Measurement of the $B^0$ lifetime using fully reconstructed hadronic decays in the 2019 Belle II dataset

TL;DR

This paper reports a measurement of the $B^0$ meson lifetime using fully reconstructed hadronic decays in the 2019 Belle II dataset, employing vertex inference techniques and maximum likelihood fitting.

Contribution

It introduces a method to measure $B^0$ lifetime with fully reconstructed hadronic decays using Belle II data and the rest-of-event technique.

Findings

Measured $B^0$ lifetime as 1.48 ps

Achieved statistical uncertainty of 0.28 ps

Systematic uncertainty of 0.06 ps

Abstract

This document presents the measurement of $B^0$ meson lifetimes using the 2019 Belle II dataset that corresponds to an integrated luminosity of $8.7 \pm 0.2$ fb$^{-1}$. Each candidate is fully reconstructed with hadronic decay final states on the signal side, while the rest-of-event technique allows to infer the decay vertex position on the other (tag) side. $B^0$ lifetime is extracted from an unbinned maximum likelihood fit to the distribution of the difference between the signal side $B^0$ candidate and the tag side decay times. The measured lifetime is $\tau_{B^0} = 1.48 \pm 0.28 \pm 0.06 $ ps, where the first uncertainty is statistical and the second is systematic.