Physics Colloquium | New Limits on Physics Beyond the Standard Model from the Qweak Experiment, Sept. 18

The Physics & Astronomy Colloquium Series presents Paul King from Ohio University, on “New Limits on Physics Beyond the Standard Model from the Qweak Experiment” on Monday, Sept. 18, at 4:10 p.m. in Walter 245.

Paul King

The Qweak collaboration is an international team of over a hundred scientists who worked together at Jefferson Lab over several years to measure the weak charge of the proton. This fundamental quantity expresses how strongly the proton couples to the weak nuclear force. The Qweak experiment tested the Standard Model’s prediction for this number, with a significant deviation revealing the existence of new weak-force carrying particles.

Profs. Paul King and Julie Roche played key roles in the experiment, and two Ohio University students received their Ph.D.s working on it. The collaboration released their final number for the proton’s weak charge about two weeks ago.

Abstract: The Standard Model of particle physics is a well-accepted theory, in which its last predicted particle, the Higgs boson, was discovered in 2012. But the theory is known to be incomplete, motivating experiments (such as at the Large Hadron Collider) to search for evidence of new particles not included in the Standard Model. Precision tests are another way to search for physics beyond the Standard Model. Deviations between precise measurements and predictions of the the Standard Model would be signatures of new physics. The neutral weak charge of the proton is one such observable.

The Qweak experiment has determined the weak charge of the proton by measuring the parity-violating asymmetry in low-mometum-transfer elastic e-p scattering to a precision of under 10 parts per billion. 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 and a 35 cm long liquid hydrogen target. 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.