

\subsection{What physics lies beyond the Standard Model?}

The Standard Model (SM) of Particle Physics is now half a century old, and in every way has been spectacularly successful. Its predictions have been confirmed over and over, as generations of increasingly sophisticated experiments in particle, nuclear, and atomic physics have pushed down the limits for possible deviations. At the ``energy frontier'' of this endeavour, collider physics has not observed any new particles beyond the Higgs, which gave closure to the SM. Neither have we found signatures of physics beyond the SM with rare meson decays or permanent electric dipole moments in atoms, to just name two methods with exquisite reach. Yet, there are extraordinarily compelling reasons to believe that the SM should not be the final answer: It does not explain dark matter nor dark energy, it gives no satisfying explanation for the extreme matter-antimatter asymmetry that we observe in our universe, and it has withstood all efforts to integrate a quantum theory of gravity, so far. In addition, aspects of the SM, while reproducing observations correctly, seem contrived, indicating that we lack deeper understanding. Why are the masses what they are? Why 3 generations of quarks and leptons? Why is only the weak interaction violating parity, why is this violation maximal, and CP violation seems unnaturally small? In addition, we only start to unravel the details of the neutrino sector. Clearly, we must press on to find answers to these fundamental questions.

Nuclear physics, and closely associated experiments in atomic and molecular (AMO) physics, at the low-energy, precision, frontier, have played an important role all along in trying to answer these questions, complementary to high energy techniques. Advantages of this community are the diversity of efforts, nimble response to the changing landscape, relatively modest budgets, and diverse HQP training. Increasingly, a connection is forming to the emerging field of ``quantum sensing'', or more broadly ``quantum technology'', promising major gains in experimental sensitivity. Canada plays a distinguished role in the domain,  with numerous efforts at two world-class domestic facilities, TRIUMF, and SNOLAB, as well as abroad, for example at JLab and CERN, covering most aspects of searches for physics beyond the SM. In the following we present some recent successes with Canadian involvement (more details are discussed in Sec.~\ref{sec:funsym}).


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\begin{figure}[ht]
	\begin{center}
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		\includegraphics[angle=0,width=0.7\textwidth]{./Figs/fs-qweak-extrap.pdf}
	\end{center}
	\caption{Determination of the proton's weak charge by extrapolation of the reduced asymmetry to zero momentum transfer. The accuracy is dominated by the Qweak result (taken from \href{https://doi.org/10.1038/s41586-018-0096-0}{D. Androi\'c {\em et al.}, Nature 557, 207 (2018)}.
     }
	\label{fig:fs-qweak-extrap}	
\end{figure} 
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The Qweak collaboration published its final result~\footnote{\href{https://doi.org/10.1038/s41586-018-0096-0}{D. Androi\'c {\em et al.}, Nature 557, 207 (2018).}} for the weak charge of the proton,  $0.0719 \pm 0.0045$, derived from the parity-violating asymmetry in the scattering of polarized electrons on protons, measured at the 9 ppb level (see Fig.~\ref{fig:fs-qweak-extrap}). The result is in excellent agreement with the SM prediction, and sets multi-TeV-scale constraints on any semi-leptonic parity-violating physics not described within the SM.
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The tour-de-force {\em nPDGamma} effort concluded by reporting the first non-zero measurement of parity violation in the neutron-proton system~\footnote{\href{https://doi.org/10.1103/PhysRevLett.121.242002}{D. Blyth {\em et al.}, Phys. Rev. Lett. 121, 242002 (2018).}}, and the {\em n3He} collaboration accomplished the same feat in the neutron-$^3$He system~\footnote{\href{https://doi.org/10.1103/PhysRevLett.125.131803}{M.~Gericke {\em et al.},Phys. Rev. Lett. 125, 131803 (2020).}}.
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The ALPHA anti-hydrogen effort produced a series of outstanding measurements. Amongst them, charge-neutrality of $\bar{H}$ was confirmed at the $10^{-9}$ level, the $1s-2s$ transition frequency was measured to $10^{-12}$, and laser cooling was demonstrated~\footnote{\href{https://doi.org/10.1038/nature16491}{M. Ahmadi {\em et al.},Nature 529, 373 (2016)}; \href{https://doi.org/10.1038/s41586-018-0017-2}{M. Ahmadi {\em et al.}, Nature 557, 71 (2018).}}.
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The EXO-200 collaboration put a lower limit for the $0\nu\beta\beta$ lifetime of $^{136}$Xe of $3.5 \times 10^{25}$ years~\footnote{\href{https://doi.org/10.1103/PhysRevLett.123.161802}{G. Anton {\em et al.}, Phys. Rev. Lett. 123, 161802 (2019).}}, which is one of the most competitive measurements. EXO-200 was the first 100-kg class $0\nu\beta\beta$ detector and was decommissioned in 2018 after almost a decade of operation.
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The TRINAT atom trap facility at TRIUMF reported the best relative accuracy of any $\beta$ asymmetry in a nucleus
% or the neutron
, with a 0.3 \% measurement on laser-trapped and nuclear spin polarized sample of $^{37}$K~\footnote{\href{https://doi.org/10.1103/PhysRevLett.120.062502}{B. Fenker {\em et al.}, Phys. Rev. Lett. 120, 062502 (2018).}}. 
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The superallowed $\beta$ decay team, amongst numerous improved branching ratios and lifetimes, carried out the first superallowed half-life measurement to better than $10^{-4}$, using $^{10}$C~\footnote{\href{https://doi.org/10.1103/PhysRevLett.116.172501}{M.R. Dunlop {\em et al.}, Phys. Rev. Lett. 116, 172501 (2016).}}.
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Teams involving theorists from Alberta~\footnote{\href{https://doi.org/10.1103/PhysRevD.100.073008}{A. Czarnecki {\em et al.}, Phys. Rev. D 100, 073008 (2019).}} and Manitoba~\footnote{\href{http://hdl.handle.net/1993/34646}{K. Shiells, Ph.D. thesis, University of Manitoba, 2020.}} refined calculations of radiative corrections in beta decay, opening up a 2 to 3 $\sigma$ tension in CKM unitarity.
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%The TUCAN collaboration reported the first production of ultra-cold neutrons at TRIUMF in 2017, and is on their way to start their neutron EDM experiment by 2023.
The TUCAN collaboration reported the first production of ultra-cold neutrons at TRIUMF in 2017~\footnote{\href{https://doi.org/10.1103/PhysRevC.99.025503}{S. Ahmed {\em et al.}, Phys. Rev. C 99, 025503 (2019).}}, and is on their way to start their neutron EDM experiment by 2023.
The team built and commissioned a new fast kicker magnet~\footnote{\href{https://doi.org/10.1103/PhysRevAccelBeams.22.102401}{S. Ahmed {\em et al.}, Phys. Rev. Accel. Beams 22, 102401 (2019).}} serving a new proton beamline with a high-power spallation target.
%\href{https://doi.org/10.1016/j.nima.2019.01.074}{S Ahmed et al., Nucl. Instrum. Meth. A 927, 108 (2019).} 
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The FrPNC experiment at TRIUMF detected in 2018 for the first time the Stark-induced $7s-8s$ transition in laser-trapped, atomic francium, preparing the ground for a parity violation experiment.

