We report a search for $X(3872)$ and $X(3915)$ in $B^+ \to \chi_{c1} \pi^0 K^+$ decays. We set an upper limit of $\mathcal{B}(B^+ \to X(3872) K^+) \times \mathcal{B}(X(3872) \to \chi_{c1} \pi^0)$ $ < ...8.1 \times 10^{-6}$ and $\mathcal{B}(B^+ \to X(3915) K^+) \times \mathcal{B}(X(3915) \to \chi_{c1} \pi^0)$ $ < 3.8 \times 10^{-5}$ at 90\% confidence level. We also measure $\mathcal{B}(X(3872) \to \chi_{c1} \pi^0)/\mathcal{B}(X(3872) \to J/\psi \pi^+ \pi^-) < 0.97$ at 90\% confidence level. The results reported here are obtained from $772 \times 10^{6}$ $B\overline{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.
Using data samples of 89.5 fb$^{−1}$, 711.0 fb$^{−1}$, and 121.4 fb$^{−1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^−$ collider at center-of-mass energies 10.52, ...10.58, and 10.867 GeV, respectively, we study the exclusive reactions $e^+ e^− →γχ_{cJ}$ (J=0, 1, 2) and $e^+ e^− →γη_c$. A significant $γχ_{c1}$ signal is observed for the first time at $√s$=10.58 GeV with a significance of 5.1$σ$ including systematic uncertainties. No significant excesses for $γχ_{c0}, γχ_{c2}$, and $γη_c$ final states are found, and we set 90% credibility level upper limits on the Born cross sections $(σB)$ at 10.52 GeV, 10.58 GeV, and 10.867 GeV. Together with cross sections measured by BESIII at lower center-of-mass energies, the energy dependency of $σ_B(e^+e^− → γχ_{c1})$ is obtained.
