We present results for Drell-Yan production from the GENEVA Monte-Carlo framework. We combine the fully differential next-to-next-to leading order (NNLO) calculation with higher-order resummation in the 0-jettiness resolution variable. The resulting parton-level events are further combined with parton showering and hadronization provided by PYTHIA8. The 0-jettiness resummation is carried out to NNLL 0 , which consistently incorporates all singular virtual and real NNLO corrections. It thus provides a natural perturbative connection between the NNLO calculation and the parton shower regime, including a systematic assessment of perturbative uncertainties. In this way, inclusive observables are correct to NNLO, up to small power corrections in the resolution cutoff. Furthermore, the perturbative accuracy of zero-jetlike resummation variables is significantly improved beyond the parton shower approximation. We provide comparisons with LHC measurements of Drell-Yan production at 7 TeV from ATLAS, CMS, and LHCb. As already observed in e þ e − collisions, for resummation-sensitive observables, the agreement with data is noticeably improved by using a lower value of α s ðM Z Þ ¼ 0.1135.

Abstract:We extend the lowest-order matching of tree-level matrix elements with parton showers to give a complete description at the next higher perturbative accuracy in α s at both small and large jet resolutions, which has not been achieved so far. This requires the combination of the higher-order resummation of large Sudakov logarithms at small values of the jet resolution variable with the full next-to-leading-order (NLO) matrix-element corrections at large values. As a by-product, this combination naturally leads to a smooth connection of the NLO calculations for different jet multiplicities. In this paper, we focus on the general construction of our method and discuss its application to e + e − and pp collisions. We present first results of the implementation in the Geneva Monte Carlo framework. We employ N -jettiness as the jet resolution variable, combining its next-tonext-to-leading logarithmic resummation with fully exclusive NLO matrix elements, and Pythia 8 as the backend for further parton showering and hadronization. For hadronic collisions, we take Drell-Yan production as an example to apply our construction. For e + e − → jets, taking α s (m Z ) = 0.1135 from fits to LEP thrust data, together with the Pythia 8 hadronization model, we obtain good agreement with LEP data for a variety of 2-jet observables.

We present a general method to match fully differential next-to-next-to-leading (NNLO) calculations to parton shower programs. We discuss in detail the perturbative accuracy criteria a complete NNLO+PS matching has to satisfy. Our method is based on consistently improving a given NNLO calculation with the leading-logarithmic (LL) resummation in a chosen jet resolution variable. The resulting NNLO+LL calculation is cast in the form of an event generator for physical events that can be directly interfaced with a parton shower routine, and we give an explicit construction of the input "Monte Carlo cross sections" satisfying all required criteria. We also show how other proposed approaches naturally arise as special cases in our method.1 To be precise, if ΦN points are generated according to a probability distribution P (ΦN ), each point gets assigned the weight w(ΦN ) = BN (ΦN )/P (ΦN ). The effective distribution of points is then w(ΦN )P (ΦN ) = BN (ΦN ), as desired. The simplest would be to use a flat sampling P (ΦN ) = 1, while P (ΦN ) ≈ BN (ΦN ) would be statistically more efficient. While the choice for P (ΦN ) is important for the statistical efficiency of the Monte Carlo integration, it is not relevant for our discussion.2 Alternatively, one can keep the ΦN point fixed during the ΦN+1 integration and evaluate the same MX (ΦN ) for all the subtraction counterterms and different MX [Φ m N +1 (ΦN )] for each different B m N +1 contribution, where m B m N +1 = BN+1. This approach might be better for efficiency reasons and more suitable for matching with the parton shower.