First direct observation of the dead-cone effect in particle physics

The dead-cone effect is a fundamental feature of the theory of the strong force that bind quarks and gluons together into protons, neutrons and, ultimately, all atomic nuclei. In addition to this, the observation provides direct experimental access to the mass of a single charm quark before it is confined inside hadrons.

Luciano Musa says that it has been difficult to observe the dead cone directly.

The partons are produced in particle collisions such as those at the LHC. Partons lose energy by emitting radiation in the form of gluons, which also emit gluons, in a cascade of events called a parton shower. The shower has a radiation pattern that depends on the mass of the parton and the direction of the parton's flight.

The dead cone was predicted thirty years ago from the first principles of the theory of the strong force. It has been difficult to observe it from the parton shower. The dead cone can be filled with particles and it is difficult to determine the changing direction of the parton during the shower process.

State-of-the-art analysis techniques were used by the ALICE collaboration to overcome the challenges. The parton shower can be rolled back in time by using these techniques. The researchers were able to identify a jet created by a charm quark and trace back the history of gluon emissions. The charm quark had a dead cone in its pattern after being compared with that of gluons and massless quarks.

The mass of the charm quark is directly exposed by the result.

The top quark and the rest of the quarks are confined inside the particles and can't be measured directly in experiments.

More information: ALICE Collaboration, Direct observation of the dead-cone effect in quantum chromodynamics, Nature (2022). DOI: 10.1038/s41586-022-04572-w Journal information: Nature Citation: First direct observation of the dead-cone effect in particle physics (2022, May 18) retrieved 18 May 2022 from https://phys.org/news/2022-05-dead-cone-effect-particle-physics.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.