MSSM fits to the ATLAS 1 lepton excess

Abstract

We use the framework of the p19MSSM to perform a fit to the mild excesses over the Standard Model background recently observed in three bins of the ATLAS 1-lepton + (b-)jets + E_T^{text {miss}} search. We find a few types of spectra that can fit the emerging signal and at the same time are not excluded by other LHC searches. They can be grouped roughly in two categories. The first class is characterized by the presence of one stop or stop and sbottoms with mass in the ballpark of 700–800~mathrm {GeV} and a neutralino LSP of mass around 400~mathrm {GeV}, with or without the additional presence of an intermediate chargino. In the second type of scenarios the stop, lightest chargino, sbottom if present, and the neutralino are about or heavier than {sim } 650~mathrm {GeV} and the signal originates from cascade decays of squarks of the 1st and 2nd generation, which should have a mass of 1.1–1.2~mathrm {TeV}. For the best-fit scenarios, we compare the global chi-squared with several ATLAS and CMS searches with the corresponding chi-squared of the Standard Model expectation, showing that the putative signal is also favored globally with respect to the background-only hypothesis. We point out that if the observed excess persists in the next round of data, it should be accompanied by associated significant excesses in all-hadronic final-state searches.