A general effective field theory description of b → sℓ+ lepton universality ratios

Gino Isidori, Davide Lancierini, Abhijit Mathad, Patrick Owen, Nicola Serra, Rafael Silva Coutinho

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


We construct an expression for a general lepton flavour universality (LFU) ratio, RX, in b→sℓ+ decays in terms of a series of hadronic quantities which can be treated as nuisance parameters. This expression allows to include any LFU ratio in global fits of b→sℓ+ short-distance parameters, even in the absence of a precise knowledge of the corresponding hadronic structure. The absence of sizeable LFU violation and the approximate left-handed structure of the Standard Model amplitude imply that only a very limited set of hadronic parameters hamper the sensitivity of RX to a possible LFU violation of short-distance origin. A global b→sℓ+ combination is performed including the measurement of RpK for the first time, resulting in a significance of new physics of 4.2σ. In light of this, we evaluate the impact on the global significance of new physics using a set of experimentally promising non-exclusive RX measurements that LHCb can perform, and find that they can significantly increase the discovery potential of the experiment.

Original languageEnglish (US)
Article number137151
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - Jul 10 2022
Externally publishedYes

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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