An observation made by the CMS experiment at CERN unambiguously demonstrates the interaction of the Higgs boson and top quarks, which are the heaviest known subatomic particles. This major milestone is an important step forward in our understanding of the origins of mass. Physicists at the University of Zurich made central contributions by incorporating sophisticated data analysis methods that allowed this benchmark to be reached much earlier than expected.
On 4 July 2012, two of the experiments at the CERN’s Large Hadron Collider (LHC), ATLAS (A Toroidal LHC ApparatuS) and CMS (Compact-Muon-Solenoid), reported independently the discovery of the Higgs boson.
The discovery confirmed the existence of the last missing elementary particle of the Standard Model, half a century after the Higgs boson was predicted theoretically. At the same time the discovery marked also the beginning of an experimental programme aimed to determine the properties of the newly discovered particle. Now, the CMS collaboration achieved an important milestone in that programme.
Higgs boson and top quark-antiquark pair produced
In the Standard Model, the Higgs boson can couple to the particles of matter called fermions, with a coupling strength proportional to the fermion mass. While associated decay processes have been observed, the decay into top quarks, the heaviest known fermions, is kinematically impossible.
Therefore, alternative routes for directly probing the coupling of the Higgs boson to the top quark are needed. One is through the production of a Higgs boson and a top quark-antiquark pair. This is the production mechanism that has now been observed for the first time, and in doing so, the CMS collaboration accomplished one of the primary objectives of the Higgs physics programme.
New techniques speed up data extraction
The extraction of these events from the LHC data is challenging as there are many mundane type of events that can mimic them. Identifying these events requires measurements from all CMS subdetectors, which makes the reconstruction quite complex.
The team of Prof. Florencia Canelli of the Department of Physics at the University of Zurich developed, in collaboration with the CMS group of the ETH, sophisticated techniques that allowed CMS to increase the sensitivity to these events. As consequence, this milestone has been passed considerably earlier than expected. «The development of these techniques also open the possibility of increasing the sensitivity in many other areas of research at the LHC», says Canelli, who is also co-leading the physics group that studies top quarks.
Search for physics beyond the Standard Model
The present achievement is a case in point. With the observation of the coupling between the two heaviest elementary particles of the Standard Model, the LHC physics programme to characterize and more fully understand the Higgs boson has taken an important step.
While the strength of the measured coupling is consistent with the Standard Model expectation, the precision of the measurement still leaves room for contributions from new physics. «In the coming years, much more data will be collected and the precision will be improved, in order to see if the Higgs boson reveals the presence of physics beyond the Standard Model», adds Florencia Canelli.
A. M. Sirunyan et al. (CMS Collaboration). Observation of t¯tH Production. Physical Review Letters. June 4, 2018. DOI: 0.1103/PhysRevLett.120.231801
Prof. Dr. Florencia Canelli
Department of Physics
University of Zürich
Phone: +41 44 635 57 84
Kurt Bodenmüller | Universität Zürich
The magic wavelength of cadmium
16.09.2019 | University of Tokyo
Tomorrow´s coolants of choice
16.09.2019 | Helmholtz-Zentrum Dresden-Rossendorf
Researchers from the Department of Atomically Resolved Dynamics of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Hamburg and the European Molecular Biology Laboratory (EMBL) outstation in the city have developed a new method to watch biomolecules at work. This method dramatically simplifies starting enzymatic reactions by mixing a cocktail of small amounts of liquids with protein crystals. Determination of the protein structures at different times after mixing can be assembled into a time-lapse sequence that shows the molecular foundations of biology.
The functions of biomolecules are determined by their motions and structural changes. Yet it is a formidable challenge to understand these dynamic motions.
At the International Symposium on Automotive Lighting 2019 (ISAL) in Darmstadt from September 23 to 25, 2019, the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, a provider of research and development services in the field of organic electronics, will present OLED light strips of any length with additional functionalities for the first time at booth no. 37.
Almost everyone is familiar with light strips for interior design. LED strips are available by the metre in DIY stores around the corner and are just as often...
Later during this century, around 2060, a paradigm shift in global energy consumption is expected: we will spend more energy for cooling than for heating....
Researchers from the Department of Atomically Resolved Dynamics of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Potsdam (both in Germany) and the University of Toronto (Canada) have pieced together a detailed time-lapse movie revealing all the major steps during the catalytic cycle of an enzyme. Surprisingly, the communication between the protein units is accomplished via a water-network akin to a string telephone. This communication is aligned with a ‘breathing’ motion, that is the expansion and contraction of the protein.
This time-lapse sequence of structures reveals dynamic motions as a fundamental element in the molecular foundations of biology.
Two research teams have succeeded simultaneously in measuring the long-sought Thorium nuclear transition, which enables extremely precise nuclear clocks. TU Wien (Vienna) is part of both teams.
If you want to build the most accurate clock in the world, you need something that "ticks" very fast and extremely precise. In an atomic clock, electrons are...
10.09.2019 | Event News
04.09.2019 | Event News
29.08.2019 | Event News
17.09.2019 | Materials Sciences
17.09.2019 | Health and Medicine
17.09.2019 | Ecology, The Environment and Conservation