At the CKM 2016 conference held last December at the Tata Institute of Fundamental Research (TIFR) in Mumbai, the Belle experiment (KEK, Tsukuba, Japan) has announced the first simultaneous measurement of P5’muon and P5’e, the two components of the universal lepton flavour observable Q5 proposed in May of 2016 in the Journal of High Energy Physics [JHEP 1610 (2016) 075].
The results show a deviation with respect to the Standard Model (SM) predictions that is not yet statistically significant (2.6 sigma for muons and 1.1 sigma for electrons) but coherent with other measurements of the muonic channel and with other observables pointing to the same type of asymmetry between muons and electrons.
If LHCb (Large Hadron Collider beauty experiment, held in CERN, Geneva) confirms with high significance the measurement by Belle, there will be a new signal of New Physics of non universal lepton flavour violation type. Simultaneously all SM attempts to try to explain the anomaly in the observable P5′ by means of long distance charm effects will be proven to be wrong. Both Belle II and LHCb will be the major players in the following years able to arrive to a firm conclusion if Nature violates lepton flavour universality or not.
Find more information in this article by UAB and IFAE researcher Joaquim Matias explaining how the latest experiments point towards the first evidences of New Physics, with the detection of observables proposed by his research group.