Search for excited electrons singly produced in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS experiment at the LHC

Abstract

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

45 pages in total, author list starting on page 29, 6 figures, 10 tables, published by Eur. Phys. J. C. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2017-22/

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