The Spin and Flavour Dependence of High-Energy Photoabsorption

We review the present data on high-energy, spin-dependent photoabsorption. We find a strong isotriplet term in (σA − σP ) which persists from Q2 ∼ 0.25GeV2 to high Q2 polarised deep inelastic scattering. For Q2 ∼ 4GeV2 and x between 0.01 and 0.12 the isotriplet part of g1 behaves as g (p−n) 1 ∼ x 1 2 , in contrast to soft Regge theory which predicts that g (p−n) 1 should converge as x → 0. The isotriplet, polarised structure function 2xg 1 is significantly greater than the isotriplet, unpolarised structure function F (p−n) 2 in this kinematic region. We analyse the low Q2 photoabsorption data from E-143 and SMC and use this data to estimate the high-energy Regge contribution to the Drell-Hearn-Gerasimov sum-rule. [email protected] [email protected]