Test of lepton universality in bottomonium decays

Particle physics is the study of elementary particles and forces. The Standard Model (SM) is the most precise theory known to date, which successfully describes the particles and their interactions at the energy level accessible by high-energy physics experiments. Despite its huge success, it`s also known to be incomplete; one of the critical issues, the three generations of leptons are identical except for their masses; in particular, electroweak gauge bosons couple similarly to the three generations of leptons. This very intuitive phenomenon of SM is known as Lepton Universality (LU). The precession test of LU has become a hot topic of current research in modern particle physics. Different experiments put their efforts into the various sectors of particle physics to find the violation of this symmetry, but no violation has been observed so far; violation of this symmetry could indicate new physics beyond the SM. However, recent measurements from different experiments challenged the SM prediction. The Belle II experiment at the SuperKEKB, an asymmetric electron-positron collider in Tsukuba, Japan, uniquely tests this phenomenon at the intensity frontier. The bottomonium sector of particle physics offers an independent way to test this phenomenon. This project aims to test the LU in bottomonium decay tagging offered by the di-pion transitions with unprecedented precision using a novel approach to reduce the experimental uncertainties significantly for the first time. The improvement technique is to simultaneously test the LU in the Upsilon(nS) resonances samples and outside them and take a ratio, using all the available datasets from the Belle and Belle II experiment, which will reduce the experimental uncertainty drastically. The combined dataset of the Belle and Belle II experiment leads us to unprecedented luminosity, and the new novel technique of experimental uncertainties reduction will help us test the LU with world-leading precision. The test of LU in the bottomonium sector also will allow us to constrain the new physics models responsible for explaining LU violation and eventually rule them out.