Search for New Physics in a Final State with Same-Sign Dileptons, Jets, and Missing Transverse Energy at 7 TeV Center of Mass Energy

We report on a search for new physics in a final state with two same sign leptons, missing transverse energy, and significant hadronic activity at a center of mass energy $sqrt{s}$ = 7 TeV. The data were collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 0.98 $mathrm{fb}^{-1}$. Data--driven methods are developed to estimate the dominant Standard Model backgrounds. No evidence for new physics is observed. The dominant background to the analysis comes from failures of lepton identification in Standard Model $tar{t}$ events. The $tar{t}$ production cross section in the dilepton final state is measured using 3.1 $mathrm{fb}^{-1}$ of data. The cross section is measured to be 194 $pm$ 72 (stat) $pm$ 24 (syst) $pm$ 21 (lumi) pb. An algorithm is developed that uses tracking information to improve the reconstruction of missing transverse energy. The reconstruction of missing transverse energy is commissioned using the first collisio ns recorded at 0.9, 2.36 and 7 TeV data. Events with abnormally large values of missing transverse energy are identified as arising from anomalous signals in the calorimeters. Tools are developed to identify and remove these anomalous signals.