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

We present the first fully ab initio calculations of
collision-induced
broadening and shift of spectral lines in antiprotonic helium (p̅He+) 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 p̅He+–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 (p̅4He+). 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.