Abstract
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 inverse femtobarns 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 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.
Highlights
Ample evidence from astrophysical measurements supports the existence of dark matter (DM), which is assumed to be responsible for galactic gravitation that cannot be attributed to baryonic matter [1,2,3]
A search for evidence for particle dark matter and unparticle production at the LHC has been performed in events containing two charged leptons, consistent with the decay of a Z boson, and large missing transverse momentum
These results are interpreted in two scenarios for physics beyond the standard model: dark matter and unparticles
Summary
Ample evidence from astrophysical measurements supports the existence of dark matter (DM), which is assumed to be responsible for galactic gravitation that cannot be attributed to baryonic matter [1,2,3]. The Z boson subsequently decays into two charged leptons (lþl−, where l 1⁄4 e or μ) producing a clean dilepton signature together with missing transverse momentum due to the undetected DM particles In this analysis, the DM particle χ is assumed to be a Dirac fermion or a complex scalar particle of which the coupling to standard model (SM) quarks q can be described by one of the effective interaction terms [28]: Vector; spin independent ðD5Þ∶. Appears as a noninteger number of invisible massless particles In this scenario, the SM is extended by introducing a scale-invariant Banks-Zaks (BZ) field, which has a nontrivial infrared fixed point [36]. The analysis is based on the full data set recorded by the CMS detector in 2012, which corresponds to an integrated luminosity of 19.7 Æ 0.5 fb−1 [38] at a center-of-mass energy of 8 TeV
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