Search for dark matter, extra dimensions, and unparticles in monojet events in proton-proton collisions at sqrt(s) = 8 TeV

TL;DR

<3-5 sentences high-level: The paper reports a CMS monojet search in 8 TeV pp collisions totaling 19.7 fb^-1, targeting dark matter production with initial-state radiation, large extra dimensions (ADD), and unparticles. It uses data-driven background estimations (Z(mu mu) and W(mu nu) control samples) and MC for other backgrounds, and derives limits on DM-nucleon cross sections (vector, axial, scalar operators), ADD fundamental scale M_D, and unparticle scale Λ_U. It also examines EFT validity with an explicit mediator model. The results are consistent with the Standard Model and set the most stringent monojet constraints to date in these channels, improving over previous collider results.

Abstract

Results are presented from a search for particle dark matter (DM), extra dimensions, and unparticles using events containing a jet and an imbalance in transverse momentum. The data were collected by the CMS detector in proton-proton collisions at the LHC and correspond to an integrated luminosity of 19.7 inverse femtobarns at a centre-of-mass energy of 8 TeV. The number of observed events is found to be consistent with the standard model prediction. Limits are placed on the DM-nucleon scattering cross section as a function of the DM particle mass for spin-dependent and spin-independent interactions. Limits are also placed on the scale parameter M[D] in the ADD model of large extra dimensions, and on the unparticle model parameter Lambda[U]. The constraints on ADD models and unparticles are the most stringent limits in this channel and those on the DM-nucleon scattering cross section are an improvement over previous collider results.

Figures (8)

• Figure 1: Feynman diagrams for the pair production of DM particles for the case of a contact interaction (left) and the exchange of a mediator (right).
• Figure 2: Feynman diagrams for the production of a graviton (G) or unparticles (U) in association with a jet.
• Figure 3: Missing transverse energy $E_{\mathrm{T}}^{\text{miss}}$ after all selections for data and SM backgrounds. The processes contributing to the SM background are from simulation, normalised to the estimation from data using the $E_{\mathrm{T}}^{\text{miss}}$ threshold of 500$\,\text{Ge\spaceV}$. The error bars in the lower panel represent the statistical uncertainty. Overflow events are included in the last bin.
• Figure 4: The model-independent observed and expected 95% CL upper limits on the visible cross section times acceptance times efficiency ($\sigma \times A \times \varepsilon$) for non-SM production of events. Shaded areas show the $\pm 1\sigma$ and $\pm 2\sigma$ bands on the expected limits.
• Figure 5: Upper limits on the DM-nucleon cross section, at 90% CL, plotted against DM particle mass and compared with previously published results. Top: limits for the vector and scalar operators from the previous CMS analysis bib:CMSEXO11059, together with results from the CoGeNT bib:COGENT, SIMPLE SIMPLE2012, COUPP bib:COUPP2012, CDMS bib:CDMSII2010bib:CDMSII2011, SuperCDMS SuperCDMS, XENON100 bib:XENON100, and LUX bib:LUX collaborations. The solid and hatched yellow contours show the 68% and 90% CL contours respectively for a possible signal from CDMS bib:CDMSSi. Bottom: limits for the axial-vector operator from the previous CMS analysis bib:CMSEXO11059, together with results from the SIMPLE SIMPLE2012, COUPP bib:COUPP2012, Super-K SUPERK, and IceCube IceCube:2011aj collaborations.