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<font color="#000099"><b><font color="#3333ff">Physics Seminar<br>
Oct. </font></b></font><font color="#3333ff"><b>19, 2012<br>
11:00 AM<br>
Cebaf Center AUD.<br>
Cookies and Coffee 10:45AM<br>
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<pre wrap=""><font face="Times New Roman, Times, serif"><big><b><font color="#cc0000">"First Results from the Qweak Measurement of the proton's Weak Charge"</font></b><b><font color="#cc0000">
Mark. M. Dalton
University of Virginia</font></b></big>
</font><tt>The Qweak experiment has made the first direct measurement of the weak charge of the proton through precision measurement of the parity-violating asymmetry in elastic scattering of longitudinally polarized electrons from unpolarized protons. The data were taken in Hall C at Jefferson Laboratory, during 12 months of running over a 2 year period, ending in May 2012. A beam current of up to 180 uA on a 35 cm long liquid-hydrogen target produced a scattered electron flux of 6.5 GHz incident on the detectors with Q2 ~ 0.026 GeV2. It is expected that the weak charge of the proton will be extracted with a 4.1% combined statistical and systematic uncertainty. The proton weak charge is suppressed in the Standard Model so that these data may be used to determine the weak mixing angle with a relative uncertainty of 0.3%, providing a competitive measurement of the running of this parameter to low Q2. In addition, these data will impose a strong constraint on a combination of t
he vect
or weak charges of the u and d quarks, C1u and C1d, which is distinct from and complementary to the combination in measurements of parity violation in atomic systems, and thereby provide an independent constraint on physics beyond the Standard Model. A first look at a subset of the data will be presented.</tt></pre>
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