Abstract
Several models of elementary particle physics beyond the Standard Model, predict the existence of neutral particles that can decay in jets of leptons and light hadrons (lepton-jets). The present contribution collects the results about the lepton-jet search with the ATLAS experiment at the proton-proton LHC collider at √ s = 8 TeV during the entire 2012 data taking (20 fb −1 ). No excess of events have been observed over the expected background and the exclusion limits for two different models, that predict the Higgs boson to decay in lepton-jets, have been computed. A new lepton-jet search is underway for the new LHC era at (√ s = 13 TeV).
Highlights
The Standard Model (SM) of particle physics and its mutual interactions has proven up to now extremely successful, but despite that it still remains incomplete, e.g. it does not explain the nature of dark matter
The corresponding limits with TYPE2-TYPE2 events excluded are shown in table 2
For the case of a hidden photon which kinetically mixes with the SM photon, these limits can be converted into exclusion limits on the kinetic mixing parameter
Summary
The Standard Model (SM) of particle physics and its mutual interactions has proven up to now extremely successful, but despite that it still remains incomplete, e.g. it does not explain the nature of dark matter. If the mass of these particles is in the MeV to GeV range, they would decay mainly to leptons and light mesons [1]. One of the most promising model is that in which the hidden sector and the visible one are coupled via the vector portal: a light hidden photon (γd) mixes kinetically with the SM photon. Due to the small mass of the γd and the size of the kinetic mixing parameter (that control both the BR and lifetime of the γd) these particles are produced with a large boost. As a consequence the decay products of the γd are collimated jets of pairs of electrons and/or muons and or pions that can be produced far from the IP of the event (displaced lepton-jet).
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