Measurement of the W Boson Mass with Early Data

We present new methods for measuring the W mass at ATLAS, and show their perfor- mance on simulated data. The experimental systematic uncertaintiess and their impact on the mW measurement are evaluated, with samples downscaled to 15 pb−1 . The electron transverse momentum analysis yields a precision of δmW = 120 (st at ) ⊕ 117 (syst ) MeV. The systematic uncertainty is dominated by the energy scale. In the muon channel, the transverse mass analysis gives δmW = 57 (st at ) ⊕ 231 (syst ) MeV, where the dominant contribution comes from the recoil calibration. PDF uncertainties contributes δmW = 25 MeV. Other theoretical uncertainties were not explicitely considered, but expected to be small in comparison to experimental uncertainties in early mW measurements.