The study of $\gamma \gamma \to \gamma \psi (2S)$ at Belle

Abstract

Using $980\mathrm{f}{\mathrm{b}}^{-1}$ of data on and around the ${\rm Y}(nS)(n=1,2,3,4,5)$ resonances collected with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider, the two-photon process $\gamma \gamma \to \gamma \psi (2S)$ is studied from the threshold to $4.2\mathrm{GeV}$ for the first time. Two structures are seen in the invariant mass distribution of $\gamma \psi (2S)$: one at $M_{R_1}=3922.4\pm 6.5\pm 2.0\mathrm{MeV}/c^2$ with a width of ${\Gamma }_{R_1}=22\pm 17\pm 4\mathrm{MeV}$, and another at $M_{R_2}=4014.3\pm 4.0\pm 1.5\mathrm{MeV}/c^2$ with a width of ${\Gamma }_{R_2}=4\pm 11\pm 6\mathrm{MeV}$; the signals are parametrized with the incoherent sum of two Breit-Wigner functions. The first structure is consistent with the $X(3915)$ or the ${\chi }_{c2}(3930)$, and the local statistical significance is determined to be $3.1\sigma$ with the systematic uncertainties included. The second matches none of the known charmonium or charmoniumlike states, and its global significance is determined to be $2.8\sigma$ including the look-elsewhere effect. The production rates are ${\Gamma }_{\gamma \gamma }\mathcal{B}(R_1\to \gamma \psi (2S))=9.8\pm 3.6\pm 1.2\mathrm{eV}$ assuming $(J^{PC},|\lambda |)=(0^{++},0)$ or $2.0\pm 0.7\pm 0.2\mathrm{eV}$ with $(2^{++},2)$ for the first structure and ${\Gamma }_{\gamma \gamma }\mathcal{B}(R_2\to \gamma \psi (2S))=6.2\pm 2.2\pm 0.8\mathrm{eV}$ with $(0^{++},0)$ or $1.2\pm 0.4\pm 0.2\mathrm{eV}$ with $(2^{++},2)$ for the second one. Here, the first errors are statistical and the second systematic, and $\lambda$ is the helicity.

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• Evidence for the decay $X(3872)\to \psi (2S)\gamma$
• Measurement of the X(3872) production cross section via decays to J/psi pi pi in pp collisions at sqrt(s) = 7 TeV
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• Does the enhancement observed in $\gamma \gamma \to D\bar{D}$ contain two $P$-wave higher charmonia?
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Cited by in corpus (12)

• Heavy- and light-flavor symmetry partners of the $T_{cc}^{+}(3875)$, the $X(3872)$ and the $X(3960)$ from light-meson exchange saturation
• Spectrum of the molecular tetraquarks: Unraveling the $T_{cs0}(2900)$ and $T_{c\bar{s}0}^a(2900)$
• Radiative decays of the spin-$2$ partner of $X(3872)$
• $X(3872)$, $X(4014)$, and their bottom partners at finite temperature
• Charmonium ${\chi }_{c0}$ and ${\chi }_{c2}$ resonances in coupled-channel scattering from lattice QCD
• Production of the $X(4014)$ as the spin-2 partner of $X(3872)$ in $e^{+}{e}^{-}$ collisions
• $P$-wave charmonium contribution to hidden-charm states from reanalysis of lattice QCD data
• hidden charm decays of $X(4014)$ in a $D^{\ast }{\bar{D}}^{\ast }$ molecule scenario
• Role of the short-range dynamics in the formation of $D^{(\ast )}{\bar{D}}^{(\ast )}/B^{(\ast )}{\bar{B}}^{(\ast )}$ hadronic molecules
• Shedding light on charmonium
• Hidden-Charm Tetraquarks in a Mixture Model: Coupled-Channel Analysis with $c\bar{c}$ and Hadronic Molecular Components
• Two-body strong decays of the hidden-charm tetraquark molecular states via the QCD sum rules