For the first time, researchers at CERN have found evidence for the direct decay of the Higgs boson into fermions – another strong indication that the particle discovered in 2012 behaves in the way the standard model of particle physics predicts. Researchers from the University of Zurich made a significant contribution to the study published in Nature Physics.
For the first time, scientists from the CMS experiment on the Large Hadron Collider (LHC) at CERN have succeeded in finding evidence for the direct decay of the Higgs boson into fermions. Previously, the Higgs particle could only be detected through its decay into bosons.
“This is a major step forwards,” explains Professor Vincenzo Chiochia from the University of Zurich’s Physics Institute, whose group was involved in analyzing the data. “We now know that the Higgs particle can decay into both bosons and fermions, which means we can exclude certain theories predicting that the Higgs particle does not couple to fermions.” As a group of elementary particles, fermions form the matter while bosons act as force carriers between fermions.
According to the standard model of particle physics, the interaction strength between the fermions and the Higgs field must be proportional to their mass. “This prediction was confirmed,” says Chiochia; “a strong indication that the particle discovered in 2012 actually behaves like the Higgs particle proposed in the theory.”
Combined data analysis
The researchers analyzed the data gathered at the LHC between 2011 and 2012, combining the Higgs decays into bottom quarks and tau leptons, both of which belong to the fermion particle group. The results reveal that an accumulation of these decays comes about at a Higgs particle mass near 125 gigaelectron volts (GeV) and with a significance of 3.8 sigma. This means that the probability of the background alone fluctuating up by this amount or more is about one in 14,000. In particle physics, a discovery is deemed confirmed from a significance of five sigma.
Measuring the Higgs decay modes
Three different processes were studied, whereby the UZH researchers analyzed the Higgs decay into taus. Because the Higgs particle is extremely short-lived, it cannot be detected directly, but rather only via its decay products. The bottom quarks and taus, however, have a long enough lifetime to be measured directly in the CMS experiment’s pixel detector.
The University of Zurich and the Large Hadron Collider
The University of Zurich is actively involved in the LHC at CERN with five experimental research groups: The groups headed by professors Florencia Canelli, Vincenzo Chiochia and Ben Kilminster conduct research with the CMS detector, Professors Ulrich Straumann’s and Nicola Serra’s groups with the LHCb detector. For the analysis and interpretation of the data, they are supported by the groups under professors Thomas Gehrmann, Stefano Pozzorini, Gino Isidori and PD Dr. Massimiliano Grazzini.
The CMS detector at CERN
The CMS detector measures the energy and impulse of photons, electrons, muons and other charged particles with high precision. Different measuring instruments are arranged in tiers inside the 12,500-ton detector. 179 institutions worldwide are involved in the construction and operation of the CMS detector. The Swiss institutions are the University of Zurich, ETH Zurich and the Paul Scherrer Institute, which jointly developed and constructed the CMS pixel detector.
The CMS Collaboration. «Evidence for the direct decay of the 125 GeV Higgs boson to fermions», Nature Physics Online. DOI: 10.1038/nphys3005
Prof. Vincenzo Chiochia
Physics Institute of the University of Zurich
Tel. + 41 22 767 60 41
Mobile: +41 76 487 57 50
University of Zurich
Tel. +41 44 634 44 39
Bettina Jakob | Universität Zürich
LIGO confirms RIT's breakthrough prediction of gravitational waves
12.02.2016 | Rochester Institute of Technology
Milestone in physics: gravitational waves detected with the laser system from LZH
12.02.2016 | Laser Zentrum Hannover e.V.
Today, plants and microorganisms are heavily used for the production of medicinal products. The production of biopharmaceuticals in plants, also referred to as “Molecular Pharming”, represents a continuously growing field of plant biotechnology. Preferred host organisms include yeast and crop plants, such as maize and potato – plants with high demands. With the help of a special algal strain, the research team of Prof. Ralph Bock at the Max Planck Institute of Molecular Plant Physiology in Potsdam strives to develop a more efficient and resource-saving system for the production of medicines and vaccines. They tested its practicality by synthesizing a component of a potential AIDS vaccine.
The use of plants and microorganisms to produce pharmaceuticals is nothing new. In 1982, bacteria were genetically modified to produce human insulin, a drug...
Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock which attains an accuracy which had only been predicted theoretically so far. Their optical ytterbium clock achieved a relative systematic measurement uncertainty of 3 E-18. The results have been published in the current issue of the scientific journal "Physical Review Letters".
Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock...
The University of Würzburg has two new space projects in the pipeline which are concerned with the observation of planets and autonomous fault correction aboard satellites. The German Federal Ministry of Economic Affairs and Energy funds the projects with around 1.6 million euros.
Detecting tornadoes that sweep across Mars. Discovering meteors that fall to Earth. Investigating strange lightning that flashes from Earth's atmosphere into...
Physicists from Saarland University and the ESPCI in Paris have shown how liquids on solid surfaces can be made to slide over the surface a bit like a bobsleigh on ice. The key is to apply a coating at the boundary between the liquid and the surface that induces the liquid to slip. This results in an increase in the average flow velocity of the liquid and its throughput. This was demonstrated by studying the behaviour of droplets on surfaces with different coatings as they evolved into the equilibrium state. The results could prove useful in optimizing industrial processes, such as the extrusion of plastics.
The study has been published in the respected academic journal PNAS (Proceedings of the National Academy of Sciences of the United States of America).
Exceeding critical temperature limits in the Southern Ocean may cause the collapse of ice sheets and a sharp rise in sea levels
A future warming of the Southern Ocean caused by rising greenhouse gas concentrations in the atmosphere may severely disrupt the stability of the West...
12.02.2016 | Event News
09.02.2016 | Event News
02.02.2016 | Event News
12.02.2016 | Physics and Astronomy
12.02.2016 | Life Sciences
12.02.2016 | Medical Engineering