Search for $e^+ e^- \to γχ_{bJ}$ ($J$ = 0, 1, 2) near $\sqrt{s} = 10.746$ GeV at Belle II

Abstract

We search for the $e^+ e^- \to γχ_{bJ}$ ($J$ = 0, 1, 2) processes at center-of-mass energies $\sqrt{s}$ = 10.653, 10.701, 10.746, and 10.804 GeV. These data were collected with the Belle II detector at the SuperKEKB collider and correspond to 3.5, 1.6, 9.8, and 4.7 fb$^{-1}$ of integrated luminosity, respectively. We set upper limits at the 90\% confidence level on the Born cross sections for $e^+ e^- \to γχ_{bJ}$ at each center-of-mass energy $\sqrt{s}$ near 10.746 GeV. The upper limits at 90\% confidence level on the Born cross sections for $e^+ e^- \to γχ_{b1}$ are significantly smaller than the corresponding measured values for $e^+e^-\toωχ_{b1}$ and $e^+e^-\toπ^+π^-Υ(2S)$ at $\sqrt{s}$ = 10.746 GeV.

Figures (2)

• Figure 1: The invariant mass spectrum of $l^+l^-$ from a combined $\sqrt{s} =$ 10,653, 10.701, 10.746, and 10.804 GeV data sample. The red dashed lines show the signal region (9.44 GeV/$c^2$$<$$M(l^+l^-)$$<$ 9.49 GeV/$c^2$).
• Figure 2: The fitted results to $M(\gamma\Upsilon(1S))$ distributions from data samples in (left) $\mu^+\mu^-$ and (right) $e^+e^-$ modes at $\sqrt{s}$$=$ (a, b) 10.653, (c, d) 10.701, (e, f) 10.746, and (g, h) 10.804 GeV, respectively. Here, the points with error bars are the data samples. The red curves show the fitted results. The blue curves show the total backgrounds. The black dot-dashed curves show the $\chi_{b0}$ candidate, the purple dashed curves show the $\chi_{b1}$ candidate, and the blue dotted curves show the $\chi_{b2}$ candidate.