Towards Dark matter Spin  Characterisation at the LHC

Determination of the nature of Dark Matter (DM) is one of the most fundamental problems of  particle physics and
cosmology.  If DM is light enough and interacts with Standard Model  particles directly or via some mediators with a
strength beyond the gravitational one, it can be directly produced at the Large Hadron Collider or future  particle
accelerators. The typical signature from DM produced in particles collisions is  missing transverse energy, MET, due
to the fact that they escape undetected from the experimental apparatus. We present study for the complete set of
dimension 5 and dimension 6 effective operators involving scalar, fermion and vector DM to explore the possibility to
distinguish these operators and characterise the spin of DM. We have found that, depending on the spin of the DM, the
DM parts of the effective operators lead to a different energy dependence of the cross-sections and to different
distributions of the invariant mass of the DM pair, and consequently to different MET   distributions. Using
statistical analysis, we have found that at the LHC  with high  luminosity, certain classes of EFT operators can be
distinguished from each other and, through this, it is possible to characterise the spin of DM in some cases. We have
also observed a drastic difference in the efficiencies (up to two orders of magnitude) for large MET cuts scenarios
with different DM spin, thus indicating that the DM discovery potential strongly depends on it. The study we perform
here can be applied more generally than within the EFT paradigm, where the DM mediator is not produced
on-the-mass-shell, where the invariant mass of the DM pair is not fixed.