Statistical issues in the parton distribution analysis of the Tevatron jet data

Abstract

We analyse a tension between the D0 and CDF inclusive jet data and the perturbative QCD calculations, which are based on the ABKM09 and ABM11 parton distribution functions (PDFs) within the nuisance parameter framework. Particular attention is paid on the uncertainties in the nuisance parameters due to the data fluctuations and the PDF errors. We show that with account of these uncertainties the nuisance parameters corresponding to the luminosity uncertainties in the D0 and the CDF data sets take the values r D0 norm = 4.1 ± 1.3 and r CDF norm = 5.4 ± 1.7, respectively, while dropping luminosity uncertainty leads to variation of the PDFs well within uncertainties. A statistical bias of the estimator based on the nuisance parameters is also discussed.

PDF4LHC recommendations for LHC Run II

“…The understanding of this issue has improved. While it is true that Tevatron and LHC jet data directly constrain the gluon distribution, and that PDF sets with a particularly small high-x gluon distribution and/or small value of α s (m 2 Z ) do not provide the best fit to these data (see [45,80] for discussions on this issue with similar results, though not the same conclusions), it is unclear whether their omission automatically leads to a small high-x gluon distribution or small α s (m 2 Z ). The results of including the jet data in the fit also show some dependence on the treatment of correlated systematic errors (additive or multiplicative) assumed, though these effects are way too small [11,29] to explain the aforementioned differences.…”

Isospin asymmetry of quark distributions and implications for single top-quark production at the LHC

“…The present analysis is based on the update of the ABM12 global fit [8] including recent data on the neutrino-induced dimuon production [5] and with the addition of recent data on W ± -and Z-boson production collected by the LHC and Tevatron experiments. This new input allows to improve the determination of the quark distributions, and, in particular, the separation of the uand d-quarks.…”

“…In this letter we study the impact of the new data on charged lepton asymmetries from W ±boson production and their rapidity distributions on the global fit of PDFs by ABM [6][7][8]. Taking the ABM12 fit [8] based on the world DIS data, measurements of Drell-Yan (DY) dimuon production from fixed targets and early LHC data on W ± -and Z-boson production as a reference the impact of individual new data sets is quantified and the resulting shifts in the up-and down quark PDFs are documented. The fit results turn out to be consistent with a non-zero iso-spin asymmetry of the sea, I(x) = x( d − ū), at small values of Bjorken x ∼ 10 −4 .…”

Parton Distributions in the Higgs Boson era

“…In this respect, the CT collaboration has studied the dependence of the gluon PDFs on various possible χ 2 definitions of the inclusive jet data [12], showing that at large-x the different χ 2 can lead to modifications comparable to the impact of jet data itself. Related issues have also been studied by ABM [55] and earlier by Thorne and Watt [56].…”