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SLAC-R-733
A Search for New Physics at the TeV Scale Via a Precise Measurement of the Weak Mixing Angle in Moller Scattering

Abstract

This dissertation reports on a precise measurement of the parity-violating asymmetry in electron-electron (M{\o}ller) scattering at a four-momentum transfer $Q^2=0.03$ (GeV/c)$^2$. The observed parity-violating asymmetry is $A_{PV}=-128 \pm 14~(\mathrm{stat.})\pm 12~(\mathrm{syst.}) \times 10^{-9}$. This is the most precise asymmetry ever measured in a parity-violating electron scattering. In the context of the Standard Model, the $A_{PV}$ result determines the weak mixing angle, which is one of the fundamental parameters of the model. The result is $\sin^2\theta_W^{eff}=0.2403 \pm 0.0014$, which is consistent with the Standard Model expectation at the current level of precision. The comparison between this measurement of the weak mixing angle at low $Q^2$ and at the $Z^0$ pole establishes the running of $\sin^2\theta_W$ with $6.5\sigma$ significance. In addition, we report on the first observation of a transverse asymmetry in electron-electron scattering. The observed asymmetry is $A_T^{M{\o}ller}= 2.7 \times 10^{-6}$, which is consistent with the theoretical predictions. We also provide a new measurement of the transverse asymmetry in $ep$ scattering $A_T^{ep}= 2 \times 10^{-6}$. The consistency of the result with the theoretical prediction provides new limits on the TeV scale physics. A limit of $0.9$ TeV was set on the mass of the extra $Z'$ boson in the SO(10) Model. A limit of $14$ TeV and $6$ TeV was set on the compositness scales $\Lambda_{ee}^+$ and $\Lambda_{ee}^-$, respectively. Finally a limit of $0.2$ TeV was set on ratio of the doubly-charged Higgs mass to the $ee\Delta$ coupling $g^2_{ee\Delta}/m_\Delta^2$.

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