Upper-case "H", lower-case "b".

Avoid the tautology "Higgs-boson particle". A boson is a particle; there is no need to repeat yourself. 

Named after the English physicist Peter Higgs, the Higgs boson is a subatomic particle whose existence is predicted by the theory that unified the weak and electromagnetic interactions.

The particle provides a mechanism called the Brout-Englert-Higgs mechanism to explain how subatomic particles get mass: they interact with the Higgs field. On 4 July 2012, the ATLAS and CMS experiments at CERN announced that they had each observed a new particle consistent with the Higgs boson at a mass of around 126 gigaelectronvolts (GeV).