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