Description
CP-asymmetry is expected to explain the huge imbalance between matter and antimatter in our universe. The CP-asymmetry observed so far at particle or nuclear physics experiments is too small to explain this imbalance. We therefore expect new, yet-unknown sources of CP-violation to exist. One way to find hints for these new sources is to precisely measure differences in the decay rates of $B^0$ and anti-$B^0$ ($\bar B^0$) particles decaying to specific final states. One important parameter quantifying CP violation — the CKM angle $\alpha$ — is poorly known. Constraints on this angle can be set by measuring the difference between the decay rates of $B^0\to \pi^0 \pi^0$ and $\bar B^0\to \pi^0 \pi^0$, as a function of the $B^0$ decay time. This measurement should be possible in the future using pairs of $B^0$ mesons produced in $e^+e^-$ collisions at the Belle II experiment situated in Tsukuba, Japan. However, due to the difficulty of measuring the decay-time of the $B^0$ when it decays to $\pi^0 \pi^0$, a very large dataset is needed, which might not be collected before the next decade.
The goal of the proposed summer student project is to try a new technique to measure the angle alpha using only information from the decay time of the other B0 produced in the $e^+e^-$ collision. This is made possible thanks to the very small size of the $e^+e^-$ collision point at Belle II, from which the displacement of the other $B^0$ can be measured to extract its lifetime. This technique has not been tried before, so the student will use simulated decays to assess whether it would allow to measure $\alpha$ with much less data than needed with usual techniques. If results are promising and if time permits, i.e. if a measurement is possible within the coming years, the technique can be further validated using control $B^0$ decays reconstructed in the real Belle II data.
| Group | BELLE |
|---|---|
| Project Category | B1. Physics Data Analysis and Performance (software-oriented) |
| Special Qualifications | Some coding experience |
