The Large Hadron Collider beauty (LHCb) experiment at CERN today announced that it has observed two new excited states of the Λb beauty baryon. Though the Standard Model of particle physics predicts the existence of these new states, this is the first time they have been confirmed in an experiment.

Baryons are subatomic particles whose mass is equal to or greater than that of a proton. Like protons and neutrons, the Λb beauty baryon is composed of three quarks. In Λb these are up, down and beauty quarks.

LHCb physicists found the signals for the Λb particlesin a sample of about 60 trillion proton—proton collisions which were delivered by the LHC operating at a centre-of-mass energy of 7 TeV in 2011. They measured the masses of the new excited states as 5912 MeV/c2 and 5920 MeV/c2 respectively - over five times greater than the mass of a proton or neutron.

The result adds to a growing list of discoveries at CERN in recent months. Last month the Compact Muon Solenoid (CMS) experiment observed a new excited state for the Ξb beauty baryon, and back in December 2011 ATLAS detected a new "quarkonium state" containing a beauty quark bound with its antiquark.

The new excited states show clear signals at masses of 5912 MeV/c2 and 5920 MeV/c2 (Image: LHCb collaboration)