Observation of a Resonancelike Structure in the π+−ψ′ Mass Distribution in Exclusive B→Kπ+−ψ′ Decays

A distinct peak is observed in the ${ensuremath{pi}}^{ifmmodepmelsetextpmfi{}}{ensuremath{psi}}^{ensuremath{‘}}$ invariant mass distribution near 4.43 GeV in $Bensuremath{rightarrow}K{ensuremath{pi}}^{ifmmodepmelsetextpmfi{}}{ensuremath{psi}}^{ensuremath{‘}}$ decays. A fit using a Breit-Wigner resonance shape yields a peak mass and width of $M=4433ifmmodepmelsetextpmfi{}4(mathrm{stat})ifmmodepmelsetextpmfi{}2(mathrm{syst})text{ }text{ }mathrm{MeV}$ and $ensuremath{Gamma}={45}_{ensuremath{-}13}^{+18}(mathrm{stat}{)}_{ensuremath{-}13}^{+30}(mathrm{syst})text{ }text{ }mathrm{MeV}$. The product branching fraction is determined to be $mathcal{B}mathbf{(}{B}^{0}ensuremath{rightarrow}{K}^{ensuremath{mp}}{Z}^{ifmmodepmelsetextpmfi{}}(4430)mathbf{)}ifmmodetimeselsetexttimesfi{}mathcal{B}mathbf{(}{Z}^{ifmmodepmelsetextpmfi{}}(4430)ensuremath{rightarrow}{ensuremath{pi}}^{ifmmodepmelsetextpmfi{}}{ensuremath{psi}}^{ensuremath{‘}}mathbf{)}=(4.1ifmmodepmelsetextpmfi{}1.0(mathrm{stat})ifmmodepmelsetextpmfi{}1.4(mathrm{syst}))ifmmodetimeselsetexttimesfi{}{10}^{ensuremath{-}5}$, where ${Z}^{ifmmodepmelsetextpmfi{}}(4430)$ is used to denote the observed structure. The statistical significance of the observed peak is $6.5ensuremath{sigma}$. These results are obtained from a $605text{ }text{ }{mathrm{fb}}^{ensuremath{-}1}$ data sample that contains $657ifmmodetimeselsetexttimesfi{}{10}^{6}$ $Boverline{B}$ pairs collected near the $ensuremath{Upsilon}(4S)$ resonance with the Belle detector at the KEKB asymmetric energy ${e}^{+}{e}^{ensuremath{-}}$ collider.