Interpreting a CMS excess in $lljj+\mathbf{\text{missing}}$-transverse-momentum with the golden cascade of the minimal supersymmetric standard model

The CMS experiment recently reported an excess consistent with an invariant mass edge in opposite-sign same flavor leptons, when produced in conjunction with at least two jets and missing transverse momentum. We provide an interpretation of the edge in terms of (anti)squark pair production followed by the “golden cascade” decay for one of the squarks: $\tilde{q}\to {\tilde{\chi }}_2^{0}q\to \tilde{l}lq\to {\tilde{\chi }}_1^{0}qll$ in the minimal supersymmetric standard model. A simplified model involving binos, winos, an on-shell slepton, and the first two generations of squarks fits the event rate and the invariant mass edge. We check consistency with a recent ATLAS search in a similar region, finding that much of the good-fit parameter space is still allowed at the 95% confidence level (C.L.). However, a combination of other LHC searches, notably two-lepton stop pair searches and jets plus ${\cancel{p}}_T$, rule out all of the remaining parameter space at the 95% C.L.

Figure 1

Invariant mass distribution of OSSF leptons in the CMS selection after cuts. The expected Standard Model background is shown (green), which is calculated from data by using OSOF events, as well as the observed data, and an example signal point (red) in the parameter space investigated here involving the golden cascade: $m_{\tilde{q}}=900\mathrm{GeV}$, $m_{{\tilde{\chi }}_2^0}=312\mathrm{GeV}$, $m_{{\tilde{l}}_R}=200\mathrm{GeV}$, $m_{{\tilde{\chi }}_1^0}=216\mathrm{GeV}$. Error bars on the observed number of events show the expected statistical standard deviation.

Figure 2

Feynman diagram for the golden cascade decay.

Figure 3

Constraint on SUSY particle masses involved in the ${\tilde{\chi }}_2^0$ decay coming from the central value $m_{ll}^{\max }=78.7\mathrm{GeV}$.

Figure 4

Example signal point that fits the edge inference: $m_{\tilde{q}}=900\mathrm{GeV}$, $m_{{\tilde{\chi }}_2^0}=312\mathrm{GeV}$, $m_{{\tilde{l}}_R}=200\mathrm{GeV}$, $m_{{\tilde{\chi }}_1^0}=216\mathrm{GeV}$. Prominent decays with branching ratios higher than 10% are shown as arrows.

Figure 5

Fit to (anti)squark production cross section at an 8 TeV LHC. The logarithm of the Prospino cross section prediction is shown by the solid line. Our quadratic fit to this is shown by the dashed line. The CMS $lljj{\cancel{p}}_T$ search region cut efficiencies for two parameter space points are shown by the points with errorbars, where the errorbars are purely from Monte Carlo statistics.

Figure 6

Constraints on golden channel parameter space from the CMS $lljj{\cancel{p}}_T$ search over the input parameter plane $m_{\tilde{l}}(M_{\mathrm{SUSY}})$ and $\mathrm{\Delta }m=M_2(M_{\mathrm{SUSY}})-m_{\tilde{l}}(M_{\mathrm{SUSY}})$. A colored box indicates a point that fits the 95% C.L. lower limit of the inferred value of CMS $lljj{\cancel{p}}_T$ signal rate and is also consistent with CMS’s edge inference.

Figure 7

Constraints on golden channel parameter space from the CMS $lljj{\cancel{p}}_T$ search over the plane of pole masses of the second-lightest neutralino and the right-handed slepton. A colored box indicates a point that fits the 95% C.L. lower limit of the inferred value of CMS $lljj{\cancel{p}}_T$ signal rate and is also consistent with CMS’s edge inference. The squark mass (upper panel) or lightest neutralino mass (lower panel) is given by reference to the scale on the right-hand side. Above the black line, the golden channel is kinematically inaccessible.

Figure 8

Constraints on golden channel parameter space from the ATLAS jets plus ${\cancel{p}}_T$ search. The squark mass consistent with the 95% C.L. lower bound on the CMS $lljj{\cancel{p}}_T$ signal is given by reference to the scale on the right-hand side. Points colored green are excluded by an ATLAS ${\cancel{p}}_T$ plus jets search at the 95% C.L.

Figure 9

Constraints on golden channel parameter space from the ATLAS $lljj{\cancel{p}}_T$ on-$Z$ search. The squark mass consistent with the 95% C.L. lower bound on the CMS $lljj{\cancel{p}}_T$ signal is given by reference to the scale on the right-hand side. Magenta points are ruled out by the ATLAS search at the 95% C.L., whereas those colored green are ruled out by ATLAS ${\cancel{p}}_T$ plus jets searches at the 95% C.L.

Figure 10

Constraints on golden channel parameter space from the CMS $4l{\cancel{p}}_T$ search. The squark mass consistent with the 95% C.L. lower bound on the CMS $lljj{\cancel{p}}_T$ signal is given by reference to the scale on the right-hand side. Light gray points are ruled out by the CMS 4-lepton search at the 95% C.L., whereas those colored green are ruled out by ATLAS jets ${\cancel{p}}_T$ searches, at the 95% C.L.

Figure 11

Constraints on the golden channel parameter space from the ATLAS stop pair production search involving two leptons. Yellow points are ruled out by the ATLAS search for leptonically decaying stops at the 95% C.L., whereas those colored green are ruled out by ATLAS jets plus ${\cancel{p}}_T$ searches at the 95% C.L.