Interaction between top quark and Higgs boson observed for the first time
Elementary particle physicists of the University of Göttingen involved in research at CERN
Experimental physicists of the ATLAS and CMS collaborations at the Large Hadron Collider (LHC) at CERN in Geneva discovered in 2012 the Higgs boson that gives mass to the other particles. Since then, they are busy to unravelling how this interaction exactly happens. For the first time they now directly observed the production of the heaviest of all elementary particles, the top quark, simultaneously with the Higgs boson. A group from the University of Göttingen played an important role in the analysis.
During a proton-proton collision in the LHC many different particles are produced, very rarely two top quarks in association with a Higgs. Its interaction can only be spotted and proven by the telltale particles produced in their decays. “The top decays into a W boson and a b quark and the Higgs decays further into for example two photons, four leptons, or a b quark and an anti-b quark”, says Göttingen physicist Prof Arnulf Quadt.
His group concentrated on finding events in which two b quarks were produced in the final state. “The observation enables us to study the direct interaction between the Higgs boson and the two most massive quarks. Our analysis as well as all others at LHC verify the Standard Model of elementary particles,” Quadt explains. The Standard Model is the theory that explains the properties of particles and how they interact with each other. “We can now have a close look and check whether we see anything unexpected,” says Göttingen scientist Elizaveta Shabalina, leader of the ATLAS top-quark physics group and former leader of the top-Higgs group.
During the last years, students and scientists of the II. Physics Institute at the University of Göttingen contributed key developments to the search for the associated top-Higgs production. Examples are a kinematic likelihood fitter and sophisticated statistical techniques, the optimisation of b-jet identification, kinematic calibration and background suppression or estimation techniques. The top-Higgs group in the ATLAS collaboration was lead for several years by scientists or former PhD students from Göttingen. In Germany, the research is funded by the Federal Ministry of Science and Education.
Prof. Arnulf Quadt
Faculty of Physics – II. Physics Institute
Friedrich-Hund-Platz 1, 37077 Göttingen