Abstract
Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. This article presents the results of a search for events containing at least one long-lived particle that decays at a significant distance from its production point into two leptons or into five or more charged particles. This analysis uses a data sample of proton-proton collisions at $\sqrt{s}$ = 8 TeV corresponding to an integrated luminosity of 20.3 fb$^{-1}$ collected in 2012 by the ATLAS detector operating at the Large Hadron Collider. No events are observed in any of the signal regions, and limits are set on model parameters within supersymmetric scenarios involving R-parity violation, split supersymmetry, and gauge mediation. In some of the search channels, the trigger and search strategy are based only on the decay products of individual long-lived particles, irrespective of the rest of the event. In these cases, the provided limits can easily be reinterpreted in different scenarios.
Highlights
Several extensions to the Standard Model (SM) predict the production at the Large Hadron Collider (LHC) of heavy particles with lifetimes of order picoseconds to nanoseconds
At the LHC experiments, the decay of a long-lived particle (LLP) with lifetime in this range could be observed as a displaced vertex (DV), with daughter particles produced at a significant distance from the interaction point (IP) of the incoming proton beams
The DV must contain at least five charged-particle tracks. This signature is divided into four different final states, in which the DV must be accompanied by a hightransverse-momentum muon or electron candidate that originates from the DV, jets, or missing transverse momentum (EmT iss)
Summary
Several extensions to the Standard Model (SM) predict the production at the Large Hadron Collider (LHC) of heavy particles with lifetimes of order picoseconds to nanoseconds (e.g., see Ref. [1] and references therein). This article presents the results of a search for DVs that arise from decays of long-lived, heavy particles, at radial distances of millimeters to tens of centimeters from the proton-proton IP in the ATLAS detector at the LHC. The DV must contain at least five charged-particle tracks This signature is divided into four different final states, in which the DV must be accompanied by a hightransverse-momentum (high-pT) muon or electron candidate that originates from the DV, jets, or missing transverse momentum (EmT iss). The CMS Collaboration has searched for decays of a long-lived particle into a final state containing two electrons, two muons [20,21], an electron and a muon [22], or a quark-antiquark pair [23]. It is composed of a hardware-based level-1 trigger that uses information from the MS trigger chambers and the calorimeters, followed by two software-based trigger levels
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