Search for B --> K(*) nu nubar and invisible quarkonium decays

TL;DR

This study searches for rare B meson decays involving neutrinos and invisible quarkonium decays, setting upper limits on their branching fractions using data from the BaBar experiment, with no significant signals observed.

Contribution

First comprehensive search for B->K(*)nu nubar and invisible quarkonium decays, providing the most stringent upper limits to date on their branching fractions.

Findings

No significant excess observed in decay channels.

Set upper limits on branching fractions at 90% confidence level.

Improved kinematic resolution enabled partial spectrum limits.

Abstract

We search for the flavor-changing neutral-current decays B->K(*)nu nubar, and the invisible decays J/psi->nu nubar and psi(2S)->nu nubar via B->K(*)J/psi and B->K(*)psi(2S) respectively, using a data sample of 471 x10^6 BB pairs collected by the BaBar experiment. We fully reconstruct the hadronic decay of one of the B mesons in the Upsilon(4S)->BB decay, and search for the B->K(*)nu nubar decay in the rest of the event. We observe no significant excess of signal decays over background and report branching fraction upper limits of BR(B+->K+nu nubar)<3.7 x10^-5, BR(B0->K0nu nubar)< 8.1 x10^-5, BR(B+->K*+nu nubar)<11.6 x10^-5, BR(B0->K*0nu nubar)<9.3 x10^-5, and combined upper limits of BR(B->Knu nubar)<3.2 x10^-5 and BR(B->K*nu nubar)<7.9 x10^-5, all at the 90% confidence level. For the invisible quarkonium decays, we report branching fraction upper limits of BR(J/psi->nu nubar)<3.9 x10^-3 and BR(psi(2S)->nu nubar)<15.5 x10^-3 at the 90% confidence level. Using the improved kinematic resolution achieved from hadronic reconstruction, we also provide partial branching fraction limits for the B->K(*)nu nubar decays over the full kinematic spectrum.