Light Resonances and the Low-$q^2$ Bin of $R_{K^{\ast }}$

Abstract

LHCb has reported hints of lepton-flavor universality violation in the rare decays $B\to K^{(\ast )}{\ell }^{+}{\ell }^{-}$, both in high- and low-$q^2$ bins. Although the high-$q^2$ hint may be explained by new short-ranged interactions, the low-$q^2$ one cannot. We thus explore the possibility that the latter is explained by a new light resonance. We find that LHCb's central value of $R_{K^{\ast }}$ in the low-$q^2$ bin is achievable in a restricted parameter space of new-physics scenarios in which the new, light resonance decays preferentially to electrons and has a mass within approximately $10$ MeV of the di-muon threshold. Interestingly, such an explanation can have a kinematic origin and does not require a source of lepton-flavor universality violation. A model-independent prediction is a narrow peak in the differential $B\to K^{\ast }{e}^{+}{e}^{-}$ rate close to the di-muon threshold. If such a peak is observed, other observables, such as the differential $B\to K{e}^{+}{e}^{-}$ rate and $R_K$, may be employed to distinguish between models. However, if a low-mass resonance is not observed and the low-$q^2$ anomaly increases in significance, then the case for an experimental origin of the lepton-flavor universality violating anomalies would be strengthened. To further explore this, we also point out that, in analogy to $J/\psi$ decays, $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ decays of $\varphi$ mesons can be used as a cross check of lepton-flavor universality by LHCb with $5$ fb${}^{-1}$ of integrated luminosity.

28 pages, 8 figures

References in corpus (12)

• Test of lepton universality using $B^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ decays
• Search for a dark photon in e+e- collisions at BABAR
• Neutrino Trident Production: A Powerful Probe of New Physics with Neutrino Beams
• Search for light massive gauge bosons as an explanation of the $(g-2{)}_{\mu }$ anomaly at MAMI
• Search for invisible decays of sub-GeV dark photons in missing-energy events at the CERN SPS
• Dark Sectors 2016 Workshop: Community Report
• Muon g-2 and searches for a new leptophobic sub-GeV dark boson in a missing-energy experiment at CERN
• A New Light Particle in B Decays?
• Experimental constraints on the coupling of the Higgs boson to electrons
• On Light Resonance Interpretations of the B Decay Anomalies
• B Physics at LHCb
• Measurement of $\varphi$(1020) meson leptonic width with CMD-2 detector at VEPP-2M Collider

Cited by in corpus (27)

• B-decay discrepancies after Moriond 2019
• Flavor probes of axion-like particles
• New Physics in $b\to s{\ell }^{+}{\ell }^{-}$ confronts new data on Lepton Universality
• Continuing search for new physics in $b\to s\mu \mu$ decays: two operators at a time
• flavio: a Python package for flavour and precision phenomenology in the Standard Model and beyond
• Discovering leptonic forces using non-conserved currents
• $R_K$ and $R_{K^{\ast }}$ in an Aligned 2HDM with Right-Handed Neutrinos
• Resolving the $(g-2{)}_{\mu }$ and $B$ anomalies with leptoquarks and a dark Higgs boson
• New physics in $b\to s\ell \ell$ decays with complex Wilson coefficients
• Implications for Electric Dipole Moments of a Leptoquark Scenario for the $B$-Physics Anomalies
• New Opportunities for Detecting Axion-Lepton Interactions
• New physics in $b\to s{e}^{+}{e}^{-}$?
• What $R_K$ and $Q_5$ can tell us about New Physics in $b\to s\ell \ell$ transitions?
• Neutrino scattering and B anomalies from hidden sector portals
• Dark photon and dark $Z$ mediated $B$ meson decays
• Supernova constraints on an axion-photon-dark photon interaction
• Flavour anomalies and the muon $g-2$ from feebly interacting particles
• A unified explanation of $b\to s{\mu }^{+}{\mu }^{-}$ anomalies, neutrino masses and $B\to \pi K$ puzzle
• The cost of an ALP solution to the neutral $B$-anomalies
• Towards excluding a light $Z^{\prime }$ explanation of $b\to s{\ell }^{+}{\ell }^{-}$
• Width effects of broad new resonances in loop observables and application to $(g-2{)}_{\mu }$
• Flavour anomalies from a split dark sector
• Probing New Physics in $b\to d$ Transitions
• Explaining $g_{\mu }-2$ and $R_{K^{(\ast )}}$ using the light mediators of $U(1{)}_{T3R}$
• Signatures of a Flavor Changing $Z^{\prime }$ Boson in $B_q\to \gamma Z^{\prime }$
• Measurements of the branching fraction ratio $\mathcal{B}(\varphi \to {\mu }^{+}{\mu }^{-})/\mathcal{B}(\varphi \to e^{+}{e}^{-})$ with charm meson decays
• Following the muon track of hierarchical sectors at LHCb