Search for a Light Higgs Boson Decaying to Long-Lived Weakly Interacting Particles in Proton-Proton Collisions at $\sqrt{s}=7\mathrm{TeV}$ with the ATLAS Detector

A search for the decay of a light Higgs boson (120–140 GeV) to a pair of weakly interacting, long-lived particles in $1.94{\mathrm{fb}}^{-1}$ of proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$ recorded in 2011 by the ATLAS detector is presented. The search strategy requires that both long-lived particles decay inside the muon spectrometer. No excess of events is observed above the expected background and limits on the Higgs boson production times branching ratio to weakly interacting, long-lived particles are derived as a function of the particle proper decay length.

Figure 1

(a) Efficiency of the trigger, as a function of the radial decay position ($r$) of the ${\pi }_v$. (b) The vertex reconstruction efficiency for ${\pi }_v$ decays in the barrel for events that pass the muon RoI cluster trigger as a function of the radial decay distance. The error bars represent the statistical uncertainty on the efficiencies.

Figure 2

Distribution of number of events vs number of muon RoIs from punch-through jets contained in the muon RoI cluster for both data and MC events. The error bands on the QCD dijet MC histogram represent the $1\sigma$ statistical uncertainty.

Figure 3

Observed 95% upper limits on the process $h^0\to {\pi }_v{\pi }_v$, vs the ${\pi }_v$ proper decay length, expressed as a multiple of the SM cross section for Higgs boson production. Exclusion limits assume 100% branching ratio for the Higgs boson decaying to ${\pi }_v$’s.