LHCb sheds light on two pieces of the matter–antimatter puzzle: Baryon and beauty hadron decays

LHCb sheds light on two pieces of the matter–antimatter puzzle ...

In the Big Bang, matter and antimatter should have been created in equal amounts. But fast forward 13.8 billion years to the present day, and the universe is made almost entirely of matter, so something must have happened to create this imbalance.

The Standard Model of particle physics predicts an asymmetry between matter and antimatter known as charge–parity (CP) violation. But the size of this asymmetry in the Standard Model is not large enough to account for the imbalance and the asymmetry has so far been observed only in certain decays of particles called mesons, which are made of a quark and an antiquark. It remains to be seen in other meson decays and in decays of other types of particles, such as three-quark particles called baryons.

In two new articles posted to the arXiv preprint server, the LHCb collaboration at the Large Hadron Collider (LHC) reports seeing evidence of CP violation in decays of baryons and in decays of beauty hadrons into charmonium particles, shedding light on these two pieces of the matter–antimatter puzzle.

Experiments, including LHCb, have previously conducted searches for CP violation in baryons, by looking for differences in the way matter and antimatter baryons decay into other particles. But these searches have essentially come up empty handed so far. Although one LHCb study has delivered evidence of the process in a particular decay of the bottom lambda baryon, that evidence has not increased in a subsequent study that analyzed a larger sample of such decays.

In the first new study, the LHCb team sifted through proton–proton collision data taken during the first and second runs of the LHC to search for different decay modes of the bottom lambda baryon, including its decay into a lambda baryon and two kaons.

It then looked for CP violation in each decay mode by basically counting the number of decays of the bottom lambda baryon and of its antimatter partner and taking the difference between the two. For the decay into a lambda baryon and two kaons, this difference showed evidence of CP violation with a significance of 3.2 standard deviations.

In the second new study, the LHCb team turned its attention to the decay of the electrically charged beauty meson into a J/psi and a charged pion. The J/psi is a charmonium particle—a meson consisting of a charm quark and a charm antiquark.

Performing a similar analysis to that of the bottom lambda baryon study, and also using data from the first and second runs of the LHC, the LHCb researchers found evidence of CP violation in this decay mode of the charged beauty meson, again with a significance of 3.2 standard deviations. The finding represents evidence of CP violation in decays of beauty hadrons to charmonium particles.

The two studies mark significant steps towards establishing whether or not CP violation exists in these types of decays. Data from the third run of the LHC and from the collider’s planned upgrade, the High-Luminosity LHC, are set to shed further light on these and other pieces of the matter–antimatter puzzle.

More information:
Study of Λ0b and Ξ0b decays to Λh+h′ and evidence for CP violation in Λ0b → ΛK+K decays, arXiv (2024). DOI: 10.48550/arxiv.2411.15441

First evidence for direct CP violation in beauty to charmonium decays, arXiv (2024). DOI: 10.48550/arxiv.2411.12178

Journal information:
arXiv

Citation:
LHCb sheds light on two pieces of the matter–antimatter puzzle: Baryon and beauty hadron decays (2024, December 16)

Subscribe
Don't miss the best news ! Subscribe to our free newsletter :