A. Uzzle

Old Dominion University, Norfolk, VA, United States

Are you A. Uzzle?

Claim your profile

Publications (31)

  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the quark dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available for the longitudinal structure function in particular. Here we present separated structure functions for hydrogen and deuterium at low four--momentum transfer squared, Q^2< 1 GeV^2, and compare these with parton distribution parameterizations and a k_T factorization approach. While differences are found, the parameterizations generally agree with the data even at the very low Q^2 scale of the data. The deuterium data show a smaller longitudinal structure function, and smaller ratio of longitudinal to transverse cross section R, than the proton. This suggests either an unexpected difference in R for the proton and neutron or a suppression of the gluonic distribution in nuclei.
    Full-text Article · Jun 2016
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A large set of cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with invariant mass squared W2>4 GeV2 (up to ≈7 GeV2) and range in four-momentum transfer squared 2<Q2<4 (GeV/c)2, and cover a range in the Bjorken scaling variable 0.2<x<0.6. The fractional energy of the pions spans a range 0.3<z<1, with small transverse momenta with respect to the virtual-photon direction, Pt2<0.2 (GeV/c)2. The invariant mass that goes undetected, Mx or W′, is in the nucleon resonance region, W′<2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark→pion production mechanisms. The x, z, and Pt2 dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for π+ and π−) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of d quarks are found to be slightly smaller than for u quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths.
    Full-text Article · Mar 2011 · Physical Review C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The kaon electroproduction reaction 1H(e,e′K+)Λ was studied as a function of the virtual-photon four-momentum, Q2, total energy, W, and momentum transfer, t, for different values of the virtual-photon polarization parameter. Data were taken at electron beam energies ranging from 3.40 to 5.75 GeV. The center of mass cross section was determined for twenty-one kinematics corresponding to Q2 of 1.90 and 2.35 GeV2, and the longitudinal, σL, and transverse, σT, cross sections were separated using the Rosenbluth technique at fixed W and t. The separated cross sections reveal a flat energy dependence at forward kaon angles not satisfactorily described by existing electroproduction models. Influence of the kaon pole on the cross sections was investigated by adopting an off-shell form factor in the Regge model, which better describes the observed energy dependence of σT and σL.
    Full-text Article · Nov 2009 · Physical Review C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Inclusive electron-proton and electron-deuteron inelastic cross sections have been measured at Jefferson Lab (JLab) in the resonance region, at large Bjorken x, up to 0.92, and four-momentum transfer squared Q2 up to 7.5 GeV2 in the experiment E00-116. These measurements are used to extend to larger x and Q2 precision, quantitative, studies of the phenomenon of quark-hadron duality. Our analysis confirms, both globally and locally, the apparent “violation” of quark-hadron duality previously observed at a Q2 of 3.5 GeV2 when resonance data are compared to structure function data created from CTEQ6M and MRST2004 parton distribution functions (PDFs). More importantly, our new data show that this discrepancy saturates by Q2~4 GeV2, becoming Q2 independent. This suggests only small violations of Q2 evolution by contributions from the higher-twist terms in the resonance region that is confirmed by our comparisons to ALEKHIN and ALLM97. We conclude that the unconstrained strength of the CTEQ6M and MRST2004 PDFs at large x is the major source of the disagreement between data and these parametrizations in the kinematic regime we study and that, in view of quark-hadron duality, properly averaged resonance region data could be used in global quantum chromodynamics fits to reduce PDF uncertainties at large x.
    Full-text Article · Sep 2009 · Physical Review C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The process $ep \to e^{\prime}p^{\prime}\pi^0$ has been measured at $Q^2$ = 6.4 and 7.7 GeV/c$^2$)$^2$ in Jefferson Lab's Hall C. Unpolarized differential cross sections are reported in the virtual photon-proton center of mass frame considering the process $\gamma^{\ast}p \to p^{\prime}\pi^0$. Various details relating to the background subtractions, radiative corrections and systematic errors are discussed. The usefulness of the data with regard to the measurement of the electromagnetic properties of the well known $\Delta(1232)$ resonance is covered in detail. Specifically considered are the electromagnetic and scalar-magnetic ratios $R_{EM}$ and $R_{SM}$ along with the magnetic transition form factor $G_M^{\ast}$. It is found that the rapid fall off of the $\Delta(1232)$ contribution continues into this region of momentum transfer and that other resonances Comment: 41 pages including numerical cross section tables, updates include new phenomenological fit for multipole extraction in addition to simplified previous method, These fits are seen in figures 24,26 and 27 and the values are reported in Table VIII
    Full-text Article · Jun 2009 · Physical Review C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The differential cross-section for the process p(e,e'p)eta has been measured at Q2 ~ 5.7 and 7.0 (GeV/c)2 for centre-of-mass energies from threshold to 1.8 GeV, encompassing the S11(1535) resonance, which dominates the channel. This is the highest momentum transfer measurement of this exclusive process to date. The helicity-conserving transition amplitude A_1/2, for the production of the S11(1535) resonance, is extracted from the data. Within the limited Q2 now measured, this quantity appears to begin scaling as 1/Q3 - a predicted, but not definitive, signal of the dominance of perturbative QCD, at Q2 ~ 5 (GeV/c)2. Comment: LaTeX, 30 pages, 29 figures, uses longtable.sty, slashbox.sty, ifthen.sty; (v2) corrected figure inclusions; (v3) changes in filenames for prc and added Report-no; (v4) correction based on comments from referee {small changes to abstract and conclusion, inserted figure 9, other small changes to the text} (v5) very minor additions to improve clarity
    Full-text Article · Apr 2008 · Physical Review C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Kaon electroproduction from light nuclei and hydrogen, using 1 H, 2 H, 3 He, 4 He, and carbon targets has been measured at Jefferson Laboratory. The quasifree angular distributions of Λ and Σ hyperons were determined at Q 2 = 0.35 (GeV/c) 2 and W = 1.91 GeV. Electroproduction on hydrogen was measured at the same kinematics for reference.
    Full-text Article · Nov 2007 · Physical Review C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets were measured for 0.2<x<0.5, 2<Q2<4 GeV2, 0.3<z<1, and . For Pt<0.1 GeV, we find the azimuthal dependence to be small, as expected theoretically. For both π+ and π−, the Pt dependence from the deuteron is found to be slightly weaker than from the proton. In the context of a simple model, this implies that the initial transverse momenta width of d quarks is larger than for u quarks and, contrary to expectations, the transverse momentum width of the favored fragmentation function is larger than the unfavored one.
    Full-text Article · Oct 2007
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Kaon electroproduction from light nuclei and hydrogen, using 1H, 2H, 3He, 4He, and Carbon targets has been measured at Jefferson Laboratory. The quasifree angular distributions of Lambda and Sigma hyperons were determined at Q^2= 0.35(GeV/c)^2 and W= 1.91GeV. Electroproduction on hydrogen was measured at the same kinematics for reference.
    Full-text Article · Aug 2007
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: We report on a study of the longitudinal to transverse cross section ratio, R=sigma(L)/sigma(T), at low values of x and Q(2), as determined from inclusive inelastic electron-hydrogen and electron-deuterium scattering data from Jefferson Laboratory Hall C spanning the four-momentum transfer range 0.06 < Q(2)< 2.8 GeV2. Even at the lowest values of Q(2), R remains nearly constant and does not disappear with decreasing Q(2), as might be expected. We find a nearly identical behavior for hydrogen and deuterium.
    Full-text Article · Apr 2007 · Physical Review Letters
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A large data set of charged-pion (pi+/-) electroproduction from both hydrogen and deuterium targets has been obtained spanning the low-energy residual-mass region. These data conclusively show the onset of the quark-hadron duality phenomenon, as predicted for high-energy hadron electroproduction. We construct several ratios from these data to exhibit the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark-->pion production mechanisms.
    Full-text Article · Jan 2007 · Physical Review Letters
  • [Show abstract] [Hide abstract] ABSTRACT: Encouraged by the success of the first hypernuclear spectroscopy through the (e,e′K+)(e,e′K+) reaction (JLab E89-009), a new improved experiment with a newly developed High resolution Kaon Spectrometer (HKS) and a new configuration of the electron spectrometer is planned at the JLab Hall C. The introduction of the HKS will improve by a factor of two, the energy resolution which was limited by the previous kaon spectrometer. The hypernuclear yield and the signal to noise ratio will be also improved by a factor of 50 and 10, respectively.
    Article · May 2005 · Nuclear Physics A
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The A(e,e′K+)X reaction has been investigated at Jefferson Laboratory. Data were taken for Q2 ≈ 0.35 GeV2 at a beam energy of 3.245 GeV for 1H,3He and 4He targets. Evidence for Λ‐hypernuclear bound states is seen for 3,4He targets. This is the first time that the electroproduction of these hypernuclei has been observed. © 2005 American Institute of Physics
    Full-text Article · May 2005
  • [Show abstract] [Hide abstract] ABSTRACT: An experimental technique for single‐Λ spectroscopy of the light and medium‐heavy mass Λ‐hypernuclei developed at the Jlab by the E01‐011 Collaboration has been described. The technique is based on the electroproduction of Λ‐hypernuclei by the (e,e′K+) reaction and newly constructed 2nd generation high resolution large solid angle kaon spectrometer (HKS).
    Article · May 2005 · AIP Conference Proceedings
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The (3,4)(Lambda)H and (4)(Lambda)H hypernuclear bound states have been observed for the first time in kaon electroproduction on (3,4)He targets. The production cross sections have been determined at Q(2)=0.35 GeV2 and W=1.91 GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the (3,4)He(e,e(')K+)(3,4)(Lambda)H processes to the elementary cross section 1H(e,e K+)Lambda on the free proton, measured during the same experiment.
    Full-text Article · Jan 2005 · Physical Review Letters
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: We report on a detailed study of longitudinal strength in the nucleon resonance region, presenting new results from in-clusive electron-proton cross sections measured at Jefferson Lab Hall C in the four-momentum transfer range 0.2 <Q 2 < 5.5 GeV 2 . The data have been used to accurately perform over 170 Rosenbluth-type longitudinal / transverse separa-tions. The precision R = σL/σT data are presented here, along with the first separate values of the inelastic structure functions F1 and FL in this regime. The resonance longitudi-nal component is found to be significant. With the new data, quark-hadron duality is observed above Q 2 = 1 GeV 2 in the separated structure functions independently.
    Full-text Article · Nov 2004
  • Source
    L Yuan · M. Sarsour · T Miyoshi · [...] · C Yan
    [Show abstract] [Hide abstract] ABSTRACT: A pioneering experiment in Lambda hypernuclear spectroscopy, undertaken at the Thomas Jefferson National Accelerator Facility (Jlab), was recently reported. The experiment used the high- precision, continuous electron beam at Jlab, and a special arrangement of spectrometer magnets to measure the spectrum from {nat}C and 7Li targets using the (e,e' K+)reaction. The 12B hypernuclear spectrum was previously published. This experiment is now reported in more detail, with improved results for the 12B hypernuclear spectrum. In addition, unpublished results of the 7He hypernuclear spectrum are also shown. This later spectrum indicates the need for a more detailed few-body calculation of the hypernucleus and the reaction process. The success of this experiment demonstrates that the (e,e'K+) reaction can be effectively used as a high resolution tool to study hypernuclear spectra, ant its use should be vigorously pursued. Comment: 24 pages, 10 figures
    Full-text Article · Aug 2004 · Physical Review C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: We report on precision measurements of the elastic cross section for electron-proton scattering performed in Hall C at Jefferson Lab. The measurements were made at 28 unique kinematic settings covering a range in momentum transfer of 0.4 < Q{sup 2} < 5.5 (/rm GeV/c){sup 2}. These measurements represent a significant contribution to the world's cross section data set in the Q{sup 2} range where a large discrepancy currently exists between the ratio of electric to magnetic proton form factors extracted from previous cross section measurements and that recently measured via polarization transfer in Hall A at Jefferson Lab.
    Full-text Article · Jul 2004 · Physical Review C
  • [Show abstract] [Hide abstract] ABSTRACT: We report on precision measurements of the elastic cross section for electron-proton scattering performed in Hall C at Jefferson Lab. The measurements were made at 28 distinct kinematic settings covering a range in momentum transfer of 0.4 < Q2 < 5.5 (GeV/c)2. These measurements represent a significant contribution to the world's cross section data set in the Q2 range, where a large discrepancy currently exists between the ratio of electric to magnetic proton form factors extracted from previous cross section measurements and that recently measured via polarization transfer in Hall A at Jefferson Lab. This data set shows good agreement with previous cross section measurements, indicating that if a heretofore unknown systematic error does exist in the cross section measurements, then it is intrinsic to all such measurements.
    Article · Jul 2004 · Physical Review C
  • [Show abstract] [Hide abstract] ABSTRACT: The A(e,e ' K+)YX reaction has been investigated in Hall C at Jefferson Laboratory for 6 different targets. Data were taken for Q(2) approximate to 0.35 and 0.5 GeV2 at a beam energy of 3.245 GeV for H-1, H-2, He-3, He-4, C and Al targets. The missing mass spectra are fitted with Monte Carlo simulations taking into account the production of A and E-0 hyperon production off the proton, and Sigma(-) off the neutron. 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 He-3,He-4 targets.
    Conference Paper · Jan 2004

Publication Stats

483 Citations

Institutions

  • 2009
    • Old Dominion University
      • Department of Physics
      Norfolk, VA, United States
  • 2000-2009
    • Hampton University
      • Department of Physics
      Hampton, VA, United States
  • 2003-2005
    • Tohoku University
      • Department of Physics
      Sendai-shi, Miyagi, Japan
  • 2004
    • Florida International University
      Miami, Florida, United States
  • 2001
    • Duke University
      Durham, North Carolina, United States
    • University of Illinois, Urbana-Champaign
      • Department of Physics
      Urbana, Illinois, United States