Search for new physics in monojet events in pp collisions at sqrt(s) = 8 TeV

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 fb^-1 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 Λ_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.

Approved plots, figures, and diagrams from EXO-12-048

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	Feynman diagrams for the pair production of DM particles for the case of a contact interaction (a) and the exchange of a mediator (b).
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	Feynman diagrams for the production of a graviton (G) or unparticles (U) in association with a jet.
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	Missing transverse energy (MET) 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 MET threshold of 500 GeV. The shaded bands in the lower panel represent the statistical uncertainty. Overflow events are included in the last bin.
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	The model-independent observed and expected 95% CL upper limits on the visible cross section times acceptance times efficiency (σ × A × ε) for non-SM production of events. Shaded areas show the ±1σ and ±2σ bands on the expected limits.
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	Upper limits on the DM-nucleon cross section, at 90% CL, plotted against DM particle mass and compared with previously published results. (a) limits for the vector and scalar operators from the previous CMS analysis, together with results from the CoGeNT, SIMPLE, COUPP, CDMS, SuperCDMS, XENON100, and LUX collaborations. The solid and hatched yellow contours show the 68% and 90% CL contours respectively for a possible signal from CDMS. (b): limits for the axial-vector operator from the previous CMS analysis, together with results from the SIMPLE, COUPP, Super-K, and IceCube collaborations.
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	Observed limits on the mediator mass divided by coupling, M/√gχgq, as a function of the mass of the mediator, M, assuming vector interactions and a dark matter mass of 50 GeV (blue, filled) and 500 GeV (red, hatched). The width, Γ, of the mediator is varied between M/3 and M/8π. The dashed lines show contours of constant coupling √gχgq.
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	Lower limits at 95% CL on MD plotted against the number of extra dimensions δ, with results from the ATLAS, CMS, LEP, CDF, and DØ collaborations.
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	The expected and observed lower limits on the unparticle model parameters ΛU as a function of dU at 95% CL, compared to previous result. The shaded region indicates the side of the curve that is excluded.
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Public supplemental material

Figure	Caption
	The transverse momentum of Jet-1 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 MET threshold of 500 GeV. The shaded bands in the lower panel represent the statistical uncertainty. Overflow events are included in the last bin.
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	The jet multiplicity disctibution 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 MET threshold of 500 GeV. The shaded bands in the lower panel represent the statistical uncertainty. Overflow events are included in the last bin.
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	Distribution of DeltaPhi betwen Jet-1 and Jet-2 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 MET threshold of 500 GeV. The shaded bands in the lower panel represent the statistical uncertainty. Overflow events are included in the last bin.
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	The invariant mass distribution of the Z(mu,mu) control sample within the Z mass window 60-120 GeV after all monojet selections are applied, except muon veto.
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	The transverse momentum distribution of the Z(mu,mu) control sample within the Z mass window 60-120 GeV. All monojet selections are applied, except the muon veto.
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	The transverse mass distribution of the W(mu,nu) control sample. No mass window selection is applied here. All monojet selections are applied, except the muon veto. Overflow events are included in the last bin.
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	The transverse momentum distribution of the W(mu,nu) control sample within the mass window 50-100 GeV. All monojet selections are applied, except the muon veto.
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Event displays from EXO-12-048

Event Details	ρφ View	ρZ View	3D View
Run 204553 Event 26729384 Monojet candidate event
Run 204553 Event 26729384 Monojet candidate event	PDF PNG	PDF PNG	PDF PNG
Run 204553 Event 36479045 W(mu+nu) + jets candidate event. The W(mu+nu) + jets events are used to predict the remaining W+jets background in monojet analysis.	PDF PNG	PDF PNG	PDF PNG
Run 204564 Event 448966153 Z(mu+mu) + jets candidate event. The Z(mu+mu) + jets events are used to predict the invisible Z background in monojet analysis.	PDF PNG	PDF PNG	PDF PNG
Run 204553 Event 36479045 W(mu+nu) + jets candidate event. The W(mu+nu) + jets events are used to predict the remaining W+jets background in monojet analysis.
Run 204564 Event 448966153 Z(mu+mu) + jets candidate event. The Z(mu+mu) + jets events are used to predict the invisible Z background in monojet analysis.