A global analysis of b rightarrow s ell ell data in heavy and light Z' models

Abstract

We perform a model-independent global fit to all b rightarrow s ell ell data in the light of recent measurements of the lepton flavour universality violating (LFUV) observables R_{K_S^0}, R_{K^{*+}}, and the updated observables in B_s rightarrow phi mu ^+ mu ^- decay, by the LHCb collaboration. Assuming NP only in the muon sector, we find that the 1D NP scenarios C_9^{textrm{NP}} <0 and C_{9}^{textrm{NP}}=-C_{10}^{textrm{NP}} continue to be the most favoured ones. However, the significance of the favoured scenario C_{9}^{textrm{NP}}=-C'_{9} has reduced and the updated data now marginally prefers C_{10}^{textrm{NP}} > 0 scenario. The 2D scenarios (C_9^{textrm{NP}}, C_{10}^{prime } ), (C_9^{textrm{NP}}, C_{9}^{prime } ) and (C_9^{textrm{NP}}, C_{10}^{textrm{NP}} ), continue to be favoured by the data in the listed order. We analyse generic TeV scale Z' models which can generate the 1D scenarios, C_9^{textrm{NP}} <0 and C_9^{textrm{NP}} = -C_{10}^{textrm{NP}} as well as 2D scenarios (C_9^{textrm{NP}}, C_{9}^{prime } ) and (C_9^{textrm{NP}}, C_{10}^{textrm{NP}} ). We find that all four models provide an equally good fit to the data. We also consider a model with a 25 MeV Z' that couples to muons only and has a q^2 dependent b - s coupling. We study the implications of the current data on the LFUV observables R_{phi }, Q_{4,5} as well as R_{K^{(*)}} in the high q^2. We find that the Q_{4,5} observables have a potential to discriminate between a few favored solutions, and disentangle different heavy and light Z' scenarios.