Matching In Pp -> TtW/Z/H+ Jet Smeft Studies

In this paper, we explore the impact of extra radiation on predictions of pp -> ttX,X=h/W +/- /Z processes within the dimension-6 SMEFT framework. While full next-to-leading order calculations are of course preferred, they are not always practical, and so it is useful to be able to capture the impacts of extra radiation using leading-order matrix elements matched to the parton shower and merged. While a matched/merged leading-order calculation for ttX is not expected to reproduce the next-to-leading order inclusive cross section precisely, we show that it does capture the relative impact of the EFT effects by considering the ratio of matched SMEFT inclusive cross sections to Standard Model values, sigma SMEFTttX+j/sigma SMttX+jequivalent to mu. Furthermore, we compare leading order calculations with and without extra radiation and find several cases, such as the effect of the operator phi dagger iD <->mu phitgamma mu t on tth and ttW, for which the relative cross section prediction increases by more than 10% - significantly larger than the uncertainty derived by varying the input scales in the calculation, including the additional scales required for matching and merging. Being leading order at heart, matching and merging can be applied to all operators and processes relevant to pp -> ttX,X=h/W+/- /Z+jet, is computationally fast and not susceptible to negative weights. Therefore, it is a useful approach in ttX + jet studies where complete next-to-leading order results are currently unavailable or unwieldy.