Leading-Order Determination of the Gluon Polarization from high-$p_T$ Hadron Electroproduction

Understand

Longitudinal double-spin asymmetries of charged hadrons with high transverse momentum $p_T$ have been measured in electroproduction using the \hermes\ detector at \hera.

• Processes involving gluons in the nucleon have been enhanced relative to others by selecting hadrons with $p_T$ typically above 1 GeV.
• In this kinematic domain the gluon polarization has been extracted in leading order making use of the model embedded in the Monte Carlo Generator \Pythia\ 6.2.
• The gluon polarization obtained from single inclusive hadrons in the $p_T$ range 1 GeV $< p_T <$ 2.5 GeV using a deuterium target is $\frac{\Delta g}{g}(\langle x\rangle, \langle \mu^2\rangle)=0.049\pm 0.034 (stat)\pm 0.010 (sys\textrm{-}exp)^{+0.126}_{-0.099}(sys\textrm{-}models)$ at a scale $\la\mu^2\ra=1.35~{\rm GeV}^2$ and $\langle x\rangle = 0.22$.