What has happened since the groundbreaking discovery of the Higgs boson at CERN’s Large Hadron collider in 2012?
Did physicists find what they expected, a Higgs boson which behaves as predicted? Or did they uncover deviations from the predicted properties, which could indicate the existence of new particles or forces that interact with the Higgs boson, or even additional Higgs boson species?
At the 53rd annual Rencontres de Moriond conference taking place in March 2018 in Italy, researchers from the ATLAS and CMS experiments, the experiments with which the Higgs boson was discovered, unveiled results from new measurements of the properties of the Higgs boson.
These results came from the examination of data from proton-proton collisions at an energy of 13 TeV that the LHC recorded in 2015 and 2016. The measurement data whose elaborate analysis led to the discovery of the Higgs boson had been taken in 2011 and 2012 during the first run of the LHC. After the discovery of the Higgs boson, no further particle collisions took place in the years 2013 and 2014 at the LHC.
Since the beginning of the second run of the LHC in 2015, the particles were brought to collision with significantly higher energies of up to 13 TeV. In that time the luminosity of the accelerator could be increased successively beyond the initial expectations defined by the original designs for the LHC. Following the discovery, the properties of the Higgs boson can be probed more precisely with data taken at 13 TeV.
The ATLAS Collaboration has released new studies of the Higgs boson using 13 TeV data collected in 2015 and 2016. The results further corroborate the standard model nature of the Higgs boson, and open doors to fresh searches for new physics.
“ATLAS is moving beyond the more straightforward Higgs boson analyses,” says ATLAS Higgs working group convener, Fabio Cerutti. “The abundance of Run 2 data has allowed us to study the Higgs boson in rare and experimentallychallenging interactions, and examine its properties with improved precision. Not only are we learning more about the standard model, we are challenging the limits of the theory, providing measurements of comparable precision.”
By analysing more than 36,000 trillion collisions recorded in 2015 and 2016, the properties of the Higgs boson have been probed more precisely than ever.
CMS and ATLAS studied the various processes through which the Higgs bosons are produced in proton-proton collisions and the different transformations they subsequently undergo. Their observations demonstrated good agreement with the theoretical predictions from the standard model of particle physics.
In a new result presented at the Rencontres de Moriond, the ATLAS collaboration examined the Higgs boson decaying into two W bosons, the charged force carriers of the weak interaction. The W bosons from the Higgs boson decay are unstable and immediately decay to lighter particles. The number of Higgs bosons counted by ATLAS that followed these production-and-decay paths is in strong agreement with the number expected according to the standard model. ATLAS also combined data from the two Higgs decay channels to pairs of photons and to pairs of Z bosons.