Search for New Phenomena in Events with Three or more Charged Leptons

We present a generic search for new phenomena in events with at least three charged leptons using 1.02 fb−1 of p p collision data recorded by the ATLAS detector at sqrt{s} = 7 TeV. Events are selected with at least three isolated, charged leptons above 20 GeV with the leading lepton above 25 GeV and no identified Z->l+l- decays. After selection, 25.9 ± 3.8(stat) ± 4.3(syst) events are expected in the signal region from Standard Model backgrounds, and 31 events are observed. In a second signal region that uses a tighter lepton pT cut at 30 GeV, 4.9 ± 1.6(stat) ± 0.9(syst) are expected from Standard Model sources, and 6 events are observed. The observed p-values for consistency with the Standard Model expectation are 27% and 33% in the two signal regions. Fiducial limits are extracted on models predicting excesses of multi-lepton events using pair production of doubly-charged Higgs bosons as a benchmark model. The observed fiducial cross-section limits are 38 fb and 14 fb in the two signal regions. Cross-section upper limits at the 95% confidence level are also set at 41 (34) pb for 200 (300) GeV excited electron neutrino pair production.