Single spin asymmetry for the Drell-Yan process

Abstract

We calculated the single spin asymmetries for the reaction $P+P(\uparrow)\rightarrow l \overline{l}+X$ in the framework of twist-3 QCD for HERA energies. The necessary imaginary phase is produced by the on-shell contribution of the quark propagator, while the long distance part is analogous to that providing the direct photon asymmetry calculated by J. Qiu and G. Sterman. The asymmetry turns out to be generally of the order percent.

Figures (4)

• Figure 1: Parton distribution functions and parton subprocesses for twist 3.
• Figure 2: Twist 3 diagramm for the process $P+P(\uparrow)\rightarrow l~\overline{l}+X$. The quark propagator generates the imaginary part when it is put on-shell, therefore the gluon has vanishing four-momentum $(x_{1}-x_{2})\approx 0$.
• Figure 3: Typical twist-2 (upper row) and twist-3 (lower row) diagrams for the case of high $p_T$ dilepton production. The outgoing photon can produce a dilepton pair. This process can be distinguished from the one treated here by the additional jet coming from the fragmenting quark.
• Figure 4: Asymmetry for the process $P+P(\uparrow)\rightarrow l~\overline{l}+X$ with the momentum fraction chosen as $x=0.5$ at the HERA energy of 820 GeV, $M^2 =10 GeV^2$.