Amplitude Analysis of the Isospin-Violating Decay $J/ψ\rightarrowγηπ^{0}$

Abstract

Using $(10087 \pm 44)\times 10^{6}$ $\jpsi$ events collected with the BESIII detector, we perform the first amplitude analysis of the process $\jpsi\toγη\piz$. The decay is dominated by the intermediate processes $\jpsi\to\piz \bo \left( \toγη\right)$, $\jpsi\to\pizρ(1450)^0 \left( \toγη\right)$ and $\jpsi\toηh_1(1170) \left( \toγ\piz\right)$. Contributions from $\jpsi\toγa_0(980)^0(\toη\piz)$, $\jpsi\toγa_2(1320)^0(\toη\piz)$ and $\jpsi\toγa_2(1700)^0(\toη\piz)$ are observed with a statistical significance exceeding $5σ$, constituting the first observation of radiative transitions of $\jpsi$ to isospin-triplet scalar mesons. The total branching fraction of $\jpsi\toγη\piz$ is measured to be \num{25.7\pm0.3\pm1.5e-6}, where the first uncertainty is statistical and the second systematic. This result is consistent with the previous measurement, with the precision improved by more than a factor of two.

Figures (4)

• Figure 1: The $\gamma\gamma$ invariant mass distributions of (a) $\pi^{0}$ and (b) $\eta$ candidates after applying all selection criteria. The dots with error bars represent data. The red solid line corresponds to the signal MC simulation normalized to the measured BF in this work.
• Figure 2: The $Q$-weighted distribution in the Dalitz plot for $J/\psi\to\gamma\eta\pi^{0}$ candidates.
• Figure 3: The $m_{\pi^{0}\eta}$ distribution at $m_{\pi^{0}\eta}< 1.0GeV/\clight^2$, where the black points with error bars correspond to data, the blue line represents the estimated background events, the red points with error bars represent the background-subtracted data, and the red line corresponds to the signal MC curve.
• Figure 4: Projections of the nominal results on the (a) $m_{\gamma\eta}$, (b) $m_{\gamma\pi^{0}}$ and (c) $m_{\eta\pi^{0}}$ distributions. The black dots with error bars represent $Q$-weighted data, the red solid lines show the total fit results, and the remaining solid, dashed, and dash dotted lines correspond to the signal contributions from individual intermediate processes, as indicated in the legend placed at the bottom right of the full figure. The pull distributions are shown in the bottom of each plot. In Fig. (c), the background subtracted data shown in Fig. \ref{['fig:mpieta_data']} is also plotted.