Identification of dark matter particles with LHC and direct detection data

Dark matter (DM) is currently searched for with a variety of detection strategies. Accelerator searches are particularly promising, but even if weakly interacting massive particles are found at the Large Hadron Collider (LHC), it will be difficult to prove that they constitute the bulk of the DM in the Universe ${\Omega }_{\mathrm{DM}}$. We show that a significantly better reconstruction of the DM properties can be obtained with a combined analysis of LHC and direct detection data, by making a simple Ansatz on the weakly interacting massive particles local density ${\rho }_{{\tilde{\chi }}_1^0}$, i.e., by assuming that the local density scales with the cosmological relic abundance, $({\rho }_{{\tilde{\chi }}_1^0}/{\rho }_{\mathrm{DM}})=({\Omega }_{{\tilde{\chi }}_1^0}/{\Omega }_{\mathrm{DM}})$. We demonstrate this method in an explicit example in the context of a 24-parameter supersymmetric model, with a neutralino lightest supersymmetric particle in the stau coannihilation region. Our results show that future ton-scale direct detection experiments will allow to break degeneracies in the supersymmetric parameter space and achieve a significantly better reconstruction of the neutralino composition and its relic density than with LHC data alone.

Figure 1

Pdf of the neutralino relic density obtained from LHC data only (left panel), LHC plus direct detection data for a fixed local density (central panel) and LHC plus direct detection data under the scaling Ansatz. The best fit point is shown by the encircled black cross, while the true value is given by the yellow/red diamond.

Figure 2

As in Fig. 1, but in the ${\sigma }_{\chi -\mathrm{p}}^{\mathrm{SI}}$ vs ${\Omega }_{{\tilde{\chi }}_1^0}{h}^2$ plane. From left to right: constraints using LHC data alone, adding direct detection data assuming a fixed local DM density, and with our scaling Ansatz for the local density. The inner and outer contours enclose 68% and 95% probability regions, respectively. The probability distributions have been smoothed with a Gaussian kernel for display purposes. The best fit point is shown by the encircled black cross, while the true value is given by the yellow/red diamond. In the center and right panels we show for reference the LHC-only contours of the left panel (light grey), along with the directions along which the different Ansätze break the degeneracy (dashed lines).