Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the standard model with the ATLAS detector

An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to $1.6{\mathrm{fb}}^{-1}$ of integrated luminosity collected in 2011 at $\sqrt{s}=7\mathrm{TeV}$ with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with $p_{\mathrm{T}}>20\mathrm{GeV}$ and $|\eta |<2.5$. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair $m(\mu \mu )$ is found to agree well with the background expectation. Upper limits on the cross section for anomalous production of two muons with the same electric charge are placed as a function of $m(\mu \mu )$ within a fiducial region defined by the event selection. The fiducial cross-section limit constrains the like-sign top-quark pair-production cross section to be below 3.7 pb at 95% confidence level. The data are also analyzed to search for a narrow like-sign dimuon resonance as predicted for e.g. doubly charged Higgs bosons ($H^{\pm \pm }$). Assuming pair production of $H^{\pm \pm }$ bosons and a branching ratio to muons of 100% (33%), this analysis excludes masses below 355 (244) GeV and 251 (209) GeV for $H^{\pm \pm }$ bosons coupling to left-handed and right-handed fermions, respectively.

Figure 1

Distribution of the dimuon invariant mass for (a) ${\mu }^{\pm }{\mu }^{\pm }$ pairs, (b) ${\mu }^{+}{\mu }^{+}$ pairs, and (c) ${\mu }^{-}{\mu }^{-}$ pairs. The data are compared to the stacked background estimates. The ratio between the data and the predicted background is also shown, where the shaded region is the total systematic uncertainty on the background prediction.

Figure 2

Upper limit at 95% C.L. on the cross section times branching ratio for pair production of doubly charged Higgs bosons decaying to two muons. Superimposed is the predicted cross section for $H_L^{++}{H}_L^{--}$ and $H_R^{++}{H}_R^{--}$ production assuming a branching ratio to muons of 100%. The bands on the predicted cross sections corresponds to the theoretical uncertainty of 10%.

Figure 3

Exclusion region at 95% C.L. of the $H^{\pm \pm }$ mass as a function of the branching ratio to muon pairs, $BR(H^{\pm \pm }\to {\mu }^{\pm }{\mu }^{\pm })$, for a) $H_L^{\pm \pm }$ bosons and b) $H_R^{\pm \pm }$ bosons. The shaded areas show the observed exclusion region, the solid lines show the expected exclusion region, and the dashed lines show the $\pm 1\sigma$ variations of the expected exclusion region.