A hyperon is a particle that contains three quarks, like a proton or a neutron, and one or more strange quarks. Physicists from the LHCb collaboration at the Large Hadron Collider (LHC) at CERN say they have observed a hyperon decay Σ+→pμ+μ- in proton-proton collisions.
A view of the LHCb detector. Image courtesy of CERN.
“Rare decays of known particles are a promising tool for exploring physics beyond the Standard Model of particle physics,” said the LHCb physicist.
“In the Standard Model, the Σ+ → pμ+μ- process is only possible through a loop diagram, meaning that the decay does not occur directly, but intermediate states have to be exchanged within the loop.”
“In quantum field theory, the probability of such a process occurring is the sum of the probabilities of all particles, both known and unknown, that can possibly be exchanged in this loop.”
“This is what makes such processes sensitive to new phenomena.”
“If a discrepancy is observed between experimental measurements and theoretical calculations, it may be caused by the contribution of some unknown particle.”
“These particles can either be exchanged within the loop or directly mediate this decay, interacting with the quarks and decaying into pairs of muons.”
“In the latter case, the new particle would leave a signature on the properties of the two muons.”
The study of the Σ+ → pμ+μ- decay has been particularly exciting thanks to hints of structure observed in the properties of muon pairs by the HyperCP collaboration in 2005.
With only three occurrences the structure was far from conclusive, and it was hoped that new research would shed light on the situation.
Finally, the LHCb data did not show any significant peak structure in the two-muon mass region highlighted by HyperCP, thus refuting the hint.
However, the new study observes the decay with a high degree of significance, followed by precise measurements of the decay probability and other parameters, which will allow further investigation of the discrepancy with the Standard Model predictions.
“In data collected in Run 2 of pp collisions at the LHCb experiment, the Σ+ → pμ+μ− decay is observed with very high significance, with a yield of NΣ+→pμ+μ− = 279 ± 19,” the authors write in their paper. paper.
“We do not see any structure in the two-muon invariant mass distribution that is consistent with the Standard Model predictions.”
“The collected signal yield allows for measurements of integral and differential branching rates, as well as other measurements such as charge-parity symmetry breaking and front-to-back asymmetry.”
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LHCb Collaboration. 2024. Observation of rare Σ+→pμ+μ− decays at LHCb. CERN-LHCb-CONF-2024-002
Source: www.sci.news
