Updating spin-dependent Regge intercepts

We use new high statistics data from CLAS and COMPASS on the nucleon's spin structure function at low Bjorken $x$ and low virtuality, $Q^2<0.5{\mathrm{GeV}}^2$, together with earlier measurements from the SLAC E-143, HERMES, and GDH experiments to estimate the effective intercept(s) for spin dependent Regge theory. We find ${\alpha }_{a_1}=0.31\pm 0.04$ for the intercept describing the high-energy behavior of spin dependent photoabsorption together with a new estimate for the high-energy part of the Gerasimov-Drell-Hearn sum rule: $-15\pm 2\mu \mathrm{b}$ from photon-proton center-of-mass energy greater than 2.5 GeV. Our value of ${\alpha }_{a_1}$ suggests QCD physics beyond a simple straight-line $a_1$ trajectory.

Figure 1

Regge fit to $({\sigma }_A-{\sigma }_P)=A_1^p({\sigma }_A+{\sigma }_P)$ with spin data from the CLAS [4], COMPASS [5], GDH [8], HERMES [7], and SLAC E-143 [6] experiments with $Q^2<0.5{\mathrm{GeV}}^2$.