Charm Production By Muons And Its Role In Scale Non-Invariance

Interactions of 209-GeV muons in the multimuon spectrometer at Fermilab have yielded more than 8\ifmmode\times\else\texttimes\fi{}${10}^{4}$ events with two muons in the final state. After reconstruction and cuts, the data contain 20 072 events with (81\ifmmode\pm\else\textpm\fi{}10)% attributed to the diffractive production of charmed states decaying to muons. The cross section for diffractive charm muoproduction is ${6.9}_{\ensuremath{-}1.4}^{+1.9}$ nb where the error includes systematic uncertainties. Extrapolated to ${Q}^{2}=0$ with $\ensuremath{\sigma}({Q}^{2})=\ensuremath{\sigma}(0){(1+\frac{{Q}^{2}}{{\ensuremath{\Lambda}}^{2}})}^{\ensuremath{-}2}$, the effective cross section for 178- (100-) GeV photons is ${750}_{\ensuremath{-}130}^{+180}$ (${560}_{120}^{200}$) nb and the parameter $\ensuremath{\Lambda}$ is 3.3\ifmmode\pm\else\textpm\fi{}0.2 (2.9\ifmmode\pm\else\textpm\fi{}0.2) GeV/c. The $\ensuremath{\nu}$ dependence of the cross section is similar to that of the photongluon-fusion model. Okubo-Zweig-Iizuka selection rules and unitarity allow the muon data to set a 90%-confidence lower limit on the $\ensuremath{\psi}N$ total cross section of 0.9 mb. A first determination of the structure function ${F}_{2}(c\overline{c})$ for diffractive charm production indicates that charm accounts for approximately $\frac{1}{3}$ of the scale noninvariance observed in inclusive muon-nucleon scattering at low Bjorken $x$.