Abstract
We describe current and future hadron collider limits on new vector-like leptons with exotic decays. We consider the possibility that, besides standard decays, the new leptons can also decay into a Standard Model charged lepton and a stable particle like a dark photon. To increase their applicability, our results are given in terms of arbitrary branching ratios in the different decay channels. In the case that the dark photon is stable at cosmological scales we discuss the interplay between the dark photon and the vector-like lepton in generating the observed dark matter relic abundance and the complementarity of collider searches and dark matter phenomenology.
Highlights
New VLL that incorporate a discrete symmetry under which SM particles are even and new particles are odd, preventing the decay of the VLL into only SM particles
For the case in which the VLL decays exclusively to SM final states (W ν, Z a√nd H ) we reproduce the analysis presented in ref. [22], an ATLAS search performed at s = 8 TeV and an integrated luminosity of L = 20.3 fb−1, looking for multi-lepton signals coming from the Z decay of a singlet VLL
Some models predict this mass to be close to the electroweak scale, such as the Littlest Higgs model with T-parity, but in other cases, we can have sub-GeV masses as is the case in feebly interacting massive particles (FIMP) in which this new particle plays the role of dark matter (DM) as we will see below
Summary
The goal of this article is to study the current and future reach of hadron colliders on new VLL that can decay into SM particles and into a SM charged lepton and a neutral particle that is stable at detector scales and appears as missing energy. We will present our results in a model-independent way whenever possible, as a function of arbitrary branching ratios in the different channels. To show actual limits we will focus on a new VLL singlet with electric charge -1, EL,R, and mass ME, and a massive vector boson AμH , as the stable (at detector scales) particle, with mass MAH < ME so that E can decay into AH and a SM lepton. We will first compare our results with the ones published by the experimental collaborations and extend the analyses by considering arbitrary decays into the different channels. We will update the analyses to take full advantage of higher luminosity and/or center of mass energy
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