The CMS collaboration has recently presented new results in searches for long-lived heavy neutral leptons (HNLs). Also known as “sterile neutrinos”, HNLs are interesting hypothetical particles that could solve three major puzzles in particle physics: they could explain the smallness of neutrino masses via the so-called “see-saw” mechanism, they could explain the matter-antimatter asymmetry of the universe, and at the same time they could provide a candidate for dark matter.
They are however very difficult to detect since they interact very weakly with known particles. The current analysis is an example of researchers having to use increasingly creative methods to detect particles that the detectors were not specifically designed to measure.
Most of the particles studied in the large LHC experiments have one thing in common: they are unstable and decay almost immediately after being produced. The products of these decays are usually electrons, muons, photons and hadrons—well-known particles that the big particle detectors were designed to observe and measure.
Studies of the original short-lived particles are performed based on careful analysis of the observed decay products. Many of the flagship LHC results were obtained this way, from the Higgs boson decaying into photon pairs and four leptons to studies of the top quark and discoveries of new exotic hadrons.
The HNLs studied in this analysis require a different approach. They are neutral particles with comparatively long lifetimes that allow them to fly for meters undetected, before decaying somewhere in the detector. The analysis presented here focuses on cases where an HNL would appear after the decay of a W boson in a proton-proton collision, and would then itself decay somewhere in the muon system of the CMS detector.
2023-07-30 08:00:04
Original from phys.org rnrn
