Measurement of $Z$ Boson production with the ATLAS Experiment at the LHC

A measurement of the differential pp ! Z / ! e + e cross section as a function of di- electron invariant mass in the region 66 < m Z < 116 GeV using 4 : 58 fb-1 of data collected at a center-of-mass energy of p s = 7 TeV in 2011 with the ATLAS detector at the LHC is performed. The measurement is performed with a comprehensive treatment of systematic and statistical uncertainties evaluated using Monte Carlo simulation and data-driven techniques. The contribution from electroweak and t t background processes is estimated using simulation, while the contribution from QCD backgrounds is estimated using a data-driven method. The measured cross section is compared with various theoretical predictions from parton distribu- tionfunction(PDF)fitstonext-to-next-to-leadingorderQCDcalculationswithnext-to-leading order electroweak corrections. The precision of the measurement is of the order of 1 - 2 % and providesstrongPDFdiscrimination,withnoneofthestateoftheartPDFsshowinggoodagree- ment with the data. The measurement can be used as an input to constrain future PDF fits. Acombinationofseparateelectronandmuon W and Z / crosssectionmeasurementsis also presented, with full treatment of each channel's systematic uncertainties and the correla- tionsbetweenthem. Thesemeasurementsareperformedasafunctionofleptonpseudo-rapidity and Z bosonrapidityforthe W and Z / productionprocessesrespectively. Theseserveasa precise probe of QCD dynamics and proton PDFs. The combined cross sections are compared withtheoreticalpredictionsandstronglydiscriminatebetween, andinsomecasesexclude, dif- ferent PDF fits. The precision of the measurements is better than the PDF uncertainties, and NNLO QCD and NLO EW theory are limiting factors in interpretation of the data