Search for the Decays ${B^0_{(s)}\to e^+\mu^-}$ and ${B^0_{(s)}\to e^+e^-}$ in CDF Run II

TL;DR

This paper reports a search for rare lepton flavor violating and flavor-changing neutral-current decays of B mesons using Fermilab Tevatron data, setting new upper limits on branching ratios and leptoquark masses.

Contribution

It provides the first stringent upper limits on these rare B meson decays and derives lower bounds on Pati-Salam leptoquark masses, improving constraints on new physics models.

Findings

No signal observed; consistent with background expectations.

Set upper limits on branching ratios: < 2.0×10^{-7} and < 6.4×10^{-8}.

Derived lower bounds on leptoquark masses: > 47.8 TeV/c^2 and > 59.3 TeV/c^2.

Abstract

We report results from a search for the lepton flavor violating decays $B^0_{(s)}\to e^+\mu^-$, and the flavor-changing neutral-current decays $B^0_{(s)} \to e^+ e^-$. The analysis uses data corresponding to ${\rm 2 fb^{-1}}$ of integrated luminosity of $p \bar{p}$ collisions at $\sqrt{s}=1.96 {\rm TeV}$ collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron. The observed number of $B^0_{(s)}$ candidates is consistent with background expectations. The resulting Bayesian upper limits on the branching ratios at 90% credibility level are $\mathcal{B}(B^0_s \to e^{+}\mu^{-}) < 2.0 \times 10^{-7}$, $\mathcal{B}(B^0 \to e^{+}\mu^{-})< 6.4 \times 10^{-8}$, $\mathcal{B}(B^0_s \to e^{+}\mu^{-}) < 2.0 \times 10^{-7}$ and $\mathcal{B}(B^0 \to e^{+}\mu^{-})< 6.4 \times 10^{-8}$. From the limits on $\mathcal{B} (B^0_{(s)}\to e^+\mu^-)$, the following lower bounds on the Pati-Salam leptoquark masses are also derived: ${M_{LQ}}(B^0_s\to e^+ \mu^-) > 47.8 {\rm TeV/c^2}$, and ${M_{LQ}}(B^0\to e^+ \mu^-) > 59.3 {\rm TeV/c^2}$, at 90% credibility level.