Speaker
Ulrich Nierste
Description
B-$\bar{\rm B}$ mixing involves three observables, the mass
difference $\Delta m$ between the two neutral B eigenstates, their width
difference $\Delta \Gamma$, and the CP phase characterising CP violation
in mixing. The latter two quantities involve the off-diagonal element
$\Gamma_{12}$ of the 2$\times 2$ decay matrix $\Gamma$. I briefly
discuss possible insights into new physics to be gained from a better
knowledge of $\Gamma_{12}$ and then describe the calculation of the
Standard-Model prediction of $\Gamma_{12}$ at next-to-next-to-leading
order of QCD. This calculation is necessary to match the experimental
precision of the LHCb measurement of $\Delta \Gamma$ in the B$_{\rm s}$
system.
Author
Ulrich Nierste
