Search for Dark Matter and Supersymmetry with a Compressed Mass Spectrum in the Vector Boson Fusion Topology in Proton-Proton Collisions at $\sqrt{s}=8\mathrm{TeV}$

A first search for pair production of dark matter candidates through vector boson fusion in proton-proton collisions at $\sqrt{s}=8\mathrm{TeV}$ is performed with the CMS detector. The vector boson fusion topology enhances missing transverse momentum, providing a way to probe supersymmetry, even in the case of a compressed mass spectrum. The data sample corresponds to an integrated luminosity of $18.5{\mathrm{fb}}^{-1}$, recorded by the CMS experiment. The observed dijet mass spectrum is consistent with the standard model expectation. In an effective field theory, dark matter masses are explored as a function of contact interaction strength. The most stringent limit on bottom squark production with mass below 315 GeV is also reported, assuming a 5 GeV mass difference with respect to the lightest neutralino.

Figure 1

Feynman diagrams for dark matter pair production in a vector boson fusion process (left) and for bottom squark pair production (right). Given a nearly degenerate bottom squark and LSP, the final-state $b$ quarks are too soft to be observed.

Figure 2

Dijet mass distribution of the data (dots), estimated background (stacked histograms), and signal samples (dashed lines) after the analysis selection. The last bin includes all events above 2250 GeV. The ratio plot (below) shows the yields in data divided by predicted yields for each bin. The shaded band in the ratio plot includes systematic and statistical uncertainties in the background prediction.

Figure 3

(left) Contact interaction scale limit at 95% C.L. as a function of the DM mass. The validity of the effective field theory is quantified by (i) $R_{\mathrm{\Lambda }}=80\%$ contours and (ii) truncated limits for different values of the effective coupling. The DM relic abundance $\mathrm{\Omega }{h}^2=0.12$ is calculated as described in the text. (right) Bottom squark pair production 95% C.L. upper cross section limit as a function of the bottom squark mass and the mass difference between the bottom squark and the LSP. The observed (expected) cross section limit includes one standard deviation bands for the theoretical (experimental) uncertainty.