Stringent limits on $C\text{\hspace{0.17em}⁣}PT$- and Lorentz-invariance violation from $B_s^0$ meson decays

Tests of fundamental symmetries, such as $C\text{\hspace{0.17em}⁣}PT$ and Lorentz invariance, provide sensitive probes of physics beyond the standard quantum-field-theory framework. Possible violations of these symmetries are investigated through interference effects in decays of $B_s^0$ mesons to $D_s^{-}{\pi }^{+}$ states. The analysis uses proton-proton collision data collected with the LHCb detector in 2015-2018 at a centre-of-mass energy of $13\mathrm{T}\mathrm{e}\mathrm{V}$, corresponding to an integrated luminosity of $6{\mathrm{f}\mathrm{b}}^{-1}$. The results are interpreted within the Standard Model Extension framework, yielding sensitivities to the Lorentz-violating parameter $\mathrm{\Delta }{a}_{\mu }$ at the $\mathcal{O}({10}^{-14})\mathrm{G}\mathrm{e}\mathrm{V}$ level. Without assuming Lorentz-invariance violation, the $C\text{\hspace{0.17em}⁣}PT$-violating parameter $z$ in the $B_s^0$ system is measured to be $\mathcal{R}e(z)=0.018\pm 0.016\pm 0.003$ and $\mathcal{I}m(z)=0.003\pm 0.004\pm 0.002$, where the first uncertainties are statistical and the second systematic. These results represent the most precise constraints on $C\text{\hspace{0.17em}⁣}PT$ violation in the $B_s^0$ system.