Branching Fractions for $\psi (2S)$-to-$J/\psi$ Transitions

We describe new measurements of the inclusive and exclusive branching fractions for $\psi (2S)$ transitions to $J/\psi$ using $e^{+}{e}^{-}$ collision data collected with the CLEO detector operating at CESR. All branching fractions and ratios of branching fractions reported here represent either the most precise measurements to date or the first direct measurements. Indirectly and in combination with other CLEO measurements, we determine $\mathcal{B}({\chi }_{cJ}\to \gamma J/\psi )$ and $\mathcal{B}[\psi (2S)\to \mathrm{\text{light hadrons}}]$.

Figure 1

For inclusively selected dimuon (left) and dielectron (right) events, the distributions of the dilepton mass in the $\psi (2S)$ data (solid circles), after subtraction of the luminosity-scaled continuum, and in MC (solid line). The two peaks above 3.2 GeV in the $m({\mu }^{+}{\mu }^{-})$ distributions correspond to backgrounds from ${\chi }_{c0,2}\to K^{+}{K}^{-}$ and ${\chi }_{c0}\to {\pi }^{+}{\pi }^{-}$.

Figure 2

For $\psi (2S)\to {\pi }^{+}{\pi }^{-}{\ell }^{+}{\ell }^{-}$ (left) and $\psi (2S)\to {\pi }^0{\pi }^0{\ell }^{+}{\ell }^{-}$ (right), $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ samples combined, candidate events in the $\psi (2S)$ data (solid circles), MC simulation of signal (solid line), and $\psi (2S)\to \eta J/\psi$ background (dashed histogram): distributions of the dilepton mass (top), the mass recoiling against the dipion pair (middle), and the invariant mass of the two pions.

Figure 3

For $\psi (2S)\to \eta (\to \gamma \gamma ,{\pi }^{+}{\pi }^{-}{\pi }^0){\ell }^{+}{\ell }^{-}$ (left) and $\psi (2S)\to {\pi }^0{\ell }^{+}{\ell }^{-}$ (right), $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ samples combined, candidate events in the $\psi (2S)$ data (solid circles) and MC simulation of signal (solid line): distributions of the dilepton mass (top), the $J/\psi$ momentum (middle), and the invariant mass of the two photons. In the lower left mass plot, the solid circles (data) and solid line (MC) apply to $\eta \to \gamma \gamma$ decays, and the open circles (data) and the dashed histogram (MC) to $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$.

Figure 4

For $\psi (2S)\to \gamma {\chi }_{cJ}$, ${\chi }_{cJ}\to \gamma J/\psi$, $J/\psi \to {\ell }^{+}{\ell }^{-}$ candidate events in the $\psi (2S)$ data (solid circles) and MC simulation of signal (solid line), the distribution of the energy of the second-most energetic photon, $E_{\gamma \mathrm{\text{−}}\mathrm{low}}$ (top), and the two-photon recoil mass (bottom). The arrows indicate nominal cut values. The inset offers a close-up of the ${\chi }_{c0}$ region. The broken lines represent ${\pi }^0{\pi }^{0}J/\psi$ MC.