title: First direct mass measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He.
abstract: The first direct mass measurement of {6}He has been performed with the TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the mass of {8}He was determined with improved precision over our previous measurement. The obtained masses are m({6}He)=6.018 885 883(57)  u and m({8}He)=8.033 934 44(11)  u. The {6}He value shows a deviation from the literature of 4σ. With these new mass values and the previously measured atomic isotope shifts we obtain charge radii of 2.060(8) and 1.959(16) fm for {6}He and {8}He, respectively. We present a detailed comparison to nuclear theory for {6}He, including new hyperspherical harmonics results. A correlation plot of the point-proton radius with the two-neutron separation energy demonstrates clearly the importance of three-nucleon forces.
authors.affiliation: TRIUMF, 4004 Wesbrook Mall, Vancouver BC, Canada V6T 2A3. brodeur@nscl.msu.edu
authors.forename: M
authors.initials: M
authors.lastname: Brodeur
authors.forename: T
authors.initials: T
authors.lastname: Brunner
authors.forename: C
authors.initials: C
authors.lastname: Champagne
authors.forename: S
authors.initials: S
authors.lastname: Ettenauer
authors.forename: M J
authors.initials: MJ
authors.lastname: Smith
authors.forename: A
authors.initials: A
authors.lastname: Lapierre
authors.forename: R
authors.initials: R
authors.lastname: Ringle
authors.forename: V L
authors.initials: VL
authors.lastname: Ryjkov
authors.forename: S
authors.initials: S
authors.lastname: Bacca
authors.forename: P
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authors.lastname: Delheij
authors.forename: G W F
authors.initials: GW
authors.lastname: Drake
authors.forename: D
authors.initials: D
authors.lastname: Lunney
authors.forename: A
authors.initials: A
authors.lastname: Schwenk
authors.forename: J
authors.initials: J
authors.lastname: Dilling