Higher-twist effects in the reactionπ−N→μ+μ−Xat 253 GeV/c

The distributions of quarks in the pion and nucleon are extracted from measurements of the reaction ${\pi }^{-}N\to {\mu }^{+}{\mu }^{-}X$ at 253 GeV/c in a naive Drell-Yan analysis, as well as QCD-corrected analyses at leading-log and next-to-leading-log order. As $x_{\pi }\to 1$ the pion structure function shows a term that varies as $\frac{1}{m_{\mu \mu }^4}$, which we interpret as a higher-twist effect. Additionally, the angular distribution of the ${\mu }^{+}$ in the muon-pair rest frame tends towards ${sin}^2\theta$ as $x_{\pi }\to 1$ and as $m_{\mu \mu }\to 0$ in a manner consistent with higher-twist effects. When the strongly mass-dependent higher-twist effects are included as part of the pion structure function, the nucleon structure function agrees well with leading-twist results from deeply inelastic lepton-hadron scattering. A significant advance of the present work is the extension of the analysis to low masses by the subtraction of the $\frac{J}{\psi }$ and ${\psi }^{\prime }$ resonances from the continuum. Our analysis covers the kinematic range $0.4<\mathrm{}{x}_{\pi }<1.0\mathrm{}$ and $0.02<\mathrm{}{x}_N<0.33\mathrm{}$ with $3.0<\mathrm{}{m}_{\mu \mu }<8.55\mathrm{}$ GeV/${\mathit{c}}^2$. Cross sections for ${\psi }^{\prime }$ production are presented in an appendix.