Abstract
A search for excited electrons produced in pp collisions at sqrt{s} = 13 text {Te}text {V} via a contact interaction q{bar{q}}rightarrow ee^* 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 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 rightarrow ee^*rightarrow eeq{bar{q}} and pp rightarrow ee^*rightarrow enu W production cross sections as a function of the excited electron mass m_{e^*} 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^*}. For m_{e^*} <0.5 text {Te}text {V}, the lower bound for Lambda is 11 text {Te}text {V}. In the special case of m_{e^*} =Lambda , the values of m_{e^*} <4.8 text {Te}text {V} are excluded. The presented limits on Lambda are more stringent than those obtained in previous searches.
Highlights
Excited leptons appear in a number of composite models [1,2,3,4,5,6] seeking to explain the existence of the three generations of quarks and leptons in the Standard Model (SM)
The SM fermions are identified as a set of left- and righthanded chiral states protected by the SU (2) symmetry from obtaining masses of the order of [6]
The Z /γ ∗ + jets and W + jets simulated event samples were normalized to the next-to-nextto-leading-order (NNLO) inclusive cross sections computed with the FEWZ program [39]
Summary
Excited leptons appear in a number of composite models [1,2,3,4,5,6] seeking to explain the existence of the three generations of quarks and leptons in the Standard Model (SM). The excited lepton model introduces two unknown parameters relevant for this analysis, the excited lepton mass me∗ and the compositeness scale , which define the preferred search channels and kinematic properties of the final states. The excited electrons are produced via a contact interaction as well, but their decay is via a gauge-mediated interaction into a W and a ν, where the W boson decays hadronically, yielding an ee∗ → eνqqfinal state. This gives final states with exactly one energetic electron, a largeradius (large-R) jet J produced by two collimated quarks, and missing transverse momentum.
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