Search for Pair Production of Light Scalar Top Quarks in $p\overline{p}$ Collisions at $\sqrt{s}=1.8\mathrm{T}\mathrm{e}\mathrm{V}$

Using $85.2\pm 3.6{\mathrm{p}\mathrm{b}}^{-1}$ of $p\overline{p}$ collisions collected at $\sqrt{s}=1.8\mathrm{T}\mathrm{e}\mathrm{V}$ with the D0 detector at Fermilab’s Tevatron Collider, we present the results of a search for direct pair production of scalar top quarks ($\tilde{t}$), the supersymmetric partners of the top quark. We examined events containing two or more jets and missing transverse energy, the signature of light scalar top quark decays to charm quarks and neutralinos. After selections, we observe 27 events while expecting $31.1\pm 6.4$ events from known standard model processes. Comparing these results to next-to-leading-order production cross sections, we exclude a significant region of $\tilde{t}$ and neutralino phase space. In particular, we exclude the $\tilde{t}$ mass $m_{\tilde{t}}<122\mathrm{G}\mathrm{e}\mathrm{V}/c^2$ for a neutralino mass of $45\mathrm{G}\mathrm{e}\mathrm{V}/c^2$.

Figure 1

Data (points) and predicted background (histograms) after final selections. The additional contributions expected from a $M_{\tilde{t}}=130\mathrm{G}\mathrm{e}\mathrm{V}/c^2$, $M_{\widetilde{{\chi }_0}}=30\mathrm{G}\mathrm{e}\mathrm{V}/c^2$ scalar top quark are shown by shaded histograms. The plots correspond to the $E_T$ of the leading jet, second jet, ${\mathrm{E̸}}_T$ (the three parameters optimized using the RGS), and $H_T$, where $H_T={\mathrm{E̸}}_T+{\Sigma }_i{E}_T\left({\mathrm{j}\mathrm{e}\mathrm{t}}_i\right)$, to demonstrate agreement with variables not directly optimized via RGS.

Figure 2

Regions in the ($m_{\tilde{t}},m_{\widetilde{{\chi }_1^0}}$) plane excluded at the 95% confidence level assuming 100% branching of $\tilde{t}\to c{\chi }_1^0$. Limits from the CERN $e^{+}{e}^{-}$ collider LEP [20] and Collider Detector and Fermilab (CDF) [21] are also shown in the figure. The dashed lines correspond to kinematic cutoffs from the masses of the ${\chi }_1^0$, $m_c$, $m_b$, and $m_W$.