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Dedicated storage rings for nuclear physics

Description: The use of internal targets in circulating beams of electron storage and stretcher rings has been widely discussed recently as a method of achieving high luminosity under conditions of low background, and good energy resolution, with minimal demands for beam from an injecting accelerator. In the two critical areas of the technology, ring design and target development, research is very active, and the prospects for major advances are very bright. Reasonable extrapolations of the current state of the art suggest for many problems in nuclear physics, particularly polarization physics of the nucleon and few body nuclei, internal target measurement may be the optimum experimental technique. This paper, discusses the comparative merit of internal target rings and external beam experiments, reviews briefly current research efforts in the critical areas of the technology, and establishes one goal for the discussions at the workshop. It appears that storage rings dedicated to internal target physics may offer a powerful option for future advances in nuclear physics.
Date: January 1, 1984
Creator: Jackson, H.E.
Partner: UNT Libraries Government Documents Department

Prospects for HERMES-spin structure studies at HERA

Description: HERMES (HERA Measurement of Spin), is a second generation experiment to study the spin structure of the nucleon by using polarized internal gas targets in the HERA 35-GeV electron storage ring. Scattered electrons and coincident hadrons will be detected in an open geometry spectrometer which will include particle identification. Measurements are planned for each of the inclusive structure functions, g{sub 1},(x), g{sub 2}(x), b{sub 1}(x) and A(x), as well as the study of semi-inclusive pion and kaon asymmetries. Targets of hydrogen, deuterium and {sup 3}He will be studied. The accuracy of data for the inclusive structure functions will equal or exceed that of current experiments. The semi-inclusive asymmetries will provide a unique and sensitive probe of the flavor dependence of quark helicity distributions and properties of the quark sea. Monte Carlo simulations of HERMES data for experiment asymmetries and polarized structure functions are discussed.
Date: December 31, 1994
Creator: Jackson, H.E.
Partner: UNT Libraries Government Documents Department

GeV C. W. Electron Microtron Design Report

Description: Rising interest in the nuclear physics community in a GeV C.W. electron accelerator reflects the growing importance of high-resolution short-range nuclear physics to future advances in the field. In this report major current problems are reviewed and the details of prospective measurements which could be made with a GeV C.W. electron facility are discussed, together with their impact on an understanding of nuclear forces and the structure of nuclear matter. The microtron accelerator has been chosen as the technology to generate the electron beams required for the research discussed because of the advantages of superior beam quality, low capital and operating cost and capability of furnishing beams of several energies and intensities simultaneously. A complete technical description of the conceptual design for a 2 GeV double-sided C.W. electron microtron is presented. The accelerator can furnish three beams with independently controlled energy and intensity. The maximum current per beam is 100 mircoamps. Although the precise objective for maximum beam energy is still a subject of debate, the design developed in this study provides the base technology for microtron accelerators at higher energies (2 to 6 GeV) using multi-sided geometries.
Date: May 1982
Creator: Jackson, H. E.
Partner: UNT Libraries Government Documents Department

Flavor structure of the nucleon as revealed at HERMES.

Description: The flavor structure of the nucleon as revealed in parton distributions (PDF's) is central to understanding the partonic structure of the nucleon. Recent data on unpolarized PDF's and their implications for the flavor-dependent quark helicity distributions are discussed. Results are presented for spin asymmetries in inclusive and semi-inclusive cross sections for production of pions, and kaons measured by the HERMES experiment in deep-inelastic scattering of polarized positrons on proton and deuterium Targets. A full 5 component extraction of polarized quark distributions for u, d, {bar u}, {bar d}, and (s + {bar s}) is reported. Resulting valence quark distributions conform to results of earlier experiments. There is no evidence for a significant polarization of the light sea. In contrast to the conclusions inferred from studies of polarized inclusive scattering, a leading order analysis of the HERMES data suggests a zero or slightly positive polarization of the strange sea. There is no evidence for a measurable flavor asymmetry in the polarized distributions for the light sea.
Date: September 5, 2002
Creator: Jackson, H. E.
Partner: UNT Libraries Government Documents Department

Nucleon spin structure functions from HERMES: The first year

Description: HERMES, {und HE}RA {und Me}asurement of {und S}pin, is a second generation exper to study the spin structure of the nucleon by using polarized internal gas targets in the HERA 28 GeV electron storage ring. Scattered positrons and coincident hadrons are detected in an open geometry spectrometer which includes particle identification. Inclusive data with polarized {sup 3}He give the spin structure function {ital g{sup n}{sub 1}(x)} and the Ellis-Jaffe integral RR{Lambda} = {integral}{sub 0}{sup 1} {ital g{sup n}{sub 1}(x)dx} for the neutron. The semi-inclusive spin asymmetries are a unique and sensitive probe of the flavor dependence of quark helicity distributions and properties of the quark sea. Data taken in 1995 with unpolarized hydrogen and deuterium targets provide measurements of the flavor distributions of sea and valence quarks. In a preliminary analysis, {Lambda}{sup {ital n}}{sub 1} = -0.032{+-}0. 013{sub {ital stat.}} {+-} O.017{sub {ital syst.}} is obtained at Q{sup 2} = 3(GeV/c){sup 2} for the Ellis-Jaffe integral.
Date: December 31, 1996
Creator: Jackson, H.E. & Collaboration, HERMES
Partner: UNT Libraries Government Documents Department

Study of a national 2-GeV continuous beam electron accelerator

Description: Current trends in research in medium energy physics with electromagnetic probes are reviewed briefly and design objectives are proposed for a continuous beam 2 GeV electron accelerator. Various types of accelerator systems are discussed and exploratory designs developed for two concepts, the linac-stretcher ring and a double-sided microtron system. Preliminary cost estimates indicate that a linac-ring system which meets all the design objectives with the exception of beam quality and uses state-of-the-art technology can be built for approximately $29 million. However, the double-sided microtron shows promise for development into a substantially less expensive facility meeting all design objectives. Its technical feasibility remains to be established. Specific areas requiring additional engineering studies are discussed, and current efforts at Argonne and elsewhere are identified.
Date: August 1, 1980
Creator: Cho, Y.; Holt, R.J.; Jackson, H.E.; Khoe, T.K. & Mavrogenes, G.S.
Partner: UNT Libraries Government Documents Department

Design of the Argonne double-sided microtron

Description: The design study of a double-sided microtron is presented. The result of beam-optic calculations in several sector-magnet configurations is described. Current limitation by beam backup is discussed.
Date: January 1, 1981
Creator: Khoe, T.K.; Cho, Y.; Holt, R.J.; Jackson, H.E. & Mavrogenes, G.S.
Partner: UNT Libraries Government Documents Department

Photon scattering by the giant dipole resonance. [15 to 22 MeV: spectra, cross sections]

Description: Although many features of the giant dipole resonance are well known, the coupling between the basic dipole oscillation and other nuclear collective degrees of freedom such as surface vibrations and rotations is poorly understood. This aspect was investigated by elastic and inelastic bremsstrahlung scattering of tagged photons over the energy range 15 to 22 MeV. Target nuclei were /sup 60/Ni, /sup 52/Cr, /sup 56/Fe, /sup 92/Mo, and /sup 96/Mo. Scattering and absorption cross sections are tabulated, along with parameters obtained from a two-Lorentzian analysis of the scattering cross sections; measured spectra are shown. It was necessary to remove Thomson scattering from the experimental results. It was found that coupling to surface vibrations in the giant dipole resonance is much weaker than the dynamic collective model suggests. The elastic scattering cross section for all targets but /sup 60/Ni showed structure that is not evident in the absorption cross section measurement. 12 figures, 2 tables. (RWR)
Date: January 1, 1979
Creator: Bowles, T.J.; Holt, R.J.; Jackson, H.E.; McKeown, R.D. & Specht, J.R.
Partner: UNT Libraries Government Documents Department

Conceptual design of a linac-stretcher ring to obtain a 2-GeV continuous electron beam

Description: In order to obtain a high duty factor, > 100 ..mu..A 2-GeV electron beam, we have designed a linac-stretcher ring system. The system is an attractive option because it draws heavily on the existing accelerator technology. The linac-stretcher ring consists of a 2-GeV SLAC-type pulsed linac which injects into a storage ring. In between linac pulses, the stored electron beam is to extract resonantly. This design differs from those discussed recently in several important respects. The storage ring includes an RF system whose purpose is to control the beam orbit and rate of extraction from the ring. With an RF system in the ring, the injection scheme consists of a few turns of synchronous transfers of beam between the linac and storage ring.
Date: January 1, 1981
Creator: Cho, Y.; Holt, R.J.; Jackson, H.E.; Khoe, T.K. & Mavrogenes, G.S.
Partner: UNT Libraries Government Documents Department

Design objectives for a GeV C. W. electron accelerator

Description: Design objectives are proposed for a continuous beam 2 GeV electron accelerator. Various accelerator concepts are examined in light of these requirements. A double-sided microtron shows promise for yielding major savings in capital cost and excellent beam characteristics.
Date: January 1, 1980
Creator: Cho, Y.; Holt, R.J.; Jackson, H.E.; Khoe, T.K. & Mavrogenes, G.
Partner: UNT Libraries Government Documents Department

Two-body photodisintegration of the deuteron above 1 GeV

Description: One of the central issues in nuclear physics is the identification of clear signatures for quarks in nuclei. A guiding principle in this search is to perform experiments with high energy electromagnetic probes of the simplest nucleus, the deuteron, a system which is particularly amenable to theoretical interpretation. It has long been known that the quark counting rules seem to apply for electron elastic scattering from the pion and nucleon. However, the rapid decline in the cross section for electron scattering from the deuteron, a six-quark system, renders an experiment at high momentum transfer unfeasible. Clearly, the dimensional-scaling region is not reached for electron-deuteron elastic scattering as indicated. This led Brodsky and Chertok to analyze these data in terms of the reduced nuclear amplitudes and produce, in effect, scaling at a lower momentum transfer. Presently, this is the only known case where the reduced nuclear amplitude analysis seems to apply. In the present work we abandon elastic electron scattering in favor of an exclusive photoreaction with the deuteron. The simplest process involving a nucleus is the ..gamma..d ..-->.. pn reaction. Here, n = 13 and an s/sup -11/ dependence is expected where the quark counting rules are valid. Naively, one would expect that the energy region where the quark counting rules are valid to be most naturally described in terms of a quark or parton basis rather than a nucleon basis, and thereby provide a signature quark effects in nuclei. Hitherto no s/sup -11/ dependence has been observed for the data below 1 GeV. As a test of the energy-dependence for the ..gamma..d ..-->.. pn reaction, we have performed the first measurements for this process above 1 GeV.
Date: January 1, 1988
Creator: Holt, R.J.; Freedman, S.J.; Geesaman, D.F.; Gilman, R.; Green, M.C.; Jackson, H.E. et al.
Partner: UNT Libraries Government Documents Department

Proposal for Drell-Yan Measurements of Nucleon and Nuclear Structure with the FNAL Main Injector

Description: We propose measuring the fractional momentum $(x)$ dependence of the ratio of the anti-down to anti-up quark distributions in the proton, $\bar{d}(x)/\bar{u}(x)$, using proton induced Drell-Yan reactions at 120 GeV. Recent measurements by FNAL E866 unexpectedly show considerable $x$ dependence in this ratio for $x$ > 0.2. A lower energy primary proton beam from the Main Injector makes it possible to extend the E866 measurements to larger x with much higher precision. The apparatus will also be used with nuclear targets to measure parton energy loss and modifications to anti-quark distributions in nuclear targets at large $x$ ($x$ > 0.2).
Date: April 1, 2001
Creator: Isenhower, L. D.; Sadler, M. E.; Arrinton, J.; Geesamn, D. F.; Holt, R. J.; Jackson, H. E. et al.
Partner: UNT Libraries Government Documents Department

Deuteron photodisintegration : new results from TJNAF.

Description: The first measurements of the differential cross section from d({gamma},p)n up to 4.0 GeV were performed at the Thomas Jefferson National Accelerator Facility (TJNAF, formerly CEBAF). Bremsstrahlung photons from electron beam impinging on a copper radiator and a liquid deuterium target were employed for this experiment. The experiment was performed in Hall C where the photoprotons at forward angles in the center-of-mass were detected in the High Momentum Spectrometer (HMS) and photoprotons at backward angles were detected in the Short Orbit Spectrometer (SOS). The bremsstrahlung photon energy was reconstructed from the measured proton momentum and angle using the two-body kinematics. We report the cross section results at the proton center-of-mass angles of 37{degree} and 90{degree}. These results are in good agreement with previous lower energy measurements. The 90{degree} data continue to show the constituent-counting-rule behavior up to 4 GeV. The results will be compared with models based on QCD as well as those based on meson-exchange theory.
Date: November 18, 1997
Creator: Abbott, D. J.; Ahmidouch, A.; Armstrong, C. S.; Arrington, J.; Cummings, W. J.; Geesaman, D. F. et al.
Partner: UNT Libraries Government Documents Department

Measurement of the deep-inelastic spin-dependent structure functions of the proton and neutron at HERA

Description: It is possible to measure the deep-inelastic spin-dependent structure functions g/sub 1//sup p/(x) and g/sub 1//sup n/(x) for the proton and neutron using internal polarized hydrogen, deuterium, and /sup 3/He targets of polarization 50% and thickness 10/sup 14/ to 10/sup 15/ cm/sup -2/ and the 60 mA longitudinally polarized 30 GeV electron beam in the HERA electron storage ring. The measurement of the deep-inelastic spin-structure of both isospin states of the nucleon at the same kinematics and using the same apparatus allows the Bjorken sum rule to be experimentally checked. In addition, it uniquely constrains the spin distribution of the u and d quarks as a function of x in any model of the nucleon. Possible target and detector configurations are described and an estimate of the accuracy of such a measurement is presented.
Date: January 1, 1988
Creator: Beck, D.H.; Filippone, B.W.; Jourdan, J.; McKeown, R.D.; Milner, R.G.; Woodward, C.E. et al.
Partner: UNT Libraries Government Documents Department

Hyperon-nucleon bound states and electroproduction of strangeness on light nuclei.

Description: The A(e,e{prime}K{sup +})Y X reaction has been investigated in Hall C at Jefferson Lab. Data were taken for Q{sup 2} {approx} 0.35 and 0.5 GeV{sup 2} at a beam energy of 3.245 GeV for {sup 1}H, {sup 2}H, {sup 3}He and {sup 4}He, C and Al targets. The missing mass spectra are fitted with Monte Carlo simulations including {Lambda}, {Sigma}{sup 0}, {Sigma}{sup -} hyperon production. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for {Lambda}-hypernuclear bound states is seen for {sup 3,4}He targets.
Date: June 25, 2002
Creator: Dohrmann, F.; Abbott, D.; Ahmidouch, A.; Ambrozewicz, P.; Armstrong, C. S.; Arrington, J. et al.
Partner: UNT Libraries Government Documents Department