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[PAST EVENT] Physics Colloquium - Greg Smith
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Greg Smith, Jefferson Lab, "The proton's weak charge and the neutron skin of aluminum: Results & Perspectives"
Abstract:
The Jefferson Lab Qweak experiment provided the first measure of the proton’s weak charge to test for physics beyond the standard model at the TeV scale. I will briefly review the experiment and summarize the final results for the weak charge Qw(p), the weak mixing angle sinw, and the mass reach -- for new physics of coupling strength g. By including results from atomic parity-violation in Cesium, the e-q couplings for the u and d quarks were also obtained. Some aspects of the liquid hydrogen target, the highest power ever used in a scattering experiment, will be discussed including its exceptionally small boiling response to the 2.2 kW of beam heating used in the experiment. Frank insights into some of the target’s design decisions will be given, including performance/safety tradeoffs. Finally, as a consequence of one of those tradeoffs, newly published results for the 27Al neutron skin thickness Rn-p are presented. These provide a baseline for the use of the electroweak method in recent measurements of Rn-p in 208Pb, which constrain the nuclear symmetry energy in models of neutron stars but are in some tension with non-electroweak determinations.