New physics effects in tree-level decays and the precision in the determination of the quark mixing angle γ
Year: 2015
Type: article
Abstract: We critically review the assumption that no new physics is acting in tree-level $B$-meson decays and study the consequences for the ultimate precision in the direct determination of the Cabibbo-Kobayashi-Maskawa (CKM) angle $\ensuremath{\gamma}$. In our exploratory study we find that sizeable universal new physics contributions, $\mathrm{\ensuremath{\Delta}}{C}_{1,2}$, to the tree-level Wilson coefficients ${C}_{1,2}$ of the effective Hamiltonian describing weak decays of the $b$ quark are currently not excluded by experimental data. In particular, we find that $\mathrm{Im}\mathrm{\ensuremath{\Delta}}{C}_{1}$ and $\mathrm{Im}\mathrm{\ensuremath{\Delta}}{C}_{2}$ can easily be of order $\ifmmode\pm\else\textpm\fi{}10%$ without violating any constraints from data. Such a size of new physics effects in ${C}_{1}$ and ${C}_{2}$ corresponds to an intrinsic uncertainty in the CKM angle $\ensuremath{\gamma}$ of the order of $|\ensuremath{\delta}\ensuremath{\gamma}|\ensuremath{\approx}4\ifmmode^\circ\else\textdegree\fi{}$, which is slightly below the current experimental precision. The accuracy in the determination of $\ensuremath{\gamma}$ can be improved by putting stronger constraints on the tree-level Wilson coefficients, in particular ${C}_{1}$. To this end we suggest a more refined theoretical study as well as more precise measurements of the observables that currently provide the strongest bounds on hypothetical new weak phases in ${C}_{1}$ and ${C}_{2}$. We note that the semileptonic $CP$ asymmetries seem to have the best prospect for improving the bound on the weak phase in ${C}_{1}$.
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Award: G3889815562
OpenAlex ID: W1479353197