Lepton universality violation from neutral pion decays in RK(*) measurements

I show that the neutral pion decay in B -> K-(*())pi(0)gamma, with pi(0) -> ee gamma, might generate large sources of lepton flavor universality violation (LFUV) in measurements of the ratios, R-K(*) : If the photons in the K-(*())ee gamma gamma fmal state are reconstructed as bremsstrahlung, the recovered electron-positron invariant mass can be pushed into the 1-6 GeV2 signal region, artificially enhancing the measured B -> K-(*())ee branching ratio compared to B -> K-(*())mu mu. I present a conservative estimate and simulation of the B -> K pi(0)gamma LFUV background at LHCb, that together suggest this effect could reduce the recovered R-K up to several percent. A reliable assessment of the size of this effect will require dedicated simulations within experimental frameworks themselves.

Automated summary

In this study, the potential sources of lepton flavor universality violation (LFUV) in the neutral pion decay of B->K-(*())pi(0)gamma, with pi(0) -> ee gamma, are investigated. The author presents a conservative estimate and simulation of the B -> K pi(0)gamma LFUV background at LHCb, indicating that this effect could reduce the recovered R-K by several percent.