Improved measurement of η/η′ mixing in $$ {B}_{(s)}^0\to J/\psi {\eta}^{\left(\prime \right)} $$ decays

A bstract Branching fraction ratios between the decays $$ {B}_{(s)}^0\to J/\psi {\eta}^{\left(\prime \right)} $$ B s 0 → J / ψ η ′ are measured using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb − 1 . The measured ratios of these branching fractions are $$ {\displaystyle \begin{array}{c}\frac{\mathcal{B}\left({B}^0\to J/{\psi \eta}^{\prime}\right)}{\mathcal{B}\left({B}^0\to J/\psi \eta \right)}=0.48\pm 0.06\pm 0.02\pm 0.01,\\ {}\frac{\mathcal{B}\left({B}_s^0\to J/{\psi \eta}^{\prime}\right)}{\mathcal{B}\left({B}_s^0\to J/\psi \eta \right)}=0.80\pm 0.02\pm 0.02\pm 0.01,\end{array}} $$ B B 0 → J / ψη ′ B B 0 → J / ψη = 0.48 ± 0.06 ± 0.02 ± 0.01 , B B s 0 → J / ψη ′ B B s 0 → J / ψη = 0.80 ± 0.02 ± 0.02 ± 0.01 , where the uncertainties are statistical, systematic and related to the precision of the η (′) branching fractions, respectively. They are used to constrain the η/η ′ mixing angle, ϕ P , and to probe the presence of a possible glueball component in the η ′ meson, described by the gluonic mixing angle ϕ G . The obtained results are $$ {\displaystyle \begin{array}{c}{\phi}_{\textrm{P}}={\left({41.6}_{-1.2}^{+1.0}\right)}^{\circ },\\ {}{\phi}_{\textrm{G}}={\left({28.1}_{-4.0}^{+3.9}\right)}^{\circ },\end{array}} $$ ϕ P = 41.6 − 1.2 + 1.0

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