ATLAS Observes B c *+ Meson, Measuring 64.5 MeV Mass Gap

1 articles · Updated · Sci.News · May 25

ATLAS physicists at CERN’s Large Hadron Collider identified the excited B c *+ meson and measured its mass difference from the B c + meson at 64.5 ± 1.4 MeV.
The signal came from B c *+ decays into a B c + meson and a very low-energy photon, which ATLAS tracked indirectly after the photon converted into an electron-positron pair.
Tracks with transverse momenta as low as 100 MeV required a dedicated reconstruction procedure because the photon was too soft for standard ATLAS photon-identification methods.
The result falls within existing theoretical expectations but deviates somewhat from the latest high-precision calculations, giving theorists new data on heavy-quark systems and the strong force.
Physics Review Letters will publish the work, which ATLAS says should help refine models of hadrons containing charm and bottom quarks.

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