Search for a light dark sector particle at LHCb

Abstract

A search is presented for a hidden-sector boson, $\chi$, produced in the decay $B^0\to K^{\ast }(892{)}^0\chi$, with $K^{\ast }(892{)}^0\to K^{+}{\pi }^{-}$ and $\chi \to {\mu }^{+}{\mu }^{-}$ . The search is performed using a $pp$-collision data sample collected at $\sqrt{s}=7$ and 8 TeV with the LHCb detector, corresponding to integrated luminosities of 1 and 2 fb${}^{-1}$ respectively. No significant signal is observed in the mass range $214\le m_{\chi }\le 4350$ MeV, and upper limits are placed on the branching fraction product $\mathcal{B}(B^0\to K^{\ast }(892{)}^0\chi )\times \mathcal{B}(\chi \to {\mu }^{+}{\mu }^{-})$ as a function of the mass and lifetime of the $\chi$ boson. These limits place the most stringent constraints to date on many theories that predict the existence of additional low-mass dark bosons.

Comments: Presentation at the DPF 2015 Meeting of the American Physical Society Division of Particles and Fields, Ann Arbor, Michigan, August 4-8, 2015