Leonard Gamberg
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Research Interests
Leonard Gamberg has a total of 139 co-authors. Here are the top co-authors by number of shared publications:
- Alexei Prokudin
Penn State University Berks
26 shared publications - Nobuo Sato
Jefferson Lab, Newport News, Virginia 23606, USA
10 shared publications - Daniel Pitonyak
Lebanon Valley College
8 shared publications - Zhong-Bo Kang
University of California
8 shared publications - Piet J. Mulders
Department of Physics and Astronomy VU University Amsterdam De Boelelaan 1081 NL-1081 HV Amsterdam the Netherlands
6 shared publications - Ted C. Rogers
Old Dominion University
6 shared publications
Latest Publications
- Open Access
- 21 October 2026
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 137 (17)
First Simultaneous Analysis of Transverse Momentum Dependent and Collinear Parton Distributions in the Proton
We present the first simultaneous global QCD analysis of unpolarized transverse momentum dependent (TMD) and collinear parton distribution functions (PDFs) in the proton. Our Letter incorporates data from deep-inelastic scattering, Drell-Yan, inclusive weak boson, W + charm, and jet production involving PDFs, as well as TMD Drell-Yan and Z -boson production data from fixed target and collider experiments sensitive to both TMD and collinear distributions. The analysis is performed at next-to-next-to-leading logarithmic accuracy for QCD resummation in TMD observables and next-to-leading order for observables described in collinear factorization. The combined analysis improves knowledge of both TMD and collinear PDFs, particularly in the sea-quark sector, providing a consistent simultaneous description of the aforementioned observables.
- 21 October 2026
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 137 (17)
Open AccessFirst Simultaneous Analysis of Transverse Momentum Dependent and Collinear Parton Distributions in the Proton
We present the first simultaneous global QCD analysis of unpolarized transverse momentum dependent (TMD) and collinear parton distribution functions (PDFs) in the proton. Our Letter incorporates data from deep-inelastic scattering, Drell-Yan, inclusive weak boson, W + charm, and jet production involving PDFs, as well as TMD Drell-Yan and Z -boson production data from fixed target and collider experiments sensitive to both TMD and collinear distributions. The analysis is performed at next-to-next-to-leading logarithmic accuracy for QCD resummation in TMD observables and next-to-leading order for observables described in collinear factorization. The combined analysis improves knowledge of both TMD and collinear PDFs, particularly in the sea-quark sector, providing a consistent simultaneous description of the aforementioned observables.
- Open Access
- 21 October 2025
- Published by Office of Scientific and Technical Information (OSTI)
Transverse Spin and Momentum Structure of Hadrons in QCD (Final Technical Report)
This final technical report summarizes the work on the award DE-FG02-07ER41460, Transverse Spin and Momentum Structure of Hadrons in QCD. During the performance period, we addressed fundamental questions in nuclear physics, focusing on how hadrons—and, by extension, light nuclei—emerge from quark and gluon interactions within Quantum Chromodynamics (QCD).
- 21 October 2025
- Published by Office of Scientific and Technical Information (OSTI)
Open AccessTransverse Spin and Momentum Structure of Hadrons in QCD (Final Technical Report)
This final technical report summarizes the work on the award DE-FG02-07ER41460, Transverse Spin and Momentum Structure of Hadrons in QCD. During the performance period, we addressed fundamental questions in nuclear physics, focusing on how hadrons—and, by extension, light nuclei—emerge from quark and gluon interactions within Quantum Chromodynamics (QCD).
- Open Access
- 9 March 2024
- Published by Elsevier in Physics Letters B
- Vol. 851
Transverse Λ polarization in unpolarized pp → jet Λ↑ X
- 9 March 2024
- Published by Elsevier in Physics Letters B
- Vol. 851
Open AccessTransverse Λ polarization in unpolarized pp → jet Λ↑ X
- Open AccessTransverse $Λ$ polarization in unpolarized $pp\rightarrow \, {\rm jet}\, Λ^\uparrow\, X $In this Letter, we investigate the spontaneous transverse polarization of $Λ$ hyperons produced in unpolarized $pp$ collisions inside a jet, by adopting a TMD approach where transverse momentum effects are included only in the fragmentation process. We will present predictions based on the parametrizations of the $Λ$ polarizing fragmentation function as extracted from fits to Belle $e^+e^-$ data. These estimates will be compared against preliminary STAR data. We will then be able to explore the universality properties of the quark polarizing fragmentation function and, for the first time, the role of its gluon counterpart.Open AccessTransverse $Λ$ polarization in unpolarized $pp\rightarrow \, {\rm jet}\, Λ^\uparrow\, X $In this Letter, we investigate the spontaneous transverse polarization of $Λ$ hyperons produced in unpolarized $pp$ collisions inside a jet, by adopting a TMD approach where transverse momentum effects are included only in the fragmentation process. We will present predictions based on the parametrizations of the $Λ$ polarizing fragmentation function as extracted from fits to Belle $e^+e^-$ data. These estimates will be compared against preliminary STAR data. We will then be able to explore the universality properties of the quark polarizing fragmentation function and, for the first time, the role of its gluon counterpart.
- Open Access
- 27 November 2023
- Published by American Physical Society (APS) in Physical Review D
- Vol. 108 (9) , L091504
Tomography of pions and protons via transverse momentum dependent distributions
We perform the first simultaneous extraction of parton collinear and transverse degrees of freedom from low-energy fixed-target Drell-Yan data in order to compare the transverse momentum dependent (TMD) parton distribution functions (PDFs) of the pion and proton. We demonstrate that the transverse separation of the quark field encoded in TMDs of the pion is more than smaller than that of the proton. Additionally, we find the transverse separation of the quark field decreases as its longitudinal momentum fraction decreases. In studying the nuclear modification of TMDs, we find clear evidence for a transverse EMC effect. We comment on possible explanations for these intriguing behaviors, which call for a deeper examination of tomography in a variety of strongly interacting quark-gluon systems.- 27 November 2023
- Published by American Physical Society (APS) in Physical Review D
- Vol. 108 (9) , L091504
Open AccessTomography of pions and protons via transverse momentum dependent distributions
We perform the first simultaneous extraction of parton collinear and transverse degrees of freedom from low-energy fixed-target Drell-Yan data in order to compare the transverse momentum dependent (TMD) parton distribution functions (PDFs) of the pion and proton. We demonstrate that the transverse separation of the quark field encoded in TMDs of the pion is more than smaller than that of the proton. Additionally, we find the transverse separation of the quark field decreases as its longitudinal momentum fraction decreases. In studying the nuclear modification of TMDs, we find clear evidence for a transverse EMC effect. We comment on possible explanations for these intriguing behaviors, which call for a deeper examination of tomography in a variety of strongly interacting quark-gluon systems. - Open Access
- 2 November 2023
- Published by American Physical Society (APS) in Physical Review D
- Vol. 108 (9) , 094004
Transverse polarization in annihilations and in SIDIS processes at the EIC within TMD factorizationWe present a phenomenological study on the role of charm contribution and isospin symmetry in the extraction of the polarizing fragmentation functions from annihilation processes. We adopt the well-established transverse-momentum-dependent factorization formalism, within the Collins-Soper-Sterman evolution scheme at next-to-leading logarithm accuracy, carefully exploiting the role of the nonperturbative component of the polarizing fragmentation function. We then discuss the impact of these results on the predictions for transverse , polarization in semi-inclusive deep inelastic scattering processes at typical energies of the future Electron-Ion Collider.- 2 November 2023
- Published by American Physical Society (APS) in Physical Review D
- Vol. 108 (9) , 094004
Open AccessTransverse polarization in annihilations and in SIDIS processes at the EIC within TMD factorizationWe present a phenomenological study on the role of charm contribution and isospin symmetry in the extraction of the polarizing fragmentation functions from annihilation processes. We adopt the well-established transverse-momentum-dependent factorization formalism, within the Collins-Soper-Sterman evolution scheme at next-to-leading logarithm accuracy, carefully exploiting the role of the nonperturbative component of the polarizing fragmentation function. We then discuss the impact of these results on the predictions for transverse , polarization in semi-inclusive deep inelastic scattering processes at typical energies of the future Electron-Ion Collider. - Open Access
- 30 August 2023
- Published by American Physical Society (APS) in Physical Review D
- Vol. 108 (3) , 036027
Shedding light on shadow generalized parton distributions
The feasibility of extracting generalized parton distributions (GPDs) from deeply virtual Compton scattering (DVCS) data has recently been questioned because of the existence of an infinite set of so-called “shadow GPDs” (SGPDs). These SGPDs depend on the process and manifest as multiple solutions (at a fixed scale ) to the inverse problem that needs to be solved to infer GPDs from DVCS data. SGPDs therefore pose a significant challenge for extracting GPDs from DVCS data. With this motivation we study the extent to which QCD evolution can provide constraints on SGPDs. This is possible because the known classes of SGPDs begin to contribute to observables after evolution, and can then be constrained (at the input scale ) by data that has a finite range. The impact that SGPDs could have on determining the total angular momentum, pressure and sheer force distributions, and tomography is also discussed. We find that evolution, given empirical data over a wide range of skewness () and scales, constrains the SGPDs studied at low and low . If this finding generalizes to all SGPDs—and we have not been able to find any SGPDs with qualitatively different behavior—then this potentially makes extraction of GPDs from DVCS possible over a limited range of and .- 30 August 2023
- Published by American Physical Society (APS) in Physical Review D
- Vol. 108 (3) , 036027
Open AccessShedding light on shadow generalized parton distributions
The feasibility of extracting generalized parton distributions (GPDs) from deeply virtual Compton scattering (DVCS) data has recently been questioned because of the existence of an infinite set of so-called “shadow GPDs” (SGPDs). These SGPDs depend on the process and manifest as multiple solutions (at a fixed scale ) to the inverse problem that needs to be solved to infer GPDs from DVCS data. SGPDs therefore pose a significant challenge for extracting GPDs from DVCS data. With this motivation we study the extent to which QCD evolution can provide constraints on SGPDs. This is possible because the known classes of SGPDs begin to contribute to observables after evolution, and can then be constrained (at the input scale ) by data that has a finite range. The impact that SGPDs could have on determining the total angular momentum, pressure and sheer force distributions, and tomography is also discussed. We find that evolution, given empirical data over a wide range of skewness () and scales, constrains the SGPDs studied at low and low . If this finding generalizes to all SGPDs—and we have not been able to find any SGPDs with qualitatively different behavior—then this potentially makes extraction of GPDs from DVCS possible over a limited range of and . - Open AccessTransverse $Λ$ polarization in $e^+e^-$ annihilations and in SIDIS processes at the EIC within TMD factorizationWe present a phenomenological study on the role of charm contribution and $SU(2)$ isospin symmetry in the extraction of the $Λ$ polarizing fragmentation functions from $e^+e^- \to Λ^\uparrow (\barΛ^\uparrow) \,h + X$ annihilation processes. We adopt the well-established transverse-momentum-dependent factorization formalism, within the Collins-Soper-Sterman evolution scheme at next-to-leading logarithm accuracy, carefully exploiting the role of the nonperturbative component of the polarizing fragmentation function. We then discuss the impact of these results on the predictions for transverse $Λ$, $\barΛ$ polarization in semi-inclusive deep inelastic scattering processes at typical energies of the future Electron-Ion Collider.Open AccessTransverse $Λ$ polarization in $e^+e^-$ annihilations and in SIDIS processes at the EIC within TMD factorizationWe present a phenomenological study on the role of charm contribution and $SU(2)$ isospin symmetry in the extraction of the $Λ$ polarizing fragmentation functions from $e^+e^- \to Λ^\uparrow (\barΛ^\uparrow) \,h + X$ annihilation processes. We adopt the well-established transverse-momentum-dependent factorization formalism, within the Collins-Soper-Sterman evolution scheme at next-to-leading logarithm accuracy, carefully exploiting the role of the nonperturbative component of the polarizing fragmentation function. We then discuss the impact of these results on the predictions for transverse $Λ$, $\barΛ$ polarization in semi-inclusive deep inelastic scattering processes at typical energies of the future Electron-Ion Collider.
- Open Access
- 24 April 2023
- Published by American Physical Society (APS) in Physical Review D
- Vol. 107 (7) , 074031
Basics of factorization in a scalar Yukawa field theory
The factorization theorems of QCD apply equally well to most simple quantum field theories that require renormalization but where direct calculations are much more straightforward. Working with these simpler theories is convenient for stress testing the limits of the factorization program and for examining general properties of the parton density functions or other correlation functions that might be necessary for a factorized description of a process. With this view in mind, we review the steps of factorization in a real scalar Yukawa field theory for both deep inelastic scattering and semi-inclusive deep inelastic scattering cross sections. In the case of semi-inclusive deep inelastic scattering, we illustrate how to separate the small transverse momentum region, where transverse momentum dependent parton density functions are needed, from a purely collinear large transverse momentum region, and we examine the influence of subleading power corrections. We also review the steps for formulating transverse momentum dependent factorization in transverse coordinate space, and we study the effect of transforming to the well-known scheme. Within the Yukawa theory, we investigate the consequences of switching to a generalized parton model approach and compare it with a fully factorized approach. Our results highlight the need to address similar or analogous issues in QCD.- 24 April 2023
- Published by American Physical Society (APS) in Physical Review D
- Vol. 107 (7) , 074031
Open AccessBasics of factorization in a scalar Yukawa field theory
The factorization theorems of QCD apply equally well to most simple quantum field theories that require renormalization but where direct calculations are much more straightforward. Working with these simpler theories is convenient for stress testing the limits of the factorization program and for examining general properties of the parton density functions or other correlation functions that might be necessary for a factorized description of a process. With this view in mind, we review the steps of factorization in a real scalar Yukawa field theory for both deep inelastic scattering and semi-inclusive deep inelastic scattering cross sections. In the case of semi-inclusive deep inelastic scattering, we illustrate how to separate the small transverse momentum region, where transverse momentum dependent parton density functions are needed, from a purely collinear large transverse momentum region, and we examine the influence of subleading power corrections. We also review the steps for formulating transverse momentum dependent factorization in transverse coordinate space, and we study the effect of transforming to the well-known scheme. Within the Yukawa theory, we investigate the consequences of switching to a generalized parton model approach and compare it with a fully factorized approach. Our results highlight the need to address similar or analogous issues in QCD. - Open Access
Transverse-momentum-dependent factorization at next-to-leading power
We study transverse momentum dependent factorization and resummation at sub-leading power in Drell-Yan and semi-inclusive deep inelastic scattering. In these processes the sub-leading power contributions to the cross section enter as a kinematic power correction to the leptonic tensor, and the kinematic, intrinsic, and dynamic sub-leading contributions to the hadronic tensor. By consistently treating the power counting of the interactions, we demonstrate renormalization group consistency. We calculate the anomalous dimensions of the kinematic and intrinsic sub-leading correlation functions at one loop and find that the evolution equations give rise to anomalous dimension matrices which mix leading and sub-leading power distribution functions. Additionally we calculate the hard and soft functions associated with each of these contributions. We find that these hard and soft contributions differ from those at the leading power. Finally, we calculate the rapidity anomalous dimension for the dynamic sub-leading distributions and find that it is the same as the leading power anomalous dimension. We then comment on the implications for the soft function associated with this contribution. Using this information, we establish the factorization formalism at sub-leading power for these processes at the one-loop level.
Open AccessTransverse-momentum-dependent factorization at next-to-leading power
We study transverse momentum dependent factorization and resummation at sub-leading power in Drell-Yan and semi-inclusive deep inelastic scattering. In these processes the sub-leading power contributions to the cross section enter as a kinematic power correction to the leptonic tensor, and the kinematic, intrinsic, and dynamic sub-leading contributions to the hadronic tensor. By consistently treating the power counting of the interactions, we demonstrate renormalization group consistency. We calculate the anomalous dimensions of the kinematic and intrinsic sub-leading correlation functions at one loop and find that the evolution equations give rise to anomalous dimension matrices which mix leading and sub-leading power distribution functions. Additionally we calculate the hard and soft functions associated with each of these contributions. We find that these hard and soft contributions differ from those at the leading power. Finally, we calculate the rapidity anomalous dimension for the dynamic sub-leading distributions and find that it is the same as the leading power anomalous dimension. We then comment on the implications for the soft function associated with this contribution. Using this information, we establish the factorization formalism at sub-leading power for these processes at the one-loop level.