events to constrain and study the shape of $\cPZ(\cPgn\cPagn)$+jets events in fully hadronic final states.

The megajets are constructed as the sum of the four-momenta of their constituent objects. After considering all possible partitions into two megajets, the combination is selected that has the smallest sum of megajet squared-invariant-mass values.

The variables ${\ensuremath{M_R}\xspace}$ and ${\ensuremath{R^2}\xspace}$ are calculated from the megajet four-momenta. The events are assigned to one of the six final state [*boxes*]{} according to whether the event has zero, one, or two isolated leptons, and according to the lepton flavor (electrons and muons), as shown in Table \[tab:boxes\]. The lepton $\pt$, ${\ensuremath{M_R}\xspace}$, and ${\ensuremath{R^2}\xspace}$ thresholds for each of the boxes are chosen so that the trigger efficiencies are independent of ${\ensuremath{M_R}\xspace}$ and ${\ensuremath{R^2}\xspace}$.

[l c]{}\
ELE-MU (loose-tight) & $\pt > 20$, $\pt > 15$\
MU-MU (loose-loose) & $\pt > 15$, $\pt > 10$\
ELE-ELE (loose-tight) & $\pt > 20$, $\pt > 10$\
MU (tight) & $\pt > 12$\
ELE (loose) & $\pt > 20$\
\

The requirements given in Table \[tab:boxes\] determine the [ *full analysis regions*]{} of the (${\ensuremath{M_R}\xspace}$, ${\ensuremath{R^2}\xspace}$) plane for each box. These regions are large enough to allow an accurate characterization of the background, while 