Discovering Higgs boson decays to lepton jets at hadron colliders

Collider Searches for Dark Matter through the Higgs Lens

Despite the fact that dark matter constitutes one of the cornerstones of the standard cosmological paradigm, its existence has so far only been inferred from astronomical observations, and its microscopic nature remains elusive. Theoretical arguments suggest that dark matter might be connected to the symmetry-breaking mechanism of the electroweak interactions or of other symmetries extending the Standard Model of particle physics. The resulting Higgs bosons, including the 125 GeV spin-0 particle discovered recently at the Large Hadron Collider, therefore represent a unique tool to search for dark matter candidates at collider experiments. This article reviews some of the relevant theoretical models as well as the results from the searches for dark matter in signatures that involve a Higgs-like particle at the Large Hadron Collider.

Searching for Higgs Decays to as Many as 8 Leptons

We propose a search for Higgs decays with as many as 8 leptons in the final state. This signal can arise in a simple model with a hidden vector (A_{d}) that gets mass via a hidden scalar (h_{d}) vacuum expectation value. The 125 GeV Higgs boson can then decay H→h_{d}h_{d}→4A_{d}→8f, where f are standard model fermions. We recast current searches and show that a branching ratio (BR) of H→h_{d}h_{d} as large as 10% is allowed. We also describe a dedicated search that could place bounds on BR(H→h_{d}h_{d}) as low as 10^{-5} using only 36  fb^{-1} of data, with significant improvements coming from greater integrated luminosity.

Jets and photons

This Letter applies the concept of "jets," as constructed from calorimeter cell four-vectors, to jets composed (primarily) of photons (or leptons). Thus jets become a superset of both traditional objects such as QCD jets, photons, and electrons, and more unconventional objects such as photon jets and electron jets, defined as collinear photons and electrons, respectively. Since standard objects such as single photons become a subset of jets in this approach, standard jet substructure techniques are incorporated into the photon finder toolbox. Using a (reasonably) realistic calorimeter model we demonstrate that, for a single photon identification efficiency of 80% or above, the use of jet substructure techniques reduces the number of QCD jets faking photons by factors of 2.5 to 4. Depending on the topology of the photon jets, the substructure variables reduce the number of photon jets faking single photons by factors of 10 to 10(3) at a single photon identification efficiency of 80%.