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Nov. 6, 2022
On 5 July, the LHC roared to life for its third run after three years of continual improvements to the machine as well as to the experiments’ detectors and analysis tools, and immediately reached a record energy of 13.6 TeV. Just three weeks later, the CMS collaboration was ready for its physics data-taking period.
Run 3 event display by CMS showing the top-quark pair decay (Image: CERN)
The CMS collaboration recently presented its first Run 3 physics results of the production rate of pairs of the heaviest elementary particle, the top quark. In just one week, from 28 July to 3 August, the CMS collaboration collected data equivalent to almost 12% of the data set that had been required for the Higgs boson discovery in 2012.
Before Run 3 began, it was hoped – and has now been confirmed — that it would be possible to gather such a vast amount of data in a very short time. It took physicists two years to collect the data used to announce the Higgs boson discovery in 2012. But now, thanks to developments in data acquisition and selection systems and to the unprecedented speed of the analyses, the Run 3 data can now be analysed in almost real time.
Due to the high number of top-quark pairs created at the LHC, physics analysis can start with even a small amount of data. The production rate of this heavy system of particles has been enhanced by about 10% thanks to the collision energy increase from 13 TeV in Run 2 to 13.6 TeV in Run 3. The CMS results, which agree with the Standard Model prediction, are important because precise measurements of top-quark properties provide, among other things, crucial input for various searches for new phenomena in Run 3. Because of its high mass, the top quark decays immediately to a b quark and a W boson, which is also an unstable particle. The decay products leave traces as they pass through the detector, making it possible to observe them and to test the detector performance.
Precision measurements of the Standard Model are an essential part of the Run 3 programme, as any significant deviation could hint at new physics. The measurement of top-quark pair production rate is only the first step into the unexplored territory of the new energy regime, where answers to fundamental physics questions may be found.
Note:
CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.
The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.
Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 23 Member States.
Related links:
Run 3: https://home.cern/press/2022/run-3
CMS experiment: https://home.cern/science/experiments/cms
Higgs boson: https://home.cern/science/physics/higgs-boson
W boson: https://home.cern/science/physics/w-boson-sunshine-and-stardust
Standard Model: https://home.cern/science/physics/standard-model
For more information about European Organization for Nuclear Research (CERN), Visit: https://home.cern/
Image (mentioned), Text, Credits: CERN/By Kristiane Bernhard-Novotny.
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