| Abstract: | The standard model (SM) of particle physics is spectacularly successful, yet
the measured value of the muon anomalous magnetic moment (g-2)_mu deviates
from SM calculations by 3.6 sigma. Several theoretical models attribute this to
the existence of a "dark photon", an additional U(1) gauge boson, which is
weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic
Heavy Ion Collider has searched for a dark photon, U, in pi^0,eta
ightarrow
gamma e^+e^- decays and obtained upper limits on U-gamma mixing at 90% CL for
the mass range 30 < m_U < 90 MeV/c^2. Combined with other experimental limits,
the remaining region in the U-gamma mixing parameter space that can explain
the (g-2)_mu deviation from its SM value is nearly completely excluded at the
90% confidence level, with only a small region of 30 < m_U < 36 MeV/c^2
remaining. |
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