2016/12/22 by Yuri V. Kovchegov, Kovchegov, Yuri V., Daniel Pitonyak +3 · 4 citations
Engineering · Physics and Astronomy · #Superconducting Materials and Applications #Quantum Chromodynamics and Particle Interactions #Particle physics theoretical and experimental studies
paper · pdf · doi:10.48550/arxiv.1612.07758
We construct small-x evolution equations which can be used to calculate quark and anti-quark helicity TMDs and PDFs, along with the g1 structure function. These evolution equations resum powers of αs ln2 (1/x) in the polarization-dependent evolution along with the powers of αs ln (1/x) in the unpolarized evolution which includes saturation effects. The equations are written in an operator form in terms of polarization-dependent Wilson line-like operators. While the equations do not close in general, they become closed and self-contained systems of non-linear equations in the large-Nc and large-Nc & Nf limits. We construct a numerical solution of the helicity evolution equations in the large-Nc limit. Employing the extracted intercept, we are able to predict directly from theory the behavior of the quark helicity PDFs at small x, which should have important phenomenological consequences. We also give an estimate of how much of the proton's spin may be at small x and what impact this has on the so-called "spin crisis." Based on JHEP 1601 (2016) 072 (arXiv:1511.06737), arXiv:1610.06197 and arXiv:1610.06188.