Search for the $Z_1(4050)^+$ and $Z_2(4250)^+$ states in $\bar B^0 \to χ_{c1} K^- π^+$ and $B^+ \to χ_{c1} K^0_S π^+$

Abstract: We search for the $Z_1(4050)<sup>+$ and $Z_2(4250)<sup>+$ states, reported by the Belle Collaboration, decaying to $\chi_{c1} \pi<sup>+$ in the decays $$\bar B⁰ \to \chi_{c1} K^- \pi<sup>+$$ and $$B⁺ \to \chi_{c1} K^0_S \pi<sup>+$$ where $\chi_{c1} \to \jpsi \gamma$. The data were collected with the BaBar detector at the SLAC PEP-II asymmetric-energy $e<sup>+e<sup>-$ collider operating at center-of-mass energy 10.58 GeV, and correspond to an integrated luminosity of 429 fb$<sup>{-1}$. In this analysis, we model the background-subtracted, efficiency-corrected $\chi_{c1}\pi$ mass distribution using the $K \pi$ mass distribution and the corresponding normalized $K \pi$ Legendre polynomial moments, and then test the need for the inclusion of resonant structures in the description of the $\chi_{c1}\pi$ mass distribution. No evidence is found for the $Z_1(4050)<sup>+$ and $Z_2(4250)<sup>+$ resonances, and 90% confidence level upper limits on the branching fractions are reported for the corresponding $B$-meson decay modes.