The apparent invariance of the strong nuclear force under combined charge conjugation and parity (CP) remains an open question in modern physics^1,2. Precision experiments with heavy atoms and molecules can provide stringent constraints on CP violation via searches for effects due to permanent electric dipole moments and other CP-odd properties in leptons, hadrons and nuclei³. Radioactive molecules have been proposed as highly sensitive probes for such searches⁴, but experiments with most such molecules have so far been beyond technical reach. Here we report the production and spectroscopic study of a gas-phase actinium molecule, ²²⁷AcF. We observe the predicted strongest electronic transition from the ground state, which is necessary for efficient readout in searches of symmetry-violating interactions. Furthermore, we perform electronic- and nuclear-structure calculations for ²²⁷AcF to determine its sensitivity to various CP-violating parameters, and find that a realistic, near-term experiment with a precision of 1 mHz would improve current constraints on the CP-violating parameter hyperspace by 3 orders of magnitude. Our results thus highlight the potential of ²²⁷AcF for exceptionally sensitive searches of CP violation.

The radiative lifetime of the $A{}^2\mathrm{\Pi }_{1/2}$ $(v=0)$ state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate $\mathrm{\Gamma }=2.86\left(8\right)\times {10}^7$ ${\text{s}}^{-1}$ are of relevance to the laser cooling of RaF via the optically closed $A{}^2\mathrm{\Pi }_{1/2}\leftarrow X{}^2\mathrm{\Sigma }_{1/2}$ transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Owing to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just three cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the $8P_{3/2}$ state in Fr to be 83(3) ns, in agreement with literature.

Aerosol–cloud interactions (ACI) are in the spotlight of atmospheric science since the limited knowledge about these processes produces large uncertainties in climate predictions. These interactions can be quantified by the aerosol–cloud interaction index (ACI index), which establishes a relationship between aerosol and cloud microphysics. The experimental determination of the ACI index through a synergistic combination of lidar and cloud radar is still quite challenging due to the difficulties in disentangling the aerosol influence on cloud formation from other processes and in retrieving aerosol-particle and cloud microphysics from remote sensing measurements. For a better understanding of the ACI and to evaluate the optimal experimental conditions for the measurement of these processes, a Lidar and Radar Signal Simulator (LARSS) is presented. LARSS simulate vertically-resolved lidar and cloud-radar signals during the formation process of a convective cloud, from the aerosol hygroscopic enhancement to the condensation droplet growth. Through LARSS simulations, it is observed a dependence of the ACI index with height, associated with the increase in number ($AC{I}_{Nd}$) and effective radius ($AC{I}_{reff}$) of the droplets with altitude. Furthermore, $AC{I}_{Nd}$ and $AC{I}_{reff}$ for several aerosol types (such as ammonium sulfate, biomass burning, and dust) are estimated using LARSS, presenting different values as a function of the aerosol model. Minimum $AC{I}_{Nd}$ values are obtained when the activation of new droplets stops, while $AC{I}_{reff}$ reaches its maximum values several meters above. These simulations are carried out considering standard atmospheric conditions, with a relative humidity of $30\%$ at the surface, reaching the supersaturation of the air mass at 3500 m. To assess the stability of the ACI index, a sensitivity study using LARSS is performed. It is obtained that the dry modal aerosol radius presents a strong influence on the ACI index fluctuations of $18\%$ cause an ACI variability of $30\%$ while the updraft velocity within the cloud and the wet modal aerosol radius have a weaker impact. LARSS ACI index uncertainty is obtained through the Monte Carlo technique, obtaining $AC{I}_{reff}$ uncertainty below $16\%$ for the uncertainty of all LARSS input parameters of $10\%$. Finally, a new ACI index is introduced in this study, called the remote-sensing ACI index ($AC{I}_{Rs}$), to simplify the quantification of the ACI processes with remote sensors. This new index presents a linear relationship with the $AC{I}_{reff}$, which depends on the Angstrom exponent. The use of $AC{I}_{Rs}$ to derive $AC{I}_{reff}$ presents the advantage that it is possible to quantify the aerosol–cloud interaction without the need to perform microphysical inversion retrievals, thus reducing the uncertainty sources.

The process of β -delayed fission ( β DF ) of Fr 230 , 232 and Ac 230 , 232 , 234 was studied in an experiment performed at the ISOLDE facility at CERN. As no fission fragments were observed for any of the nuclei investigated, upper limits for their β DF probability ( P β DF ) were determined. The experimental results were compared with theoretical calculations that were first benchmarked on Tl 178 , 180 P β DF experimental values. The P β DF values were calculated using the code TALYS to which β -strength functions obtained from the D1M Gogny parametrization and from the Skyrme functional SKO' were given as input together with fission paths obtained with BSkG3 and BSk14 models. Sensitivity studies of different β -strength functions, and fission paths scaling on the P β DF values were conducted, suggesting a stronger dependence of the P β DF on the fission paths rather than on the β -strength function used. Published by the American Physical Society 2025

The apparent invariance of the strong nuclear force under combined charge conjugation and parity (CP) remains an open question in modern physics. Precision experiments with heavy atoms and molecules can provide stringent constraints on CP violation via searches for effects due to permanent electric dipole moments and other CP-odd properties in leptons, hadrons, and nuclei. Radioactive molecules have been proposed as highly sensitive probes for such searches, but experiments with most such molecules have so far been beyond technical reach. Here we report the first production and spectroscopic study of a gas-phase actinium molecule, $^{227}$AcF. We observe the predicted strongest electronic transition from the ground state, which is necessary for efficient readout in searches of symmetry-violating interactions. Furthermore, we perform electronic- and nuclear-structure calculations for $^{227}$AcF to determine its sensitivity to various CP-violating parameters, and find that a realistic, near-term experiment with a precision of 1 mHz would improve current constraints on the CP-violating parameter hyperspace by three orders of magnitude. Our results thus highlight the potential of $^{227}$AcF for exceptionally sensitive searches of CP violation.