THE SCIENCE OF CONFINEMENT AND THE GLUEX/HALL D PROJECT AT JEFFERSON LAB

2003 ◽  
Vol 18 (03) ◽  
pp. 397-404 ◽  
Author(s):  
Alex R. Dzierba
Keyword(s):  
Degrees Of Freedom ◽  
Meson Production ◽  
First Year ◽  
Jefferson Lab ◽  
Coherent Bremsstrahlung ◽  
Linearly Polarized ◽  
Quantitative Understanding ◽  
Current Maximum ◽  
Photo Production ◽  
Photoproduction Data

One of the outstanding and fundamental questions in physics is the quantitative understanding of the confinement of quarks and gluons in quantum chromodynamics (QCD). Confinement is a unique feature of QCD. Exotic hybrid mesons manifest gluonic degrees of freedom and their spectroscopy will provide the crucial data needed to test assumptions in lattice QCD and phenomenology leading to confinement. Photo-production is expected to be particularly effective in producing exotic hybrids but data using photon probes are sparse. At Jefferson Lab, plans are underway to use the coherent bremsstrahlung technique to produce a linearly polarized photon beam. A solenoid-based hermetic detector will be used to collected data on meson production and decays with statistics that will exceed the current photoproduction data in hand by several orders of magnitude after the first year of running. In order to reach the ideal photon energy of 9 GeV/c for this mapping of the exotic spectra, the energy of the Jefferson Lab electron accelerator, CEBAF, will be doubled from its current maximum of 6 GeV to 12 GeV. The physics and project are described.

scholarly journals Latest results from GlueX

2019 ◽  
Vol 199 ◽  
pp. 01004 ◽  
Author(s):  
Thomas Britton
Keyword(s):  
Degrees Of Freedom ◽  
Beam Polarization ◽  
Accelerator Facility ◽  
Exotic Mesons ◽  
Newport News ◽  
Hybrid Mesons ◽  
Quantum Numbers ◽  
Coherent Bremsstrahlung ◽  
Linearly Polarized ◽  
Beam Incident

The GlueX experiment is housed in the newest experimental hall at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. It was successfully commissioned in 2015 and is in its third year of data taking. GlueX uses a 12 GeV electron beam incident on a diamond radiator, producing a linearly polarized, coherent Bremsstrahlung photon beam. The ultimate goal of GlueX is to search for exotic hybrid mesons (e.g. qq̄g), with either exotic or conventional quantum numbers, whose existence, or lack thereof, would allow for the exploration of the gluon-gluon coupling present in QCD through the manifestation of hadrons with gluonic degrees of freedom. Photo-production at these energies is fairly unexplored and the linear beam polarization allows GlueX to discriminate between various production mechanisms which may be an effective way to identify such exotic hybrid mesons. In addition to exotic mesons, GlueX will also be poised to map out the conventional meson spectrum and to study the spectrum of excited vector mesons, which are often poorly understood. In these proceedings, we will present an overview of the GlueX experiment, its goals, current physics results, and future plans.

scholarly journals Studying neutron structure at Jefferson Lab through electron scattering off the deuteron, using CLAS12 and the Central Neutron Detector

2020 ◽  
Vol 1643 (1) ◽  
pp. 012191
Author(s):  
Paul Naidoo ◽  
Daria Sokhan ◽  
Pierre Chatagnon ◽  
Silvia Niccolai ◽  
Katheryne Price
Keyword(s):  
Neutron Detector ◽  
Meson Production ◽  
Deeply Virtual Compton Scattering ◽  
Virtual Compton Scattering ◽  
High Energy ◽  
Neutral Meson ◽  
Deuteron Target ◽  
Jefferson Lab ◽  
3D Tomography ◽  
Large Acceptance

Abstract Generalised Parton Distributions (GPDs) offer a way of imaging nucleons through 3D tomography. They can be accessed experimentally in processes such as Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP), where a high energy electron scatters from a quark inside a nucleon and a high energy photon or meson is produced as a result. Jefferson Lab has recently completed its energy upgrade and Hall B houses the new, large-acceptance CLAS12 detector array optimised for measurements of DVCS and DVMP in the newly accessible kinematic regime. Measurements on the proton and neutron are complementary and both are necessary to facilitate access to the full set of GPDs and enable their flavour separation. Neutron DVCS and DVMP are possible with the use of a deuteron target – the first CLAS12 experiment with which has started taking data this year. To enable exclusive reconstruction of DVCS and neutral-meson DVMP, a dedicated detector for recoiling neutrons – the Central Neutron Detector (CND) – was integrated into CLAS12. We present the first CLAS12 deuteron-target experiment, with a focus on the performance of the CND.

An Unlearned Principle for Controlling Natural Movements

1999 ◽  
Vol 82 (1) ◽  
pp. 255-259 ◽  
Author(s):  
Frank T.J.M. Zaal ◽  
Kristin Daigle ◽  
Gerald L. Gottlieb ◽  
Esther Thelen
Keyword(s):  
Degrees Of Freedom ◽  
Sagittal Plane ◽  
Arm Movement ◽  
First Year ◽  
Strong Constraint ◽  
A Value ◽  
Pointing Movements ◽  
Before And After ◽  
First Year Of Life ◽  
Coordination Patterns

Recently, Gottlieb and colleagues discovered a linear relation between elbow and shoulder dynamic torque in natural pointing movements in the sagittal plane. The present study investigates if the process of learning to reach involves discovering this linearity principle. We inspected torque data from four infants who were learning to reach and grab a toy in front of them. In a longitudinal study, we collected data both in the period before and after they performed their first successful reaches. Torque profiles at the shoulder and elbow were typically multipeaked and became more and more biphasic toward the end of the first year of life. Torques at the shoulder and elbow were correlated tightly for movements in the prereaching period as well as for reaches later in the year. Furthermore, slopes of a regression of shoulder dynamic torque on elbow dynamic torque were remarkably constant at a value ∼2.5–3.0. If linear synergy is used by the nervous system to reduce the controlled degrees of freedom, it will act as a strong constraint on the complex of possible coordination patterns for arm movement early in life. Natural reaching movements can capitalize on this constraint because it simplifies the process of learning to reach.

scholarly journals CHARGED PION PHOTOPRODUCTION FROM HYDROGEN AND DEUTERIUM AT JEFFERSON LAB

2003 ◽  
Vol 18 (02n06) ◽  
pp. 215-224
Author(s):  
◽  
HAIYAN GAO
Keyword(s):  
Cross Sections ◽  
Degrees Of Freedom ◽  
Charged Pion ◽  
Center Of Mass ◽  
Oscillatory Behavior ◽  
Color Transparency ◽  
Jefferson Lab ◽  
Glauber Theory ◽  
Nuclear Dependence ◽  
Exclusive Processes

The γn → π-p and γp → π+n reactions are essential probes of the transition from meson-nucleon degrees of freedom to quark-gluon degrees of feedom in exclusive processes. The cross sections of these processes are also, advantageous, for the investigation of oscillatory behavior around the quark counting prediction, since they decrease relatively slower with energy compared with other photon-induced processes. Moreover, these photoreactions in nuclei can probe the QCD nuclear filtering and color transparency effects. In this talk, I discuss the preliminary results on the γp → π+n and γn → π-p processes at a center-of-mass angle of 90° from Jefferson Lab experiment E94-104. I also discuss a new experiment in which singles γp → π+n measurement from hydrogen, and coincidence γn → π-p measurements at the quasifree kinematics from deuterium and 12 C for photon energies between 2.25 GeV to 5.8 GeV in fine steps at a center-of-mass angle of 90° are planned. The proposed measurement will allow a detailed investigation of the oscillatory scaling behavior in photopion production processes and the study of the nuclear dependence of rather mysterious oscillations with energy that previous experiments have indicated. The various nuclear and perturbative QCD approaches, ranging from Glauber theory, to quark-counting, to Sudakov-corrected independent scattering, make dramatically different predictions for the experimental outcomes.

scholarly journals STUDIES OF NUCLEON RESONANCE STRUCTURE IN EXCLUSIVE MESON ELECTROPRODUCTION

2013 ◽  
Vol 22 (06) ◽  
pp. 1330015 ◽  
Author(s):  
I. G. Aznauryan ◽  
A. Bashir ◽  
V. M. Braun ◽  
S. J. Brodsky ◽  
V. D. Burkert ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Chiral Symmetry Breaking ◽  
Theoretical Interpretation ◽  
Resonance Structure ◽  
First Year ◽  
Key Factors ◽  
High Q ◽  
Reaction Theory ◽  
Meson Electroproduction ◽  
Resonance Formation

Studies of the structure of excited baryons are key factors to the N* program at Jefferson Lab (JLab). Within the first year of data taking with the Hall B CLAS12 detector following the 12 GeV upgrade, a dedicated experiment will aim to extract the N* electrocouplings at high photon virtualities Q2. This experiment will allow exploration of the structure of N* resonances at the highest photon virtualities ever achieved, with a kinematic reach up to Q2 = 12 GeV 2. This high-Q2 reach will make it possible to probe the excited nucleon structures at distance scales ranging from where effective degrees of freedom, such as constituent quarks, are dominant through the transition to where nearly massless bare-quark degrees of freedom are relevant. In this document, we present a detailed description of the physics that can be addressed through N* structure studies in exclusive meson electroproduction. The discussion includes recent advances in reaction theory for extracting N* electrocouplings from meson electroproduction off protons, along with Quantum Chromodynamics (QCD)-based approaches to the theoretical interpretation of these fundamental quantities. This program will afford access to the dynamics of the nonperturbative strong interaction responsible for resonance formation, and will be crucial in understanding the nature of confinement and dynamical chiral symmetry breaking in baryons, and how excited nucleons emerge from QCD.

scholarly journals Coherent oscillations of a levitated birefringent microsphere in vacuum driven by nonconservative rotation-translation coupling

2020 ◽  
Vol 6 (23) ◽  
pp. eaaz9858 ◽  
Author(s):  
Yoshihiko Arita ◽  
Stephen H. Simpson ◽  
Pavel Zemánek ◽  
Kishan Dholakia
Keyword(s):  
Degrees Of Freedom ◽  
Detailed Balance ◽  
Optical Trap ◽  
Underlying Mechanism ◽  
Thermal Fluctuations ◽  
Mechanical Quality Factor ◽  
Mechanical Quality ◽  
Linearly Polarized ◽  
Translation Coupling ◽  
Equipartition Of Energy

We demonstrate an effect whereby stochastic, thermal fluctuations combine with nonconservative optical forces to break detailed balance and produce increasingly coherent, apparently deterministic motion for a vacuum-trapped particle. The particle is birefringent and held in a linearly polarized Gaussian optical trap. It undergoes oscillations that grow rapidly in amplitude as the air pressure is reduced, seemingly in contradiction to the equipartition of energy. This behavior is reproduced in direct simulations and captured in a simplified analytical model, showing that the underlying mechanism involves nonsymmetric coupling between rotational and translational degrees of freedom. When parametrically driven, these self-sustained oscillators exhibit an ultranarrow linewidth of 2.2 μHz and an ultrahigh mechanical quality factor in excess of 2 × 108 at room temperature. Last, nonequilibrium motion is seen to be a generic feature of optical vacuum traps, arising for any system with symmetry lower than that of a perfect isotropic microsphere in a Gaussian trap.

scholarly journals MEASUREMENTS OF SPIN OBSERVABLES IN PSEUDOSCALAR-MESON PHOTOPRODUCTION USING POLARIZED NEUTRONS IN SOLID HD

2014 ◽  
Vol 26 ◽  
pp. 1460079 ◽  
Author(s):  
◽  
TSUNEO KAGEYA
Keyword(s):  
Scalar Meson ◽  
Photon Beams ◽  
Accelerator Facility ◽  
Polarized Neutrons ◽  
Spin Observables ◽  
Free Neutron ◽  
Linearly Polarized ◽  
Complete Set ◽  
Solid Hd ◽  
Photo Production

Psuedo-scalar meson photo production measurements have been carried out with longitudinally-polarized neutrons using the circularly and linearly polarized photon beams and the CLAS at Thomas Jefferson National Accelerator Facility (Jlab). The experiment aims to obtain a complete set of spin observables on an efficient neutron target. Preliminary E asymmetries for the exclusive reaction, γ + n(p) → π- + p(p), selecting quasi free neutron kinematics are discussed.

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