Search for long-lived particles that decay into final states containing two electrons or two muons in proton-proton collisions at sqrt(s) = 8 TeV

TL;DR

This paper reports a search for long-lived particles decaying into electron or muon pairs with displaced vertices, setting the most stringent limits to date on such signals in proton-proton collisions at 8 TeV.

Contribution

It introduces a model-independent method to set upper limits on long-lived particle decays into dileptons, applicable across various theoretical models.

Findings

No significant excess observed above standard model expectations.

Established the most stringent upper limits on cross section times branching fraction.

Limits are sensitive to Higgs boson branching fractions as low as 10^-4.

Abstract

A search is performed for long-lived particles that decay into final states that include a pair of electrons or a pair of muons. The experimental signature is a distinctive topology consisting of a pair of charged leptons originating from a displaced secondary vertex. Events corresponding to an integrated luminosity of 19.6 (20.5) inverse femtobarns in the electron (muon) channel were collected with the CMS detector at the CERN LHC in proton-proton collisions at sqrt(s) = 8 TeV. No significant excess is observed above standard model expectations. Upper limits on the product of the cross section and branching fraction of such a signal are presented as a function of the long-lived particle's mean proper decay length. The limits are presented in an approximately model-independent way, allowing them to be applied to a wide class of models yielding the above topology. Over much of the investigated parameter space, the limits obtained are the most stringent to date. In the specific case of a model in which a Higgs boson in the mass range 125-1000 GeV decays into a pair of long-lived neutral bosons in the mass range 20-350 GeV, each of which can then decay to dileptons, the upper limits obtained are typically in the range 0.2-10 fb for mean proper decay lengths of the long-lived particles in the range 0.01-100 cm. In the case of the lowest Higgs mass considered (125 GeV), the limits are in the range 2-50 fb. These limits are sensitive to Higgs boson branching fractions as low as 1E-4.