Search for scalar top quarks in the acoplanar charm jets and missing transverse energy final state in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV

Abstract

We present a search for the pair production of scalar top quarks, $\tilde{t}$, using 995 pb$^{-1}$ of data collected in $p\bar{p}$ collisions with the D0 detector at the Fermilab Tevatron Collider at $\sqrt{s} = 1.96$ TeV. Both scalar top quarks are assumed to decay into a charm quark and a neutralino ($\tildeχ^{0}_{1}$), where $\tildeχ^{0}_{1}$ is the lightest supersymmetric particle. This leads to a final state with two acoplanar charm jets and missing transverse energy. We find the yield of such events to be consistent with the standard model expectation, and exclude sets of $\tilde{t}$ and $\tildeχ^{0}_{1} $ masses at the 95% C.L. that substantially extend the domain excluded by previous searches.

Figures (5)

• Figure 1: Distributions of the asymmetry ${\it A} = (~\hbox{$\slash emE_{T}$}-\hbox{$\slash emH_{T}$}) / (~\hbox{$\slash emE_{T}$}+\hbox{$\slash emH_{T}$})$ with the requirement on $\mathit{D} = \Delta \phi _{\mathrm{max}} - \Delta\phi _{\mathrm{min}}$ inverted (a) and applied (c). Distributions of $\mathit{D}$ with the requirement on ${\it A}$ inverted (b) and applied (d) for data (points with error bars), for SM backgrounds (histogram), and for a signal with $m_{\tilde{t}} = 150$ GeV and $m_{\tilde{\chi}_1^0} = 70$ GeV (hatched histogram). In all plots the signal contribution has been scaled up by five and $\hbox{$\slash emE_{T}$} > 60$ GeV is required. The excess in data at ${\it A}=0$ and $\mathit{D} = 0-10$ degrees is consistent with the systematic uncertainties on the predicted background.
• Figure 2: Distributions of $\mathit{S} = \Delta\phi_{\mathrm{max}} + \Delta\phi_{\mathrm{min}}$ for data (points with error bars), SM background (histogram), and a signal with $m_{\tilde{t}}= 150$ GeV and $m_{\tilde{\chi}_{1}^{0}}= 70$ GeV (hatched histogram) after requiring HF tagging but before optimization.
• Figure 3: Distributions of $H_{T}$ after applying optimized requirements on $\hbox{$\slash emE_{T}$}$ and $\mathit{S}$ for data (points with error bars), SM background (histogram), and a signal with $m_{\tilde{t}}= 150$ GeV and $m_{\tilde{\chi}_{1}^{0}}= 70$ GeV (hatched histogram).
• Figure 4: Final distributions of $\hbox{$\slash emE_{T}$}$ for data (points with error bars), SM background (histogram), and a signal with $m_{\tilde{t}}= 150$ GeV and $m_{\tilde{\chi}_{1}^{0}}= 70$ GeV (hatched histogram).
• Figure 5: Region in the $\tilde{t}$--$\tilde{\chi}_1^0$ mass plane excluded at the $95\%$ C.L. by the present search. The observed (expected) exclusion contour is shown as the green solid (dashed) line. The yellow band represents the theoretical uncertainty on the scalar top quark pair production cross section due to PDF and renormalization and factorization scale choice. Results from previous searches lepcdf2dzeroruntwo are also shown.