Rare FCNC top, beauty and charm decays

TL;DR

This paper reviews recent experimental results on rare FCNC decays of top, beauty, and charm quarks, highlighting potential deviations from the Standard Model and emphasizing the need for further research.

Contribution

It provides a comprehensive review of recent LHCb measurements of FCNC processes, including angular distributions and photon polarization, and discusses their implications for new physics.

Findings

Discrepancy of 3.7 sigma in $B^{0} o K^{*0} \mu^{+} \mu^{-}$ angular distribution

Photon polarization measurement in $B^{+} o K^{+}\pi^{-}\pi^{+}\gamma$ decay

Indications that Standard Model may not fully explain FCNC processes

Abstract

Rare flavour changing neutral current (FCNC) decays of top, beauty and charm quarks can provide a powerful probe for as yet unobserved particles. Recent results on FCNC $b \to s$, $c \to u$ and $t$ transitions from the LHC experiments are reviewed. Particular attention is paid to the angular distribution of the $B^{0} \to K^{*0} \mu^{+} \mu^{-}$ decay, where a measurement performed by LHCb shows a local discrepancy of 3.7 standard deviations with respect to the SM prediction. Using the decay $B^{+} \to K^{+}\pi^{-}\pi^{+}\gamma$, LHCb have also been able to demonstrate the polarisation of photons produced in $b \to s\gamma$ transitions. More work is needed both experimentally and theoretically to understand if the Standard Model description of these rare FCNC processes is correct.