New limit on millicharged particles from reactor neutrino experiments and the PVLAS anomaly

Abstract

It has been recently suggested that the vacuum magnetic dichroism observed by the PVLAS experiment could be explained by pair production of a new light, ${m}_{\ensuremath{\epsilon}}\ensuremath{\simeq}0.1\text{ }\text{ }\mathrm{eV}$, millicharged, ${q}_{\ensuremath{\epsilon}}\ensuremath{\simeq}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}e$, fermions ($\ensuremath{\epsilon}$). In addition, it has been pointed out that millicharged particles with ${q}_{\ensuremath{\epsilon}}\ensuremath{\gtrsim}{10}^{\ensuremath{-}9}e$ appear naturally in models based on the string theory. We show that low energy reactor neutrino experiments provide a sensitive probe of millicharged particles. Considering, as an example, recent results of the TEXONO experiment searching for the neutrino magnetic moment, a new upper bound ${q}_{\ensuremath{\epsilon}}\ensuremath{\lesssim}{10}^{\ensuremath{-}5}e$ for the mass region ${m}_{\ensuremath{\epsilon}}<1\text{ }\text{ }\mathrm{keV}$ is derived. These results enhance motivations for a more sensitive search for such particles in near future experiments. Furthermore, a direct experimental limit on the electric charge of the electron antineutrino ${q}_{{\overline{\ensuremath{\nu}}}_{e}}<3.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}e$ is obtained.