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Most frequent decay of the Higgs particle detected

Working group at the University of Freiburg has made contributions to the latest ATLAS experiment findings

Freiburg, Aug 29, 2018

Most frequent decay of the Higgs particle detected

A Higgs boson breaks down into two bottom quarks (blue, cone-shaped). Source: CERN

As part of the ATLAS collaboration, a Freiburg working group of experimental particle physics headed by Dr. Christian Weiser has helped demonstrate the decay of the Higgs particle into so-called bottom quarks. The researchers analyzed data sets that were recorded between 2015 and 2017 using the ATLAS detector at the world’s largest particle accelerator, the Large Hadron Collider (LHC) at the European Organization for Nuclear Research CERN in Geneva, Switzerland. “The unequivocal proof of the decay of the Higgs particle in quarks is an extremely important step in understanding this particle,” says Weiser. “This confirms that also quarks get their mass through the Higgs mechanism. The goal now is to more accurately measure the properties of the Higgs particle in this decay process.” Accurate measurements are important, according to the researchers, because measurable deviations from the predictions of standard theory point to (a) so-called new physics beyond this standard model.

The discovery of the Higgs particle by the ATLAS and CMS experiments at the LHC accelerator in 2012 represented a milestone in physics, as the existence of this particle was predicted almost 50 years earlier. The Higgs is a short-lived particle that decays into other particles almost immediately after its production. The frequency with which these decays occur can be calculated using the underlying theory. So far, scientists have unequivocally detected decays into other particles - so-called W and Z bosons, photons and tau leptons. Thus far, the researchers have not been able to observe the decay into a pair of bottom quarks, which should occur with a probability of almost 60 percent most frequently. The reason is that there is a variety of other processes that are difficult to distinguish from decays of the Higgs particle into bottom quarks and occur at a much higher rate. Only through the analysis of the largest data sets available could this decay be clearly distinguished from background processes by reconstruction of the decay products. As a further result, the researchers demonstrated a special production process - the so-called associated production of the Higgs particle with a W or Z boson - which the scientists also unambiguously observed for the first time.

The presentation of these results was one of the highlights of the International Conference on High Energy Physics, which took place July 4-11, 2018 in Seoul, South Korea. The simultaneous publications of the ATLAS and CMS collaborations will be accompanied by a special seminar at CERN. In addition to the Freiburg scientists, other German groups within the collaborative research of the Federal Ministry of Education and Research were involved in these findings.


CERN press release

Federal Ministry of Education and Research press release (German only)


Dr. Christian Weiser
Institute of Physics
University of Freiburg
Tel.: 0761/203-5753