Off-shell single-top production at NLO matched to parton showers

109

Abstract:We calculate the complete-NLO predictions for ttW ± and tttt production in proton-proton collisions at 13 and 100 TeV. All the non-vanishing contributions of O(α i s α j ) with i + j = 3, 4 for ttW ± and i + j = 4, 5 for tttt are evaluated without any approximation. For ttW ± we find that, due to the presence of tW → tW scattering, at 13(100) TeV the O(α s α 3 ) contribution is about 12(70)% of the LO, i.e., it is larger than the so-called NLO EW corrections (the O(α 2 s α 2 ) terms) and has opposite sign. In the case of tttt production, large contributions from electroweak tt → tt scattering are already present at LO in the O(α 3 s α) and O(α 2 s α 2 ) terms. For the same reason we find that both NLO terms of O(α 4 s α), i.e., the NLO EW corrections, and O(α 3 s α 2 ) are large (±15% of the LO) and their relative contributions strongly depend on the values of the renormalisation and factorisation scales. However, large accidental cancellations are present (away from the threshold region) between these two contributions. Moreover, the NLO corrections strongly depend on the kinematics and are particularly large at the threshold, where even the relative contribution from O(α 2 s α 3 ) terms amounts to tens of percents.

Section: Numerical Resultsmentioning

confidence: 99%

Large NLO corrections in t t ¯ W ± $$ t\overline{t}{W}^{\pm } $$ and

Frederix

Pagani

Zaro

2018

109

“…The calculation that is described in this section, fixed-order complete-NLO predictions for the signature (2.1), has been performed via the latest version of MadGraph5_aMC@NLO [42], which is public. In the MadGraph5_aMC@NLO framework [57] infrared singularities are dealt with via the FKS method [58,59], which is automated in the module MadFKS [52,60]. The evaluation of one-loop amplitudes is performed by dynamically switching among different types of techniques for integral reduction, i.e., the so called OPP method [61], Laurent-series expansion [62], and tensor integral reduction [63][64][65].…”

Section: Fixed-order Complete-nlo Predictionsmentioning

confidence: 99%

“…[48], respectively. Monte Carlo simulations, in which the NLO single-top production processes have been matched to a parton shower are available in the MC@NLO [45,[49][50][51][52], Sherpa [53] and POWHEG [51,54,55] frameworks. Within the latter framework, also the consistent inclusion of the single-top plus one-jet NLO matrix elements has been considered through the (extended) MINLO method [56].…”

Section: Introductionmentioning

confidence: 99%

Precise predictions for single-top production: the impact of EW corrections and QCD shower on the t-channel signature

Frederix

Pagani

Tsinikos

2019

In this work we calculate and provide precise predictions for the signature that is typically exploited at the LHC for the measurement of t-channel single-top production: 1 lepton, 1 light jet, 1 b-jet, / E T and no additional jets or leptons. We apply the cuts that define the fiducial region and we take into account all the contributions to this signature; not only those from resonant t-channel single-top production. On the one hand, we calculate the complete-NLO corrections, i.e., all NLO effects of QCD and EW origin. On the other hand, we study in detail the impact of a QCD parton shower for the fiducial region we consider. We provide predictions in different approximations at the inclusive level and for several differential distributions. Our study demonstrates the relevance of both EW corrections and shower effects for obtaining precise and reliable theoretical predictions for the single-top-production fiducial region.

“…[78] and [79,80] resonance aware matching has been proposed within the MC@NLO and Powheg frameworks respectively, with focus on narrow coloured resonances. In our configuration the resonances are broader and the interference plays a more important role.…”

Section: Jhep10(2017)096mentioning

confidence: 99%

Scalar production and decay to top quarks including interference effects at NLO in QCD in an EFT approach

Franzosi

Vryonidou

Zhang

2017

Scalar and pseudo-scalar resonances decaying to top quarks are common predictions in several scenarios beyond the standard model (SM) and are extensively searched for by LHC experiments. Challenges on the experimental side require optimising the strategy based on accurate predictions. Firstly, QCD corrections are known to be large both for the SM QCD background and for the pure signal scalar production. Secondly, leading order and approximate next-to-leading order (NLO) calculations indicate that the interference between signal and background is large and drastically changes the lineshape of the signal, from a simple peak to a peak-dip structure. Therefore, a robust prediction of this interference at NLO accuracy in QCD is necessary to ensure that higher-order corrections do not alter the lineshapes. We compute the exact NLO corrections, assuming a point-like coupling between the scalar and the gluons and consistently embedding the calculation in an effective field theory within an automated framework, and present results for a representative set of beyond the SM benchmarks. The results can be further matched to parton shower simulation, providing more realistic predictions. We find that NLO corrections are important and lead to a significant reduction of the uncertainties. We also discuss how our computation can be used to improve the predictions for physics scenarios where the gluon-scalar loop is resolved and the effective approach is less applicable.