Which is the newest law of physics

New results call physical laws into question

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Researchers at UZH and CERN have published amazing new results. According to the international research collaboration LHCb, which runs the Large Hadron Collider beauty experiment, the latest measurements reinforce the evidence of a deviation from theoretical expectations. If the results can be confirmed, they point to physics beyond the Standard Model - such as a new fundamental force. A media release from the University of Zurich.



Very rare decay of a beauty quark with the participation of an electron and positron, which was observed with the LHCb detector.
(Image: CERN)
March 23, 2021 - If so-called beauty quarks are formed during the collision of high-energy proton beams in the Large Hadron Collider (LHC) - the particle accelerator at CERN in Geneva, they disintegrate practically immediately on the spot. Researchers in the Large Hadron Collider beauty experiment (LHCb experiment) reconstruct the properties of the short-lived, composite particles based on their decay products. According to the established laws of particle physics - the so-called standard model - the beauty quarks should decay into a final state with electrons or muons, the much heavier siblings of electrons, with the same probability. However, measurements at the LHC since 2014 have indicated that this “lepton universality” could be violated in some decays. These decays showed small deviations in the ratio of the two types of particles from the theoretical prediction of one.

Decay measurements do not agree with the prediction of particle physics
Members of Nicola Serra's group, professor at the Physics Institute of the University of Zurich (UZH), are part of the small research team that carried out the measurements. In the latest LHCb analysis, the ratio of the decay products containing electrons and muons was determined with much better precision than previous measurements. All data collected so far by the LHCb detector were used. The result indicates a deviation from the ratio one - and thus a violation of the "lepton universality" in beauty quark decays. The probability that the data is compatible with the theoretical prediction is about 0.1%. If this deviation is confirmed, it would imply a physics beyond the Standard Model - such as a new fundamental force in addition to the four basic forces: gravitation, electromagnetism, weak interaction, which is responsible for radioactivity, and strong interaction, which holds matter together.



The LHCb experiment is one of the four large experiments at the Large Hadron Collider at CERN.
(Image: CERN)
Too early for final statements, but great potential for future measurements
«The standard model has proven to be very successful for decades. It is our job as experimenters to test the model more and more precisely and to see whether it can withstand the stricter tests, ”says UZH researcher Patrick Owen, who played a leading role in the analysis. In elementary particle physics, observations become real discoveries when the probability of an error, including all known errors, is less than one in three million, or 0.00003%. “So it's too early to come to a final conclusion. However, the new anomaly is consistent with the pattern of anomalies that have emerged over the past decade, ”says Nicola Serra. “But the LHCb collaboration has all the prerequisites to clarify the possible existence of effects of a new physics in beauty quark decays. What we need for this are many more measurements, ”Serra concludes.

The result was presented for the first time today at the Moriond Conference on Electroweak Interactions and Unified Theories and an online seminar at CERN, the European Organization for Nuclear Research in Geneva.



Opening the LHCb detector to install an upgrade.
(Image: CERN)
Literature:
LHCb collaboration: R. Aaij et. al. Test of lepton universality in beauty-quark decays. arXiv.org. 23 March 2021. https://arxiv.org/abs/2103.11769

The Large Hadron Collider beauty experiment (LHCb)
The LHCb experiment is one of the four large experiments at the Large Hadron Collider (LHC) at CERN in Geneva. It was developed to study the decay of elementary particles that contain a beauty quark. This is the quark with the highest mass that forms bound states. The resulting precision measurements of matter-antimatter differences and the rare decay of particles that contain a beauty quark enable sensitive tests of the Standard Model of particle physics.

Research groups from UZH and ETH Lausanne have been members of the LHCb collaboration since 1999. You have made important contributions to the design and construction of the LHCb detector and are involved in its upgrades. These enhancements to the detector will be key to gathering the data we need and finding out whether the observed anomalies in the beauty curd decays are actually real. Since data collection began in 2009, Nicola Serra's UZH group has played a leading role in measuring the decay of particles containing beauty quarks.

The group works closely with two other UZH teams who are working on the theoretical description of these phenomena. Professor Gino Isidori works on the theoretical interpretation of these decays and deals with open questions about the nature of the basic building blocks of matter and their fundamental interactions. Andreas Crivellin, SNSF professor at UZH, is investigating possible implications of these results for other experiments at the Paul Scherrer Institute (PSI). Together, the UZH research teams effectively combine theory and experiment in current particle physics research.

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Source: University of Zurich