Data-Driven Estimation of the Invisible Z Background to the SUSY MET Plus Jets Search

The large missing transverse momentum (MET) plus jets final state topology has great potential for discovery of new physics involving dark matter candidates early in LHC running, if Standard Model backgrounds can be understood. The irreducible background of high transverse momentum (\pt) Z bosons, with Z$\rightarrow\nu\bar{\nu}$ produced in conjunction with high $E_{\rm{T}}$ jets, can be estimated from samples of photon plus jets and W$\rightarrow\mu\nu$ plus jets. These samples have much higher statistics than the previously studied Z$\rightarrow\mu\mu$ plus jets method. In addition, new physics will likely contribute to these control samples differently; they thus provide useful cross checks in the presence of new particles. For 100~\pb, the contribution of ``invisible Z'' events to the MET~$>$~200 GeV region can be estimated with a statistical uncertainty of order 10~$\%$ using photon plus jets. Experimental systematic uncertainties obtained via data-driven techniques are expected to be roughly 20~$\%$ and are statistically limited. Theoretical uncertainties on photon production are under study and will be reported in an update to this note, along with methods for obtaining the relative normalizations directly from data. For W plus jets, the statistical, systematic and theoretical uncertainties are estimated to be 29~$\%$, 23~$\%$, and 8~$\%$ respectively. %The relative normalizations of photons to Z's %will be obtained directly from data.