CMS-PAS-SUS-14-019

CMS-PAS-SUS-14-019
Search for dark matter and compressed mass-spectra supersymmetry with the vector boson fusion topology in pp collisions at $\sqrt{s} =$ 8 TeV
CMS Collaboration
August 2015

Abstract: The first search for dark matter candidate production through pure electroweak vector boson fusion processes is presented. Events with two jets in the vector boson fusion topology and large missing transverse momentum are analyzed using data from proton-proton collisions at $\sqrt{s} =$ 8 TeV collected with the CMS detector. In the context of supersymmetric models with a compressed mass spectrum, which may yield visible particles with momenta too low to detect efficiently, the vector boson fusion topology boosts the momentum imbalance from the escaping lightest supersymmetric particle (a dark matter candidate), providing a distinct signature to discriminate signal events from backgrounds. The dijet mass spectrum measured in data is observed to be compatible with the expected standard model prediction. Limits are set on the production cross section and mass of fermionic dark matter particles in the context of an effective field theory with a heavy mediator, as well as pairs of scalar bottom quarks that are nearly mass degenerate with the lightest supersymmetric particle.
Links: CDS record (PDF) ; Public twiki page ; CADI line (restricted) ; Figures are also available from the CDS record. These preliminary results are superseded in this paper, PRL 118 (2017) 021802. The superseded preliminary plots can be found here.

Figures
png ; pdf	Figure 1-a: (a) $m_{\mathrm{jj}}$ distribution after all signal region selections, where the shaded band in the ratio plot includes the systematic and statistical uncertainties in the background prediction. (b, upper) Upper limit at the 95% CL on the cross-section as a function of mass $M = m_{\chi } = m_{ \tilde{\mathrm{b}}}$ . (b, lower) The 95% CL on the contact interaction scale, $\Lambda$ , as a function of the DM mass, $M_{\chi }$ , for the scalar effective field theory DM model. The validity of the effective field theory is quantified by $R_{\Lambda }$ = 80% contours, corresponding to different values of the effective coupling $\textrm {g}_{eff}$ .
png ; pdf	Figure 1-b: (a) $m_{\mathrm{jj}}$ distribution after all signal region selections, where the shaded band in the ratio plot includes the systematic and statistical uncertainties in the background prediction. (b, upper) Upper limit at the 95% CL on the cross-section as a function of mass $M = m_{\chi } = m_{ \tilde{\mathrm{b}}}$ . (b, lower) The 95% CL on the contact interaction scale, $\Lambda$ , as a function of the DM mass, $M_{\chi }$ , for the scalar effective field theory DM model. The validity of the effective field theory is quantified by $R_{\Lambda }$ = 80% contours, corresponding to different values of the effective coupling $\textrm {g}_{eff}$ .

Tables
png ; pdf	Table 1: Predicted and observed rates for the control regions and signal region. The yields are used to calculate correction factors for the {\it central selections} and VBF selection efficiencies. Statistical uncertainties are cited for both the predicted and observed yields.
png ; pdf	Table 2: Predicted rates after various stages of the cut flow for backgrounds and $\mathrm{ \tilde{b} \tilde{b} jj }$ signal events with $m_{\tilde{ \mathrm{b} } } =$ 300 GeV.

Summary

In conclusion, a search has been performed for DM and compressed-mass spectra using events with significant

$E_{\mathrm{T}}^{\text{miss}}$ and two jets in a VBF topology. The data corresponds to an integrated luminosity of 18.5 fb

$^{-1}$ collected by the CMS detector in proton-proton collisions at

$\sqrt{s} =$ 8 TeV. It is the first search for pair production of DM particles in pure electroweak processes with couplings to the Z and W bosons of the SM. The observed

$m_{ \mathrm{jj} }$ distribution does not reveal evidence for new physics. Assuming the DM particle is a Dirac fermion, the results are used to exclude a range of masses up to 420 GeV in an effective field theory model with an interaction scale

$\Lambda =$ 600 GeV and Higgs portal operators of scaling dimension

$d =$ 5 containing the 4-point

$\chi \chi VV$ contact interactions. This analysis also produces the most stringent limits to date on the pair production of

$\tilde{ \mathrm{b} }$ in a compressed-mass spectra scenario defined by mass separation

$m_{ \tilde{ \mathrm{ b } } } - m_{ \tilde{ \chi }_1^0 } =$ 5 GeV, excluding masses below 315 GeV.

Compact Muon Solenoid
LHC, CERN