Multi-lepton Signatures of a Hidden Sector in Rare B Decays

TL;DR

This paper investigates how rare B meson decays can reveal hidden GeV-scale particles through enhanced lepton pair signatures, providing new experimental search strategies for hidden sectors coupled via Higgs, vector, and axion portals.

Contribution

It introduces novel decay channels and analyzes existing bounds, highlighting the potential of B decays to probe hidden sectors with multiple portals and suggesting new experimental search modes.

Findings

Existing measurements constrain light sector parameters more than naturalness requires.

New decay modes like B -> X_s + n(l+l-) can improve sensitivity to hidden sectors.

Accessible to future B factories and colliders.

Abstract

We explore the sensitivity of flavour changing b -> s transitions to a (sub-)GeV hidden sector with generic couplings to the Standard Model through the Higgs, vector and axion portals. The underlying two-body decays of B mesons, B -> X_s S and B0 -> SS, where S denotes a generic new GeV-scale particle, may significantly enhance the yield of monochromatic lepton pairs in the final state via prompt decays of S to a dilepton pair. Existing measurements of the charged lepton spectrum in neutral-current semileptonic B decays provide bounds on the parameters of the light sector that are significantly more stringent than the requirements of naturalness. New search modes, such as B -> X_s + n(l+l-) and B0 -> n(l+l-) with n > 1 can provide additional sensitivity to scenarios in which both the Higgs and vector portals are active, and are accessible to (super-)B factories and hadron colliders.