Search for chargino-neutralino production in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ with high-$p_T$ leptons

We present a search for the associated production of charginos and neutralinos in $\mathrm{p}\overline{\mathrm{p}}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The data were collected at the Collider Detector at Fermilab (CDF II) and correspond to integrated luminosities between 0.7 and $1.0{\mathrm{fb}}^{-1}$. We look for final states with one high-$p_{\mathrm{T}}$ electron or muon, and two additional leptons. Our results are consistent with the standard model expectations, and we set limits on the cross section as a function of the chargino mass in three different supersymmetric scenarios. For a specific minimal supersymmetric standard model scenario with no slepton mixing, we set a 95% C.L. limit at $151\mathrm{GeV}/c^2$.

Figure 1

Leading-order Feynman diagrams for chargino and neutralino associated production. The interaction is mediated through virtual $W$ (left diagram) and squark ($\tilde{q}$, right diagram).

Figure 2

Chargino and neutralino decay modes. The $\tilde{\ell }$ and the $\tilde{\nu }$ are the SUSY counterparts of the lepton and the neutrino.

Figure 3

The identification efficiency of tight electrons as a function of $E_{\mathrm{T}}$ using the Drell-Yan selection.

Figure 4

The identification efficiency (including stub finding efficiency) of CMUP muons as a function of $p_{\mathrm{T}}$ using the Drell-Yan selection.

Figure 5

Fake rate of loose central electrons. The solid line represents the linear fit to the average, and the dotted lines are $\pm 50\%$.

Figure 6

Fake rate of CMUP muons. The solid line represents the linear fit to the average, and the dotted lines are $\pm 50\%$.

Figure 7

Sketch of the $r\mathrm{\text{−}}\varphi$ view of a photon conversion signature with CES cluster locations. The magnetic field $B$ is along the $z$ direction.

Figure 8

Conversion identification efficiency as a function of the seed electron $E_{\mathrm{T}}$.

Figure 9

Invariant mass of same-flavor, oppositely charged leptons in $\mu \mu \ell$ events. The SM backgrounds are stacked, while the benchmark SUSY signal is superimposed. Observed events are shown as points with error bars indicating the statistical uncertainty.

Figure 10

Invariant mass of same-flavor lepton pairs. The SM backgrounds are stacked, while the benchmark SUSY signal is superimposed. Observed events are shown as points with error bars indicating the statistical uncertainty (overflows are added to the last bin).

Figure 11

Missing transverse energy in $\mu \mu$ and $ee$ events. The SM backgrounds are stacked, while the benchmark SUSY signal is superimposed. Observed events are shown as points with error bars indicating the statistical uncertainty (overflows are added to the last bin).

Figure 12

Missing transverse energy in $\mu e$ and $e\mu$ events. The SM backgrounds are stacked, while the benchmark SUSY signal is superimposed. Observed events are shown as points with error bars indicating the statistical uncertainty (overflows are added to the last bin). The expected benchmark SUSY signals in the $\mu e$ and $e\mu$ channels are $\sim 3$ and $\sim 6$ events, respectively.

Figure 13

Number of jets in $ee$ events with invariant mass between 76 and $106\mathrm{GeV}/c^2$. The SM backgrounds are stacked, while the benchmark SUSY signal is superimposed. Observed events are shown as points with error bars indicating the statistical uncertainty.

Figure 14

Missing transverse energy before the final cut of 15 GeV in $\mu \mu \ell$ and $\mu e\ell$. The SM backgrounds are stacked, while the benchmark SUSY signal is superimposed. Observed events are shown as points with error bars indicating the statistical uncertainty.

Figure 15

Missing transverse energy before the final cut of 20 GeV in $ee\ell$ and $e\mu \ell$. The SM backgrounds are stacked, while the benchmark SUSY signal is superimposed. Observed events are shown as points with error bars indicating the statistical uncertainty.

Figure 16

The $r$-$\varphi$ view of the $\mu \mu \mu$ candidate event in the CDF detector. Only tracks with $p_{\mathrm{T}}\ge 1\mathrm{GeV}/c$ are shown in the central tracking detector. The three highlighted straight tracks are labeled with the muon category and momentum. The dotted black line shows the direction of the ${\mathrm{E̸}}_T$ (MET). The energy deposit is illustrated in the histograms around the tracking view. Innermost (light) towers show the electromagnetic energy in the calorimeter towers; outermost (dark) show the hadronic component of the energy.

Figure 17

Branching ratios for neutralino ${\tilde{\chi }}_2^0$ (top panel) and chargino ${\tilde{\chi }}_1^{+}$ (bottom panel) in the mSUGRA and MSSM-no-mix scenarios for different slepton flavors. The ${\tilde{\chi }}_1^{+}$ has $\mathrm{BR}(\ell \nu {\tilde{\chi }}_1^0)\approx \mathrm{BR}(\overline{d}u{\tilde{\chi }}_1^0)=\mathrm{BR}(\overline{s}c{\tilde{\chi }}_1^0)$ in both scenarios.

Figure 18

Total acceptance of the channels for the three scenarios considered.

Figure 19

Exclusion limits for the mSUGRA scenario. The bands indicate the range of expected limits given the possible outcomes that could have been observed if a signal were not there.

Figure 20

Exclusion limits for the MSSM-$W/Z$ scenario. The bands indicate the range of expected limits given the possible outcomes that could have been observed if a signal were not there.

Figure 21

Exclusion limits for the MSSM-no-mix scenario. The bands indicate the range of expected limits given the possible outcomes that could have been observed if a signal were not there.

Figure 22

Projection of the current expected result with increased data size for the mSUGRA scenario assuming no signal is observed. Also shown is the current observed limit (top solid line).

Figure 23

Projection of the current expected result with increased data size for the MSSM-$W/Z$ scenario assuming no signal is observed. Also shown is the current observed limit (top solid line).

Figure 24

Projection of the current expected result with increased data size for the MSSM-no-mix scenario assuming no signal is observed. Also shown is the current observed limit (top solid line).