Observation potential of the decays $B^0_{s,d} \to J/\psi\eta$ in the ATLAS experiment at the LHC

The observation potential of the decays $\mathrm{B^0_{s,d} \rightarrow J/\psi\eta}$ with the ATLAS detector at the LHC is described in this paper. At present there exist only upper limits for the branching fractions, but at LHC, a clear signal for the decay mode $\mathrm{B^0_{s} \rightarrow J/\psi\eta}$ is expected. The branching fraction of this decay mode can thus be measured, and other parameters such as $\mathrm{B^0_{s}}$ lifetime can be measured as well The decay mode $\mathrm{B^0_{s} \rightarrow J/\psi\eta}$ is analogous to the mode $\mathrm{B^0_{s} \rightarrow J/\psi\phi}$, which has been studied extensively in view of CP violation measurements. In these two decay modes, the C asymmetry predicted by the Standard Model is very small, and the observation of a sizeable effect would be a signal of physics beyond the Standard Model. The decay mode $\mathrm{J/\psi\eta}$ constitutes thus a cross-check for the mode $\mathrm{J/\psi\phi}$. Furthermore, the former final state is a CP-eigenstate and no angular analysis is thus needed. The reconstruction of $\etasmesons at LHC experiments has not been addressed before, and therefore the study presented here can also be regarded as an example of the physics prospects with $\etasmesons at the LHC.