Xiangdong Ji

Spin Structure of the Nucleon in the Asymptotic Limit

In analogy with the Altarelli-Parisi equation for quark and gluon helicity contributions to the nucleon spin, we derive an evolution equation for quark and gluon orbital angular momenta. Solution of the combined equations yields asymptotic fractions of the nucleon spin carried by quarks and gluons: DSy2 1 Lq › 3nf ys16 1 3nf d and Dg 1 Lg › 16ys16 1 3nfd, respectively, with nf the number of active quark flavors. These are identical to the well-known asymptotic partitions of the nucleon momentum between quark and gluon contributions. The axial-anomaly contribution to the quark helicity is canceled with a similar contribution to the quark orbital angular momentum, making the total quark contribution to the nucleon spin anomaly free. PACS numbers: 13.88.+e, 12.38.Bx, 13.60.Hb, 14.20.Dh What is the composition of the nucleon spin in terms of its quark and gluon constituents? In the last few years, the answer has become the holy grail for the nuclear and particle spin community. The motivation is quite clear: given quantum chromodynamics (QCD) is difficult to solve, such information gives us valuable insights into the nonperturbative wave function of the nucleon. A satisfactory understanding of the spin structure would be to know, for instance, how much spin of the nucleon is carried, respectively, by the quark and gluon helicities and orbital angular momenta, in the same way as one now understands how the mass of the nucleon is partitioned among contributions from the quark and gluon kinetic energies, quark masses, and the trace anomaly [1]. The theoretical basis for separating the spin of the nucleon into different contributions begins with the QCD expression for the generators of Lorentz transformations [2],

Q2-dependence of the nucleon's G1 structure function sum rule☆

We study the

Chiral-odd and spin-dependent quark fragmentation functions and their applications

Q^2

Tensor charge of the nucleon.

variation of the first moment of the nucleons spin-dependent structure function

Parton-hadron duality: Resonances and higher twists

G_1

QCD sum rule calculation for the tensor charge of the nucleon

. As

Breakup of hadron masses and the energy-momentum tensor of QCD.

Q^2 \rightarrow 0

Locality of the strange sea in the nucleon

the moment is determined by the low energy theorem for Compton scattering. In the deep-inelastic region the moment is calculated using twist expansion to order

Soffer’s inequality

1/Q^2

Probing quark fragmentation functions for spin 1/2 baryon production in unpolarized e+ e- annihilation

. Based on these limits, we construct a formula which smoothly interpolates between the two regions.