Author
David Gaskell
Bio: David Gaskell is an academic researcher from Thomas Jefferson National Accelerator Facility. The author has contributed to research in topics: EMC effect & Quark. The author has an hindex of 9, co-authored 14 publications receiving 390 citations.
Topics: EMC effect, Quark, Quantum chromodynamics, Gluon, Photon
Papers
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Blaise Pascal University1, Centre national de la recherche scientifique2, Syracuse University3, Texas A&M University–Kingsville4, Massachusetts Institute of Technology5, California State University, Los Angeles6, Florida International University7, Thomas Jefferson National Accelerator Facility8, Old Dominion University9, Ohio University10, Hampton University11, Université Paris-Saclay12, University of Bari13, Mississippi State University14, Rutgers University15, Temple University16, Carnegie Mellon University17, Kharkov Institute of Physics and Technology18, North Carolina Central University19, Longwood University20, The Catholic University of America21, Duke University22, University of Regina23, Seoul National University24, College of William & Mary25, Tel Aviv University26, University of Virginia27, Kent State University28, University of Massachusetts Amherst29, University of Valencia30, University of Ljubljana31, Los Alamos National Laboratory32, Norfolk State University33, Argonne National Laboratory34, Kasetsart University35, Yerevan Physics Institute36, George Washington University37
TL;DR: The present experiment exploits the interference between the deeply virtual Compton scattering (DVCS) and the Bethe-Heitler processes to extract a linear combination of generalized parton distributions (GPDs) particularly sensitive to E_{q}, the least constrained GPD.
Abstract: The three-dimensional structure of nucleons (protons and neutrons) is embedded in so-called generalized parton distributions, which are accessible from deeply virtual Compton scattering. In this process, a high-energy electron is scattered off a nucleon by exchanging a virtual photon. Then, a highly energetic real photon is emitted from one of the quarks inside the nucleon, which carries information on the quark’s transverse position and longitudinal momentum. By measuring the cross-section of deeply virtual Compton scattering, Compton form factors related to the generalized parton distributions can be extracted. Here, we report the observation of unpolarized deeply virtual Compton scattering off a deuterium target. From the measured photon-electroproduction cross-sections, we have extracted the cross-section of a quasifree neutron and a coherent deuteron. Due to the approximate isospin symmetry of quantum chromodynamics, we can determine the contributions from the different quark flavours to the helicity-conserved Compton form factors by combining our measurements with previous ones probing the proton’s internal structure. These results advance our understanding of the description of the nucleon structure, which is important to solve the proton spin puzzle. The internal structure of the neutron has now been probed by highly energetic photons scattering off it. Combined with previous results for protons, these measurements reveal the contributions of quark flavours to the nucleon structure.
131 citations
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TL;DR: In this paper, the EMC effect has been studied in deep inelastic scattering kinematics and the current status of the theoretical understanding of this thirty-year old effect is discussed.
Abstract: Since the discovery that the ratio of inclusive charged lepton (per-nucleon) cross-sections from a nucleus A to the deuteron is not unity — even in deep inelastic scattering kinematics — a great deal of experimental and theoretical effort has gone into understanding the phenomenon. The EMC effect, as it is now known, shows that even in the most extreme kinematic conditions the effects of the nucleon being bound in a nucleus cannot be ignored. In this paper, we collect the most precise data available for various nuclear to deuteron ratios, as well as provide a commentary on the current status of the theoretical understanding of this thirty year old effect.
109 citations
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TL;DR: In this article, the EMC effect has been studied in deep inelastic scattering kinematics and the current status of the theoretical understanding of this thirty year old effect is discussed.
Abstract: Since the discovery that the ratio of inclusive charged lepton (per-nucleon) cross sections from a nucleus A to the deuteron is not unity - even in deep inelastic scattering kinematics - a great deal of experimental and theoretical effort has gone into understanding the phenomenon. The EMC effect, as it is now known, shows that even in the most extreme kinematic conditions the effects of the nucleon being bound in a nucleus can not be ignored. In this paper we collect the most precise data available for various nuclear to deuteron ratios, as well as provide a commentary on the current status of the theoretical understanding of this thirty year old effect.
78 citations
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TL;DR: The fundamental theory of the strong interaction, quantum chromodynamics (QCD), provides the foundational framework with which to describe and understand the key properties of atomic nuclei as discussed by the authors, but a deep understanding of the explicit role of quarks and gluons in nuclei remains elusive.
Abstract: The fundamental theory of the strong interaction -- quantum chromodynamics (QCD) -- provides the foundational framework with which to describe and understand the key properties of atomic nuclei. A deep understanding of the explicit role of quarks and gluons in nuclei remains elusive however, as these effects have thus far been well-disguised by confinement effects in QCD which are encapsulated by a successful description in terms of effective hadronic degrees of freedom. The observation of the EMC effect has provided an enduring indication for explicit QCD effects in nuclei, and points to the medium modification of the bound protons and neutrons in the nuclear medium. Understanding the EMC effect is a major challenge for modern nuclear physics, and several key questions remain, such as understanding its flavor, spin, and momentum dependence. This manuscript provides a contemporary snapshot of our understanding of the role of QCD in nuclei and outlines possible pathways in experiment and theory that will help deepen our understanding of nuclei in the context of QCD.
32 citations
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TL;DR: The fundamental theory of the strong interaction-quantum chromodynamics (QCD) provides the foundational framework with which to describe and understand the key properties of atomic nuclei as mentioned in this paper.
Abstract: The fundamental theory of the strong interaction-quantum chromodynamics (QCD)—provides the foundational framework with which to describe and understand the key properties of atomic nuclei. A deep understanding of the explicit role of quarks and gluons in nuclei remains elusive however, as these effects have thus far been well-disguised by confinement effects in QCD which are encapsulated by a successful description in terms of effective hadronic degrees of freedom. The observation of the EMC effect has provided an enduring indication for explicit QCD effects in nuclei, and points to the medium modification of the bound protons and neutrons in the nuclear medium. Understanding the EMC effect is a major challenge for modern nuclear physics, and several key questions remain, such as understanding its flavor, spin, and momentum dependence. This manuscript provides a contemporary snapshot of our understanding of the role of QCD in nuclei and outlines possible pathways in experiment and theory that will help deepen our understanding of nuclei in the context of QCD.
30 citations
Cited by
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01 Dec 1984
TL;DR: In a recent review as mentioned in this paper, the authors reflect some of the shifts of emphasis that are occurring among the fields of astrophysics, nuclear physics, and elementary particle physics and discuss the role of rotational degrees of freedom in heavy-ion collisions at low and moderate energies.
Abstract: The contents of this review reflect some of the shifts of emphasis that are occurring among the fields of astrophysics, nuclear physics, and elementary particle physics. Particle physics has made great advances in the unification of the fundamental forces of nature. Discussions and planning for a next big step in accelerator-colliders are presented. The technology of superconducting magnet systems as well as the fundamental physical principles of particle accelerators are discussed. Also presented are: high-resolution electronic particle detectors; nuclear physics changes such as pion interactions within nuclei; discussion of future relativistic heavy-ion colliders; the role of rotational degrees of freedom in heavy-ion collisions at low and moderate energies; hyperon beta decays; and the analysis of materials via nuclear reaction techniques. Neutrinos, their interactions and possible masses, have an important bearing on cosmology and the matter density of the universe in addition to their inherent interest in the microscopic world and this is also examined.
676 citations
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TL;DR: The nCTEQ15 set of nuclear parton distribution functions with uncertainties is presented in this article, where the uncertainties are determined using the Hessian method with an optimal rescaling of the eigenvectors to accurately represent the uncertainties for the chosen tolerance criteria.
Abstract: We present the new nCTEQ15 set of nuclear parton distribution functions with uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear dependence using data on nuclei all the way up to 208^Pb. The uncertainties are determined using the Hessian method with an optimal rescaling of the eigenvectors to accurately represent the uncertainties for the chosen tolerance criteria. In addition to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY) processes, we also include inclusive pion production data from RHIC to help constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of the data sets with specific nPDF flavor components, and asses the impact of individual experiments. We also provide comparisons of the nCTEQ15 set with recent fits from other groups.
429 citations
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TL;DR: In this paper, the authors review the present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon.
Abstract: This article reviews our present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon. Present experimental investigations of the nucleon's internal spin structure, the theoretical interpretation of the different measurements, and the open questions and challenges for future investigation are discussed.
421 citations
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TL;DR: In this paper, the EMC effect for valence quarks, a reduction in the Deep Inelastic Scattering (DIS) cross-section ratios for nuclei relative to deuterium, and its possible connection to nucleon-nucleon Short-Range Correlations (SRC) in nuclei are discussed.
Abstract: This article reviews our current understanding of how the internal quark structure of a nucleon bound in nuclei differs from that of a free nucleon. We focus on the interpretation of measurements of the EMC effect for valence quarks, a reduction in the Deep Inelastic Scattering (DIS) cross-section ratios for nuclei relative to deuterium, and its possible connection to nucleon-nucleon Short-Range Correlations (SRC) in nuclei. Our review and new analysis (involving the amplitudes of non-nucleonic configurations in the nucleus) of the available experimental and theoretical evidence shows that there is a phenomenological relation between the EMC effect and the effects of SRC that is not an accident. The influence of strongly correlated neutron-proton pairs involving highly virtual nucleons is responsible for both effects. These correlated pairs are temporary high-density fluctuations in the nucleus in which the internal structure of the nucleons is briefly modified. This conclusion needs to be solidified by the future experiments and improved theoretical analyses that are discussed herein.
260 citations
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Idaho State University1, Texas A&M University2, University of Zagreb3, California State University, Los Angeles4, College of William & Mary5, Thomas Jefferson National Accelerator Facility6, Istituto Nazionale di Fisica Nucleare7, Louisiana Tech University8, Mississippi State University9, University of Manitoba10, University of Virginia11, State University of New York System12, Carnegie Mellon University13, University of Connecticut14, Hampton University15, University of Massachusetts Amherst16, Old Dominion University17, Temple University18, Indiana University19, Ohio University20, Syracuse University21, Duquesne University22, University of Winnipeg23, Veer Kunwar Singh University24, Virginia Tech25, Argonne National Laboratory26, Yerevan Physics Institute27, University of Mainz28, Christopher Newport University29, Shandong University30
TL;DR: In this paper, the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons from 208 Pb was measured, leading to an extraction of the neutral weak form factor F = 0.0036(exp)±0.0013(theo)
Abstract: We report a precision measurement of the parity-violating asymmetry A_{PV} in the elastic scattering of longitudinally polarized electrons from ^{208}Pb. We measure A_{PV}=550±16(stat)±8(syst) parts per billion, leading to an extraction of the neutral weak form factor F_{W}(Q^{2}=0.00616 GeV^{2})=0.368±0.013. Combined with our previous measurement, the extracted neutron skin thickness is R_{n}-R_{p}=0.283±0.071 fm. The result also yields the first significant direct measurement of the interior weak density of ^{208}Pb: ρ_{W}^{0}=-0.0796±0.0036(exp)±0.0013(theo) fm^{-3} leading to the interior baryon density ρ_{b}^{0}=0.1480±0.0036(exp)±0.0013(theo) fm^{-3}. The measurement accurately constrains the density dependence of the symmetry energy of nuclear matter near saturation density, with implications for the size and composition of neutron stars.
239 citations