Today at CERN joint seminars were given by the two major experiments (ATLAS and CMS) at the Large Hadron Collider (LHC) in which they announced the observation of a new particle that could be the Higgs Boson. The mass of this particle is 126 GeV, roughly that of a Barium atom. The level of statistical significance of the new particle is five standard deviations, which is general considered the threshold level of observation needed to make a claim of discovery. Higgs Boson has been long sought to complete the Standard Model of Particle Physics. The Brandeis High Energy Physics Group, along with many colleagues from around the world, has been working for the last 18 years designing, building, commissioning, running and analyzing data from the ATLAS experiment (at CERN).
The Standard Model of Particle Physics is our best understanding of the laws of nature that govern the behavior of all the things in the universe that we can see. One outstanding question in this theory has been: “where does mass come from?”. One proposed solution to this problem (by Peter Higgs) was the addition a field to our picture of the universe that adds a drag on each particle, different for each kind of particle, which we interpret as inertia or mass. This theory predicts a new particle, the Higgs Boson. Finding this particle is considered proof of this version of the standard model. One comment on “physics speak”, a particle being “consistent with the Higgs Boson” is not the same as “discovery of the Higgs Boson”. The predicted properties of this particle are very specific and much more work needs to be done to establish the exact nature of this new object. Is it the object that completes that Standard Model or is it a slightly different object that will point to a new direction in the understanding of nature? This question will be hotly pursued in the future running of the experiments.
On a local note, in a more technical vein; one of the two decay modes that were used by the ATLAS experiment to look for the Higgs Boson decays into four leptons, either four muons or four electrons or two of each. The electron and muon being two of the three leptons (meaning these particles don’t participate in the strong or nuclear force) of the Standard Model. The Brandeis HEP group has been instrumental in the design, construction and operation of the system that identifies and measures muons produced in the collisions at the LHC.
July 4, 2012
editor’s note: see also interview at Brandeis NOW