Parton Helicity Evolution at Small-x

The proton is well known to be a spin-1/2 particle, however current experimental measurements of the quark and gluon spins do not add up to 1/2. Experiments can only provide data up to the energy limit of their colliders, but our theoretical approach can extrapolate the helicity of quarks and gluons to arbitrarily small-x (arbitrarily high energy). In this talk I will discuss how we use a polarized dipole formulation of DIS and SIDIS to predict the small-x (high-energy) asymptotics of quark and gluon helicity. Our method defines spin related observables, such as the helicity parton distribution functions (hPDFs), using a set a of polarized dipole amplitudes. We then construct and solve the evolution equations of these polarized dipoles to describe their behaviour at small-x, and apply their small-x asymptotics to the hPDFs. In this way we can use theory to predict how much spin resides inside the proton in regions beyond current experimental possibilities. Using a combination of numerical and analytic solutions, our theory predicts that at small-x the quark and gluon hPDFs, ΔΣ and ΔG, grow with the power scaling ΔΣ ∼ ΔG ∼ (1/x)^{3.66 √(α_sN_c/2π)} implying that a potentially large amount of the proton spin may be hidden in this small-x region. Our current focus is to further optimize our theoretical and numerical representation of this formalism, and to perform a global analysis of inclusive DIS at small-x using the latest refinements.