Research
Photons in light rays do no crosstalk
Why can we see each other? Because light rays intersect without scattering! At the time of Huygens almost 400 years ago, this led to the wave theory of light. Today we know that light consists of photons that interact only with objects carrying electrical charge. Since photons themselves are electrically neutral, they simply move through each other. Lightsabers will remain science fiction.
Candidate of a W± W± -> W± W± event in the ATLAS detector with two muons of equal electric charge (red) and missing transient momentum (cyan) of the neutrinos from the W decays, as well as two particle jets (yellow) emerging from the initial quarks.
In the extremely short-range weak interaction, in contrast to the electromagnetic interaction, the messenger particles W and Z scatter from one another, because they have weak charge themselves. For observing this scattering in proton-proton collisions at the Large Hadron Collider (LHC) at CERN, coincidentally one quark in each proton must emit a W or Z at the same time and these in turn have to come closer than 1/1000 of a proton diameter to interact.
In 2014, our group was able to observe for the first time the process W± W± -> W± W± using the ATLAS detector at the LHC, and in 2016 the first indications of the scattering of WZ -> WZ were detected.
In the Standard Model the "Lagrange Density", the energy density of the quantum fields in the Universe, predicts all possible particle interactions. It is uniquely determined by symmetries. Each term on the cup describes a specific class of processes via vertices in Feynman diagrams. With our research, it is possible for the first time to examine the red-framed vertex of the "quartic coupling" between four W particles.
With this scattering, for the first time the so far unexplored "quartic gauge coupling" between four W or Z particles is measured and its prediction from the Standard Model can be checked. Since the exchange of Higgs particles significantly dampens the scattering, the measured attenuation will also yield new insights into the Brout-Englert-Higgs field breaking the electroweak symmetry of our universe. The field could e.g. have new, so far unknown excitations, or the Higgs particle, discovered in 2012, could have a sub-structure of further particles. With the new data of the LHC "Run 3" from 2022-2026 at highest energies we want to find out more.
To investigate this further, our group has been part of the EU-COST-Network "VBScan" from 2017 to 2021, where scientists from the ATLAS and CMS experiments and the Theoretical Particle Physics worked together throughout Europe. Since 2023, the successor network COMETA is running within COST, which in addition includes artificial intelligence experts from outside particle physics.
On the two subpages you can find more about the scientific results of this research as well as a complete List of publications, lectures or theses of the group members.
The first observation of the process W± W± -> W± W± in 2014 received a lot of attention in Germany and worldwide:
- First evidence for scattering of W bosons (FSP-101 ATLAS)
- For the first time observed scattering of W bosons (Weltmaschine.de)
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Physicists Detect Process Even Rarer than the Long-Sought Higgs Particle (Interactions.org)
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Had there been no Higgs boson, this observation would have been the bomb
(science.org)
In 2025, a detailed analysis of all data from “Run 2” (2015–2018) revealed, for the first time, longitudinal polarization components that allow conclusions to be drawn about the role of the Higgs boson. This also generated significant attention both nationally and internationally: