Exploring Source and Detector Non-Standard Neutrino Interactions at ESS$\nu$SB

We investigate source and detector non-standard neutrino interactions at the proposed ESS$\nu$SB experiment. We analyze the effect of non-standard physics at the probability level, the event-rate level and by a full computation of the ESS$\nu$SB setup. We find that the precision measurement of the leptonic mixing angle $\theta_{23}$ at ESS$\nu$SB is robust in the presence of non-standard interactions, whereas that of the leptonic CP-violating phase $\delta$ is worsened at most by a factor of two. We compute sensitivities to all the relevant source and decector non-standard interaction parameters and find that the sensitivities to the parameters $\varepsilon^s_{\mu e}$ and $\varepsilon^d_{\mu e}$ are comparable to the existing limits in a realistic scenario, while they improve by a factor of two in an optimistic scenario. Finally, we show that the absence of a near detector compromises the sensitivity of ESS$\nu$SB to non-standard interactions.