CMS-SUS-14-019

CMS-SUS-14-019 ; CERN-EP-2016-096
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 TeV
CMS Collaboration
30 May 2016
Phys. Rev. Lett. 118 (2017) 021802
Abstract: A first search for pair production of dark matter candidates through vector boson fusion in proton-proton collisions at $\sqrt{s} = $ 8 TeV is performed with the CMS detector. The vector boson fusion topology enhances missing transverse momentum, providing a way to probe supersymmetry also in the case of a compressed mass spectrum. The data sample corresponds to an integrated luminosity of 18.5 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.
Links: e-print arXiv:1605.09305 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Feynman diagrams for dark matter pair production in a vector boson fusion process (a) and for bottom squark pair production (b). Given a nearly degenerate bottom squark and LSP, the final state b-quarks are too soft to be observed.
png pdf	Figure 1-a: Feynman diagrams for dark matter pair production in a vector boson fusion process (a) and for bottom squark pair production (b). Given a nearly degenerate bottom squark and LSP, the final state b-quarks are too soft to be observed.
png pdf	Figure 1-b: Feynman diagrams for dark matter pair production in a vector boson fusion process (a) and for bottom squark pair production (b). Given a nearly degenerate bottom squark and LSP, the final state b-quarks are too soft to be observed.
png pdf	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.
png pdf	Figure 3: (a) Contact interaction scale limit at 95% CL as a function of the DM mass. The validity of the effective field theory is quantified by (i) ${\rm R}_{\Lambda } = 80%$ contours and (ii) truncated limits for different values of the effective coupling. The DM relic abundance $\Omega h^{2}= $ 0.12 is calculated as described in the text. (b) Bottom squark pair production 95% CL 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.

Tables
png pdf	Table 1: Event yields predicted from MC in the control regions and observed in the signal region (SR). Only statistical uncertainties are shown. Dashes indicate cases where a background contribution is negligible. The units for the yields are given in the header row of the table.

Summary

In summary, we have searched for new physics that results in large $p_{\mathrm{T}}^{\text{miss}}$ and jets with a VBF topology. The data sample used corresponds to an integrated luminosity of 18.5 fb$^{-1}$ collected by the CMS detector in proton-proton collisions at $\sqrt{s} =$ 8 TeV. The low multijet background demonstrates the power of the VBF topology approach for DM and compressed mass spectrum SUSY searches. This is the first search for pure electroweak DM production at a hadron collider. The production of DM via VBF with masses below 420 GeV is excluded at a 95% confidence level for a chosen contact interaction scale $\Lambda =$ 600 GeV. Limits for different values of $\Lambda$ can be obtained by scaling the $\chi\chi \mathrm{j j}$ cross section, which is proportional to $1 / \Lambda^{2}$. For a nearly mass-degenerate bottom squark and LSP this analysis sets the most stringent limits reported to date, excluding scalar bottom quarks up to masses of 315 GeV at a 95% confidence level.

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