Search for excited electrons singly produced in proton–proton collisions at $$\sqrt{s} ~=~13~\text {Te}\text {V}$$ with the ATLAS experiment at the LHC

Abstract A search for excited electrons produced inppcollisions at $$\sqrt{s}$$ s = 13 $$\text {Te}\text {V}$$ Te via a contact interaction $$q{\bar{q}}\rightarrow ee^*$$ qq¯→ee∗ is presented. The search uses 36.1 fb $$^{-1}$$ -1 of data collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider. Decays of the excited electron into an electron and a pair of quarks ( $$eq{\bar{q}}$$ eqq¯ ) are targeted in final states with two electrons and two hadronic jets, and decays via a gauge interaction into a neutrino and a $$W$$ W boson ( $$\nu W$$ νW ) are probed in final states with an electron, missing transverse momentum, and a large-radius jet consistent with a hadronically decaying $$W$$ W boson. No significant excess is observed over the expected backgrounds. Upper limits are calculated for the $$pp \rightarrow ee^*\rightarrow eeq{\bar{q}} $$ pp→ee∗→eeqq¯ and $$pp \rightarrow ee^*\rightarrow e\nu W $$ pp→ee∗→eνW production cross sections as a function of the excited electron mass $$m_{e^*}$$ me∗ at 95% confidence level. The limits are translated into lower bounds on the compositeness scale parameter $$\Lambda $$ Λ of the model as a function of $$m_{e^*}$$ me∗ . For $$m_{e^*} <0.5$$ me∗<0.5 $$\text {Te}\text {V}$$ Te , the lower bound for $$\Lambda $$ Λ is 11 $$\text {Te}\text {V}$$ Te . In the special case of $$m_{e^*} =\Lambda $$ me∗=Λ , the values of $$m_{e^*} <4.8$$ me∗<4.8 $$\text {Te}\text {V}$$ Te are excluded. The presented limits on $$\Lambda $$ Λ are more stringent than those obtained in previous searches.

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