Download or read book Deeply Virtual Exclusive Processes and Generalized Parton Distributions written by and published by . This book was released on 2011 with total page 12006 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of the comprehensive program in Deeply Virtual Exclusive Scattering at Jefferson Laboratory is to create transverse spatial images of quarks and gluons as a function of their longitudinal momentum fraction in the proton, the neutron, and in nuclei. These functions are the Generalized Parton Distributions (GPDs) of the target nucleus. Cross section measurements of the Deeply Virtual Compton Scattering (DVCS) reaction ep 2!ep[gamma] in Hall A support the QCD factorization of the scattering amplitude for Q^2 e"2 GeV^2. Quasi-free neutron-DVCS measurements on the Deuteron indicate sensitivity to the quark angular momentum sum rule. Fully exclusive H(e, e'p[gamma]) measurements have been made in a wide kinematic range in CLAS with polarized beam, and with both unpolarized and longitudinally polarized targets. Existing models are qualitatively consistent with the JLab data, but there is a clear need for less constrained models. Deeply virtual vector meson production is studied in CLAS. The 12 GeV upgrade will be essential for for these channels. The [rho] and [omega] channels reactions offer the prospect of flavor sensitivity to the quark GPDs, while the [phi]-production channel is dominated by the gluon distribution.
Download or read book Deeply Virtual Compton Scattering and Generalized Parton Distributions at CLAS written by and published by . This book was released on 2008 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The exclusive electroproduction of real photons and mesons at high momentum transfer allows us to access the Generalized Parton Distributions (GPDs). The formalism of the GPDs provides a unified description of the hadronic structure in terms of quark and gluonic degrees of freedom. In particular, the Deeply Virtual Compton Scattering (DVCS), ep â e2p2Å, is one of the key reactions to determine the GPDs experimentally, as it is the simplest process that can be described in terms of GPDs. A dedicated experiment to study DVCS has been carried out in Hall B at Jefferson Lab. Beam-spin asymmetries, resulting from the interference of the Bethe-Heitler process and DVCS have been extracted over the widest kinematic range ever accessed for this reaction (1.2
Download or read book Generalized Parton Distributions written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Applications of perturbative QCD to deeply virtual Compton scattering and hard exclusive electroproduction processes require a generalization of the usual parton distributions for the case when long-distance information is accumulated in non-diagonal matrix elements of quark and gluon light-cone operators. I describe two types of nonperturbative functions parametrizing such matrix elements: double distributions and skewed parton distributions, discuss their general properties, relation to the usual parton densities and form factors, evolution equations for both types of generalized parton distributions (GPD), models for GPDs and their applications in virtual and real Compton scattering.
Download or read book The Spin Structure of the Proton written by Steven D. Bass and published by World Scientific. This book was released on 2008 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the main challenges in nuclear and particle physics in the last 20 years has been to understand how the proton's spin is built up from its quark and gluon constituents. Quark models generally predict that about 60% of the proton's spin should be carried by the spin of the quarks inside, whereas high energy scattering experiments have shown that the quark spin contribution is small - only about 30%. This result has been the underlying motivation for about 1000 theoretical papers and a global program of dedicated spin experiments at BNL, CERN, DESY and Jefferson Laboratory to map the individual quark and gluon angular momentum contributions to the proton's spin, which are now yielding exciting results. This book gives an overview of the present status of the field: what is new in the data and what can be expected in the next few years. The emphasis is on the main physical ideas and the interpretation of spin data. The interface between QCD spin physics and the famous axial U(1) problem of QCD (eta and etaprime meson physics) is also highlighted. Book jacket.
Download or read book Deeply Virtual Compton Scattering at Jefferson Lab written by Frédéric Georges and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introduced in the mid 90's, Generalized Parton Distributions (GPDs) are now a key element in the study of the nucleon internal structure. GPDs are a generalization of Form Factors and Parton Distribution Functions. They encapsulate both spatial and momentum distributions of partons inside a nucleon, allowing to perform its three-dimensional tomography. Furthermore, they allow to derive the total orbital angular momentum of quarks through the Ji sum rule, which is a crucial point to unravel the nucleon spin structure. By providing a more complete description of hadrons in terms of quarks and gluons, a deeper understanding of Quantum Chromodynamics can be reached.GPDs are experimentally accessible through deeply exclusive electro-production processes, and one of the simplest channels available is Deeply Virtual Compton Scattering (DVCS). A worldwide experimental program was started in the early 2000's to extract these GPDs. The DVCS experiment E12-06-114 performed at Jefferson Laboratory Hall A (Virginia, USA) between 2014 and 2016, is encompassed in this program. The aim of this experiment is to extract with high precision the DVCS helicity-dependent cross sections as a function of the momentum transfer Q2, for fixed values of the Bjorken variable xBj, on a proton target. The recent upgrade of the accelerator facility to 12 GeV allows to cover a larger Q2 range than in previous measurements and probe yet unexplored kinematic regions, while the polarized electron beam allows the separation of the contributions from the real and imaginary parts of the DVCS amplitude to the total cross section. In this document, a brief summary of the worldwide experimental program for the study of GPDs will be provided, followed by a description of the E12-06-114 apparatus and data analysis. Finally, the results of the unpolarized and polarized cross-section measurements are presented and compared to a few selected models.
Download or read book Generalized Parton Distributions And Deeply Virtual Compton Scattering At Clas written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The deeply virtual Compton scattering is the simplest process to access the generalized parton distributions of the nucleon. A dedicated large statistics experiment for the measurement of deeply virtual Compton scattering with a 6 GeV polarized electron beam on a proton target has been performed at the Hall-B of Jefferson Laboratory with the CLAS spectrometer. The experiment covered a wide kinematic range, allowing the study of the beam spin asymmetry as function of the Bjorken variable xB, the Mandelstam variable t, the virtual photon four-momentum squared Q2 and the angle phi between leptonic and hadronic planes. The preliminary results are in agreement with previous measurements and with the predicted twist-2 dominance.
Download or read book Generalized Parton Distributions written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We summarize recent developments in understanding the concept of generalized parton distributions (GPDs), its relation to nucleon structure, and its application to high-Q^2 electroproduction processes. Following a brief review of QCD factorization and transverse nucleon structure, we discuss (a) new theoretical methods for the analysis of deeply-virtual Compton scattering (t-channel-based GPD parametrizations, dispersion relations); (b) the phenomenology of hard exclusive meson production (experimental tests of dominance of small-size configurations, model-independent comparative studies); (c) the role of GPDs in small-x physics and pp scattering (QCD dipole model, central exclusive diffraction). We emphasize the usefulness of the transverse spatial (or impact parameter) representation for both understanding the reaction mechanism in hard exclusive processes and visualizing the physical content of the GPDs.
Download or read book Study of Generalized Parton Distributions and Deeply Virtual Compton Scattering on the Nucleon with the CLAS and CLAS12 Detectors at the Jefferson Laboratory written by and published by . This book was released on 2012 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt: The exclusive leptoproduction of a real photon is considered to be the "cleanest" way to access the Generalized Parton Distribution (GPD). This process is called Deeply Virtual Compton Scattering (DVCS) lN 2!lN[gamma], and is sensitive to all the four GPDs. Measuring the DVCS cross section is one of the main goals of this thesis. In this thesis, we present the work performed to extract on a wide phase-space the DVCS cross-section from the JLab data at a beam energy of 6 GeV.
Download or read book Exclusive Processes at High Momentum Transfer written by A. V. Radyushkin and published by World Scientific. This book was released on 2002 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on the physics of exclusive processes at high momentum transfer and their description in terms of generalized parton distributions, perturbative QCD, and relativistic quark models. It covers recent developments in the field, both theoretical and experimental.
Download or read book Deeply Virtual Compton Scattering on the Neutron at JLab Hall A written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Deeply virtual Compton scattering (DVCS) is the simplest hard exclusive process to access generalized parton distributions (GPDs). In the case of a neutron this process is mostly sensitive to E, the least constrained GPD, which enters Ji's sum rule linking GPDs to the total quark angular momentum. We present the first dedicated DVCS experiment on the neutron which took place in the Hall A of Jefferson Lab in fall 2004. Experimental setup and preliminary results are discussed.
Download or read book Illuminating the 1 written by and published by . This book was released on 2007 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Weisberger relation, an exact statement of the parton model, elegantly relates a high-energy physics observable, the 1/x moment of parton distribution functions, to a nonperturbative low-energy observable: the dependence of the nucleon mass on the value of the quark mass or its corresponding quark condensate. We show that contemporary fits to nucleon structure functions fail to determine this 1/x moment; however, deeply virtual Compton scattering can be described in terms of a novel F1/x(t) form factor which illuminates this physics. An analysis of exclusive photon-induced processes in terms of the parton-nucleon scattering amplitude with Regge behavior reveals a failure of the high Q2 factorization of exclusive processes at low t in terms of the Generalized Parton-Distribution Functions which has been widely believed to hold in the past. We emphasize the need for more data for the DVCS process at large t in future or upgraded facilities.
Download or read book Study of Generalized Parton Distributions with CLAS at Jefferson Lab written by and published by . This book was released on 2002 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: The program to study the Generalized Parton Distributions in deeply exclusive processes with CLAS at Jefferson Lab is discussed.
Download or read book Deeply Virtual Compton Scattering Cross Section Measured with CLAS written by and published by . This book was released on 2014 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Generalized Parton Distributions (GPDs) provide a new description of nucleon structure in terms of its elementary constituents, the quarks and the gluons. Including and extending the information provided by the form factors and the parton distribution functions, they describe the correlation between the transverse position and the longitudinal momentum fraction of the partons in the nucleon. Deeply Virtual Compton Scattering (DVCS), the electroproduction of a real photon on a single quark in the nucleon eN --> e'N'g, is the exclusive process most directly interpretable in terms of GPDs. A dedicated experiment to study DVCS with the CLAS detector at Jefferson Lab has been carried out using a 5.9-GeV polarized electron beam and an unpolarized hydrogen target, allowing us to collect DVCS events in the widest kinematic range ever explored in the valence region : 1.0
Download or read book Generalized Parton Distributions from Hadronic Observables written by Saeed Ahmad and published by . This book was released on 2008 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Exclusive Reactions At High Momentum Transfer Iv Proceedings Of The 4th Workshop written by Anatoly Radyushkin and published by World Scientific. This book was released on 2011-02-25 with total page 486 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Proceedings include talks given at the 4th Workshop on Exclusive Reactions at High Momentum Transfer at Jefferson Lab, Newport News, VA USA, the world's leading facility performing research on nuclear, hadronic and quark-gluon structure of matter. Exclusive reactions are becoming one of the major sources of information about the deep structure of the nucleons and other hadrons. The workshop focused on the application of a variety of exclusive reactions at high momentum transfer, utilizing unpolarized and polarized beams and targets, to obtain information about nucleon ground state and excited state structure at short distances. This is a subject which is central to the programs of current accelerators and especially planned future facilities. The topics include: generalized parton distributions, deeply virtual Compton scattering, deeply virtual meson production (DVMP), transverse structure of hadrons (TMD), hadron form factors — elastic and transition, quantum chromodynamics (perturbative, non-perturbative, lattice calculations), and physics to study at an Electron Ion Collider.
Download or read book Exclusive Reactions at High Momentum Transfer IV written by Anatoly Radyushkin and published by World Scientific. This book was released on 2011 with total page 486 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Proceedings include talks given at the 4th Workshop on Exclusive Reactions at High Momentum Transfer at Jefferson Lab, Newport News, VA USA, the world's leading facility performing research on nuclear, hadronic and quark-gluon structure of matter. Exclusive reactions are becoming one of the major sources of information about the deep structure of the nucleons and other hadrons. The workshop focused on the application of a variety of exclusive reactions at high momentum transfer, utilizing unpolarized and polarized beams and targets, to obtain information about nucleon ground state and excited state structure at short distances. This is a subject which is central to the programs of current accelerators and especially planned future facilities. The topics include: generalized parton distributions, deeply virtual Compton scattering, deeply virtual meson production (DVMP), transverse structure of hadrons (TMD), hadron form factors ? elastic and transition, quantum chromodynamics (perturbative, non-perturbative, lattice calculations), and physics to study at an Electron Ion Collider.
Download or read book Exclusive Processes at JLab at 6 GeV written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Deeply virtual exclusive reactions provide a unique opportunity to probe the complex internal structure of the nucleon. They allow to access information about the correlations between parton transverse spatial and longitudinal momentum distributions from experimental observables. Dedicated experiments to study Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP) have been carried out at Jefferson Lab using continuous electron beam with energies up to 6 GeV. Unpolarized cross sections, beam, target and double spin asymmetries have been measured for DVCS as well as for [pi]0 exclusive electroproduction. The data from Hall B provide a wide kinematic coverage with Q2=1-4.5 GeV2, xB=0.1-0.5, and -t up to 2 GeV2. Hall A data have limited kinematic range partially overlapping with Hall B kinematics but provide a high accuracy measurements. Scaling tests of the DVCS cross sections provide solid evidence of twist-2 dominance, which makes chiral-even GPDs accessible even at modest Q2. We will discuss the interpretation of these data in terms of Generalized Parton Distributions (GPDs) model. Successful description of the recent CLAS [pi]0 exclusive production data within the framework of the GPD-based model provides a unique opportunity to access the chiral-odd GPDs.
