${\boldsymbol {\boldsymbol c}}$ ${\boldsymbol {\overline{\boldsymbol c}}}$ MESONS
(including possibly non- ${\boldsymbol {\boldsymbol q}}$ ${\boldsymbol {\overline{\boldsymbol q}}}$ states)
INSPIRE search

${{\boldsymbol X}{(4020)}}$ $I^G(J^{PC})$ = $1^+(?^{? -})$

Properties incompatible with a ${{\mathit q}}{{\overline{\mathit q}}}$ structure (exotic state). See the review on non- ${{\mathit q}}{{\overline{\mathit q}}}$ states. Charged X(4020) seen by ABLIKIM 2013X from ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit h}_{{c}}{(1P)}}$ at c.m. energy from 3.90 to 4.42 GeV as a peak in the invariant mass distribution of the ${{\mathit \pi}^{\pm}}{{\mathit h}_{{c}}{(1P)}}$ system, and by ABLIKIM 2014B from ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ( ${{\mathit D}^{*}}{{\overline{\mathit D}}^{*}}){}^{+-}{{\mathit \pi}^{\mp}}$ events in ( ${{\mathit D}^{*}}{{\overline{\mathit D}}^{*}}$ )${}^{+-}$ mass. A neutral X(4020) seen by ABLIKIM 2014P at three c.m. energies in the same range in ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit h}_{{c}}{(1P)}}$ as a peak in the larger of the two masses recoiling against a ${{\mathit \pi}^{0}}$. ABLIKIM 2015AA observes a 5.9 $\sigma $ signal in ( ${{\mathit D}^{*}}{{\overline{\mathit D}}^{*}}$ )${}^{0}$ in ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ( ${{\mathit D}^{*}}{{\overline{\mathit D}}^{*}}$ )${}^{0}{{\mathit \pi}^{0}}$ events using collisions at two c.m. energies. Production rates and mass values support grouping neutral and charged X(4020) together as manifestations of a single $\mathit I = $ particle.
${{\mathit X}{(4020)}}$ MASS   $4024.1 \pm1.9$ MeV 
${{\mathit X}{(4020)}}$ WIDTH   $13 \pm5$ MeV (S = 1.7)
$\Gamma_{1}$ ${{\mathit h}_{{c}}{(1P)}}{{\mathit \pi}}$ seen450
$\Gamma_{2}$ ${{\mathit D}^{*}}{{\overline{\mathit D}}^{*}}$ seen85
$\Gamma_{3}$ ${{\mathit D}}{{\overline{\mathit D}}^{*}}$ + c.c. not seen542
$\Gamma_{4}$ ${{\mathit \eta}_{{c}}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ not seen872
$\Gamma_{5}$ ${{\mathit J / \psi}{(1S)}}{{\mathit \pi}^{\pm}}$ not seen811