Ponente
Descripción
Atoms can act as electron accelerators, effectively providing a scan in energy when fixed-energy positrons from a beam collide with them. This talk explores the potential of this phenomenon for new physics searches, particularly for new vector bosons or pseudoscalars coupling to fermions, such as Dark Photons and ALPs. We propose using a positron beam directed at a fixed high-$Z$ target, such as $^{92}$U, at available facilities like JLab, PADME or the H3 beam at CERN. We find that the spread in electron momentum significantly enhances the experimental reach when compared to the electron-at-rest approximation, probing parts of the parameter space currently unexplored. Additionally, we show how this effect, using a $12$ GeV beam as foreseen at JLab, can achieve high statistical accuracy in measuring the hadronic cross section for electron-positron annihilation across the relevant range of center-of-mass energies. This provides a new method to study the hadronic vacuum polarization contribution to $(g-2)_\mu$, adding a new piece of information to the existing puzzle.
