To cite pacman in publications, please use:

  Rinker, T. W. & Kurkiewicz, D. (2019). pacman: Package Management for
  R. version 0.5.3. Buffalo, New York. http://github.com/trinker/pacman

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {{pacman}: {P}ackage Management for {R}},
    author = {Tyler W. Rinker and Dason Kurkiewicz},
    address = {Buffalo, New York},
    note = {version 0.5.3},
    year = {2019},
    url = {http://github.com/trinker/pacman},
  }