Quark-Antiquark Tag Analyses

Figure: Definition of the correlation regions in terms of $\Delta \Phi$ and the relative charges of the $D^*$ meson and the muon. The sketches illustrate the $\Delta \Phi -\Delta Q$ correlations in $c\bar{c}$ and $b\bar{b}$ quark decays to $D^*\mu$.

Figure: Distribution of the invariant mass $M(Q\bar{Q})$ of the quark pair as simulated in Pythia for the selected sample of $D^*\mu$ events (solid line) and for the selection of the beauty enriched di-jet event sample in which two jets at transverse momenta of 6 and 7 GeV are required in addition to a muon (see section 6.2.1).

Events in which both heavy quarks are identified are of particular interest for the study of final state configurations. These `two-quark tag' events provide access to new tests of higher order QCD effects. For instance, in the photon-gluon rest frame the angle between the heavy quarks is $180^{\circ}$ in the leading order picture, but in next-to-leading order it can deviate significantly due to hard gluon radiation. In the $k_t$ factorization approach, the $q\bar{q}$ pair is expected to be sensitive to possible transverse momenta $k_t$ of the gluons entering the quark pair production process. Furthermore, in semileptonic decays the charge of the final state lepton in combination with the relative angle to the reconstructed charm hadron can be used to separate charm and beauty contributions to the heavy quark cross section.