A search for evidence of particle dark matter (DM) and unparticle production at the LHC has been performed using events containing two charged leptons, consistent with the decay of a $Z$ boson, and large missing transverse momentum. This study is based on data collected with the CMS detector corresponding to an integrated luminosity of $19.7{\mathrm{fb}}^{-1}$ of $pp$ collisions at the LHC at a center-of-mass energy of 8 TeV. No significant excess of events is observed above the number expected from the standard model contributions. The results are interpreted in terms of 90% confidence level limits on the DM-nucleon scattering cross section, as a function of the DM particle mass, for both spin-dependent and spin-independent scenarios. Limits are set on the effective cutoff scale $\mathrm{\Lambda }$, and on the annihilation rate for DM particles, assuming that their branching fraction to quarks is 100%. Additionally, the most stringent 95% confidence level limits to date on the unparticle model parameters are obtained.

• Received 30 November 2015

DOI:https://doi.org/10.1103/PhysRevD.93.052011

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© 2016 CERN, for the CMS Collaboration