CERN scientists measure top quark mass with unprecedented accuracy

The researchers analyzed data collected by the Compact Muon Solenoid (CMS) during experiments on

particle collisions at the Large Hadroncollider. The scientists measured the created top quarks using five different kinematic variables sensitive to the mass of the top quark, instead of the three used in previous studies. The inclusion of new variables increased the accuracy of the measurements. Physicists estimated the mass of the top quark to be 171.77 ± 0.38 GeV, an error of about 0.22%.

CERN notes that for measurementsextremely precise calibration of the CMS data and a deep understanding of the remaining experimental and theoretical uncertainties and their interdependencies were required. The researchers have worked out in detail the uncertainties associated with the accuracy of measurements of particle properties by the CMS detector and with theoretical descriptions of the formation of top quarks.

Signature of two quarks: 4 hadron jets (yellow cones), one muon (red line) and missing neutrino energy (pink arrow). Image: CMS, CERN

Researchers note that accurate knowledge of the massThe top quark is essential for understanding our world on a microscale. Getting as close as possible to the mass of this heaviest elementary particle allows us to test the internal consistency of the Standard Model. For example, given the exact masses of the W boson and the Higgs boson, the Standard Model can predict the mass of the top quark, and the mass of the W boson can be determined using the mass of the top quark and the mass of the Higgs boson.

Scientists say that understanding the degreeThe stability of our Universe depends on the exact masses of the Higgs boson and top quark. Current measurements show that the Universe is very close to a metastable state. But if the mass of the top quark is even slightly different, the Universe will be less stable in the long term and potentially end up disappearing in a Big Bang-like event.

The researchers hope to get even better measurement accuracy when the new approach is applied to data from experiments in 2017 and 2018.

Cover image: CMS, CERN

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