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

TL;DR

This study searches for the $Z_1(4050)^+$ and $Z_2(4250)^+$ states in B meson decays but finds no evidence for their existence, setting upper limits on their branching fractions.

Contribution

The paper provides the first search for these states using BaBar data and models the background using $K ext{pi}$ distributions and Legendre moments.

Findings

No evidence for $Z_1(4050)^+$ and $Z_2(4250)^+$ resonances.

Sets 90% confidence level upper limits on branching fractions.

Uses background modeling with $K ext{pi}$ mass and Legendre moments.

Abstract

We search for the $Z_1(4050)^+$ and $Z_2(4250)^+$ states, reported by the Belle Collaboration, decaying to $\chi_{c1} \pi^+$ in the decays $\bar B^0 \to \chi_{c1} K^- \pi^+$ and $B^+ \to \chi_{c1} K^0_S \pi^+$ where $\chi_{c1} \to \jpsi \gamma$. 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 $\chi_{c1}\pi$ 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 $Z_1(4050)^+$ and $Z_2(4250)^+$ resonances, and 90% confidence level upper limits on the branching fractions are reported for the corresponding $B$-meson decay modes.