2021/05/14 by R. D. Moise, Moise, R. D.
Physics and Astronomy · #Particle physics theoretical and experimental studies #High-Energy Particle Collisions Research #Cosmology and Gravitation Theories
paper · pdf · doi:10.48550/arxiv.2105.06921
The Standard Model of particle physics predicts that charged leptons have the same electroweak interaction strength. This symmetry, called lepton flavour universality, was found to hold in a wide range of particle decays. One observable that is sensitive to lepton flavour universality is the ratio of branching fractions RK=\mathcal B(B+→ K+μ+μ-) / \mathcal B(B+→ K+e+e-). This quantity is measured using 9 fb-1 of proton-proton collision data recorded by the LHCb experiment at CERN's Large Hadron Collider. For the dilepton invariant mass squared range q2∈(1.1 Ge\kern -0.1em \text V2, 6.0 Ge\kern -0.1em \text V2), the result is RK=0.846+0.042-0.039+0.013-0.012, where the first uncertainty is statistical and the second systematic. The measured value is in tension with the Standard Model prediction at the level of 3.1 σ, thus providing evidence for the violation of lepton flavour universality in B+→ K+ℓ+ℓ- decays.