Study of $χ_{b1,2}(2P) \to ωΥ(1S)$ transitions in $Υ(3S) \to γχ_{b1,2}(2P)$ decays at BaBar

TL;DR

This BaBar study probes the radiative production and subsequent transitions of $χ_{b1}(2P)$ and $χ_{b2}(2P)$ to $ωΥ(1S)$ via $Υ(3S) ightarrow γχ_{b1,2}(2P)$ decays, using a 28.0 fb$^{-1}$ data sample corresponding to $121.3 imes 10^{6}$ $Υ(3S)$ decays. It reports clean signals for both $χ_{b1}(2P)$ and $χ_{b2}(2P)$, performs the first angular-distribution measurements for these states, and delivers improved branching fractions with a comprehensive account of systematic uncertainties. The analysis employs a Channel Likelihood method to extract signal fractions, validates spin-parity expectations through angular observables, and tests for a possible $χ_{b0}(2P) ightarrow ωΥ(1S)$ channel, for which a 90% C.L. upper limit of $<0.23 ext{%}$ is set. The resulting branching fractions and their ratio, $r_{2/1}=(0.27 \,\pm\,0.03_{stat} \,\pm\,0.02_{sys} \,\pm\,0.04_{pdg})$, are in agreement with prior CLEO and Belle findings but show a notable tension with the predicted value $ oughly 1.3$ in Voloshin’s framework, underscoring subtleties in spin-dependent bottomonium transitions.

Abstract

Results are presented on $χ_{b1,2}(2P) \to ωΥ(1S)$ transitions from $e^+e^- \to Υ(3S) \to γχ_{b1,2}(2P)$ decays. The data were collected with the BaBar detector at the PEP-II asymmetric-energy $e^+e^-$ collider at SLAC. The integrated luminosity of the data sample is 28.0 fb$^{-1}$, corresponding to $121.3 \times 10^6$ $Υ(3S)$ decays. Signals of $χ_{b1,2}(2P)$ are observed over a negligible background. Improved precision measurements of branching fractions are obtained. First measurements of the $χ_{b1,2}(2P)$ angular distributions are performed. No evidence is found for the presence of a $χ_{b0}(2P) \to ωΥ(1S)$ decay mode.

Figures (12)

• Figure 1: Recoil mass to the $\hbox{${\pi^{+}}$} \hbox{${\pi^{-}}$}$ system $m_{rec}(\hbox{${\pi^{+}}$} \hbox{${\pi^{-}}$})$ for: (a) MC simulation of the decay channel (\ref{['eq:back1']}), (b) reconstructed events from data selection of the decay channel (\ref{['eq:back2']}).
• Figure 2: (a) Distribution of the recoil mass against the $\hbox{${\pi^{+}}$} \hbox{${\pi^{-}}$}$ system, for events selected as candidates for the signal decay channel (\ref{['eq:sig']}). The lines are the results from the fit described in the text. (b) Recoil mass to the $\hbox{${\pi^{+}}$} \hbox{${\pi^{-}}$}$ system for signal MC decay channel (\ref{['eq:sig']}) events. The vertical lines indicate the region removed by the veto on background events from channels (\ref{['eq:back1']}) and (\ref{['eq:back2']}).
• Figure 3: Combinatorial recoil mass $m_{rec}(\hbox{${\pi^{+}}$} \hbox{${\pi^{-}}$} \hbox{${\pi^{0}}$} \gamma_s)$. The shaded area shows the region of selected $焇{(1S)}$ candidates. The enhancement above the $焇{(1S)}$ mass region is produced by the combinatorial combinatorial.
• Figure 4: The $\hbox{${\pi^{+}}$} \hbox{${\pi^{-}}$} \hbox{${\pi^{0}}$}$ invariant mass distribution. The shaded area indicates the range of the $\omega$ selection.
• Figure 5: Distribution of $\it \Delta\xspace^2$ for the candidate events. The shaded area indicates the range of the final selection.