Top-pair production and decay at the LHC
- A large number of differential distributions for top-pair production with decay have been computed in NNLO QCD in this paper [arXiv:2008.11133]. All predictions are available for download here.
Spin correlations in top-pair production at the LHC
Based on the paper arXiv:1901.05407 by Arnd Behring, Michal Czakon, Alexander Mitov, Andrew S. Papanastasiou and Rene Poncelet.
- The data for all plots shown in the paper can be downloaded here. In particular, the tarball contains the NNLO QCD predictions for the normalized delta-phi and |delta-eta| distributions for both the fiducial and inclusive phase-space.
- A large number of additional results can be downloaded here. See the README file inside the tarball for more information.
A Note regarding the delta-phi distribution for slices in Mtt: please keep in mind that there is a slight mismatch in the definition of the fiducial volume used in our calculation of the 2-dim distribution (which is as defined in the paper above or in the README file, i.e. we require at least 1 b-jet) while ATLAS requires exactly 2 b-jets. This leads to a noticeable change in the absolute distribution. Given the size of the current uncertainty of the experimental measurement such a difference is perhaps acceptable for the normalized distributions. Please feel free to contact us if you think a calculation with a matching fiducial volume is really needed for your analysis and we will do our best to provide it.
An update (June 2019): the status of the spin correlations measurement continues to be a subject of hot debate (see the related presentations at the latest LHCtopWG meeting). During the discussions a point was raised that the QCD+EW prediction by W. Bernreuther et al, included in the ATLAS paper arXiv:1903.07570 (the green curve/band in fig. 13b of that paper) is computed by expanding the ratio (i.e. the normalized distribution) in powers of the coupling(s). While the exact definition used in the calculation is not available in a publication (to the best of our knowledge) following the discussions at the WG meeting we decided to present our predictions for the normalized distribution expanded in the strong coupling and accurate through NNLO.
Here are our predictions for the inclusive selection, compared to the usual un-expanded way of computing normalized distributions, and for two different scales:
From the above two plots we conclude that the expansion shifts the NLO prediction significantly towards the data and the shift behaves in a way that is consistent with the prediction of W. Bernreuther et al mentioned above. However, at NNLO the shift is much reduced and the two NNLO predictions (expanded and un-expanded one) agree very well with each other. We thus conclude that expanding or not the definition of the normalized distribution cannot account for the discrepancy between QCD predictions and ATLAS data in the Inclusive case. Clearly, the NNLO accuracy is indispensable in reaching this conclusion.
An update (May 2020): Predictions for the inclusive phase-space, 6-bin Δ(φ) measurement in the CMS paper arXiv:1907.03729 can be found here. We provide both the expanded and unexpanded predictions through NNLO in QCD.
Additional plots (June 2019): Here are two additional plots that show the diagonal scales muF=muR=(HT/2,HT/4,HT/8) versus all scales (diagonal and off-diagonal) in the NNLO absolute and normalized distributions. We thank the referees of our paper for this suggestion.