Search for microscopic black holes in a like-sign dimuon final state using large track multiplicity with the ATLAS detector

A search is presented for microscopic black holes in a like-sign dimuon final state in proton–proton collisions at $\sqrt{s}=8\mathrm{TeV}$. The data were collected with the ATLAS detector at the Large Hadron Collider in 2012 and correspond to an integrated luminosity of $20.3{\mathrm{fb}}^{-1}$. Using a high track multiplicity requirement, $0.6\pm 0.2$ background events from Standard Model processes are predicted and none observed. This result is interpreted in the context of low-scale gravity models and 95% C.L. lower limits on microscopic black hole masses are set for different model assumptions.

Figure 1

The leading-muon $p_{\mathrm{T}}$ distribution for the predicted background and observed data for all like-sign dimuon events passing the preselection criteria. The background histograms are stacked. The signal histogram is overlaid. The last bin along the $x$ axis shows the overflows. The bottom panel shows the ratio of data to the expected background (points) and the total uncertainty on the background (shaded area).

Figure 2

The dimuon invariant mass (${\mathrm{M}}_{\mu \mu }$) distribution for the predicted background and observed data for like-sign dimuon events where the leading muon satisfies $p_{\mathrm{T}}>100\mathrm{GeV}$. The background histograms are stacked. The signal histogram is overlaid. The last bin along the $x$ axis shows the overflows. The bottom panel shows the ratio of data to the expected background (points) and the total uncertainty on the background (shaded area).

Figure 3

The dimuon azimuthal separation ($\Delta {\varphi }_{\mu \mu }$) distribution for the predicted background and observed data for like-sign dimuon events where the leading muon satisfies $p_{\mathrm{T}}>100\mathrm{GeV}$, and with $N_{\mathrm{trk}}\ge 10$. The background histograms are stacked. The signal histogram is overlaid. The bottom panel shows the ratio of data to the expected background (points) and the total uncertainty on the background (shaded area).

Figure 4

The track multiplicity (N-trk) distribution ($p_{\mathrm{T}}^{\mathrm{trk}}>10\mathrm{GeV}$) for the predicted background and observed data for events where the leading muon has $p_{\mathrm{T}}>100\mathrm{GeV}$. The background histograms are stacked. The signal histogram is overlaid. The bottom panel shows the ratio of data to the expected background (points) and the total uncertainty on the background (shaded area).

Figure 5

The 95% C.L. exclusion contours for nonrotating black holes in models with $n=2$, 4, and 6. The dashed lines show the expected exclusion contour, the solid lines show the observed exclusion contour. The regions below the contours are excluded by this analysis. The $1\sigma$ uncertainty on the expected limit for $n=2$ is shown as a band. Lines of constant slope $k=M_{\mathrm{TH}}/M_{\mathrm{D}}=2$, 3, 4, and 5 are also shown. Only slopes $k\gg 1$ correspond to physical models.

Figure 6

The 95% C.L. exclusion contours for rotating black holes in models with $n=2$, 4, and 6. The dashed lines show the expected exclusion contour, the solid lines show the observed exclusion contour. The regions below the contours are excluded by this analysis. The $1\sigma$ uncertainty on the expected limit for $n=2$ is shown as a band. Lines of constant slope $k=M_{\mathrm{TH}}/M_{\mathrm{D}}=2$, 3, 4, and 5 are also shown. Only slopes $k\gg 1$ correspond to physical models.

Figure 7

The 95% C.L. exclusion contours for string balls in models with $n=6$. The dashed line shows the expected exclusion contour with the $1\sigma$ uncertainty shown as a band. The solid line shows the observed exclusion contour. The region below the contour is excluded by this analysis. Lines of constant $k=M_{\mathrm{TH}}/M_{\mathrm{D}}=2$, 3, 4, and 5 are also shown. Only the values $k\gg 1$ correspond to physical models.