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Sept. 2, 2015
Image above: Candidate Higgs boson event from collisions in 2012 between protons in the ATLAS detector on the LHC (Image: ATLAS/CERN).
Three years after the announcement of the discovery of a new particle, the so-called Higgs boson, the ATLAS and CMS Collaborations present for the first time combined measurements of many of its properties, at the third annual Large Hadron Collider Physics Conference (LHCP 2015). By combining their analyses of the data collected in 2011 and 2012, ATLAS and CMS draw the sharpest picture yet of this novel boson. The new results provide in particular the best precision on its production and decay and on how it interacts with other particles. All of the measured properties are in agreement with the predictions of the Standard Model and will become the reference for new analyses in the coming months, enabling the search for new physics phenomena. This follows the best measurement of the mass of the Higgs boson, published in May 2015 after a combined analysis by the two collaborations: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.191803
“The Higgs boson is a fantastic new tool to test the Standard Model of particle physics and study the Brout-Englert-Higgs mechanism that gives mass to elementary particles,” said CERN Director General Rolf Heuer. “There is much benefit in combining the results of large experiments to reach the high precision needed for the next breakthrough in our field. By doing so, we achieve what for a single experiment, would have meant running for at least 2 more years.”
Image above: Candidate Higgs boson event from collisions between protons in the CMS detector on the LHC (Image: CMS/CERN).
There are different ways to produce a Higgs boson, and different ways for a Higgs boson to decay to other particles. For example, according to the Standard Model, the theory that describes best forces and particles, when a Higgs boson is produced, it should decay immediately in about 58% of cases into a bottom quark and a bottom antiquark. By combining their results, ATLAS and CMS determined with the best precision to date the rates of the most common decays.
Such precision measurements of decay rates are crucially important as they are directly linked to the strength of the interaction of the Higgs particle with other elementary particles, as well as to their masses. Therefore, the study of its decays is essential in determining the nature of the discovered boson. Any deviation in the measured rates compared to those predicted by the Standard Model would bring into question the Brout-Englert-Higgs mechanism and possibly open the door to new physics beyond the Standard Model.
For a longer version of this article, see the CERN press release: http://press.web.cern.ch/press-releases/2015/09/atlas-and-cms-experiments-shed-light-higgs-properties
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 22 Member States.
Related links:
Large Hadron Collider (LHC): http://home.web.cern.ch/topics/large-hadron-collider
ATLAS experiment: http://home.web.cern.ch/about/experiments/atlas
CMS experiment: http://home.web.cern.ch/about/experiments/cms
The Standard Model: http://home.web.cern.ch/about/physics/standard-model
The Higgs boson: http://home.web.cern.ch/topics/higgs-boson
Brout-Englert-Higgs mechanism: http://home.web.cern.ch/topics/higgs-boson/origins-brout-englert-higgs-mechanism
For more information about the European Organization for Nuclear Research (CERN), visit: http://home.web.cern.ch/
Images (mentioned), Text, Credits: CERN/Matilda Heron.
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