Observation of two resonancelike structures in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>π</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:mrow></mml:msub></mml:math>mass distribution in exclusive<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mover accent="true"><mml:mi>B</mml:mi><mml:mo>¯</mml:mo></mml:mover><mml:mn>0</mml:mn></mml:msup><mml:mo>→</mml:mo><mml:msup><mml:mi>K</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:msup><mml:mi>π</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:mrow></mml:msub></mml:math>decays

We report the first observation of two resonancelike structures in the ${\ensuremath{\pi}}^{+}{\ensuremath{\chi}}_{c1}$ invariant mass distribution near $4.1\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ in exclusive ${\overline{B}}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\chi}}_{c1}$ decays. From a Dalitz plot analysis in which the ${\ensuremath{\pi}}^{+}{\ensuremath{\chi}}_{c1}$ mass structures are represented by Breit-Wigner resonance amplitudes, we determine masses and widths of: ${M}_{1}=(4051\ifmmode\pm\else\textpm\fi{}{14}_{\ensuremath{-}41}^{+20})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, ${\ensuremath{\Gamma}}_{1}=({82}_{\ensuremath{-}17\ensuremath{-}22}^{+21+47})\text{ }\text{ }\mathrm{MeV}$, ${M}_{2}=({4248}_{\ensuremath{-}29\ensuremath{-}35}^{+44+180})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, and ${\ensuremath{\Gamma}}_{2}=({177}_{\ensuremath{-}39\ensuremath{-}61}^{+54+316})\text{ }\text{ }\mathrm{MeV}$; and product branching fractions of $\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{Z}_{1,2}^{+})\ifmmode\times\else\texttimes\fi{}\mathcal{B}({Z}_{1,2}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\chi}}_{c1})=({3.0}_{\ensuremath{-}0.8\ensuremath{-}1.6}^{+1.5+3.7})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and $({4.0}_{\ensuremath{-}0.9\ensuremath{-}0.5}^{+2.3+19.7})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, respectively. Here the first uncertainty is statistical, the second is systematic. The significance of each of the ${\ensuremath{\pi}}^{+}{\ensuremath{\chi}}_{c1}$ structures exceeds $5\ensuremath{\sigma}$, including the systematic uncertainty from various fit models. This analysis is based on $657\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ events collected at the $\ensuremath{\Upsilon}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider.