Color-octet mechanism inγ+p→Jψ+X

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Abstract

Photoproduction of $\frac{J}{\ensuremath{\psi}}$ is considered including the color-octet contributions from the various partial wave states, $^{2S+1}L_{J}=^{1}S_{0}, ^{3}S_{1}, \mathrm{and} ^{3}P_{J}$. The production cross section depends on three new nonperturbative parameters defined in NRQCD, called the color-octet matrix elements. Using the color-octet matrix elements determined by fitting the $\frac{J}{\ensuremath{\psi}}$ production at the Fermilab Tevatron, we find that the color-octet ${(c\overline{c})}_{8}(^{1}S_{0}\mathrm{and} ^{3}P_{J})$ contributions to the $\frac{J}{\ensuremath{\psi}}$ photoproduction at the fixed target experiments and at DESY HERA are too large compared to the data on $\ensuremath{\sigma}(\ensuremath{\gamma}+p\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}}+X)$ in the forward direction, and the $z$ distribution of $\frac{J}{\ensuremath{\psi}}$. The ${P}_{T}^{2}$ distribution of $\frac{J}{\ensuremath{\psi}}$ and the total inelastic $\frac{J}{\ensuremath{\psi}}$ production rate as a function of $\sqrt{{s}_{\ensuremath{\gamma}p}}$ are predicted including color-octet contributions. We also briefly digress on the $B\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}}+X$ and observe the similar situation. This may be an indication that the color-octet matrix elements determined from the $\frac{J}{\ensuremath{\psi}}$ production at the Tevatron, especially $〈0|{\mathcal{O}}_{8}^{\ensuremath{\psi}}(^{1}S_{0})|0〉$ and $〈0|{\mathcal{O}}_{8}^{\ensuremath{\psi}}(^{3}P_{J})|0〉$, might have been overestimated by an order of magnitude.

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