We study the transverse momentum dependent (TMD) evolution of the Collins azimuthal asymmetries in e + e − annihilations and semi-inclusive hadron production in deep inelastic scattering (SIDIS) processes. All the relevant coefficients are calculated up to the next-to-leading logarithmic (NLL) order accuracy. By applying the TMD evolution at the approximate NLL order in the Collins-Soper-Sterman (CSS) formalism, we extract transversity distributions for u and d quarks and Collins fragmentation functions from current experimental data by a global analysis of the Collins asymmetries in back-to-back di-hadron productions in e + e − annihilations measured by BELLE and BABAR Collaborations and SIDIS data from HERMES, COMPASS, and JLab HALL A experiments. The impact of the evolution effects and the relevant theoretical uncertainties are discussed. We further discuss the TMD interpretation for our results, and illustrate the unpolarized quark distribution, transversity distribution, unpolarized quark fragmentation and Collins fragmentation functions depending on the transverse momentum and the hard momentum scale. We make detailed predictions for future experiments and discuss their impact.

Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p+ Pb collisions at [Formula: see text] are compiled and compared. When test run data are available, they are compared to the model predictions.

We study the single transverse spin asymmetries in the single inclusive particle production within the framework of the generalized parton model (GPM). By carefully analyzing the initial-and final-state interactions, we include the process-dependence of the Sivers functions into the GPM formalism. The modified GPM formalism has a close connection with the collinear twist-3 approach. Within the new formalism, we make predictions for inclusive π 0 and direct photon productions at RHIC energies. We find the predictions are opposite to those in the conventional GPM approach.

We investigate the nucleon tensor charge from current experiments by a combined analysis of the Collins asymmetries in two hadron production in e + e − annihilations and semi-inclusive hadron production in deep inelastic scattering processes. The transverse momentum dependent evolution is taken into account, for the first time, in the global fit of the Collins fragmentation functions and the quark transversity distributions at the approximate next-to-leading logarithmic order. We obtain the nucleon tensor charge contribution from up and down quarks as: δu = +0.30

Future experiments at the Jefferson Lab 12 GeV upgrade, in particular, the Solenoidal Large Intensity Device (SoLID), aim at a very precise data set in the region where the partonic structure of the nucleon is dominated by the valence quarks. One of the main goals is to constrain the quark transversity distributions. We apply recent theoretical advances of the global QCD extraction of the transversity distributions to study the impact of future experimental data from the SoLID experiments. Especially, we develop a simple strategy based on the Hessian matrix analysis that allows one to estimate the uncertainties of the transversity quark distributions and their tensor charges extracted from SoLID data simulation. We find that the SoLID measurements with the proton and the effective neutron targets can improve the precision of the u-and d-quark transversity distributions up to one order of magnitude in the range 0.05 < x < 0.6.

We investigate the Collins azimuthal asymmetry of hadrons produced inside jets in transversely polarized proton-proton collisions. Recently, the quark transversity distributions and the Collins fragmentation functions have been extracted within global analyses from data of the processes semi-inclusive deep inelastic scattering and electron-positron annihilation. We calculate the Collins azimuthal asymmetry for charged pions inside jets using these extractions for RHIC kinematics at center-of-mass energies of 200 and 500 GeV. We compare our results with recent data from the STAR Collaboration at RHIC and find good agreement, which confirms the universality of the Collins fragmentation functions. In addition, we further explore the impact of transverse momentum dependent evolution effects.Comment: 12 pages, 5 figures, expanded version published in PL

A set of quasi-parton distribution functions (quasi-PDFs) have been recently proposed by Ji. Defined as the matrix elements of equal-time spatial correlations, they can be computed on the lattice and should reduce to the standard PDFs when the proton momentum P z is very large. Since taking the P z → ∞ limit is not feasible in lattice simulations, it is essential to provide guidance for which values of P z the quasi-PDFs are good approximations of standard PDFs. Within the framework of the spectator diquark model, we evaluate both the up and down quarks' quasi-PDFs and standard PDFs for all leading-twist distributions (unpolarized distribution f 1 , helicity distribution g 1 , and transversity distribution h 1 ). We find that, for intermediate parton momentum fractions x, quasi-PDFs are good approximations to standard PDFs (within 20-30%) when P z 1.5-2 GeV. On the other hand, for large x ∼ 1 much larger P z > 4 GeV is necessary to obtain a satisfactory agreement between the two sets. We further test the Soffer positivity bound, and find that it does not hold in general for quasi-PDFs.

We present an attempt of global analysis of Semi-Inclusive Deep Inelastic Scattering (SIDIS) ℓp ↑ → ℓ ′ πX data on single spin asymmetries and data on left-right asymmetry AN in p ↑ p → πX in order to simultaneously extract information on Sivers function and twist-three quark-gluon EfremovTeryaev-Qiu-Sterman (ETQS) function. We explore different possibilities such as node of Sivers function in x or k ⊥ in order to explain "sign mismatch" between these functions. We show that π ± SIDIS data and π 0 STAR data can be well described in a combined TMD and twist-3 fit, however π ± BRAHMS data are not described in a satisfactory way. This leaves open a question to the solution of the "sign mismatch". Possible explanations are then discussed.