Prospects for probing the structure of the proton with low-mass Drell-Yan events in ATLAS

The biggest scientific experiment in history will begin taking data in late 2009 using the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland. The LHC is designed to collide protons at an unprecedented 14 TeV centre of mass energy, enabling physicists to explore the constituents of matter at smaller scales than ever before. The Parton Distribution Functions (PDFs) are parametrizations of the proton structure and are best determined from experimental data. The PDFs are needed to calculate cross-sections or in other words the likelihood of observed physical processes, which are crucial in exploiting the discovery potential of the LHC. The prospects for measuring the Drell-Yan (DY) spectrum are assessed in the low invariant mass region below the Z boson resonance using electron-positron pairs from the initial LHC data in order to probe the proton structure and further constrain the PDFs. The analysis is based on the full simulation of the ATLAS detector response to DY electrons and background processes. Assuming 100 pb^{-1} of LHC data, the total DY cross-section in the invariant mass range from 10 GeV to 60 GeV is expected to be measured as sigma_{DY} = 5.90 pm 0.24(stat) pm 0.18(syst) nb. The result predicts an improvement over a current theoretical uncertainty of 7.6% and indicates that the PDF uncertainties can be reduced significantly with the early LHC data.