One of the goals of the Belle II experiment is the study of the CP asymmetries in the time evolution of the neutral B mesons. A clean laboratory to study the two-state system of B0 and anti-B0 mesons is provided by the Υ(4S) resonance which can be produced in e+ e− annihilation at the center of mass energy of 10.58 GeV. In SuperKEKB, the beam energies to form the Υ(4S) are chosen asymmetrically in order to translate the decay time difference into a length: ∆t = ∆l/βγc, where l is the boost direction.
The B0 and anti-B0 produced by the decay of the Υ(4S) cannot oscillate independently before they decay but are locked in a quantum-entangled state. Thus the identification of one of the B mesons as a B0 (anti-B0 ) yields the flavor of the other B meson as anti-B0 (B0 ) at the same time. If the anti-B0 (B0) is fully reconstructed to a CP eigenstate, the difference between the particle and the antiparticle can be studied using the shape of the distribution of the difference of their decay times. The goal is to determine the experimental resolution function of the distance (translated to the difference of the decay times) between the vertices of the two B mesons as a function of the different decay vertex qualities and vertex detector running conditions.