A first sighting of the Higgs boson decay to quarks with the ATLAS experiment at the Large Hadron Collider

A comparison of the excess of collision data (black points) over the background processes (which have been subtracted from the data),  which clearly shows the H→bb decays (filled red area) and the well understood diboson Z→bb decay (grey area) used to validate the result.  (Image: ATLAS Collaboration/CERN)
A comparison of the excess of collision data (black points) over the background processes (which have been subtracted from the data), which clearly shows the H→bb decays (filled red area) and the well understood diboson Z→bb decay (grey area) used to validate the result. (Image: ATLAS Collaboration/CERN)

ISU News Service Article

Since its discovery in 2012, the Higgs boson had been observed decaying to pairs of photons, tau-leptons, and W and Z bosons. However, these decays represent only 30% of all Higgs boson decays! The Higgs boson’s favored decay to a pair of b-quarks (H→bb), which is predicted to happen around 58% of the time, had so far remained elusive. The observation of this decay would establish the role of the Higgs boson in giving mass to quarks. Unfortunately, such an observation is extremely challenging as the Large Hadron Collider (LHC) produces pairs of b-quarks 10 million times more frequently through processes not involving the Higgs boson than actual Higgs bosons.

After analyzing the data collected in 2015 and 2016, the ATLAS experiment have finally reached the level of precision where we can say we’ve evidence for the Higgs boson decay to a b-quark pair, with an observed significance of 3.6 standard deviations. Together with their ATLAS colleagues, the researchers (Prof. Chunhui Chen, Prof. Soeren Prell, postdoc Jie Yu and graduate student Carlos Vergel-Infante) from the ATLAS group at Iowa State University made a significant contribution to the discovery. The work has been reported at the 2017 European Physical Society conference on High Energy Physics in Venice (Italy) and subsequently submitted to the Journal of High-Energy Physics for publication. The ISU ATLAS group is continuing their research with additional data from the LHC in order to study in greater detail the properties of the H→bb decay.