title: Angle-Resolved Spectroscopy of Positronium Emission from a Cu(110) Surface.
abstract: The affinity A_{Ps} of positronium (Ps) atoms for a metal is the negative of the maximum kinetic energy with which Ps is emitted into vacuum when thermalized positrons in a metal encounter the surface. When this quantity is measured by ground state Ps time of flight (TOF), the precision is severely limited by the short triplet state lifetime of 142 ns. By quickly converting the emitted Ps atoms into long-lived Rydberg states, we are able to dramatically increase the TOF to allow precision measurements of A_{Ps}. From our measurements made on a Cu(110) sample at T=128  K, we find A_{Ps}(128  K)=(-2.476±0.010_{stat}±0.013_{syst})  eV, compared with the result A_{Ps}(128  K)=(-2.545±0.010_{num}±0.010_{syst})  eV found using highly accurate generalized gradient approximations for both electrons and positrons within density functional theory. Such precision opens up opportunities in the quest for an improved density functional.
authors.affiliation: Department of Physics and Astronomy, University of California Riverside, Riverside, California 92521, USA.
authors.forename: A C L
authors.initials: AC
authors.lastname: Jones
authors.affiliation: Department of Physics and Astronomy, University of California Riverside, Riverside, California 92521, USA.
authors.forename: H J
authors.initials: HJ
authors.lastname: Rutbeck-Goldman
authors.affiliation: Department of Physics and Astronomy, University of California Riverside, Riverside, California 92521, USA.
authors.forename: T H
authors.initials: TH
authors.lastname: Hisakado
authors.affiliation: Department of Physics and Astronomy, University of California Riverside, Riverside, California 92521, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Piñeiro
authors.affiliation: Department of Physics and Astronomy, University of California Riverside, Riverside, California 92521, USA.
authors.forename: H W K
authors.initials: HW
authors.lastname: Tom
authors.affiliation: Department of Physics and Astronomy, University of California Riverside, Riverside, California 92521, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Mills
authors.affiliation: Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: B
authors.initials: B
authors.lastname: Barbiellini
authors.affiliation: Department of Low Temperature Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, CZ-180 00 Prague, Czech Republic.
authors.forename: J
authors.initials: J
authors.lastname: Kuriplach