Hadroproduction of the ${\chi }_1$ and ${\chi }_2$ states of charmonium in 800-$\mathrm{GeV}/c$ proton-silicon interactions

The cross sections for the hadroproduction of the ${\chi }_1$ and ${\chi }_2$ states of charmonium in proton-silicon collisions at $\sqrt{s}=38.8\mathrm{}$ GeV have been measured in Fermilab fixed target experiment 771. The χ states were observed via their radiative decay to $J/\psi \gamma ,$ where the photon converted to $e^{+}{e}^{-}$ in the material of the spectrometer. The estimated values for the ${\chi }_1$ and ${\chi }_2$ cross sections for $x_F>0\mathrm{}$ are $263\pm 69\left(\mathrm{stat}\right)\pm 32\left(\mathrm{syst}\right)$ and $498\pm 143\left(\mathrm{stat}\right)\pm 67\left(\mathrm{syst}\right)$ nb per nucleon, respectively. The resulting $\sigma \left({\chi }_1\right)/\sigma \left({\chi }_2\right)$ ratio of $0.53\pm 0.20\left(\mathrm{stat}\right)\pm 0.07\left(\mathrm{syst}\right),$ although somewhat larger than most theoretical expectations, can be accommodated by the latest theoretical estimates.