6533b851fe1ef96bd12a95e0

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Radiative decays χcJ→Vγ within the QCD factorization framework

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We present a discussion of radiative decays ${\ensuremath{\chi}}_{cJ}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\rho}(\ensuremath{\omega},\ensuremath{\phi})$. The decay amplitudes are computed within the QCD factorization framework. NRQCD has been used in the heavy meson sector as well as a collinear expansion in order to describe the overlap with light mesons in the final state. The color-singlet contributions to all helicity amplitudes have been computed using the light-cone distribution amplitudes of twist-2 and twist-3. All obtained expressions are well defined at least in the leading-order approximation. The color-octet contributions have also been studied in the Coulomb limit in order to exhibit their scaling behavior. In order to understand the relevance of the different contributions we perform numerical estimates using the color-singlet contributions. For the ${\ensuremath{\chi}}_{c1}\ensuremath{\rightarrow}\ensuremath{\gamma}{V}_{\ensuremath{\perp}}$ decays, to vector mesons with transverse polarization, we find that the color-singlet contribution potentially allows for a reliable description. On the other hand, for the ${\ensuremath{\chi}}_{c1}\ensuremath{\rightarrow}\ensuremath{\gamma}{V}_{\ensuremath{\parallel}}$ decays, to vector mesons with longitudinal polarization, our findings indicate that the color-octet mechanism may be important for a good description. We expect that more accurate measurements of the decay ${\ensuremath{\chi}}_{c2}\ensuremath{\rightarrow}\ensuremath{\gamma}{V}_{\ensuremath{\perp},\ensuremath{\parallel}}$ can help to better understand the mechanism of radiative decays.