Observation of $B_s^0 \to \overline{D}^{*0} \phi$ and search for $B^0 \to \overline{D}^0 \phi$ decays

TL;DR

This paper reports the first observation of the $B_s^0 o ar{D}^{*0} \, \phi$ decay with a significance over seven standard deviations, measures its branching fraction and polarization, and sets limits on related decays and mixing angles.

Contribution

The study provides the first observation and precise measurement of the $B_s^0 \to \bar{D}^{*0} \phi$ decay, including its branching fraction and polarization, expanding understanding of $B_s^0$ decay modes.

Findings

First observation of $B_s^0 \to \bar{D}^{*0} \phi$ decay.

Measured branching fraction: $(3.7 \pm 0.5 \pm 0.3 \pm 0.2) \times 10^{-5}$.

Polarization fraction $f_L = (73 \pm 15 \pm 3)\%$.

Abstract

The first observation of the $B_s^0 \to \overline{D}^{*0} \phi$ decay is reported, with a significance of more than seven standard deviations, from an analysis of $pp$ collision data corresponding to an integrated luminosity of 3 fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of $7$ and $8$ TeV. The branching fraction is measured relative to that of the topologically similar decay $B^0 \to \overline{D}^0 \pi^+\pi^-$ and is found to be $\mathcal{B}(B_s^0 \to \overline{D}^{*0} \phi) = (3.7 \pm 0.5 \pm 0.3 \pm 0.2) \times 10^{-5}$, where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the $B^0 \to \overline{D}^0 \pi^+\pi^-$ decay. The fraction of longitudinal polarisation in this decay is measured to be ${f_{\rm L} =(73 \pm 15 \pm 3)\%}$. The most precise determination of the branching fraction for the $B_s^0 \to \overline{D}^{0} \phi$ decay is also obtained, $\mathcal{B}(B_s^0 \to \overline{D}^{0} \phi) = (3.0 \pm 0.3 \pm 0.2 \pm 0.2) \times 10^{-5}$. An upper limit, $\mathcal{B}(B^0 \to \overline{D}^{0} \phi) < 2.0 \ (2.2) \times 10^{-6}$ at $90\%$ (95\%) confidence level is set. A constraint on the $\omega-\phi$ mixing angle $\delta$ is set at $|\delta| < 5.2^\circ~ (5.5^\circ)$ at $90\%$ ($95\%$) confidence level.