Speaker
Description
The Standard Model makes a definite prediction for the neutral weak charge of
the proton; deviation from this value would be a signature of physics beyond
the Standard Model.
The Qweak experiment has determined the weak charge of the proton by measuring
the parity-violating asymmetry in elastic e-p scattering at
$Q^2=0.03\ (\mathrm{GeV}/c)^2$ with a total precision of less than 10 ppb.
The experiment was carried out in Hall C of Jefferson Laboratory in the period
2010-2012, using longitudinally-polarized electrons of energy 1.16~GeV, a
35 cm long liquid hydrogen target, and custom detector apparatus.
This determination of the proton's weak charge may be used to determine
the running of the weak mixing angle, $\sin^2\theta_W$, to low $Q^2$ with a
relative error of about a half percent.
Further, in combination with measurements from atomic parity violation, this
measurement imposes a strong constraint on the values of the vector weak
charges of the $u$ and $d$ quarks, $C_{1u}$ and $C_{1d}$.
The final results of Qweak will be presented, along with a discussion of
the new constraints imposed by these results on additional parity-violating
physics beyond the Standard Model.
