Perturbative QCD description of jet data from LHC Run-I and Tevatron Run-II

Abstract

We present a systematic comparison of jet predictions at the LHC and the Tevatron, with accuracy up to next-to-next-to-leading order (NNLO). The exact computation at NNLO is completed for the gluons-only channel, so we compare the exact predictions for this channel with an approximate prediction based on threshold resummation, in order to determine the regions where this approximation is reliable at NNLO. The kinematic regions used in this study are identical to the experimental setup used by recently published jet data from the ATLAS and CMS experiments at the LHC, and CDF and D0 experiments at the Tevatron. We study the effect of choosing different renormalisation and factorisation scales for the NNLO exact prediction and as an exercise assess their impact on a PDF fit including these corrections. Finally we provide numerical values of the NNLO k-factors relevant for the LHC and Tevatron experiments.

Parton distributions for the LHC run II

“…In the kinematical region covered by the Tevatron and LHC jet cross-sections, see figure 2, the gluon channel is not necessarily dominant, however both theoretical arguments and the known NLO behavior suggest that the pattern of agreement or disagreement of the JHEP04(2015)040 threshold and exact computations is similar in all partonic channels [124]. This result then suggests that the threshold approximation can be used provided all channels are included, and a sufficiently conservative cut is applied in order to keep only the regions in which the size of the deviation between the exact and threshold computations in the gg channel does not exceed a suitable low threshold.…”

“…This was done recently in a systematic study [124], to which we refer for a more detailed treatment. An important consequence of the analysis of ref.…”

“…An important consequence of the analysis of ref. [124] is that some of the comparisons between the exact computations and the threshold approximation performed hitherto [100] were marred by the fact that the renormalization scale was set equal to the jet transverse momentum p T in the threshold calculation, while the transverse momentum of the hardest jet p lead T was used instead for the exact calculation. It turns out that the perturbative expansion is rather better behaved, with smaller perturbative corrections, when the scale p T is used, and also, that the regions of agreement are rather different if a consistent scale choice is made: specifically, when using p T as a scale in the large rapidity region the accuracy of the threshold approximation appears to be very poor (while there is a better, accidental agreement when an inconsistent scale choice is made).…”

“…[124] and compute approximate NNLO C-factors, eq. (2.1), using the threshold calculation, while restricting the fitted dataset to the region where, thanks to the comparison with the exact gg calculation, we know the former to be reliable.…”

Dynamical scales for multi-TeV top-pair production at the LHC

“…[47]. An often made choice in inclusive jet production is p T or p T,max [48][49][50] while for dijet mass distributions one typically has p T,ave and p T,max e 0.3y * [48,51]. A recent summary of existing LHC jet measurements can be found in ref.…”