Physicists set strictest limits yet on exotic particle decay
Researchers using the Large Hadron Collider found no evidence that Z bosons decay into mismatched lepton pairs—a process that would violate fundamental physics rules. The null result, with record-breaking sensitivity, constrains theories of new particles and physics beyond the Standard Model that could reshape how companies develop quantum technologies and materials.
Originaltitel: Search for charged lepton flavor violating 𝑍 and 𝑍′ boson decays in proton-proton collisions at √𝑠 =13 TeV
<p>A search for flavor violating decays of the 𝑍 boson to charged leptons is performed using data from proton-proton collisions at √𝑠 =13 TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb−1. Each of the decays 𝑍 →𝑒𝜇, 𝑍 →𝑒𝜏, and 𝑍 →𝜇𝜏 is considered. The data are consistent with the backgrounds expected from standard model processes. For the 𝑍 →𝑒𝜇 channel the observed (expected) 95% confidence level upper limit on the branching fraction is 1.9(2.0) ×10−7, which is the most stringent direct limit to date on this process; the corresponding limits for the 𝑍 →𝑒𝜏 and 𝑍 →𝜇𝜏 channels are 13.8(11.4) ×10−6 and 12.0(5.3) ×10−6, respectively. Additionally, the 𝑒𝜇 final state is used to search for lepton flavor violating decays of 𝑍′ resonances in the mass range from 110 to 500 GeV. No significant excess is observed above the predicted background levels.</p>