Figure 1: A collision event with a candidate long-lived particle that decays into a pair of muons away from the interaction point, reconstructed in the CMS detector. The yellow lines correspond to the two muons, which are detected only in the muon system. The muon tracks are used to calculate a combined vertex, indicated by the white circle, where the long-lived particle is hypothesised to have decayed. Copyright: CERN/CMS
In a new search, CMS-PAS-EXO-21-006, researchers at HEPHY have scrutinized data of the CMS experiment for signs of pairs of muons produced in the decay of an invisible particle between the proton-proton interaction point and the muon detectors situated in the outermost part of the CMS experiment. The analysis explores hypothesised long-lived dark sector particles such as dark photons with average decay lengths ranging from a few hundredths of a millimetre to several kilometres, which can arise from decays of the known or new heavier species of the Higgs boson. This study was performed in collaboration with physicists from the University of California, Los Angeles.
The results of this search, based on LHC data recorded between 2015-2018, set world leading constraints on the production rate for the hypothesised long-lived dark sector particles. "The results of this search establish the strongest constraints to date for most of the probed dark photon masses and lifetimes in the considered extensions of the Standard Model of particle physics.", says Dr. Alberto Escalante del Valle, leader of the analysis team. However, the quest is not yet over; HEPHY scientists are working on new detection and analysis strategies for the upcoming LHC data taking period (2022-2025) to search for even more experimentally challenging but equally plausible long-lived particles predicted in extensions of the Standard Model.
Read more about this result in the CMS Physics briefing, and for a more detailed description, check out CMS-PAS-EXO-21-006 and CERN-THESIS-2021-281.