Constraining extra neutral gauge bosons with atomic parity violation measurements

Abstract

The discovery of a new neutral gauge boson ${Z}^{\ensuremath{'}}$ could provide the first concrete evidence of physics beyond the standard model. We explore how future parity violation experiments, especially atomic parity violation experiments, can be used to constrain ${Z}^{\ensuremath{'}}$ bosons. We use the recent measurement of the $^{133}\mathrm{Cs}$ nuclear weak charge to estimate lower bounds on the mass of ${Z}^{\ensuremath{'}}$ bosons for a number of representative models and to put constraints on the couplings of a newly discovered ${Z}^{\ensuremath{'}}$ boson. We also consider how these constraints might be improved by future atomic parity violation experiments that will measure nuclear weak charges of multiple isotopes. We show how measurements of a single isotope and combining measurements into ratios and differences can be used to constrain the couplings of a ${Z}^{\ensuremath{'}}$ and discriminate between models. We include in our results the constraints that can be obtained from the experiments Qweak and P2 that measure the proton weak charge. We find that current and future parity violation experiments could potentially play an important role in unravelling new physics if a ${Z}^{\ensuremath{'}}$ were discovered.