Quantum Calculation of the Collision-Induced Line-Shape Effects in Antiprotonic Helium and the New Accurate Ab Initio p¯He+-He Potential Energy Surface

We present the first fully ab initio calculations of collision-induced broadening and shift of spectral lines in antiprotonic helium $\left(\overline{p}H{e}^{+}\right)$ perturbed by atomic helium. To overcome critical limitations of previous studies, we construct a new highly accurate potential energy surface (PES) that spans a wide range of $\overline{p}H{e}^{+}$-He geometries relevant to all metastable states of the exotic helium atom. Rigorous quantum scattering calculations performed using the new PES yield scattering S-matrices from which we extract pressure broadening and shift coefficients for 50 transitions in antiprotonic helium-4 $\left({\overline{p}}^{4}H{e}^{+}\right)$. This data set provides the first rigorous benchmark for earlier semiclassical calculations and establishes a robust theoretical reference for high-precision spectroscopy of antiprotonic helium, which is used to test the fundamental charge, parity, and time reversal (CPT) symmetry. The results extend to temperatures relevant to nongaseous phases of helium, supporting a new class of precision measurements. This study introduces a methodological framework for future investigations of other exotic systems, such as pionic or kaonic helium atoms, enabling the development of reference data for high-precision spectroscopy of these species─an essential component for improving the determination of the pion and kaon masses.