Measurement of $Z$ boson production using $Z \rightarrow ee$ decays with one of the electrons detected in the forward calorimeters of the ATLAS detector using 4.6 fb$^{-1}$ of data collected at $\sqrt{s} = 7$ TeV

The double differential cross-section for $Z$ bosons decaying in the electron channel was measured as a function of the di-electron invariant mass and rapidity. For this measurement, the data collected at the ATLAS detector at the LHC during 2011 at a center-of-mass energy of $\sqrt{s} = 7$ TeV was used.The analysis is focused on the central-forward $Z$ bosons, i.e. the bosons that decay into two electrons, one of which is reconstructed in the central region of the detector ($|\eta| < 2.5$) and the other in the forward region of the detector ($|\eta| > 2.5$). Several sources of the systematic uncertainties were taken into account, including the electron reconstruction and identification efficiencies, pileup effects, PDF sets for the initial protons, and differences between various Monte Carlo simulations. The main sources of uncertainties were found to be the efficiency scales of the forward electron identification and the forward electron energy resolution. The results of the analysis are in agreement with measurements in other decay channels of the $Z$ boson and with theoretical predictions.The fast simulation method called Frozen Showers was developed to speed up the simulation of Monte Carlo data samples. This method increases the simulation speed by $\sim$25% while introducing additional errors of less than 1% in the energy scale and resolution of the reconstructed particles. The method was used to speed up the production of all Monte Carlo samples used in this analysis.