42%, and for the $tcZ$ coupling by about 51% and 43% at the Tevatron and LHC, respectively. The NLO corrections, for the $tug$ couplings, can enhance the total cross sections by about 27%, and by about 42% for the $tcg$ coupling at the LHC. We also con…
We calculate the complete next-to-leading-order (NLO) QCD corrections (including SUSY QCD corrections) to the inclusive total cross sections of the associated production processes $pp\rightarrow A^{0}γ+X$ in the minimal supersymmetric standard model (MSSM) at the CERN Large Hadron Collider (LHC). Our results show that the enhancement of the total cross sections from the NLO QCD corrections can reach $15%\sim20%$ for 200 GeV$<m_{A}<500$ GeV and $\tanβ=50$. The scale dependence of the total cross section is improved by the NLO corrections, which is less than 5%. We also show the Monte Carlo simu…
We report on the calculation of the next-to-leading order QCD corrections to the production of W-boson pairs in association with a hard jet at the Tevatron and the LHC, which is an important source of background for Higgs and new-physics searches. Leptonic decays of the W bosons are included by applying an improved version of the narrow-width approximation that treats the W bosons as on-shell particles, but keeps the information on the W spin. A selection of differential NLO QCD cross sections is provided both for the LHC and the Tevatron. The QCD corrections stabilize the LO prediction for th…
We present details of a calculation of the cross section for hadronic top-antitop production in next-to-leading order (NLO) QCD, including the decays of the top and antitop into bottom quarks and leptons. This calculation is based on matrix elements for νe e+ μ- \barν_μb\bar{b} production and includes all non-resonant diagrams, interferences, and off-shell effects of the top quarks. Such contributions are formally suppressed by the top-quark width and turn out to be small in the inclusive cross section. However, they can be strongly enhanced in exclusive observables that play an important role…
We summarize the status of automated NLO SM corrections for hadron and lepton collider processes in the multi-purpose event generator WHIZARD. The focus will be on NLO EW and QCD-EW mixed corrections at the LHC. Also, recent progress on the inclusion of EW corrections in future lepton collider processes and on the POWHEG-matched event generation in the NLO automated setup will be discussed.
If the lighter top squark has no kinematically allowed two-body decays that conserve flavor, then it will live long enough to form hadronic bound states. The observation of the diphoton decays of stoponium could then provide a uniquely precise measurement of the top squark mass. In this paper, we calculate the cross section for the production of stoponium in a hadron collider at next-to-leading order (NLO) in QCD. We present numerical results for the cross section for production of stoponium at the LHC and study the dependence on beam energy, stoponium mass, and the renormalization and factori…
We review recently derived NNLO QCD results for top-pair production at hadron colliders. We compare the size of the NNLO corrections in $q\bar q\to t\bar t+X$ with the LO and NLO ones, and address the question of convergence of perturbative series. We compare the NLO and NNLO K-factors for the Tevatron.
We compute the QCD corrections to the production of a top quark pair in association with one hard jet at the Tevatron and the LHC, using the method of generalized D-dimensional unitarity. Top quark decays are included at leading order in perturbative QCD. We present kinematic distributions of top quark decay products in lepton plus jets and dilepton final states at the Tevatron and the LHC, using realistic selection cuts. We confirm a strong reduction of the top quark forward-backward asymmetry for the process ttbar+jet at the Tevatron at next-to-leading order, first observed by Dittmaier, Uwe…
We compute the complete next-to-leading order (NLO) SUSY-QCD corrections for the associated production of a pseudoscalar Higgs boson with a bottom quark via bottom-gluon fusion at the CERN Large Hadron Collider (LHC) and the Fermilab Tevatron. We find that the NLO QCD correction in the MSSM reaches $40%\sim50%$ at the LHC and $45%\sim80%$ at the Tevatron in our chosen parameter space.
We present the calculations of the next-to-leading order (NLO) QCD corrections to the inclusive total cross sections for the associated production of the $W^{\pm}H^{\mp}$ through $b\bar{b}$ annihilation in the Minimal Supersymmetric Standard Model at the CERN Large Hadron Collider. The NLO QCD corrections can either enhance or reduce the total cross sections, but they generally efficiently reduce the dependence of the total cross sections on the renormalization/factorization scale. The magnitude of the NLO QCD corrections is about 10% in most of the parameter space and can reach 15% in some pa…
We perform the precision calculations for the \eeqq ($q_-\bar{q}_-=u_-\bar u_-, ~c_-\bar c_-,~ d_-\bar d_-,~s_-\bar s_-$) processes up to the QCD next-to-leading order (NLO) including full weak decays for the final $T$-odd mirror quarks in the littlest Higgs model with $T$-parity (LHT) at the Compact Linear Collider (CLIC). We show the dependence of the leading order (LO) and NLO QCD corrected cross sections on the colliding energy $\sqrt{s}$, and provide the LO and QCD NLO kinematic distributions of final particles. The results show that the LO cross section can be enhanced by the NLO QCD cor…
We report on numerical studies of the NLO corrections to exclusive meson electroproduction, both in collider and fixed-target kinematics. Corrections are found to be huge at small xB and sizeable at intermediate or large xB.
We present total and differential cross sections for the production of a hard photon with up to two b jets at both the Tevatron with center-of-mass energy 1.96 TeV and the Large Hadron Collider with center-of-mass energy 8 TeV, including Next-to-Leading Order (NLO) QCD corrections and full b-quark mass effects. We study the theoretical uncertainty due to the residual renormalization- and factorization-scale dependence and explain its origin on the basis of the different subprocesses contributing to the NLO cross section. We specifically address the case of the production of a hard photon with …
QCD corrections to $e^+e^- \ra WW \ra q_1 \bar q_1 q_2 \bar q_2$ are computed and presented in a form which allows to impose realistic cuts on the structure of the observed events. QCD radiation substantially modifies the jet--jet invariant mass distributions from which the value of the $W$ mass will be extracted. When the range of allowed jet--jet masses is restricted, as it has been proposed in order to suppress non--$WW$ backgrounds, the total cross section is also deeply affected. If all events are forced to four jets, combining the two partons with smallest invariant mass, and the reconst…
