Measurement of upper limits for ${\rm Y}\to \gamma +\mathcal{R}$ decays

We report on a study of exclusive radiative decays ${\rm Y}(nS)\to \gamma +\mathcal{R}$ ($n=1$, 2, 3), with $\mathcal{R}$ a narrow resonant hadronic state decaying into four or more charged particles (plus possible neutrals). Using data collected from the CLEO III detector at the Cornell Electron Storage Ring, we present upper limits of order ${10}^{-4}$ for such bottomonium two-body decays as a function of the mass $M_{\mathcal{R}}$ recoiling opposite the photon.

Figure 1

The 95% confidence level $M_{\mathcal{R}}$-dependent ${\rm Y}(nS)\to \mathcal{B}(\gamma \mathcal{R})$ upper limit contours obtained for ${\rm Y}\to \gamma +\mathcal{R}$, $\mathcal{R}\to \ge 4$ charged tracks for the ${\rm Y}(1S)$, ${\rm Y}(2S)$, ${\rm Y}(3S)$, and ${\rm Y}(4S)$. Limits are obtained by dividing upper limits on yield by reconstruction efficiency and number of resonant events, and also incorporating systematic uncertainties. Limits are of order $\mathcal{B}(\gamma \mathcal{R})\approx {10}^{-4}$.

Figure 2

The 95% confidence level $M_{\mathcal{R}}$-dependent cross-section upper limit contours obtained for $e^{+}{e}^{-}\to \gamma +\mathcal{R}$, $\mathcal{R}\to \ge 4$ charged tracks for the below ${\rm Y}(1S)$, ${\rm Y}(2S)$, ${\rm Y}(3S)$, and ${\rm Y}(4S)$ continua (nb). This plot is obtained by dividing the result of our fitting procedure on the continuum by the off-resonance luminosity. The angular correction here is based on the expected distribution appropriate for continuum initial state radiation. Systematic errors have also been incorporated into these limits.

Figure 3

The 95% confidence level upper limit contours derived from applying our procedure to fabricated Monte Carlo signal spectra.