[Prex] PREX-II result due to BSM Physics? (arxiv)

[Jay Benesch]

https://arxiv.org/abs/2112.09717

Incorporating the weak mixing angle dependence to reconcile the neutron 
skin measurement on 208Pb by PREX-II
Mattia Atzori Corona, Matteo Cadeddu, Nicola Cargioli, Paolo Finelli, 
Matteo Vorabbi

     The only available electroweak measurement of the 208Pb neutron 
skin, ΔRnp, performed by the PREX-II Collaboration through polarized 
electron-lead scattering, shows a mild tension with respect to both the 
theoretical nuclear-model predictions and a host of measurements. 
However, the dependence on the weak mixing angle should be incorporated 
in the calculation, since its low-energy value is experimentally poorly 
known. We first repeat the PREX-II analysis confirming their measurement 
by fixing the weak mixing angle to its standard model value. Then, we 
show the explicit dependence of the PREX-II measurement on the weak 
mixing angle, obtaining that it is fully degenerate with the neutron 
skin. To break this degeneracy, we exploit the weak mixing angle 
measurement from atomic parity violation on lead, obtaining a slightly 
thinner neutron skin but with about doubled uncertainties, possibly 
easing the PREX tension. Relying on the theoretical prediction, 
ΔRthnp∼0.13−0.19 fm, and using it as a prior in the fit, we find a weak 
mixing angle value about 1.2σ smaller than the standard model 
prediction. Thus, we suggest a possible solution of the PREX-II tension 
by showing that, considering its underlying dependence on the weak 
mixing angle, the PREX-II neutron skin determination could be in 
agreement with the other available measurements and predictions if the 
weak mixing angle at the proper energy scale is smaller than the 
standard model prediction.

Comments: 	5 pages, 4 figures
Subjects: 	High Energy Physics - Phenomenology (hep-ph); Nuclear 
Experiment (nucl-ex); Nuclear Theory (nucl-th)
Cite as: 	arXiv:2112.09717 [hep-ph]

They also predict CREX will measure a thin skin on page 5, just above 
Conclusions.