  In this article we investigate the benefits of increasing the maximum nuclear
recoil energy analysed in dark matter (DM) direct detection experiments. We
focus on elastic DM-nucleus interactions, and work within the framework of
effective field theory (EFT) to describe the scattering cross section. In
agreement with previous literature, we show that an increased maximum energy
leads to more stringent upper bounds on the DM-nucleus cross section for the
EFT operators, especially those with an explicit momentum dependence. In this
article we extend the energy region of interest (ROI) to show that the optimal
values of the maximum energy for xenon and argon are of the order of 500 keV
and 300 keV, respectively. We then show how, if a signal compatible with DM is
observed, an enlarged energy ROI leads to a better measurement of the DM mass
and couplings. In particular, for a xenon detector, DM masses of the order of
200 GeV (2 TeV) or lower can be reconstructed for momentum-independent
(-dependent) operators. We also investigate three-dimensional parameter
reconstruction and apply it to the specific case of scalar DM and anapole DM.
We find that opening the energy ROI is an excellent way to identify the linear
combination of momentum-dependent and momentum-independent operators, and it is
crucial to correctly distinguish these models. Finally, we show how an enlarged
energy ROI also allows us to test astrophysical parameters of the DM halo, such
as the DM escape speed.
