Scientists measure rare particle decays with high precision

CMS måler sjældne partikelhenfald med høj præcision

Visualization of a decay of a Bs meson in run 2 data. The two red lines correspond to the two muons from the decay. Credit: CERN

At CERN’s Large Hadron Collider (LHC), studies of rare processes allow researchers to deduce the presence of heavy particles, including undetected particles, that cannot be produced directly. Such particles are widely expected to exist beyond the standard model and could help explain some of the mysteries of the universe, such as the existence of dark matter, the masses of neutrinos (evasive particles that were originally thought to be massless), and the matter’s antibody. asymmetry.

One such process is the rare decay of neutral B-mesons into a muon and antimony pair: the electron’s heavier cousin paired with its corresponding antiparticle. There are two types of neutral B mesons: B0 meson consists of a beauty antique quark and a down quark, while for Bs meson, the down quark is replaced by a strange quark. If there are no new particles affecting these rare decays, researchers have predicted that only one in 250 million B.s mesons will decay to a muon-antimuon pair; for B0 meson, the process is even more rare, only one in 10 billion.

Researchers have been searching for experimental confirmation of these decays since the 1980s. Only recently, in 2014, was the first observation of Bs to myon decay reported in a combined analysis of data taken by the LHCb and CMS collaboration, later confirmed by the ATLAS, CMS, and LHCb experiments individually. However, B0 decay still eludes any attempt to observe it.

Using data from run 2 of the LHC, the CMS experiment has released a new study of the decay rate and lifetime of the Bs meson decay, as well as a search for B0 decay. The new study, presented at the International Conference on High Energy Physics (ICHEP), benefits from not only a large amount of analyzed data, but also advanced machine learning algorithms that highlight the rare decay events from the overwhelming background of events produced by millions of particle collisions in the second.

The results revealed a very clear signal about Bs meson decays into a myon-antimuon pair. The accuracy of the decay rate measurement exceeds that obtained in previous measurements in other experiments.

Both the observed Bs the decay rate, which has been found to be 3.8 ± 0.4 parts per billion, and its lifetime measurement of 1.8 ± 0.2 picoseconds (one picosecond is one trillionth of a second), is very close to the values ​​predicted by the standard model .

As for B0 decay, although no evidence was found from these results, physicists with 95% statistical certainty can determine that its decay rate is less than 1 part out of 5 billion.

In recent years, a number of anomalies have been observed in other rare B-meson decays, with discrepancies between the theoretical predictions and the data – indicating the potential existence of new particles. The new CMS result is much closer to theoretical predictions than these other rare decays and can therefore help scientists understand the nature of the anomalies.

Rare B-meson decays remain of great interest to scientists. With Bs meson to muons decays solidly established and measured with high precision, scientists are now turning their attention to the ultimate price: B.0 decay. With large datasets expected from LHC Run 3, they hope to get the first glimpse of this extremely rare process and learn more about the confusing anomalies.


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Citation: Scientists Measure Rare Particle Decay with High Precision (2022, July 14) Retrieved July 15, 2022 from https://phys.org/news/2022-07-rare-particle-high-precision.html

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