About

Professor Zhongbo Kang is a faculty member in the Department of Physics and Astronomy at UCLA and the leader of the Kang Research Group. His research is dedicated to exploring fundamental questions in theoretical physics, with a focus on Quantum Chromodynamics (QCD) and strong interactions. His work encompasses QCD theory and phenomenology, aiming to understand how the fundamental laws of nature manifest in observable phenomena, and maintains close connections to experimental programs at facilities such as the Large Hadron Collider (LHC), the Relativistic Heavy Ion Collider (RHIC), and the future Electron–Ion Collider (EIC). Professor Kang's research integrates advanced theoretical frameworks like Soft Collinear Effective Theory (SCET) and QCD factorization, alongside state-of-the-art computational methodologies including quantum simulations and machine learning, to study real-time dynamics, non-perturbative challenges, and complex data analysis in high-energy nuclear and particle physics. He has received notable awards such as the Friedrich Wilhelm Bessel Research Award from the Alexander von Humboldt Foundation and the NSF Faculty CAREER Award, and is recognized for his teaching excellence with the Abelmann Award. Before joining UCLA, he served as a staff scientist at Los Alamos National Laboratory and is affiliated with several research institutes, including the Mani L. Bhaumik Institute for Theoretical Physics, the UCLA Center for Quantum Science and Engineering, and the Center for Frontiers in Nuclear Science at Stony Brook University and Brookhaven National Laboratory. His group is committed to training the next generation of physicists through hands-on experience in theoretical methods, numerical simulations, and computational tools.

Research topics

• Particle physics
• Physics
• Nuclear physics
• Computer Science
• Engineering
• Systems engineering
• Optics
• Engineering physics
• Astronomy
• Quantum mechanics

Selected publications

• Dihadron Fragmentation Framework for Near-Side Energy-Energy Correlators

  Physical Review Letters · 2026-01-02 · 2 citations

  articleOpen access1st authorCorresponding

  We establish an approach to analyze the free hadron and transition (nonperturbative) regions of near-side energy-energy correlators (EECs) based on dihadron fragmentation functions (DiFFs). We introduce a (nonperturbative) function we call the "EEC DiFF" and explicitly show that expanding it for large relative transverse momentum between the two hadrons gives the O(α_{s}) expression for the "EEC jet" function used in the quark-gluon (perturbative) region. This connection indicates that a formal theoretical matching will be able to bridge the free-hadron region, transition, and quark-gluon regions and allow all of them to be analyzed simultaneously. We further derive a result valid for near-side EECs in the free hadron and transition regions of e^{+}e^{-} annihilation in terms of the EEC DiFF. Using a simple model for the function, we perform the first fit within the dihadron framework to experimental data in this regime. We find reasonable agreement with the measurements and reproduce the salient features of near-side EECs in the free hadron and transition regions.

  PublisherDOI

• Parton distributions in the shockwave formalism

  Journal of High Energy Physics · 2026-04-10

  articleOpen access

  A bstract In this work, we calculate a broad class of parton distributions — including parton distribution functions (PDFs), transverse-momentum-dependent distributions (TMDs), generalized parton distributions (GPDs), generalized transverse-momentum-dependent distributions (GTMDs), and diffractive parton distributions — directly from their operator-level definition in the shockwave approximation for the target nucleon. This approximation is valid in the high-energy limit of scattering, corresponding to the small- x regime. The shockwave framework allows us to employ the eikonal approximation and express the parton distributions in terms of Wilson-line correlators, naturally formulated within the color-glass condensate effective field theory. We present a comprehensive set of Feynman rules for evaluating parton distributions in this limit, and demonstrate how they can be systematically applied to calculate all phenomenologically relevant leading-twist parton distributions at leading order. This work establishes a unified starting point for future studies that aim to bridge the color-glass condensate approach with the partonic description of the nucleon.

  PublisherOA PDFDOI

• Determination of the initial condition for the Balitsky-Kovchegov equation with transformers

  Journal of High Energy Physics · 2026-03-03 · 1 citations

  articleOpen access

  A bstract In the high-energy limit of QCD, scattering off nucleons and nuclei can be described in terms of Wilson-line correlators whose energy dependence is perturbative. The energy dependence of the two-point correlator, called the dipole amplitude, is governed by the Balitsky-Kovchegov (BK) equation. The initial condition for the BK equation can be fitted to the experimental data, which requires evolving the dipole amplitude for a large set of different parameter values. In this work, we train a transformer model to learn the energy dependence of the dipole amplitude, thereby replacing repeated time-consuming numerical BK evolutions during the fit by fast emulator predictions. The transformer predicts the learned dipole amplitude and the leading order inclusive deep inelastic scattering cross section very accurately, allowing for efficient fitting of the initial condition to the experimental data. Using this setup, we fit the initial condition of the BK equation to the inclusive deep inelastic scattering data from HERA and consider two different starting points x 0 for the evolution. We find better agreement with the experimental data for a smaller x 0 . This work paves the way for future studies involving global fits of the dipole amplitude at leading order and beyond.

  PublisherOA PDFDOI

• Color glass condensate meets high twist expansion

  Physical review. D/Physical review. D. · 2025-06-05 · 2 citations

  preprintOpen access

  We establish the correspondence between two well-known frameworks for quantum chromodynamics (QCD) multiple scattering in nuclear media: the color glass condensate (CGC) and the high-twist (HT) expansion formalism. We argue that a consistent matching between both frameworks, in their common domain of validity, is achieved by incorporating the subeikonal longitudinal momentum phase in the CGC formalism, which mediates the transition between coherent and incoherent scattering. We perform a detailed calculation and analysis of direct photon production in proton-nucleus scattering as a concrete example to establish the matching between HT and CGC up to twist-4, including initial- and final-state interactions, as well as their interferences. The techniques developed in this work can be adapted to other processes in electron-nucleus and proton-nucleus collisions, and they provide a potential avenue for a unified picture of dilute-dense dynamics in nuclear media.

  PublisherDOI

• Collinear limit of the energy-energy correlator in $e^+ e^-$ collisions: transition from perturbative to non-perturbative regimes

  ArXiv.org · 2025-07-23

  preprintOpen access

  We study the collinear limit of the energy-energy correlator (EEC) in $e^+e^-$ collisions, focusing on the transition from the perturbative QCD regime at relatively large angles to the non-perturbative region at small angles. To describe this transition, we introduce a non-perturbative jet function and perform a global analysis at NNLO+NNLL accuracy using experimental data spanning center-of-mass energies from $Q = 29.0$ to $91.2$ GeV. This marks the first accurate description of the EEC across the entire near-side region ($0^\circ<χ<90^\circ$) within a unified theoretical framework. Our analysis also provides, for the first time, a quantitative extraction of the non-perturbative contribution to the EEC quark jet function, identifying a characteristic transition scale around $2.3$ GeV - distinct from the scale observed in EEC-in-jet measurements in $pp$ collisions at the LHC, which are dominated by gluon jets. These results offer the first evidence for flavor dependence (quark vs. gluon) in the EEC and provide new insights into the interplay between perturbative and non-perturbative QCD dynamics.

  PublisherOA PDFDOI

• Hadronic scattering in (1+1)D SU(2) lattice gauge theory from tensor networks

  arXiv (Cornell University) · 2025-10-31

  preprintOpen access

  We present a first real-time study of hadronic scattering in a (1+1)-dimensional SU(2) lattice gauge theory with fundamental fermions using tensor-network techniques. Working in the gaugeless Hamiltonian formulation -- where the gauge field is exactly integrated out and no truncation of the electric flux is required -- we investigate scattering processes across sectors of fixed global baryon number $B = 0, 1, 2$. These correspond respectively to meson-meson, meson-baryon, and baryon-baryon collisions. At strong coupling, the $B = 0$ and $B = 2$ channels exhibit predominantly elastic dynamics closely resembling those of the U(1) Schwinger model. In contrast, the mixed $B = 1$ sector shows qualitatively new behavior: meson and baryon wave packets become entangled during the collision, and depending on their initial kinematics, the slower state becomes spatially delocalized while the faster one propagates ballistically. We characterize these processes through local observables, entanglement entropy, and the information-lattice, which together reveal how correlations build up and relax during the interaction. Our results establish a first benchmark for non-Abelian real-time scattering from first principles and open the path toward quantum-simulation studies of baryon-number dynamics and inelastic processes in gauge theories.

  PublisherOA PDFDOI

• Transverse energy-energy correlators at small <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>x</mml:mi></mml:math> for photon-hadron production

  Physical review. D/Physical review. D. · 2025-10-07 · 2 citations

  articleOpen access1st authorCorresponding

  We study the transverse energy-energy correlator (TEEC) observable in photon-hadron and photon-jet production in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mi mathvariant="normal">p</a:mi><a:mo>+</a:mo><a:mi mathvariant="normal">p</a:mi></a:mrow></a:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:mi mathvariant="normal">p</e:mi><e:mo>+</e:mo><e:mi mathvariant="normal">A</e:mi></e:mrow></e:math> collisions at small <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mi>x</i:mi></i:math>. We derive the relevant expressions in the high-energy limit of the scattering where the dipole picture is applicable and show how the dependence on the fragmentation function of the hadron cancels due to the momentum-sum rule. The nonperturbative scattering with the target nucleus is expressed in terms of the dipole amplitude, which also describes nonlinear gluon saturation effects. The TEEC observable is computed in the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) kinematics, and we show that it can be sensitive to the dipole amplitude, making it a potentially good observable for studying saturation effects.

  PublisherDOI

• Partonic distribution functions and amplitudes using tensor network methods

  Journal of High Energy Physics · 2025-09-23 · 7 citations

  articleOpen access1st author

  A bstract Calculations of the parton distribution function (PDF) and distribution amplitude (DA) are highly relevant to core experimental programs as they provide non-perturbative inputs to inclusive and exclusive processes, respectively. Direct computation of the PDFs and DAs remains challenging because they are non-perturbative quantities defined as light-cone correlators of quark and gluon fields, and are therefore inherently time-dependent. In this work, we use a uniform quantum strategy based on tensor network simulation techniques to directly extract these hadronic quantities from first principles using the matrix product state of the hadrons in the same setup. We present exemplary numerical calculations with the Nambu-Jona-Lasinio model in 1+1 dimensions and compare with available exact diagonalization and quantum circuit simulation results. Using tensor networks, we evaluate the PDF and DA at various strong couplings in the large-qubit limit, which is consistent with expectations at perturbative and non-relativistic limits.

  PublisherOA PDFDOI

• Transverse Energy--Energy Correlators at Small $x$ for Photon--Hadron Production

  ArXiv.org · 2025-03-31

  preprintOpen access1st authorCorresponding

  We study the transverse energy--energy correlator (TEEC) observable in photon--hadron and photon--jet production in p+p and p+A collisions at small $x$. We derive the relevant expressions in the high-energy limit of the scattering where the dipole picture is applicable and show how the dependence on the fragmentation function of the hadron cancels due to the momentum-sum rule. The nonperturbative scattering with the target nucleus is expressed in terms of the dipole amplitude, which also describes nonlinear gluon saturation effects. The TEEC observable is computed in the RHIC and LHC kinematics, and we show that it can be sensitive to the dipole amplitude, making it a potentially good observable for studying saturation effects.

  PublisherOA PDFDOI

• Correspondence between Color Glass Condensate and High-Twist Formalism

  Physical Review Letters · 2025-07-16 · 2 citations

  articleOpen access

  The color glass condensate (CGC) effective theory and the collinear factorization at high twist (HT) are two well-known frameworks describing perturbative QCD multiple scatterings in nuclear media. It has long been recognized that these two formalisms have their own domain of validity in different kinematic regions. Taking direct photon production in proton-nucleus collisions as an example, we clarify for the first time the relation between CGC and HT at the level of a physical observable. We show that the CGC formalism beyond shock-wave approximation, and with the Landau-Pomeranchuk-Migdal interference effect is consistent with the HT formalism in the transition region where they overlap. Such a unified picture paves the way for mapping out the phase diagram of parton density in nuclear medium from dilute to dense region.

  PublisherOA PDFDOI

Recent grants

• Perturbative QCD Study for Jet and Heavy Flavor Production

  NSF · $180k · 2017–2020

• CAREER: Hadron's Transverse Structure and Associated QCD Dynamics

  NSF · $573k · 2020–2025

Frequent coauthors

• Jian-Wei Qiu

  111 shared

• Hongxi Xing

  South China Normal University

  87 shared

• Daniel Pitonyak

  Lebanon Valley College

  81 shared

• Alexei Prokudin

  Thomas Jefferson National Accelerator Facility

  81 shared

• Andreas Metz

  70 shared

• Shohini Bhattacharya

  University of Bonn

  61 shared

• Ivan Vitev

  60 shared

• Xiaohui Liu

  Beijing Normal University

  59 shared

Awards & honors

• Friedrich Wilhelm Bessel Research Award from the Alexander v…
• NSF Faculty CAREER Award