Search for Universal Extra Dimensions in $p\overline{p}$ Collisions

We present a search for Kaluza-Klein (KK) particles predicted by models with universal extra dimensions (UED) using a data set corresponding to an integrated luminosity of $7.3{\mathrm{fb}}^{-1}$, collected by the D0 detector at a $p\overline{p}$ center-of-mass energy of 1.96 TeV. The decay chain of KK particles can lead to a final state with two muons of the same charge. This signature is used to set a lower limit on the compactification scale of $R^{-1}>260\mathrm{GeV}$ in a minimal UED model.

Figure 1

(a) Production of a pair of KK quarks ($Q_1{\overline{Q}}_1$). (b) Decay of a KK quark into a jet, two oppositely charged leptons, and the LKP. Double lines indicate KK excitations. A similar cascade decay occurs for the second KK quark, leading to several leptons of the same charge in the final state.

Figure 2

Distribution of (a) ${\mathrm{E̸}}_T$ and (b) $p_{T_1}$ for data and background, compared to a signal with $R^{-1}=260\mathrm{GeV}$. The shaded band shows the statistical uncertainty on the background estimation. All entries exceeding the range of the histogram are added to the last bin.

Figure 3

Distribution of the BDT output for data and background, compared to a signal with $R^{-1}=260\mathrm{GeV}$. The shaded band shows the statistical uncertainty on the background estimation.

Figure 4

Observed and median expected $95\%$ C.L. limits on $\sigma \mathcal{B}({\mu }^{\pm }{\mu }^{\pm })$ as a function of $R^{-1}$ compared to $\sigma \mathcal{B}({\mu }^{\pm }{\mu }^{\pm })$ calculated with the mUED model. The bands represent $\pm 1$ and $\pm 2$ standard deviations (SD) around the median expected limits.