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Momentum Transfer by Laser Ablation of Irregularly Shaped Space Debris

Description: Proposals for ground-based laser remediation of space debris rely on the creation of appropriately directed ablation-driven impulses to either divert the fragment or drive it into an orbit with a perigee allowing atmospheric capture. For a spherical fragment, the ablation impulse is a function of the orbital parameters and the laser engagement angle. If, however, the target is irregularly shaped and arbitrarily oriented, new impulse effects come into play. Here we present an analysis of some of these effects.
Date: February 4, 2010
Creator: Liedahl, D A; Libby, S B & Rubenchik, A
Partner: UNT Libraries Government Documents Department

Parton Distributions and Spin-Orbital Correlations

Description: In this talk, I summarize a recent study showing that the large-x parton distributions contain important information on the quark orbital angular momentum of nucleon. This contribution could explain the conflict between the experimental data and the theory predictions for the polarized quark distributions. Future experiments at JLab shall provide further test for our predictions.
Date: September 24, 2007
Creator: Yuan, Feng
Partner: UNT Libraries Government Documents Department

The Pion Form-Factor

Description: The experimental situation with regard to measurements of the pion charge form factor is reviewed. Both existing data and planned experiments are discussed.
Date: May 1, 2002
Creator: Blok, H.P.; Huber, G.M. & Mack, D.J.
Partner: UNT Libraries Government Documents Department

The origins of quark-hadron duality: How does the square of the sum become the sum of the squares?

Description: Bloom-Gilman duality demonstrates empirically that the electroproduction of N*'s at low momentum transfers averages smoothly around the scaling curve measured at large momentum transfers. The latter is proportional to the sum of the squares of the constituent charges whereas the former involves the coherent excitation of resonances and is driven by the square of summed constituent charges. We determine the minimal necessary conditions for this equality to be realized so that duality can occur and consider the implications for a range of processes that may be studied soon at CEBAF.
Date: January 30, 2001
Creator: Close, Frank E. & Isgur, Nathan
Partner: UNT Libraries Government Documents Department

Importance of Coulomb Corrections In Extraction of the Proton Form Factors

Description: Results of recent polarization transfer experiments indicate that the ratio of the proton's electric to magnetic form factor decreases with increasing momentum transfer, yet the polarization transfer results are in sharp disagreement with the many Rosenbluth separation results. In this paper, it will be shown that the inclusion of a Coulomb correction to the Rosenbluth separation data slightly reduces this discrepancy.
Date: June 1, 2003
Creator: Higinbotham, Douglas
Partner: UNT Libraries Government Documents Department


Description: The second part of the sixth RHIC Spin Collaboration (RSC) meeting was held on November 15, 2001 at Brookhaven National Laboratory. Previous meetings have elaborated on the new generation of proton spin-structure studies (e.g. gluon polarization and flavor separation of q and {bar q} polarizations via real W{sup {+-}} production) enabled by studying polarized proton collisions at energies and momentum transfers where perturbative QCD models are expected to be applicable. The focus of this meeting was on many of the experimental issues that must be resolved to achieve these physics goals. This summary is written with the benefit of hindsight following the completion of the first-ever run of a polarized proton collider. This first run can be considered as a successfully completed milestone of the RHIC Spin Collaboration. Other milestones remain important. Long term machine items were identified in Waldo Mackay's talk, the most important being the completion of the spin rotator magnets that will be installed in 2002 to allow the flexible orientation of the proton beam polarization at the PHENM and STAR experiments. At the meeting Waldo discussed a stronger partial snake magnet for the AGS as a means of producing highly polarized proton beams to inject into RHIC. Developments subsequent to this meeting suggest that a superconducting helical dipole magnet may be feasible for the AGS, and is likely to be needed to achieve the 70% beam polarization in RHIC. Longer term items were also presented, including potential increases in luminosity by the addition of electron cooling to RHIC and the possibility of increasing the collision energy by {approx}20% by replacement of the DX magnets. These items could be considered for a second generation of RHIC spin experiments. The other topics covered at the meeting were related to polarimetry and to the absolute calibration of the proton ...
Date: November 15, 2001
Creator: Bland, L. & Saito, N.
Partner: UNT Libraries Government Documents Department

The Upgrade of CEBAF to 12 GeV: Physics Motivations and Technical Aspects

Description: The Continuous Electron Beam Accelerator Facility, CEBAF, makes use of electron and photon beams with an energy up to 6 GeV to investigate the electromagnetic structure of mesons, nucleons, and nuclei. We discuss the physics motivation for upgrading the facility to a maximum energy of 12 GeV and some of the key technological aspects of the upgrade.
Date: August 1, 2002
Creator: Mecking, Bernhard & Cardman, Larry
Partner: UNT Libraries Government Documents Department

Exclusive photon-photon processes

Description: Exclusive gamma gamma right arrow hadron pairs are among the most fundamental processes in QCD, providing a detailed examination of Compton scattering in the crossed channel. In the high momentum transfer domain (s, t, large, Theta cm for t/s fixed), these processes can be computed from first principles in QCD, yielding important information on the nature of the QCD coupling data and the form of hadron distribution amplitudes. Similarly, the transition form factors gamma star gamma, gamma star gamma right arrow pi(o), Eta (0), Eta`, Eta(c)... provide rigorous tests of QCD and definitive determinations of the meson distribution amplitudes Phi H(x,Q). We show that the assumption of a frozen coupling at low momentum transfers can explain the observed scaling of two-photon exclusive processes.
Date: July 1, 1997
Creator: Brodsky, S.J.
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

Virtual Compton Scattering on the proton at high s and low t

Description: Virtual Compton Scattering (VCS) at low transferred momenta to the proton (t) and sufficiently high c.m. energies (s) may be used to (a) study Q{sup 2}-dependence of leading t-channel exchanges and (b) look for onset of scaling behavior with increasing Q{sup 2}. The author discusses the implications for perturbative and nonperturbative QCD and suggests possible experiments.
Date: August 1, 1996
Creator: Afanasev, Andrei
Partner: UNT Libraries Government Documents Department

Neutron Charge Form Factor at Large Q{sup 2 }

Description: The neutron charge form factor G{sub En}(q) is determined from an analysis of the deuteron quadrupole form factor F{sub C2}(q) data. Recent calculations, based on a variety of different model interactions and currents, indicate that the contributions associated with the uncertain two-body operators of shorter range are relatively small for F{sub C2}(q), even at large momentum transfer q. Hence, G{sub En}(q) can be extracted from F{sub C2}(q) at large q{sup 2} without undue systematic uncertainties from theory.
Date: September 1, 2001
Creator: Schiavilla, R. & Sick, I.
Partner: UNT Libraries Government Documents Department

Moments of the proton F{sub 2} structure function at low Q{sup 2}

Description: The authors review the status of inclusive electron-proton scattering F{sub 2} structure function data in both the nucleon resonance region and the deep inelastic region, at momentum transfers below 5 (GeV/c){sup 2}. From these data they construct moments of F{sub 2}, down to momentum transfers of Q{sup 2}{approx}0.1(GeV/c){sup 2}. The second moment is only slowly varying with Q{sup 2} down to Q{sup 2}{approx}1, which is a reflection of duality. Below Q{sup 2} of 1 (GeV/c){sup 2}, the Q{sup 2} dependence of the moments is predominantly governed by the elastic contribution, whereas the inelastic channels still seem governed by local duality.
Date: May 1, 2000
Creator: Armstrong, C.S.; Ent, R.; Keppel, C.E.; Liuti, S.; Niculescu, G. & Niculescu, I.
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

Nucleon form factors '99

Description: The authors review recent progress in the experimental knowledge of and theoretical speculations about nucleon form factors, with special emphasis on the large Q{sup 2} region. There is now a long history of continuous progress in the understanding of electromagnetic form factors at large momentum transfer. After the pioneering works leading to the celebrated quark counting rules, the understanding of hard scattering exclusive processes has been solidly founded. A perturbative QCD subprocess is factorized from a wave function-like distribution amplitude {var_phi}(x{sub i},Q{sup 2}) (x{sub i} being the light cone fractions of momentum carried by valence quarks), the Q{sup 2} dependence of which is analyzed in the renormalization group approach. Although an asymptotic expression emerges from this analysis for the x dependence of the distribution, it was quickly understood that the evolution to the asymptotic Q{sub 2} is very slow and that indeed some non perturbative input is required to get reliable estimates of this distribution amplitude at measurable Q{sup 2}.
Date: June 1, 1999
Creator: Jager, Kees de & Pire, B.
Partner: UNT Libraries Government Documents Department

QCD sum rules and soft-hard interplay for hadronic form factors

Description: The authors discuss two types of contributions to hadronic form factors in QCD: hard gluon exchange and soft wave function overlap. Within the QCD sum rule approach, the hard contribution has strong numeric suppression by factor ({alpha}{sub s}/{pi}) {approximately} 0.1 for each exchange. For this reason, the soft contribution dominates at accessible momentum transfers. The ``humpy'' distribution amplitudes used to enhance hard terms cannot be derived from QCD sum rules in a self-consistent way. The estimates of soft terms obtained within the local quark-hadronic duality approach in all cases are close to existing data, providing an experimental evidence that hard terms are small.
Date: November 1, 1998
Creator: Radyushkin, A.V.
Partner: UNT Libraries Government Documents Department


Description: Neutron inelastic scattering measurements of the polar TO phonon mode in the cubic relaxor Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}, at room temperature, reveal anomalous behavior similar to that recently observed in Pb(Zn{sub 1/3}Nb{sub 2/3}){sub 0.92}Ti{sub 0.08}O{sub 3} in which the optic branch appears to drop precipitously into the acoustic branch at a finite value of the momentum transfer q = 0.2 {angstrom}{sub {minus}1}, measured from the zone center. By contrast, a recent neutron study indicates that PMN exhibits a normal TO phonon dispersion at 800 K. The authors speculate this behavior is common to all relaxor materials, and is the result of the presence of nanometer-scale polarized domains in the crystal that form below a temperature T{sub d}, which effectively prevent the propagation of long wavelength (q = 0) phonons.
Date: March 9, 2000
Partner: UNT Libraries Government Documents Department

Measurement of color transparency by C(p,2p) reactions at large momentum transfer

Description: The subject of color transparency, the enhancement of the ability of hadrons to penetrate nuclear matter by kinematic selection, is both interesting and controversial. The description of the collision of hadrons with nucleons inside nuclei, and the connection with initial and final state interactions involve fundamental questions of quantum mechanics, and nuclear and particle physics. Interest in color transparency was greatly increased by AGS Experiment 834 which observed dramatic changes with incident momentum for a variety of nuclei. A new experiment, E850, has studied the (p,2p) quasi-elastic reaction near 90{degree} cm for momenta between 5.9 and 9 GeV/c. The quasi-elastic reaction was compared to the elastic reaction on free protons to determine the transparency. With limited statistics, but with better kinematic definition in a new detector, the authors have confirmed the rise in Carbon transparency ratio seen in Expt 834. The Tr(D/H) for deuterium is consistent with no energy dependence. Unlike the free d{sigma}/dt for hydrogen, the d{sigma}/dt from protons in a nucleus is consistent with the exact s{sup {minus}10} scaling. This suggests two components to the pp scattering amplitude; one small and perturbative, the other spatially large and varying, but filtered away by the nuclear matter in the Carbon nucleus. The plan is to complete the repairs of the superconducting solenoid early this fall, reassemble the detector, and collect data starting next spring.
Date: December 1, 1997
Creator: Carroll, A.S. & Collaboration, E850
Partner: UNT Libraries Government Documents Department

Formation of pre-sheath boundary layers in electronegative plasmas

Description: In electronegative plasmas Coulomb scattering between positive and negative ions can lead to the formation of a pre-sheath boundary layer containing the bulk of the negative ions. The negative ion boundary layer forms when momentum transfer from positive to negative ions dominates the negative ion acceleration from the electric field. This condition is met in Inductively Coupled Plasma reactors that operate at low pressure and high plasma density. Simulations of the GEC reactor for Chlorine and Oxygen chemistries using the INDUCT95 2D model are presented showing the pre-sheath boundary layer structure as a function of applied power and neutral pressure.
Date: May 1, 1998
Creator: Vitello, P., LLNL
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

Reply to ''Comment on 'Nucleon Elastic Form Factors and Local Duality'''

Description: Recently, we extracted [Phys.Rev.D 62, 073008 (2000)] the proton magnetic form factor from duality-averaging purely inelastic nucleon resonance data. The point stressed by Simula is that this extraction at larger values of momentum transfer is dominated by an unconstrained kinematic region. We will show at which momentum transfers this point is relevant, and argue the need for additional precise nucleon resonance data.
Date: January 1, 2001
Creator: Ent, R.; Keppel, C.E. & Niculescu, I.
Partner: UNT Libraries Government Documents Department

Tau neutrino component to tritium beta decay

Description: A framework is given for explaining anomalous results of neutrino mass experiments that measure the high energy electron spectrum of tritium {beta} decay. The experimental results have been fit to a negative neutrino mass square. We show that there is a consistent phenomenological interpretation due to a positive mass tau neutrino component of the {beta} decay spectrum, with strong near threshold final state interactions with the He nucleus. If this enhancement is due to new interactions between low energy tau neutrinos and nuclei, then the tritium 0 decay experiments could be used as detectors for cosmic background tau neutrinos. The model predicts a distinctive spectrum shape that is consistent with a recent high statistics LLNL experiment. A fit to the experiment gives a tau neutrino mass of 23 eV. Tau neutrinos of this mass would dominate the mass of the universe. Requirements for a theoretical model are given, as well as models that realize different aspects of these requirements. While qualitatively successful, the theoretical models have such severe quantitative difficulties that the accuracy of the molecular physics of the T-{sup 3}He ion, assumed in the analysis of the experimental data, is called into question.
Date: June 1, 1995
Creator: Snyderman, N.J.
Partner: UNT Libraries Government Documents Department

A highly portable, rapidly deployable system for eddy covariance measurements of CO2 fluxes

Description: To facilitate the study of flux heterogeneity within a region, the authors have designed, built, and field-tested a highly portable, rapidly deployable, eddy covariance CO{sub 2} flux measurement system. The system is built from off-the-shelf parts and was assembled at a minimal cost. The unique combination of features of this system allow for a very rapid deployment with a minimal number of field personnel. The system is capable of making high precision, unattended measurements of turbulent CO{sub 2} fluxes, latent heat (LE) fluxes, sensible heat fluxes (H), and momentum transfer fluxes. In addition, many of the meteorological and ecosystem variables necessary for quality control of the fluxes and for running ecosystem models are measured. A side-by-side field comparison of the system at a pair of established AmeriFlux sites has verified that, for single measurements, the system is capable of CO{sub 2} flux accuracy of about {+-} 1.2 {micro}mole/m{sup 2}/sec, LE flux accuracy of about {+-} 15 Watts/m{sup 2}, H flux accuracy of about {+-} 7 Watts/m{sup 2}, and momentum transfer flux accuracy of about {+-} 11 gm-m/sec/sec. System deployment time is between 2 and 4 hours by a single person. The system was measured to draw between 30 and 35 Watts of power and may be run from available line power, storage batteries, or solar panels.
Date: September 19, 2001
Creator: Billesbach, David P.; Fischer, Marc L.; Torn, Margaret S. & Berry, Joe A.
Partner: UNT Libraries Government Documents Department