Improved search for B+ -> K+ nu nubar at Belle II

This project explores the possibility that a rare missing-energy decay of a subatomic particle called a B meson might reveal new forces or previously unknown particles. In this decay, the B meson transforms into a lighter particle known as a kaon and also releases two invisible particles called neutrinos. Because neutrinos very rarely interact with matter, we can only detect them indirectly by observing what is left behind. Measuring this challenging process provides a powerful test of our current theory of particle physics, known as the Standard Model. Small deviations from the Standard Models predictions may signal entirely new forces or unknown particles. In fact, evidence for this decay was already reported by the Belle II experiment, hinting at a possible mismatch with current theory. To investigate whether this mismatch arises from new physics or other factors, we will use more data collected by Belle II, a detector operating at the SuperKEKB electron-positron collider in Japan. Our analysis will rely on advanced computing methods, including deep neural networks, to sort through billions of collisions and find the few events that match this rare decay. Our findings could help refine our understanding of fundamental physics or even point to unknown processes in nature. All results will be shared openly so that other researchers and the public can benefit from what we learn.