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A program in medium energy nuclear physics. Progress report, January 1, 1992--March 31, 1995

Description: This progress report and continuation proposal summarizes our achievements for the period from July 1, 1994 to September 30, 1995 and requests continued funding for our program in experimental medium-energy nuclear physics. The focus of our program remains the understanding of the short-range part of the strong interaction in the nuclear medium. In the past year we have focused our attention ever more sharply on experiments with real tagged photons, and we have successfully defended two new experimental proposals: Photofission of Actinide and Preactinide Nuclei at SAL and Photoproduction of the {rho} Meson from the Proton with Linearly Polarized Photons at CEBAF. (We are co-spokespersons on two previously approved Hall-B experiments at CEBAF, Photoreactions on {sup 3}He and Photoabsorption and Photofission of Nuclei.) As part of the team that is instrumenting the Photon Tagger for Hall B; we report excellent progress on the focal-plane detector array that is being built at our Nuclear Detector Laboratory, as well as progress on our plans for instrumentation of a tagged polarized-photon beam using coherent bremsstrahlung. Also, we shall soon receive a large computer system (from the SSC) which will form the basis for our new Data Analysis Center, which, like the Nuclear Detector Laboratory, will be operated under the auspices of The George Washington University Center for Nuclear Studies. Finally, during the past year we have published six more papers on the results of our measurements of pion scattering at LAMPF and of electron scattering at NIKHEF and Bates, and we can report that nearly all of the remaining papers documenting this long series of measurements are in the pipeline.
Date: October 1, 1995
Creator: Berman, B.L. & Dhuga, K.S.
Partner: UNT Libraries Government Documents Department

Radiative corrections for (e,e{prime}p) reactions at GeV energies

Description: A general framework for applying radiative corrections to (e,e{prime}p) coincidence reactions at GeV energies is presented, with special emphasis to higher-order Bremsstrahlung effects, radiation from the scattered hadron, and the validity of peaking approximations. The sensitivity to the assumptions made in practically applying radiative corrections to (e,e{prime}p) data is extensively discussed. The general framework is tested against experimental data of the {sup 1}H(e,e{prime}p) reaction at momentum transfer values larger than 1.0 (GeV/c){sup 2}, where radiative processes become a dominant source of uncertainty. The formulas presented here can easily be modified for any other electron-induced coincidence reaction.
Date: May 1, 2000
Creator: Ent, R.; Filippone, B. W.; Makins, N. C. R.; Milner, R. G.; O'Neill, T. G. & Wasson, D. A.
Partner: UNT Libraries Government Documents Department

Quasielastic (e,e{prime}p) scattering at large momentum transfer

Description: Coincidence cross sections for (e, e{prime} p) quasi-elastic scattering were measured at CEBAF with high statistical precision for C, Fe, and Au targets for 0.6 < Q{sup 2} < 3.3 GeV{sup 2}. Missing energy and missing momentum distributions obtained from a preliminary analysis are in reasonable agreement with prior data from SLAC. The preliminary results are compared with a PWIA calculation to determine the nuclear transparency as a function of Q{sup 2} and A. At both A{sup 2} = 0.6 and Q{sup 2} = 1.8 GeV{sup 2} data were taken to perform a Rosenbluth separation to extract the longitudinal and transverse cross sections. The preliminary missing-energy distributions of the forward and backward angle measurements do not indicate an obvious excess of transverse strength.
Date: August 1, 1997
Creator: Ent, R.; Abbott, D. & Dunne, J.
Partner: UNT Libraries Government Documents Department

Effective neutron targets

Description: Because of the lack of a free neutron target, deuterium targets have been used extensively in studying the neutron structure. The unique spin structure of the {sup 3}He ground state wave function and the recent developments in laser technologies made polarized {sup 3}He targets widely used in many experiments from neutron electromagnetic form factor studies to nucleon spin structure function measurements at all major electron accelerator facilities. In this talk, the current status of the polarized {sup 3}He targets will be reviewed. The author will focus on neutron electromagnetic form factor studies using polarized {sup 3}He targets. The polarized nucleon spin structure function measurements using polarized {sup 3}He targets will also be discussed.
Date: July 1, 1997
Creator: Gao, H.
Partner: UNT Libraries Government Documents Department

Hypernuclear physics at TJNAF

Description: The strangeness electroproduction experiments, just starting to take data at TJNAF, are very promising for giving very useful information to understand the nuclear and nucleonic structure and reaction mechanism. The experimental program on hypernuclei already approved concerns few body, light nuclei and heavy nuclei. It will be possible to investigate these hypernuclear systems for the first time by photo- and electro-induced reactions, allowing to obtain very useful information such as {Lambda}-N interaction and weak interaction in the nuclear medium in a complementary way with respect to what can be done with hadron probes.
Date: November 1, 1999
Creator: Cisbani, E.; Frullani, S.; Garibaldi, F.; Iodice, M.; Urciuoli, G.M.; Leo, R. De et al.
Partner: UNT Libraries Government Documents Department

The Sharp Lepton Quandary: Reasonable cautions

Description: Surprisingly, the new APEX experiment designed to measure a definitive invariant mass distribution of the sharp pairs previously reported in similar heavy ion studies reports null results. Although it asserts no direct conflict with any data reported by EPOS/I, the APEX report nevertheless seems to have encouraged the view that the earlier (EPOS/I) observations were erroneous, and by extrapolation, that the whole (e{sup +}e{sup {minus}}) Puzzle data set can be dismissed as an unfortunate set of physically meaningless statistical fluctuations. We wish here to argue that such sweeping judgments should be postponed, on the grounds that (1) the published APEX analysis of their data is self-inconsistent, and can therefore sustain no valid inference about the EPOS/I data; (2) the data which supports the occurrence of sharp (e{sup +}e{sup {minus}}) pairs is much more extensive than the EPOS/I data, so that the APEX surprise must be considered as one episode in a much longer struggle finally to settle the question of whether these weak signals are significant or not; (3) a qualitative phenomenology exists which can organize the whole range of data of the Sharp Lepton Problem, and which suggests that (4) certain low energy (and low cost) experiments ought to be explored for their creation of sharp pairs; as follows: the study of pairs emitted following scattering of few MeV electron and positron beams from neutral U and Th atoms, and the study of pairs emitted following the resonant absorption of photons of 1.5 to 2.0 MeV on U and Th atoms. We first present a brief data-oriented history of the Sharp Lepton Problem, to show that no single unexpected null result can provide an adequate basis for rejecting the great range and quantity of data which evidences the occurrence of sharp pairs. We then consider the Quadronium Composite Particle ...
Date: February 1, 1996
Creator: Griffin, J.J.
Partner: UNT Libraries Government Documents Department

Measurement of elastic electron-deuteron scattering at large momentum transfers

Description: Coincidence measurements of elastic electron-deuteron cross-sections have been performed in the range of Q{sup 2} between 0.7 and 6.0 (GeV/c){sup 2}. The extracted values of the deuteron electric structure function [A(Q-squared)] in this kinematic range are presented. Values of the deuteron magnetic structure function [B(Q-squared)] in the range of 0.7 &lt; or = Q-squared &lt; or = 1.3(GeV/c)-squared were also extracted and preliminary values are presented. These data are compared with theoretical predictions of both nucleon-meson and quark-gluon based models.
Date: September 1, 1999
Creator: Gomez, J.
Partner: UNT Libraries Government Documents Department

Precision measurement of the neutron spin dependent structure functions

Description: In experiment E154 at the Stanford Linear Accelerator Center the spin dependent structure function g{sub 1}{sup n} (x, Q{sup 2}) of the neutron was measured by scattering longitudinally polarized 48.3 GeV electrons off a longitudinally polarized {sup 3}He target. The high beam energy allowed the author to extend the kinematic coverage compared to the previous SLAC experiments to 0.014 {le} x {le} 0.7 with an average Q{sup 2} of 5 GeV{sup 2}. The author reports the integral of the spin dependent structure function in the measured range to be {integral}{sub 0.014}{sup 0.7} dx g{sub 1}{sup n}(x, 5 GeV{sup 2}) = {minus}0.036 {+-} 0.004(stat.) {+-} 0.005(syst.). The author observes relatively large values of g{sub 1}{sup n} at low x that call into question the reliability of data extrapolation to x {r_arrow} 0. Such divergent behavior disagrees with predictions of the conventional Regge theory, but is qualitatively explained by perturbative QCD. The author performs a Next-to-Leading Order perturbative QCD analysis of the world data on the nucleon spin dependent structure functions g{sub 1}{sup p} and g{sub 1}{sup n} paying careful attention to the experimental and theoretical uncertainties. Using the parameterizations of the helicity-dependent parton distributions obtained in the analysis, the author evolves the data to Q{sup 2} = 5 GeV{sup 2}, determines the first moments of the polarized structure functions of the proton and neutron, and finds agreement with the Bjorken sum rule.
Date: February 1, 1997
Creator: Kolomensky, Y.G.
Partner: UNT Libraries Government Documents Department

Recent results for (e,e{prime}p) reactions at Jefferson Lab

Description: Coincidence cross sections for (e, e{prime}p) quasi-elastic scattering were measured at CEBAF with high statistical precision for C, Fe, and Au targets for 0.6 < Q{sup 2} < 3.3 GeV{sup 2}. Missing energy and missing momentum distributions obtained from a preliminary analysis are in reasonable agreement with prior data from SLAC. The preliminary analysis are compared with a PWIA calculation to determine the nuclear transparency as a function of Q{sup 2} and A. A Rosenbluth analysis to extract the longitudinal and transverse cross sections from these data is anticipated.
Date: September 1, 1997
Creator: Potterveld, D.; Cummings, W.J. & Geesaman, D.F.
Partner: UNT Libraries Government Documents Department

A program in medium-energy nuclear physics. Progress report, August 1, 1991--August 31, 1992

Description: This report reviews progress on our nuclear-physics program for the last year, and includes as well copies of our publications and other reports for that time period, The structure of this report follows that of our 1991 Renewal Proposal and Progress Report: Sec. II outlines our research activities aimed at future experiments at CEBAF, NIKHEF, and Bates; Sec. III gives results of our recent research activities at NIKHEF, LAMPF, and elsewhere; Sec. IV provides an update of our laboratory activities at GWU, including the acquisition of our new Nuclear Detector Laboratory at our new Virginia campus; and Sec. V is a list of our publications, proposals, and other reports. Copies of those on medium-energy nuclear physics are reproduced in the Appendix.
Date: June 1, 1998
Creator: Berman, B.L. & Dhuga, K.S.
Partner: UNT Libraries Government Documents Department

Precise measurement of the neutron magnetic form factor from quasielastic {sup 3}{rvec H}e({rvec e},e`)

Description: Polarized {sup 3}He targets have proven to be a useful tool for studying the electric and magnetic form factors of the neutron, and the spin structure of the neutron. The neutron magnetic form factor at low Q{sup 2} was determined previously at MIT-Bates from the quasielastic {sup 3}{ital {rvec H}e({rvec e}, e{sup `})} process. New experiment was planned at TJNAF to systematically measure the inclusive {sup 3}He quasielastic transverse asymmetry, A{sub T{sup `}}, at Q{sup 2} = 0.1 - 0.5 (GeV/c){sup 2} with high statistical and systematic accuracy. A 2% statistical uncertainty is aimed at all the pro- posed values of Q{sup 2} , and 3% systematic uncertainty for A{sub T{sup `}} can be achieved for this experiment. The precise data will constrain theoretical calculations of {sup 3}He quasielastic asymmetry. Furthermore, the neutron magnetic form factor at Q{sup 2} = 0.1 - 0.5 (GeV/c){sup 2} will be extracted from the measured asymmetries with an overall uncertainty of 2%. Precise measurements of {ital G{sup n}{sub M}} at low Q{sup 2} will resolve the discrepancy among the existing data in the same Q{sup 2} region.
Date: February 1, 1997
Creator: Gao, H.
Partner: UNT Libraries Government Documents Department

A-dependence of nuclear transparency in quasielastic A(e,e{prime}p) at high Q{sup 2}

Description: The A-dependence of the quasielastic A(e,e{prime}p) reaction has been studied with {sup 3}H, C, Fe, and Au nuclei at momentum transfers Q{sup 2} = 1, 3, 5, and 6.8(GeV/c){sup 2}. The authors extract the nuclear transparency T(A,Q{sup 2}), a measure of the average probability of escape of a proton from a nucleus A. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as color transparency. No statistically significant rise is seen for any of the nuclei studied.
Date: May 1, 1994
Creator: O`Neill, T.G.; Lorenzon, W. & Arrington, J.
Partner: UNT Libraries Government Documents Department

The reaction dynamics of the {sup 16}O(e,e{prime}p) cross section at high missing energies

Description: The authors measured the cross section and response functions (R-L, R-T, and R-LT) for the {sup 16}O(e,e{prime}p) reaction in quasielastic kinematics for missing energies 25 &lt;= E-miss &lt;= 120 MeV at various missing momenta P-miss &lt;= 340 MeV/c. For 25 &lt; E-miss &lt; 50 MeV and P-miss approx 60 MeV/c, the reaction is dominated by single-nucleon knockout from the 1s1/2-state. At larger P-miss, the single-particle aspects are increasingly masked by more complicated processes. For E-miss &gt; 60 MeV and P-miss &gt; 200 MeV/c, the cross section is relatively constant. Calculations which include contributions from pion exchange currents, isobar currents and short-range correlations account for the shape and the transversity but only for half of the magnitude of the measured cross section.
Date: September 1, 2000
Creator: Jefferson Lab Hall A Collaboration: N. Liyanage, et alia
Partner: UNT Libraries Government Documents Department

Neutron electromagnetic form factors

Description: Because of the lack of a free neutron target, deuterium targets had been used extensively in studying the neutron structure in the past from unpolarized electron-deuteron scattering experiments. Only recently polarized electron-deuteron scattering measurements have been performed which yield more precise information on the charge form factor of the neutron. The unique spin structure of the {sup 3}He ground state wave function and the recent developments in polarized target technologies have been employed in the last decade or so at all major electron accelerator facilities in experiments probing the neutron electromagnetic structure. In this talk, the author reviews the experimental status of the neutron electromagnetic form factor studies. The recently completed Jefferson Lab experiment E95-001, a precision measurement of the neutron magnetic form factor at low Q{sup 2} is discussed, also discussed are some of the future experiments.
Date: November 1, 1999
Creator: Collaboration, Haiyan Gao for the Hall A
Partner: UNT Libraries Government Documents Department

Electron-capture delayed fission properties of neutron-deficient einsteinium nuclei

Description: Electron-capture delayed fission (ECDF) properties of neutron-deficient einsteinium isotopes were investigated using a combination of chemical separations and on-line radiation detection methods. {sup 242}Es was produced via the {sup 233}U({sup 14}N,5n){sup 242}Es reaction at a beam energy of 87 MeV (on target) in the lab system, and was found to decay with a half-life of 11 {+-} 3 seconds. The ECDF of {sup 242}Es showed a highly asymmetric mass distribution with an average pre-neutron emission total kinetic energy (TKE) of 183 {+-} 18 MeV. The probability of delayed fission (P{sub DF}) was measured to be 0.006 {+-} 0.002. In conjunction with this experiment, the excitation functions of the {sup 233}U({sup 14}N,xn){sup 247{minus}x}Es and {sup 233}U({sup 15}N,xn){sup 248{minus}x}Es reactions were measured for {sup 243}Es, {sup 244}Es and {sup 245}Es at projectile energies between 80 MeV and 100 MeV.
Date: January 5, 2000
Creator: Shaughnessy, Dawn A.
Partner: UNT Libraries Government Documents Department

Associated {Lambda} production at Jefferson Lab

Description: The {sup 1}H(e, e{prime}K{sup +}){Lambda} and {sup 1}H(e, e{prime}K{sup +}){Sigma}{sup 0} reactions were studied as a function of the squared four-momentum-transfer, Q{sup 2}, and the virtual photon polarization, {var_epsilon}, thus enabling the separation of the longitudinal and transverse parts of the cross section. The existence of a sensibly large longitudinal component for the {sup 1}H(e, e{prime}K{sup +}){Lambda} reaction seems to be sustained by these data.
Date: December 31, 1997
Creator: Niculescu, G.; Baker, O.K.; Avery, S. & Collaboration, E93018
Partner: UNT Libraries Government Documents Department

Overview of nuclear structure with electrons

Description: Following a broad summary of the author's view of nuclear structure in 1974, he will discuss the key elements they have learned in the past 25 years from the research at the M.I.T. Bates Linear Accelerator center and its sister electron accelerator laboratories. Electron scattering has provided the essential measurements for most of the progress. The future is bright for nuclear structure research as their ability to realistically calculate nuclear structure observables has dramatically advanced and they are increasingly able to incorporate an understanding of quantum chromodynamics into their picture of the nucleus.
Date: December 3, 1999
Creator: Geesaman, D. F.
Partner: UNT Libraries Government Documents Department

Proton propagation through nuclei and the quasi-free reaction mechanism studied with (e,e{prime}p) reactions

Description: Jefferson Lab experiment E91-013 measured the energy dependence of proton propagation in nuclei, using the quasi-free (e, e{prime}p) reaction. The ratios of the experimental (e, e{prime}p) cross-sections integrated over the quasi-free region to PWIA calculations are presented as a function of momentum transfer, (0.6 < Q{sup 2} < 3.3 GeV{sup 2}) and target nucleus (C, Fe and Au). As a first step towards a longitudinal and transverse separation of the quasi-free cross-section, a super ratio of the measured to the calculated cross-sections at forward and backward angles is presented.
Date: September 1, 1997
Creator: Dutta, D.; Abbott, D. & Amatuni, T.A.
Partner: UNT Libraries Government Documents Department

Recent experiments using polarization observables at Bates

Description: In this talk I summarize the experiments completed at the MIT-Bates electron accelerator in the last few years and compare their results with those of recent experiments performed elsewhere that address the same or similar physics issues. The experiments described here focus on measurements of the nucleon form factors and studies of the three-body system in inclusive quasielastic electron scattering from polarized {sup 3}He.
Date: August 1, 1995
Creator: Jones, C.E.
Partner: UNT Libraries Government Documents Department

Theoretical studies in high energy nuclear physics. Progress report

Description: This paper is a progress report for the period 1-1-93 to 6-30-95 on a project primarily directed at the application of high energy physics techniques to nuclear structure studies, and the ability to study hadron dynamics through interactions with nuclear targets. This work has included the first legitimate QCD calculations of hard coherent diffractive processes off nucleon (nuclear) targets which established novel features of color transparency phenomenon not anticipated in the previous intuitive or QCD inspired model calculations and predicted the fast increase of the cross section for electroproduction of {rho}-mesons with increase of the energy, which was confirmed very recently by the first HERA data on this reaction. First theoretical demonstration that color transparency phenomenon for the hard diffractive processes follow from QCD in the kinematics when both x{yields}0 and Q{sup 2}{yields}{infinity}. Establishing the pattern of color (cross section) fluctuations in hadrons. Confirmed by the FNAL inelastic diffraction data. Finding that in realistic quark, skyrmion models of a hadron large momentum transfer elastic lepton-hadron scattering occurs through formation of small spatial size configurations. Discovering a novel class of color transparency sensitive double interaction processes which is complementary to quasielastic reactions originally suggested by S. Brodsky and A. Mueller. Adopting ideas suggested elsewhere for hadron initiated reactions they developed a method for taking into account nuclear correlations in (e,e{prime}p) reactions. Such an approach gives practical possibility to overcome ambiguities of optical model approximation used before and to reliably interpret color transparency effects at intermediate Q{sup 2}.
Date: August 1, 1995
Partner: UNT Libraries Government Documents Department

Electron-atom collision studies using optically state selected beams. Progress report, May 15, 1988--May 14, 1991

Description: This report discusses progress made during the current contract period on the authors research program to study collisions between spin-polarized electrons and spin-polarized atoms. The objective of this work is to stimulate a deeper theoretical understanding of the electron-atom interaction by providing the most complete possible experimental characterization of the colliding system. Through the use of optical state preparation techniques to prepare both the incident electrons and atom in well-defined initial states, the authors are able to extract substantially more information about the scattering process than is available from more conventional measurements of differential scattering cross sections. Their primary interest is to study in detail the role played by spin in electron-atom collisions at low to intermediate energies. The additional information provided by these spin-dependent measurements greatly enhances understanding of both exchange and the spin-orbit interaction in the scattering process. During this three-year period they have made substantial progress in measurements of both elastic and superelastic scattering of spin-polarized electrons from optically pumped sodium. The elastic scattering measurements in particular were made possible by several important improvements to the experimental apparatus.
Date: November 15, 1990
Creator: Celotta, R. J. & Kelley, M. H.
Partner: UNT Libraries Government Documents Department