Improved D0 W Boson Mass Determination PDF Download

In the first part, we describe what is the W boson mass in the context of the Standard Model. We discuss the prominent role this physical observable plays in the determination of the internal self consistency of the Electroweak Sector. We review measurements and calculation of the W boson mass done in past and argue about the importance and feasibility of improving the experimental determination. We give a description of the Fermilab Tevatron Collider and the D0 detector, highlighting the relevant parts for the measurement described in this Dissertation. In the second part, we give a detailed description of a measurement of the W boson mass using the D0 Central Calorimeter. The measurement uses 1.68 x 106 candidates from W → en decays, corresponding to 4.3 fb-1 of integrated luminosity collected from 2006 to 2009. We measure the mass using the transverse mass, electron transverse momentum, and missing transverse energy distributions. The transverse mass and electron transverse momentum measurements are the most precise and are combined to give MW = 80.367 ± 0.013(stat) ± 0.023 (syst) GeV = 80.367 ± 0.026 GeV. This is combined with an earlier D0 result determined using an independent 1 fb-1 data sample, also with central electrons only, to give MW = 80.375± 0.023 GeV. The uncertainty in the measurement is dominated by the determination of the calorimeter electron energy scale, the W sample size, the knowledge of the parton distribution function. In the third part, we discuss methods of reducing the dominant uncertainties in the W boson mass measurements. We show that introducing electrons detected in the End Calorimeters greatly reduce the measurement systematic uncertainty, especially the on related to the parton distribution functions. We describe a precise calibration of the End Calorimeter using Z → ee events corresponding to 4.3 fb-1 of integrated luminosity. The calibration is an important milestone in a measurement that explores a larger part of the D0 Calorimeter. We present parametrized models that describe the response of the End Calorimeters to electron showers and soft hadronic particles, giving special attention to the specific challenges of a measurement in the forward region: the inhomogeneity of the uninstrumented materials, the large hadronic energy flow in the calorimeter and the jet misidentification probability.