Measurement of the proton structure parameters in the forward-backward charge asymmetry

The forward-backward asymmetry (AFB) in the Drell-Yan process pp/p p over bar -> Z gamma* -> l -l is sensitive to the proton structure information. Such information has been factorized into well-defined proton structure parameters which can be regarded as experimental observables. In this paper, we extract the structure ffiffiparameters from the AFB distributions reported by the CMS Collaboration in pp collisions at p = 8 TeV, s ffiffiand by the D0 Collaboration in pp over bar collisions at p s = 1.96 TeV. It is the first time that the unique parton information in the AFB spectrum can be decoupled from the electroweak calculation and measured as standalone observables, which can be used as new data constraints in the global quantum chromodynamics analysis of the parton distribution functions. Although the parton information in the pp and pp over bar collisions are different, and the precisions are statistically limited, the results from both the hadron colliders indicate that the down quark contribution might be higher in the data than their theoretical predictions.