Search for New Physics in Events with Four Charged Leptons

We present two searches for new phenomena in events with four charged leptons, using data from $pp$ collisions at $\sqrt{s}= 7$\ TeV collected by the ATLAS detector corresponding to an integrated luminosity of 1.02 fb$^{-1}$. The first search examines the four-lepton dataset for events that contain no identified $Z\rightarrow\ell^+\ell^-$ decays. Owing to the very low expected background, even a small number of such events would be of interest. After selection, $0.7^{+1.3}_{-0.6}{\rm (stat)}\ ^{+0.9}_{-0.5}{\rm (syst)}$ events are expected from standard model backgrounds, and no events are observed. Using doubly-charged Higgs production as a benchmark model, upper limits are set on a fiducial cross-section for four-lepton production of 4.7 fb. A second search examines events with two identified $Z\rightarrow\ell^+\ell^-$ decays for evidence of resonant production of $ZZ$ pairs via a massive graviton. For $M_{\ell\ell\ell\ell}>300$ GeV, $1.9^{+1.0}_{-0.1}{\rm (stat)}\ ^{+0.8}_{-0.1}{\rm (syst)}$ events are expected from standard model processes, and 3 events are observed. Limits are set on production of $ZZ$ from high-mass sources, $< 0.9$\ pb in the fiducial region at 95\% C.L. Using the Randall-Sundrum framework to quantify the result we report limits on $\sigma(pp\rightarrow G) \times BF(G\rightarrow ZZ)$ of 2.6-3.3\,pb, depending on the resonance mass. For a coupling of $k/\bar{M_{pl}}=0.1$, the median expected 95\% C.L. lower limit on the mass of the graviton is $M_{G}>575$ GeV, equal to the observed limit.