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A new LHCb analysis confirms a previously observed tension with the Standard Model, but more data and improved theoretical calculations are needed to determine whether new physics is at play.

The LHCb collaboration has released the results of its latest analysis of the rare decay of the beauty meson B⁰ into a K* meson and a pair of muons (B⁰→K^*μ⁺μ^–). Based on data from the first and second runs of the LHC, the new analysis confirms a tension with predictions from the Standard Model that was observed in previous analyses. However, such predictions are highly complex and are a topic of debate within the theoretical physics community.

The B⁰→K^*μ⁺μ^– decay offers a to search for new phenomena, as it is sensitive to contributions from undiscovered particles that may have masses beyond the reach of direct searches at the LHC. By comparing precise measurements of the decay's properties with Standard Model predictions, possible signs of new fundamental particles or interactions could be revealed.

The best sensitivity to new particles comes from the study of the angular distributions of the decay products, namely a kaon and a pion from the K^* decay and the two muons. The LHCb team had previously measured these angular observables first using proton–proton collision from LHC Run 1 and then a that also included LHC Run 2 data taken in 2016.

In all of these earlier analyses, one of the observables, called P₅^', showed a significant deviation from the Standard Model. This result had a statistical significance below the "five-sigma" gold standard required to claim a discovery, but it was significant enough to warrant attention in future studies.

The represents the most sophisticated study of the B⁰→K^*μ⁺μ^– decay properties to date, using proton–proton collision data collected by LHCb in 2011, 2012 and 2016–2018. This analysis confirms that the P₅^' observable is in significant tension with theoretical predictions. The results are in good agreement with the previous LHCb measurements and also with a recent .

"The new measurements show the same pattern of tensions with the Standard Model that we have seen before," says Mark Smith, who presented the details of the analysis at a recent LHC seminar. "Further clarifying the experimental picture with the LHC Run 3 dataset and improving theoretical calculations should help determine the origin of the observed patterns," says Leon Carus, who presented the results at the latest LHC Committee Open Session.