Abstract
We introduce PineAPPL, a library that produces fast-interpolation grids of physical cross sections, computed with a general-purpose Monte Carlo generator, accurate to fixed order in the strong, electroweak, and combined strong-electroweak couplings. We demonstrate this unique ability, that distinguishes PineAPPL from similar software available in the literature, by interfacing it to MadGraph5_aMC@NLO. We compute fast-interpolation grids, accurate to next-to-leading order in the strong and electroweak couplings, for a representative set of LHC processes for which EW corrections may have a sizeable effect on the accuracy of the corresponding theoretical predictions. We formulate a recommendation on the format of the experimental deliverables in order to consistently compare them with computations that incorporate EW corrections, and specifically to determine parton distribution functions to the same accuracy.
Highlights
Only if theoretical predictions become comparatively precise
We introduce PineAPPL, a library that produces fast-interpolation grids of physical cross sections, computed with a general-purpose Monte Carlo generator, accurate to fixed order in the strong, electroweak, and combined strong-electroweak couplings
Because Quantum Chromodynamics (QCD) dominates the interactions occurring within colliding protons at the LHC, much effort has been devoted to the computation of higher-order QCD corrections: fully-differential next-to-leading order (NLO) results, possibly matched to a parton shower, are currently automated in various general-purpose Monte Carlo generators [4,5,6], while an increasing number of next-to-next-to-leading order (NNLO) predictions are becoming available for processes with various degrees of inclusiveness
Summary
Only if theoretical predictions become comparatively precise. This entails the computation of additional higher-order contributions to the fixed-order perturbative expansion, on the one hand, and an increasingly sophisticated determination of the Parton Distribution Functions (PDFs) of the proton [2, 3], on the other hand. A problem of efficiency: fast-interpolation grids should be constructed, whereby partonic matrix elements, accurate to NLO QCD+EW, are precomputed in such a way that the numerical convolution with generic input PDFs can be efficiently approximated by means of interpolation techniques Such grids are essential whenever the evaluation of the hadronic cross section needs to be performed a large number of times, as is the case in the evaluation of scale variations or of PDF fits. Examples are the subtraction of background processes which should not be considered as such (e.g. the t-channel photon-induced component in neutral-current Drell-Yan, which is not a separate process beyond leading order) or of just a part of the EW effects (e.g. multiple-photon radiation from light particles in the final state of neutralor charged-current Drell-Yan, especially with electrons) Be that as it may, if EW effects are systematically included in theoretical predictions, they should not be subtracted from experimental results, otherwise they will be double counted
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