At the world’s most powerful particle physics accelerator, physicists have confirmed the existence of the Higgs boson in the highest energy proton collisions conducted at the facility to date. The Higgs boson is the particle associated with a force field that couples to, or interacts with, other elementary particles. The strength of this coupling is what determines each particle’s mass.
The Higgs particle “signature” the scientists working on the international ATLAS experiment observed is consistent with earlier results from lower energy collisions. It is also consistent with scientists’ expectations of how this particle decays. The new results help build the data sets to explore the particles’ properties. The discovery paves the way to answer fundamental questions about how our universe works and to search for physics beyond the Standard Model, the theory that describes the fundamental building blocks of nature and the forces through which they interact.
The 2012 discovery of a Higgs boson by two of the Large Hadron Collider’s (LHC’s) experiments—ATLAS (for A Toroidal LHC Apparatus) and CMS (the Compact Muon Solenoid)—was a significant achievement for high-energy physics. This short-lived particle, which transforms into a cascade of other more stable particles immediately after it is produced, was the last remaining undiscovered particle predicted by the Standard Model. According to the Standard Model, the Higgs boson is associated with a force field that generates the masses of all elementary particles.
Scientists searched for the Higgs boson by looking for signs of its more stable decay products. The first round of experiments that showed definitive signs of these decay products (photons, W bosons, and Z bosons) came from collisions of protons at center-of-mass energy of 7 and 8 trillion electron volts (TeV). Since 2015, the LHC has been running at 13 TeV center-of-mass energy, producing collisions about 1.6 times more energetic, allowing rare particles such as the Higgs boson to be produced more copiously. At the 38th International Conference on High Energy Physics held in Chicago August 3-10, 2016, the ATLAS collaboration presented new results related to the production of Higgs bosons that are consistent with the Standard Model expectations for the rate of Higgs boson production and decay in these more energetic collisions. It was important to verify the rate of production as a function of the colliding protons’ center-of-mass energy to test whether the signal seen at lower energies increases with energy as expected. Any significant deviation in the rate could signal new physics. This decay channel is also an excellent place to search for possible production of heavier particles that exist beyond the Standard Model. Such particles have been predicted by theoretical models but have yet to be discovered.