17 Search Results

We present compact analytic results for tree-level amplitudes containing a $$t\bar{t}$$ pair accompanied by up to four massless partons $$t\bar{t}gg$$, $$t\bar{t}ggg$$, $$t\bar{t}gggg$$, $$t\bar{t}q\bar{q}$$, $$t\bar{t}q\bar{q}g$$, $$t\bar{t}q\bar{q}gg$$, and $$t\bar{t}q\bar{q}q'\bar{q'}$$. The results, obtained using BCFW on-shell recursion, are based both on previous published results and on the new calculations performed in this paper. These amplitudes are sufficient to calculate the production of a $$t\bar{t}$$ pair and zero, one, or two light parton jets, with the option to include the tree-level decays t → bνe⁺ and $$\bar{t} → \bar{b}e^-\bar{v}$$ efficiently. Our results are part of the NNLO corrections to $$t\bar{t}$$ production including the decaymore » correlations for on-shell top quarks.« less

Vetoing energetic jet activity is a crucial tool for suppressing backgrounds and enabling new physics searches at the LHC, but the introduction of a veto scale can introduce large logarithms that may need to be resummed. We present an implementation of jet-veto resummation for color-singlet processes at the level of N³LL_p matched to fixed-order NNLO predictions. Our public code MCFM allows for predictions of a single boson, such as Z/γ*, W^± or H, or with a pair of vector bosons, such as W⁺W^–, W^±Z or ZZ. The implementation relies on recent calculations of the soft and beam functions in themore » presence of a jet veto over all rapidities, with jets defined using a sequential recombination algorithm with jet radius R. However one of the ingredients that is required to reach full N³LL accuracy is only known approximately, hence N³LL_p. We describe in detail our formalism and compare with previous public codes that operate at the level of NNLL. Our higher-order predictions improve significantly upon NNLL calculations by reducing theoretical uncertainties. We demonstrate this by comparing our predictions with ATLAS and CMS results.« less

Diboson processes are one of the most accessible and stringent probes of the electroweak gauge structure of the Standard Model at the LHC. They will be probed at the percent level at the high-luminosity LHC, challenging current theory predictions. We present transverse momentum resummed calculations at N³LL+NNLO for the processes ZZ, WZ, WH and ZH, compare our predictions with most recent LHC data and present predictions at 13.6 TeV including theory uncertainty estimates. For W⁺W^- production we further present jet-veto resummed results at N³LL_p+NNLO. Our calculations will be made publicly available in the upcoming MCFM release and allow future analysesmore » to take advantage of improved predictions.« less

We outline a new technique for the fully-differential matching of final-state parton showers to NNLO calculations, focussing here on the simplest case of leptonic collisions with two final-state jets. The strategy is facilitated by working in the antenna formalism, making use of NNLO antenna subtraction on the fixed-order side and the sector-antenna framework on the shower side. As long as the combined real-virtual and double-real corrections do not overcompensate the real-emission term in the three-jet region, negative weights can be eliminated from the matching scheme. We describe the implementation of all necessary components in the VINCIA antenna shower in PYTHIAmore » 8.3.« less

We present compact analytic results for the one-loop amplitude for the process 0 → $$q\bar{q}$$$$ℓ\bar{ℓ}$$$$ℓ'\bar{ℓ}'g$$, relevant for both the production of a pair of Z and W-bosons in association with a jet. We focus on the gauge-invariant contribution mediated by a loop of quarks. We explicitly include all effects of the loop-quark mass m, appropriate for the production of a pair of Z-bosons. In the limit m → 0, our results are also applicable to the production of W-boson pairs, mediated by a loop of massless quarks. Implemented in a numerical code, the results are fast. The calculation uses novelmore » advancements in spinor-helicity simplification techniques, for the first time applied beyond five-point massless kinematics. We make use of primary decompositions from algebraic-geometry, which now involve non-radical ideals, and p-adic numbers from number theory. We show how to infer whether numerator polynomials belong to symbolic powers of non-radical ideals through numerical evaluations.« less

We present the implementation of several processes at Next-to-Next-to Leading Order (NNLO) accuracy in QCD in the parton-level Monte Carlo program MCFM. The processes treated are pp → H, W^±, Z, W^±H, ZH, W^±γ, Zγ and γγ and, for the first time in the code, W⁺W^-, W^±Z and ZZ. Decays of the unstable bosons are fully included, resulting in a flexible fully differential Monte Carlo code. The NNLO corrections have been calculated using two non-local slicing approaches, isolating the doubly unresolved region by cutting on the zero-jettiness, $$\mathscr{T}_0$$, or on q_T, the transverse momentum of the colour singlet final-state particles.more » We find that for most, but not all processes the q_T slicing method leads to smaller power corrections for equal computational burden.« less

In these proceedings, we apply the recently developed S-ACOT-MPS factorization scheme at the next-to-leading order to prompt charm production at hadron colliders. It provides a good agreement with experimental data on charm meson production measured by LHCb at 7 and 13 TeV. The low-$$p_T$$ data are on the margins of the theoretical error bands, emphasizing the importance of including contributions beyond the next-to-leading order.

We present details of the calculation of the pp → W(→ lν)γ process at next-to-next-to-leading order in QCD, calculated using the jettiness slicing method. The calculation is based entirely on analytic amplitudes. Because of the radiation zero, the NLO QCD contribution from the gq channel is as important as the contribution from the Born $$ q\overline{q} $$ process, disrupting the normal counting of leading and sub-leading contributions. We also assess the importance of electroweak (EW) corrections, including the EW corrections to both the six-parton channel 0 →$$ \overline{u} d\nu {e}^{+}\gamma g $$ and the five-parton channel 0 →$$ \overline{u} d\numore » {e}^{+}\gamma $$. Previous experimental results have been shown to agree with theoretical predictions, taking into account the large experimental errors. With the advent of run II data from the LHC, the statistical errors on the data will decrease, and will be competitive with the error on theoretical predictions for the first time. We present numerical results for $$ \sqrt{s} $$ = 7 and 13 TeV. Analytic results for the one-loop six-parton QCD amplitude and the tree-level seven-parton QCD amplitude are presented in appendices.« less

We present compact analytic formulae for the one-loop amplitudes for Higgs + 4 parton scattering, $$0 \to g g g g h$$, $$0 \to \bar{q} q gg h$$ and $$0\to \bar{q} q \bar{q}^\prime q^\prime h$$, mediated by a loop of massive coloured quarks. We exploit the correspondence with a theory in which a massive coloured scalar circulates in the loop to avoid a proliferation in the number of terms in the result. In addition, we use momentum twistors and high precision numerical evaluations to simplify the expressions. The analytic results in this paper, in terms of spinor products, allow constructionmore » of an efficient numerical program to calculate the amplitude.« less

In this paper we present a next-to-next-to-leading order (NNLO) QCD calculation of the processes $$pp\rightarrow l^+l^-\gamma$$ and $$pp\rightarrow \nu\bar\nu\gamma$$ that we have implemented in MCFM. Our calculation includes QCD corrections at NNLO both for the Standard Model (SM) and additionally in the presence of $$Z\gamma\gamma$$ and $$ZZ\gamma$$ anomalous couplings. We compare our implementation, obtained using the jettiness slicing approach, with a previous SM calculation and find broad agreement. Focusing on the sensitivity of our results to the slicing parameter, we show that using our setup we are able to compute NNLO cross sections with numerical uncertainties of about $$0.1\%$$, whichmore » is small compared to residual scale uncertainties of a few percent. We study potential improvements using two different jettiness definitions and the inclusion of power corrections. At $$\sqrt{s}=13$$ TeV we present phenomenological results and consider $$Z\gamma$$ as a background to $$H\to Z\gamma$$ production. Here, we find that, with typical cuts, the inclusion of NNLO corrections represents a small effect and loosens the extraction of limits on anomalous couplings by about $$10\%$$.« less