Simultaneous Determination of Fragmentation Functions and Test on Momentum Sum Rule.

We perform a simultaneous global analysis of hadron fragmentation functions (FFs) to various charged hadrons (π^{±}, K^{±}, and p/p[over ¯]) at next-to-leading order in QCD. The world data include results from electron-positron single-inclusive annihilation, semi-inclusive deep inelastic scattering, as well as proton-proton collisions including jet fragmentation measurements for the first time, which lead to strong constraints on the gluon fragmentations. By carefully selecting hadron kinematics to ensure the validity of QCD factorization and the convergence of perturbative calculations, we achieve a satisfying best fit with χ^{2}/d.

Unraveling gluon jet quenching through J/ψ production in heavy-ion collisions.

Jet quenching has long been regarded as one of the key signatures for the formation of quark-gluon plasma in heavy-ion collisions. Despite significant efforts, the separate identification of quark and gluon jet quenching has remained as a challenge. Here we show that J/ψ in high transverse momentum (p) region provides a uniquely sensitive probe of in-medium gluon energy loss since its production at high p is particularly dominated by gluon fragmentation.

Nuclear Modification of Transverse Momentum Dependent Parton Distribution Functions by a Global QCD Analysis.

We perform the first simultaneous global QCD extraction of the transverse momentum dependent (TMD) parton distribution functions and the TMD fragmentation functions in nuclei. We have considered the world set of data from semi-inclusive electron-nucleus deep inelastic scattering and Drell-Yan dilepton production. In total, this data set consists of 90 data points from HERMES, Fermilab, RHIC, and LHC.

The time-reversal odd side of a jet.

We re-examine the jet probes of the nucleon spin and flavor structures. We find for the first time that the time-reversal odd (T-odd) component of a jet, conventionally thought to vanish, can survive due to the non-perturbative fragmentation and hadronization effects. This additional contribution of a jet will lead to novel jet phenomena relevant for unlocking the access to several spin structures of the nucleon, which were thought to be impossible by using jets.

Deciphering the Nature of X(3872) in Heavy Ion Collisions.

Exploring the nature of exotic multiquark candidates such as the X(3872) plays a pivotal role in understanding quantum chromodynamics (QCD). Despite significant efforts, consensus on their internal structures is still lacking. As a prime example, it remains a pressing open question to decipher the X(3872) state between two popular exotic configurations: a loose hadronic molecule or a compact tetraquark.

J/ψ Production and Polarization within a Jet.

We study the production and polarization of J/ψ mesons within a jet in proton-proton collisions at the LHC. We define the J/ψ-jet fragmentation function as a ratio of differential jet cross sections with and without the reconstructed J/ψ in the jet. We demonstrate that this is a very useful observable to help explore the J/ψ production mechanism, and to differentiate between different nonrelativistic QCD global fits based on inclusive J/ψ cross sections.

Next-to-leading-order forward hadron production in the small-x regime: the role of rapidity factorization.

Single inclusive hadron production at forward rapidity in high energy p+A collisions is an important probe of the high gluon density regime of QCD and the associated small-x formalism. We revisit an earlier one-loop calculation to illustrate the significance of the "rapidity factorization" approach in this regime. Such factorization separates the very small-x unintegrated gluon density evolution and leads to a new correction term to the physical cross section at one-loop level.

Next-to-leading order QCD factorization for semi-inclusive deep inelastic scattering at twist 4.

Within the framework of a high-twist approach, we calculate the next-to-leading order (NLO) perturbative QCD corrections to the transverse momentum broadening in semi-inclusive hadron production in deeply inelastic e+A collisions, as well as lepton pair production in p+A collisions. With explicit calculations of both real and virtual contributions, we verify, for the first time, the factorization theorem at twist 4 in NLO for the nuclear-enhanced transverse momentum weighted differential cross section and demonstrate the universality of the associated twist-4 quark-gluon correlation function. We also identify the QCD evolution equation for the twist-4 quark-gluon correlation function in a large nucleus, which can be solved to determine the scale dependence of the jet transport parameter in the study of jet quenching.