A Precision Measurement of the Weak Mixing Angle in Møller Scattering at Low Q₂

• Main Author: Jones, Gary Mark
• Format: Others
• Language: en
• Published: 2004
• Online Access: https://thesis.library.caltech.edu/2138/1/thesis.pdf; Jones, Gary Mark (2004) A Precision Measurement of the Weak Mixing Angle in Møller Scattering at Low Q₂. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/S506-PZ85. https://resolver.caltech.edu/CaltechETD:etd-05272004-172049 <https://resolver.caltech.edu/CaltechETD:etd-05272004-172049>

<p>The electroweak theory has been probed to a high level of precision at the mass scale of the Z^o through the joint contributions of LEP at CERN and the SLC at SLAC. The E158 experiment at SLAC complements these results by measuring the weak mixing angle at a Q² of 0.026 (GeV/c)², far below the weak scale.</p> <p>The experiment utilizes a 48 GeV longitudinally polarized electron beam on unpolarized atomic electrons in a target of liquid hydrogen to measure the parity-violating asymmetry A^PV in Moller scattering.</p> <p>The tree-level prediction for A^PV is proportional to 1-4sin²θ_W. Since sin²θ_W is approximately 0.25, the effect of radiative corrections is enhanced, allowing the E158 experiment to probe for physics effects beyond the Standard Model at the TeV scale.</p> <p>This work presents the results from the first two physics runs of the experiment, covering data collected in the year 2002. The parity-violating asymmetry A^PV was measured to be <center>A^PV = -158 ppb +/- 21 ppb (stat) +/- 17 ppb (sys).</center> The result represents the first demonstration of parity violation in Moller scattering. The observed value of A^PV corresponds to a measurement of the weak mixing angle of <center>sin²θ_W^eff = 0.2380 +/- 0.0016 (stat) +/- 0.0013 (sys),</center> which is in good agreement with the theoretical prediction of <center>sin²θ_W^eff = 0.2385 _+/- 0.0006 (theory).</center> </p>