title: Observation of Anomalous Internal Pair Creation in ^{8}Be: A Possible Indication of a Light, Neutral Boson.
abstract: Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV (J^{π}=1^{+}, T=1) state→ground state (J^{π}=0^{+}, T=0) and the isoscalar magnetic dipole 18.15 MeV (J^{π}=1^{+}, T=0) state→ground state transitions in ^{8}Be. Significant enhancement relative to the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of >5σ. This observation could possibly be due to nuclear reaction interference effects or might indicate that, in an intermediate step, a neutral isoscalar particle with a mass of 16.70±0.35(stat)±0.5(syst)  MeV/c^{2} and J^{π}=1^{+} was created.
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: A J
authors.initials: AJ
authors.lastname: Krasznahorkay
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: M
authors.initials: M
authors.lastname: Csatlós
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: L
authors.initials: L
authors.lastname: Csige
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: Z
authors.initials: Z
authors.lastname: Gácsi
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: J
authors.initials: J
authors.lastname: Gulyás
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: M
authors.initials: M
authors.lastname: Hunyadi
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: I
authors.initials: I
authors.lastname: Kuti
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: B M
authors.initials: BM
authors.lastname: Nyakó
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: L
authors.initials: L
authors.lastname: Stuhl
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: J
authors.initials: J
authors.lastname: Timár
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: T G
authors.initials: TG
authors.lastname: Tornyi
authors.affiliation: Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: Zs
authors.initials: Z
authors.lastname: Vajta
authors.affiliation: Nikhef National Institute for Subatomic Physics, Science Park 105, 1098 XG Amsterdam, Netherlands.
authors.forename: T J
authors.initials: TJ
authors.lastname: Ketel
authors.affiliation: CERN, CH-1211 Geneva 23, Switzerland and Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), P.O. Box 51, H-4001 Debrecen, Hungary.
authors.forename: A
authors.initials: A
authors.lastname: Krasznahorkay