Combination of electroweak and QCD corrections to single W production at the Fermilab Tevatron and the CERN LHC

Abstract

Precision studies of the production of a high-transverse momentum lepton in association with missing energy at hadron colliders require that electroweak and QCD higher-order contributions are simultaneously taken into account in theoretical predictions and data analysis. Here we present a detailed phenomenological study of the impact of electroweak and strong contributions, as well as of their combination, to all the observables relevant for the various facets of the pp (−) → lepton + X physics programme at hadron colliders, including luminosity monitoring and Parton Distribution Functions constraint, W precision physics and search for new physics signals. We provide a theoretical recipe to carefully combine electroweak and strong corrections, that are mandatory in view of the challenging experimental accuracy already reached at the Fermilab Tevatron and aimed at the CERN LHC, and discuss the uncertainty inherent the combination. We conclude that the theoretical accuracy of our calculation can be conservatively estimated to be about 2% for standard event selections at the Tevatron and the LHC, and about 5% in the very high W transverse mass/lepton transverse momentum tails. We also provide arguments for a more aggressive error estimate (about 1% and 3%, respectively) and conclude that in order to attain a one per cent accuracy: 1) exact mixed O(αα s ) corrections should be computed in addition to the already available NNLO QCD contributions and two-loop electroweak Sudakov logarithms; 2) QCD and electroweak corrections should be coherently included into a single event generator.

Precision measurement of the W -boson mass: Theoretical contributions and uncertainties

“…As it can be seen from figure 7, the shape and size of the QED FSR corrections to the transverse mass distribution is largely maintained after the inclusion of QCD corrections; the mixed QCD-QED contributions are moderate but not negligible, with an effect at the few per mille level. On the contrary, the lepton p T distribution is strongly modified by mixed QCD-QED effects, which amount to some per cent and, more importantly, smear the varying shape of the QED FSR contribution, especially around the Jacobian peak, as emphasized in previous studies [64,66,67].…”

“…QCD and EW results have to be combined together to obtain a realistic description of the DY final states: general purpose Shower Monte Carlo programs, like Pythia [55,56], Herwig [57] or Sherpa [58], include the possibility of multiple photon, gluon and quark emissions via a combined application of QCD and QED Parton Shower (PS), retaining only LL accuracy in the respective large logarithmic factors. In the absence of an exact calculation of the first mixed O(αα s ) corrections, several recipes have been devised to include the bulk of the two sets of effects including factorizable subleading effects both of QCD and EW origin [59][60][61][62][63][64], and preserving the NLO-QCD and NLO-EW accuracy on the quantities inclusive with respect to additional radiation [65][66][67].…”

Search for physics beyond the standard model in final states with a lepton and missing transverse energy in proton-proton collisions ats=8 TeV

“…To combine the EW and QCD differential cross sections, two different approaches have been used [79]: an additive and a multiplicative combination. As both the EW and QCD K-factor include the NLO PDF information, a correction must be made to not account for the NLO PDF twice.…”

QCD parton showers and NLO EW corrections to Drell-Yan

“…It is worth noting that these two programs use essentially different parton shower algorithms: Pythia8 uses an evolution scheme based on transversemomentum ordering [5] and Herwig++ uses the coherent branching algorithm based on angular ordering of emissions in the parton shower [6]. Earlier the combination of the effects due to parton showers (PS) and due to EW radiative corrections for charged current process was considered in [7,8]. In those studies an interface between HORACE [9,10] and fortran event generator Herwig [11] was developed.…”