Differential distributions for t-channel single top-quark production and decay at next-to-next-to-leading order in QCD

Abstract

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 the pseudo-rapidity distributions of the leading jet in the event. In all cases the perturbative hard-scale uncertainties are greatly reduced after the NNLO corrections are included. We also show a comparison of the normalized parton-level distributions to recent data from the 8 TeV measurement of the ATLAS collaboration. The NNLO corrections tend to shift the theoretical predictions closer to the measured transverse momentum distribution of the top (anti)-quark. Importantly, for the LHC at 13 TeV, we present NNLO cross sections in a fiducial volume with decays of the top quark included.

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

“…In Appendix A we perform a detailed comparison with the results in refs. [38,39], showing how these effects can have an impact and motivating the features that are found in the results presented in this section, especially at the differential level.…”

“…Indeed, although in Ref. [39] a reduction of scale uncertainties is progressively observed moving from LO to NLO and then to NNLO accuracy, this reduction is very sensitive to the definition of the fiducial region (which is different in Ref. [39] and in this work), see also Appendix A.…”

“…We remind the reader that NLO (and also NNLO) QCD corrections to t-channel singletop with leptonic top decays have already been calculated in a similar fiducial region in refs. [38,39]. However, this calculation is based on the narrow-width approximation for the top decay, therefore non-resonant effects, and s-channel and tW contributions are not taken into account.…”

“…On the theoretical front, predictions for t-channel single-top quark production have been known at the NLO accuracy in QCD for quite some time [30][31][32][33] in the five flavour scheme (5FS), and for about ten years in the four-flavour scheme (4FS) [34][35][36]. Much more recently, also the NNLO corrections have been computed [37], also including the decay of the top quark in the narrow width approximation up to the same level of accuracy, but neglecting some interference contributions in the NNLO corrections [38,39]. The NLO corrections in the electroweak coupling have been computed [40][41][42] and are found to be small for the inclusive production, but can be significantly enhanced in certain regions of phase space.…”

Symbolic expressions for fully differential single top quark production cross section and decay width of polarized top quark in the presence of anomalous Wtb couplings

“…T -odd correlations in polarized top quark decays have been studied in [31]. Decays of polarized top quarks in frame of SM at Next-to-Leading and Next-to-Next-to Leading Order in QCD have been studied in papers [32][33][34][35] As well known in the SM, the positively charged lepton from the top quark decay in its rest frame tends to follow the top quark spin direction [16,17]. In the t-and s-channel single top production the direction of the top quark spin in the top rest frame is highly correlated with the d-quark momentum for the t-channel (outgoing light jet) and anti d-quark momentum (incoming parton corresponding to the beam axis) for the s-channel [18,19].…”