The branching fraction of B0 -> K* mu mu decay is a measure of the probability that a B0 meson will decay into a K* meson and two muons. It is typically expressed as a percentage or a decimal value.
The branching fraction is determined through experiments that measure the number of B0 -> K* mu mu decays compared to the total number of B0 meson decays. This data is then used to calculate the branching fraction using statistical methods.
There are several factors that can affect the branching fraction, including the mass of the B0 and K* mesons, the energy of the muons, and the decay mode of the B0 meson. Other experimental conditions, such as the detector efficiency and background noise, can also impact the measured branching fraction.
Studying the branching fraction of B0 -> K* mu mu decay can provide valuable insights into the underlying physics processes involved in this decay. It can also help to test the predictions of theoretical models and search for new physics beyond the Standard Model.
The current measured branching fraction for B0 -> K* mu mu decay is about 4.2 x 10^-7, with a precision of about 10%. However, ongoing experiments at facilities such as the Large Hadron Collider (LHC) are working towards improving this measurement with higher precision and sensitivity.