What RK and Q5 can tell us about New Physics in b→sℓℓ transitions?

Abstract

The deviations with respect to the Standard Model that are currently observed in b → s transitions, or B anomalies, can be interpreted in terms of different New Physics (NP) scenarios within a model-independent effective approach. We identify a set of internal tensions of the fit that require further attention and whose theoretical or experimental nature could be determined with more data. In this landscape of NP, we discuss possible ways to discriminate among favoured NP hypotheses in the short term thanks to current and forthcoming observables. While an update of R K should help to disentangle the type of NP we may be observing (Lepton-Flavour Universality Violating and/or Lepton Flavour Universal), additional observables, in particular Q 5 , turn out to be central to determine which NP hypothesis should be preferred. We also analyse the preferences shown by the current global fit concerning various NP hypotheses, using two different tools: the behaviour of the pulls of individual observables under NP scenarios and the directions favoured by approximate quadratic parametrisations of the observables in terms of Wilson coefficients.

New Physics in $${\varvec{b \rightarrow s \ell ^+ \ell ^-}}$$ confronts new data on lepton universality

“…Only corresponding LFUV combinations as the one proposed in Ref. [35,36] and recently reanalyzed in [186] may help to disentangle genuine NP effects from hadronic contributions theoretically not well-understood. At present, the only available measurement of this sort is given by Belle [14] and it is (unfortunately) of limited statistical significance, but more will certainly come in the next years [34].…”

“…Our choice is, once more, primarily driven by our focus on LFUV effects. On more general grounds, one should stress that decoding LFU-conserving NP effects in current b → s data -a possibility recently considered in [185] -may be a challenging task [186], especially in light of unknown hadronic contributions.…”

Angular analysis of the rare decay $$ {\Lambda}_b\to \Lambda (1520)\left(\to N\overline{K}\right){\ell}^{+}{\ell}^{-} $$

“…In this context, it is particularly interesting to confirm and constrain further the scenarios of New Physics in b → s + − transitions. On the experimental side, one can increase the size of the data sample (as currently done by LHCb, CMS and ATLAS), add new observables and exploit different experimental environments (soon provided by Belle II) [28]. On the theory side, one can improve the determination of hadronic contributions to these decays, i.e.…”

Unified explanation of b→sμ+μ− anomalies, neutrino masses, and B→πKDatta1, Waite2, Sachdeva3 2019Phys. Rev. D240120View full textAdd to dashboardCite

“…where c ij and s ij represent cos θ ij and sin θ ij , respectively. In the case of Majorana neutrinos, α 21 and α 31 are the extra CP phases that cannot be determined by the oscillation experiments. However, these phases could be sensitive to the upcoming neutrinoless double beta decay searches.…”

“…There are several scenarios that give a good fit to the data and results of recent fits can be found in Ref. [17][18][19][20][21][22]. One popular scenario is C μμ 9;NP ¼ −C μμ 10;NP which can arise from the tree-level exchange of leptoquarks (LQ) or a Z 0 which may be heavy [23][24][25][26] or light [16,[27][28][29][30][31].…”