Abstract
Soft-drop grooming of hadron-collision final states has the potential to significantly reduce the impact of non-perturbative corrections, and in particular the underlying-event contribution. This eventually will enable a more direct comparison of accurate perturbative predictions with experimental measurements. In this study we consider soft-drop groomed dijet event shapes. We derive general results needed to perform the resummation of suitable event-shape variables to next-to-leading logarithmic (NLL) accuracy matched to exact next-to-leading order (NLO) QCD matrix elements. We compile predictions for the transverse-thrust shape accurate to NLO + NLL′ using the implementation of the Caesar formalism in the Sherpa event generator framework. We complement this by state-of-the-art parton- and hadron-level predictions based on NLO QCD matrix elements matched with parton showers. We explore the potential to mitigate non-perturbative corrections for particle-level and track-based measurements of transverse thrust by considering a wide range of soft-drop parameters. We find that soft-drop grooming indeed is very efficient in removing the underlying event. This motivates future experimental measurements to be compared to precise QCD predictions and employed to constrain non-perturbative models in Monte-Carlo simulations.
Highlights
In this article we considered soft-drop grooming final states of hadronic collisions prior to the evaluation of QCD event-shape variables
This offers great potential to largely remove final-state contributions originating from the underlying event, enabling more direct comparisons of accurate theoretical predictions with experimental data
To compile first accurate perturbative results, we have extended the well-known CAESAR formalism for the resummation of next-to-leading logarithmic (NLL) soft-gluon corrections to groomed eventshape observables in hadronic collisions
Summary
With all final-state particles contributing to the observable calculation, event-shape variables can be sensitive to non-perturbative corrections This we illustrate here for the transverse-thrust observable, which we will use throughout the paper as concrete example. Hadronisation pushes events to somewhat higher values of transverse thrust, resulting in corrections of order 10% in the peak region and even more sizeable in the low-τ⊥ tail, i.e. ln(τ⊥) −3 This strong susceptibility of the observable to non-perturbative effects over its whole range makes the comparison of experimental measurements with purely perturbative calculations rather indirect and plagued by significant modelling uncertainties. Recent measurements are based on reconstructed jets as inputs to the observable calculation, which simplifies dealing with the large underlying event contributions but prevents a direct comparison to perturbative predictions, see for example the discussion in [25] Those have so far been presented at NLO QCD [54] and resummed to NLO + NLL. We focus on transverse thrust, as the “standard candle” event-shape variable, in our phenomenological studies
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