Helium anion formation inside helium droplets Elias Jabbour Al Maalouf, Julia Reitshammer, Anita Ribar, Paul Scheier and Stephan Denifl Eur. Phys. J. D, 70 7 (2016) 148 Published online: 05 July 2016 DOI: 10.1140/epjd/e2016-70136-3