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CERN ATLAS observes excited Bc*+ meson, measures 64.5 MeV mass gap.

5/27/2026

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Summary

Story summary

The CERN ATLAS Collaboration observed the excited Bc*+ meson in LHC collisions.
The meson decayed to a Bc+ and a photon, detected via conversion to an electron-positron pair with 100 MeV momentum.
The measured mass difference between Bc*+ and Bc+ is 64.5 ± 1.4 MeV, within expectations but slightly off high-precision calculations.
The Bc+ decays into a muon, two antimuons and a neutrino, a channel about twenty times more common than other modes.

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Story summary

The CERN ATLAS Collaboration observed the excited Bc*+ meson in LHC collisions.
The meson decayed to a Bc+ and a photon, detected via conversion to an electron-positron pair with 100 MeV momentum.
The measured mass difference between Bc*+ and Bc+ is 64.5 ± 1.4 MeV, within expectations but slightly off high-precision calculations.
The Bc+ decays into a muon, two antimuons and a neutrino, a channel about twenty times more common than other modes.