According to SM predictions, just two signal events are expected in the Run-2 data, potentially making this the rarest decay ever recorded. Though primarily designed for the study of heavy-flavour particles, LHCb’s unique ability to select low transverse-momentum muons in real time makes the search feasible. These particles could significantly enhance the decay rate, up to existing experimental limits, but could also suppress it via quantum interference with the Standard Model (SM) amplitude.ĭespite the unprecedented K 0 S production rate at the LHC, searching for K 0 S → μ + μ – is challenging due to the low transverse momentum of the two muons, typically of a few hundred MeV/c. Like the better known B s → μ + μ – decay, which was first observed jointly by LHCb and CMS in 2013, the decay rate is very sensitive to possible contributions from yet-to-be discovered particles that are too heavy to be observed directly at the LHC, such as leptoquarks or supersymmetric partners. The observed number of signal decays is consistent with zero.įor every trillion K 0 S, only five are expected to decay to two muons. The K 0 L → μ +μ – background (orange) is suppressed with respect to K 0 S due to the longer distance of flight. The invariant mass of K 0 S → μ +μ – candidates, and the fit to one of the most sensitive search regions.
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