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November 13, 2014
The highlight of the first run of the Large Hadron Collider (LHC) was undoubtedly the discovery by the ATLAS and CMS Collaborations of a new elementary particle of a type never seen before. All the properties of this particle measured so far are consistent with those predicted for the Higgs boson of the Standard Model. It was predicted to have zero spin (angular momentum), and every alternative option tested has by now been ruled out with a high degree of confidence. It was predicted to couple with other particles proportionally to their masses, and this is strongly supported by the data. This is why the committee that awarded the 2013 Nobel Physics Prize to Francois Englert and Peter Higgs stated “Beyond any reasonable doubt, it is a Higgs boson.”
Image above: An artist’s approximation of a collision of two protons that produce a Higgs boson. Image Credit: CERN.
Physicists are now asking themselves follow-up questions. Is there any difference between its properties and those predicted in the Standard Model? Is it the only Higgs boson, or are there others? Many of its couplings to other particles have been measured, but what about its coupling to the heaviest known particle, the top quark? Or its couplings to lighter particles like the muon? What gives its mass to this Higgs boson? Is it truly an elementary particle, or is it made of some smaller constituents? Is it a portal to some new physics beyond the Standard Model, such as dark matter?
The next run of the LHC, starting in the spring of 2015, will set about answering some of these questions. For example, its higher energy will enable the LHC experiments to probe more deeply for deviations from the Standard Model predictions, and to search for heavier Higgs bosons. It will be possible to measure directly this Higgs boson's coupling to the top quark, and to box in its possible coupling to the muon. These measurements may reveal some substructure inside this Higgs boson, or provide some other evidence for physics beyond the Standard Model. Time will tell!
Note:
CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.
The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.
Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 20 Member States.
Related links:
Large Hadron Collider (LHC): http://home.web.cern.ch/topics/large-hadron-collider
ATLAS: http://home.web.cern.ch/about/experiments/atlas
CMS: http://home.web.cern.ch/about/experiments/cms
Standard Model: http://home.web.cern.ch/about/physics/standard-model
The basics of the Higgs boson: http://home.web.cern.ch/about/updates/2013/05/basics-higgs-boson
The origins of the Brout-Englert-Higgs mechanism: http://home.web.cern.ch/topics/higgs-boson/origins-brout-englert-higgs-mechanism
Image, Text, Credits: CERN/John Ellis.
Cheers, Orbiter.ch