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A top quark candidate in the CMS detector. Credit: CMS Collaboration
Top quark pair production cross section measurements compared to the Standard Model predictions as a function of the center-of-mass energy. The new result of the CMS collaboration at 13 TeV is displayed in red and is in agreement with the theory prediction (green band). Credit: CMS Collaboration
CMS experiment publishes first test at new LHC energy of 13 TeV
Shortly after the start of Run 2 at the in June 2015, scientists from DESY and their colleagues from the experiments CMS and ATLAS have performed a first important test of the Standard Model of particle physics at the new energy frontier, using data from proton-proton collisions at higher proton beam energies than ever achieved before. They looked at the production rate of a well-known particle called the top quark to see if it behaves differently at higher collision energies. Their study shows: it doesn’t.
A collision event involving top quarks
The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
Top quarks are the heaviest and among the most puzzling elementary particles. They weigh even more than the Higgs boson discovered in 2012 and might have a special connection to it. To analyse this relation and to test if the top quark is exactly the particle predicted by the current theory, physicists at the LHC perform high-precision measurements of the properties of the top quark.
LHC at CERN
One of the most exciting studies to that respect is to measure the production rate, or cross section, for top quark pairs in the new energy range never explored before because it provides an excellent test of the Standard Model and might give scientists a first glimpse of new physics beyond.
DESY scientists led the effort to measure the top quark pair production cross section at a proton-proton collision energy of 13 TeV. “The results are in good agreement with what we expected. This is a another huge success of the Standard Model,” said Alexander Grohsjean from DESY’s CMS group. The results are presented and discussed this week at the international high energy physics conference “XXVII International Symposium on Lepton Photon Interaction at High Energies”.
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DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.