Search for long-lived particles decaying to leptons with large impact parameter in proton–proton collisions at $$\sqrt{s} = 13\,\text {Te}\text {V} $$

Abstract

A search for new long-lived particles decaying to leptons using proton–proton collision data produced by the CERN LHC at $$\sqrt{s}=13\,\text {Te}\text {V} $$ s = 13 Te is presented. Events are selected with two leptons (an electron and a muon, two electrons, or two muons) that both have transverse impact parameter values between 0.01 and 10$$\,\text {cm}$$ cm and are not required to form a common vertex. Data used for the analysis were collected with the CMS detector in 2016, 2017, and 2018, and correspond to an integrated luminosity of 118 (113)$$\,\text {fb}^{-1}$$ fb - 1 in the $${{\mathrm{e}}_{\mathrm{}}^{\mathrm{}}} {{\mathrm{e}}_{\mathrm{}}^{\mathrm{}}} $$ e e channel ($${{\mathrm{e}}_{\mathrm{}}^{\mathrm{}}} {\upmu } $$ e μ and $${\upmu } {\upmu } $$ μ μ channels). The search is designed to be sensitive to a wide range of models with displaced $${{\mathrm{e}}_{\mathrm{}}^{\mathrm{}}} {\upmu } $$ e μ , $${{\mathrm{e}}_{\mathrm{}}^{\mathrm{}}} {{\mathrm{e}}_{\mathrm{}}^{\mathrm{}}} $$ e e , and $${\upmu } {\upmu } $$ μ μ final states. The results constrain several well-motivated models involving new long-lived particles that decay to displaced leptons. For some areas of the available phase space, these are the most stringent constraints to date.

Searching for dark radiation at the LHC

“…A similar search by CMS used 118 fb −1 of data in the ee channel and 113 fb −1 in the eµ and µµ channels [28]. Compared to the ATLAS analysis, the CMS search is aimed at LLPs with shorter decay lengths and hence requires the transverse impact parameter |d 0 | of the leptons to fall between 0.1 mm and 100 mm.…”

“…While the general mechanism discussed in this work applies to a wide range of models, we focus for concreteness on the case of a scalar LLP with electroweak charges that decays into a charged lepton and an invisible DR particle. The most relevant prompt searches are therefore those for the direct production of sleptons [25,26], whereas LLPs with sizeable decay lengths are constrained by searches for displaced leptons [27,28]. We perform a detailed reinterpretation of these searches in order to identify the allowed regions of parameter space.…”

Track-Based Triggers for Exotic Signatures

“…While relatively rare, the fully-leptonic scenario produces the distinctive signature of a pair of displaced, but otherwise high-quality leptons, and is thus the easiest to target from the reconstruction perspective. The fully leptonic decay mode is the only scenario that has currently been explored, with Run 2 results from both ATLAS [17] and CMS [23]. Triggering in these cases is also the most straightforward: photon triggers can be used to recover displaced electrons, and the relatively clean environment of the muon spectrometer allow for triggers without impact parameter requirements.…”

Searching for dark radiation at the LHC

“…In the case of LLP signatures we can rely on searches for displaced leptons [7,8]. Deriving the constraints for our model is straightforward since the ATLAS and CMS collaborations provide limits on the production cross section for right-handed sleptons.…”