Xiangdong Ji

Xiangdong Ji is the director of the Center for Nuclear Femtography, and a Distinguished University Professor at University of Maryland. 

Ji studied at Tongji University in Shanghai, receiving a Bachelor's Degree in Physics in 1982 and entered Peking University as a graduate student in the fall. In 1983, he went to Drexel University as a graduate student through CUPEA program initiated by Chinese-American Nobel Laureate Tsung-Dao Lee, graduated with a Ph.D. in theoretical nuclear physics in 1987. He was a postdoc fellow 

at Caltech and MIT, before appointed as a junior faculty in the Center for Theoretical Physics at MIT in 1991. In 1996, he moved to U. Maryland of Maryland, and appointed as a Distinguished University Professor since 2016. Ji had served as a Dean of Physics, Shanghai Jiao Tong University from 2009-2014 and has been a Senior Fellow at Tsung-Dao Lee Institute that he helped to create. 

Ji’s main research interest has been in the quark and gluon structure of the proton and neutron in Quantum Chromodynamics (QCD), a quantum field theory of strong interactions. He formulated the spin structure of the proton in terms of local and gauge-invariant spin and orbital angular momentum contributions of quarks and gluons (Ji spin decomposition), showed that they can be obtained (Ji sum rule) from a class of physical quantities called Generalized Parton Distributions (GPDs) he introduced independently [1].  GPDs are the special cases of Wigner distributions which provide simultaneous space and momentum information of partons.  

Ji found a new class of QCD hard scattering called Deep Exclusive Processes in lepton-nucleon collisions, which allow to probe the GPDs experimentally. The simplest example is production of a high-energy photon and a recoil nucleon in hard scattering, which he named it as Deeply-Virtual Compton scattering (DVCS) [2]. DVCS was first confirmed at the HERA collider, also observed at HERMES and JLab 6 GeV experiments.  Deep Exclusive Processes will be an important part of the experimental program at Jefferson Lab 12 GeV facility and the up-coming Electron-Ion Collider at Brookhaven National Laboratory. 

In 2013, he found that the fundamental quantities charactering the high-energy properties of the nucleon, the parton distributions introduced by R. Feynman, can be directly calculated in Euclidean lattice field theory [4]. He developed this into Large-Momentum Effective Theory which allows calculating parton physics or light-cone correlations in terms of numerical simulations on lattice. 

Since 2008, Xiangdong Ji has created and led a dark matter collaboration, PandaX, with mainly a group of Chinese scientists, aiming to search for Weakly-Interacting Massive Particles, a leading dark matter candidate, in China’s Jinping Underground Lab in Sichuan, China. After a decade, PandaX has become one of the three leading liquid-xenon dark-matter search experiments in the world (the other two, XENON in Italy and LZ in US). PandaX’s 500kg liquid xenon detector has obtained the leading WIMP search sensitivity in both 2016 and 2017 [4], made one of the 2017 American Physical Society highlights of the year.

Ji is a fellow of American Physical Society (APS), and received 2016 Herman Feshbach Prize in Theoretical Nuclear Physics by APS, Jefferson Science Associates (JAS) 2015 Outstanding Nuclear Physicist Award, and Alexander von Humboldt Foundation Research Award (2014).

[1] X. Ji, Phys. Rev. Lett. 78 (1997) 610-613
[2] X. Ji, Phys. Rev. D 55 (1997) 7114-7125
[3] X. Ji, Phys. Rev. Lett. 110 (2013) 262002
[4] PandaX-II Collaboration, Xiangyi Cui et al., Phys. Rev. Lett. 119 (2017) 181302.