Speaker
Mr
Carl-Oscar Gullstroem
(Uppsala University)
Description
The decay of the π 0 meson into an electron–positron pair is heavily sup-
pressed in the Standard Model (SM) with an expected branching ratio of
6 × 108 . The decay is therefore sensitive to contributions from physics be-
yond the SM. Recently, the KTeV collaboration at Fermilab has performed
a precise measurement of the π 0 → e+ e− decay branching ratio using a data
sample of 800 events. The result is three standard deviations above the SM
value. This has triggered speculations of e.g. a contribution from a light vec-
tor boson responsible for the annihilation of a hypothetical light dark matter
particle. In one scenario a new light vector boson U (mass 10 − 100 MeV) is
weakly coupled to the π 0 . This boson is expected to decay into a lepton pair
and hence gives an extra contribution to the π 0 → e+ e branching ratio. The
aim for WASA-at-COSY is to confirm the KTeV measurement. The status
of the analysis is presented and prospects for a measurement at the KTeV
sensitivity are discussed.
Primary author
Mr
Carl-Oscar Gullstroem
(Uppsala University)
