Measurement of jet charge in dijet events from $\sqrt{s}=8$ TeV $pp$ collisions with the ATLAS detector

The momentum-weighted sum of the charges of tracks associated to a jet is sensitive to the charge of the initiating quark or gluon. This paper presents a measurement of the distribution of one class of momentum-weighted sums, called the jet charge, in dijet events using 20.3 fb$^{-1}$ of data recorded with the ATLAS detector at $\sqrt{s}=8$ TeV in $pp$ collisions at the LHC. The jet charge distribution is unfolded to remove distortions from detector effects and the resulting particle level distribution is compared with several models. The $p_T$-dependence of the jet charge distribution average and standard deviation are compared to predictions obtained with several LO and NLO parton density functions and the best description of the data is found with CTEQ6L1. The data are also compared to different Monte Carlo predictions of QCD using various settings of the free parameters within these models. The choice of the strong coupling constant $\alpha_s$ used to calculate QCD radiation is found to have a significant impact on the predicted jet charge. There is evidence for a $p_\text{T}$-dependence of the jet charge distribution for a given jet flavor. In agreement with perturbative QCD predictions, the data show that the average jet charge of quark-initiated jets decreases in magnitude as the energy of the jet increases.