Scientists discover support for disputed universal truth of particle physics


Credit: The Atlas Collaboration

A measurement of a basic concept of the basic design of particle physics—lepton flavour universality—recorded by the ATLAS detector at the Large Hadron Collider, is reported in a paper released in Nature Physics.


The findings supersede the enduring arise from the Large Electron–Positron Collider.

Our understanding of primary particles—the foundation of the Universe—and the electro-magnetic, weak and strong essential forces that act in between them, is developed in the basic design of particle physics. In the theory, electrons, muons and τ leptons represent 3 ranges (or flavours) of an electrically charged type of primary particle referred to as leptons. The basic design presumes that the strength of the couplings in between leptons and the particles that moderate the weak force—referred to as ‘W’ or ‘Z’ electroweak gauge bosons—is independent of the lepton flavour. This long-held concept, referred to as lepton flavour universality, has actually just recently been challenged by experiments at B-factories and at the LHC.

The ATLAS Collaboration—including an international group of scientists consisting of specialists from Lancaster –studied whether this ‘universal truth’ is true for the muon and the τ lepton in around half a million proton–proton crashes taped with the ATLAS detector at the Large Hadron Collider. By taking a look at decays of W bosons into τ leptons and muons and determining the ratio of their decay rates, the authors had the ability to conclude that the weak force engages with both types of lepton in the very same method.

This arise from the ATLAS Collaboration is the most accurate measurement to date, with practically two times the accuracy acquired from experiments at the Large Hadron Collider’s predecessor at CERN—the Large Electron–Positron Collider (LEP).

Lancaster University Physics Professor Guennadi Borissov stated: “The measurements at LEP indicated that there may be a difference between the decays to different sorts of leptons. This intriguing hint of deviation from the standard model has been unconfirmed for about 20 years. Although our latest measurements do not back up the result of the LEP, it has been exciting to find a new and remarkably precise way to test this using the power of the Large Hadron Collider, with Lancaster being at the heart of each step of the analysis.”

Professor Roger Jones, head of the Lancaster ATLAS group, stated: “Tests such as ours of essential theoretical presumptions are presently a hot location of research study in particle physics. Recent arises from the LHCb experiment, and extremely accurate measurements of muons made by the g-2 cooperation (which likewise has Lancaster physicists in the group) have actually offered brand-new tips that leptons might not all act the very same method as our theories forecast.

“In contrast, new and very precise measurements show that in important ways the leptons really do behave the same way. It will be exciting to see if the hints from other experiments become clear evidence. If so, theories will have to account for our strong evidence for leptons behaving in the same way in the process we have studied and yet behaving differently in other processes.”


Long-standing stress in the Standard Model dealt with


More info:
Test of the universality of τ and μ lepton couplings in W-boson rots with the ATLAS detector, Nature Physics (2021). DOI: 10.1038/s41567-021-01236-w

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Scientists discover support for disputed universal truth of particle physics (2021, July 6)
obtained 6 July 2021
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