CMS discovers new particle – Meet the Ξb beauty baryon

The Compact Muon Solenoid (CMS) experiment at CERN has submitted a paper for publication describing the first observation of a new fundamental particle, an excited beauty baryon called the Ξb (pronounced "Sai - bee").

Baryons are subatomic particles whose mass is equal to or greater than that of a proton. The Standard Model of particle physics predicts the existence of Ξb baryons in charged, neutral or excited states. Though charged and neutral Ξb baryons have been seen in detectors before, this is the first time an excited Ξb beauty baryon has been observed. CMS measured the mass of the new particle to be 5945.0 ± 2.8 MeV.

CMS physicists found the Ξb signal in a sample of about 530 trillion proton—proton collisions (an integrated luminosity of 5.3 inverse femtobarns) which were delivered by the Large Hadron Collider (LHC) operating at a centre-of-mass energy of 7 TeV in 2011.

The Ξb adds to a growing list of discoveries at CERN in recent months. In December the ATLAS experiment announced the observation of a new "quarkonium state" containing a beauty quark bound with its antiquark, and in November the LHCb experiment reported a new effect in the decays of particles containing a charm quark (or antiquark).

With the LHC now running at 4TeV per beam, the collision number is set to increase, which enhances the machine's discovery potential considerably, and opens up new possibilities for searches for new and heavier particles.