R. J. Holt

Precision Rosenbluth measurement of the proton elastic form factors

We report the results of a new Rosenbluth measurement of the proton electromagnetic form factors at Q2 values of 2.64, 3.20, and 4.10 GeV2. Cross sections were determined by detecting the recoiling proton, in contrast to previous measurements which detected the scattered electron. Cross sections were determined to 3%, with relative uncertainties below 1%. The ratio mu(p)G(E)/G(M) was determined to 4%-8% and showed mu(p)G(E)/G(M) approximately 1. These results are consistent with, and much more precise than, previous Rosenbluth extractions. They are inconsistent with recent polarization transfer measurements of similar precision, implying a systematic difference between the techniques.

Laser Spectroscopic Determination of the ^6He Nuclear Charge Radius

We have performed precision laser spectroscopy on individual 6He (t(1/2)=0.8 s) atoms confined and cooled in a magneto-optical trap, and measured the isotope shift between 6He and 4He to be 43 194.772+/-0.056 MHz for the 2(3)S1-3(3)P2 transition. Based on this measurement and atomic theory, the nuclear charge radius of 6He is determined for the first time in a method independent of nuclear models to be 2.054+/-0.014 fm. The result is compared with the values predicted by a number of nuclear structure calculations and tests their ability to characterize this loosely bound halo nucleus.

Nuclear charge radius of 8He.

The root-mean-square (rms) nuclear charge radius of 8He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of 6He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from 6He to 8He is an indication of the change in the correlations of the excess neutrons and is consistent with the 8He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.

New Measurements of the European Muon Collaboration Effect in Very Light Nuclei

J. Seely, A. Daniel, D. Gaskell, J. Arrington, ∗ N. Fomin, P. Solvignon, R. Asaturyan, † F. Benmokhtar, W. Boeglin, B. Boillat, P. Bosted, A. Bruell, M.H.S. Bukhari, M.E. Christy, B. Clasie, S. Connell, ‡ M.M. Dalton, D. Day, J. Dunne, D. Dutta, 12 L. El Fassi, R. Ent, H. Fenker, B.W. Filippone, H. Gao, 12 C. Hill, R.J. Holt, T. Horn, 3 E. Hungerford, M.K. Jones, J. Jourdan, N. Kalantarians, C.E. Keppel, D. Kiselev, M. Kotulla, C. Lee, A.F. Lung, S. Malace, D.G. Meekins, T. Mertens, H. Mkrtchyan, T. Navasardyan, G. Niculescu, I. Niculescu, H. Nomura, Y. Okayasu, A.K. Opper, C. Perdrisat, D.H. Potterveld, V. Punjabi, X. Qian, P.E. Reimer, J. Roche, V.M. Rodriguez, O. Rondon, E. Schulte, E. Segbefia, K. Slifer, G.R. Smith, V. Tadevosyan, S. Tajima, L. Tang, G. Testa, R. Trojer, V. Tvaskis, W.F. Vulcan, F.R. Wesselmann, S.A. Wood, J. Wright, L. Yuan, and X. Zheng Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA, USA University of Houston, Houston, TX, USA Thomas Jefferson National Laboratory, Newport News, VA, USA Physics Division, Argonne National Laboratory, Argonne, IL, USA University of Virginia, Charlottesville, VA, USA Yerevan Physics Institute, Armenia University of Maryland, College Park, MD, USA Florida International University, Miami, FL, USA Basel University, Basel, Switzerland Hampton University, Hampton, VA, USA Mississippi State University, Jackson, MS, USA Triangle Universities Nuclear Laboratory, Duke University, Durham, NC, USA Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, CA, USA University of the Witwatersrand, Johannesburg, South Africa James Madison University, Harrisonburg, VA, USA Tohoku University, Sendai, Japan Ohio University, Athens, OH, USA College of William and Mary, Williamsburg, VA, USA Norfolk State University, Norfolk, VA, USA (Dated: October 27, 2009)

New Measurements of High-Momentum Nucleons and Short-Range Structures in Nuclei

We present new measurements of electron scattering from high-momentum nucleons in nuclei. These data allow an improved determination of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data also include the kinematic region where three-nucleon correlations are expected to dominate.

Nucleon and pion distribution functions in the valence region

We provide an experimental and theoretical perspective on the behavior of unpolarized distribution functions for the nucleon and pion on the valence-quark domain; namely, Bjorken-x ∼ 0.4. This domain is key to much of hadron physics; e.g., a hadron is defined by its flavor content and that is a valence-quark property. Furthermore, its accurate parametrization is crucial to the provision of reliable input for large collider experiments. We focus on experimental extractions of distribution functions via electron and muon inelastic scattering, and from Drell-Yan interactions; and on theoretical treatments that emphasize an explanation of the distribution functions, providing an overview of major contemporary approaches and issues. Valence-quark physics is a compelling subject, which probes at the heart of our understanding of the Standard Model. There are numerous outstanding and unresolved challenges, which experiment and theory must confront. In connection with experiment, we explain that an upgraded Jefferson Lab facility is well-suited to provide new data on the nucleon, while a future electron ion collider could provide essential new data for the mesons. There is also great potential in using Drell-Yan interactions, at FNAL, J-PARC and GSI, to push into the large-x domain for both mesons and nucleons. We argue furthermore that explanation, in contrast to modeling and parametrization, requires a widespread acceptance of the need to adapt theory: to the lessons learnt already from the methods of nonperturbative quantum field theory; and a fuller exploitation of those methods. Electronic address: holt@anl.gov Electronic address: cdroberts@anl.gov

Optimizing luminescent solar concentrator design

Luminescent Solar Concentrators (LSCs) use fluorescent materials and light guides to convert direct and diffuse sunlight into concentrated wavelength-shifted light that produces electrical power in small photovoltaic (PV) cells with the goal of significantly reducing the cost of solar energy utilization. In this paper we present an optimization analysis based on the implementation of a genetic algorithm (GA) subroutine to a numerical ray-tracing Monte Carlo model of an LSC, SIMSOLAR-P. The initial use of the GA implementation in SIMSOLAR-P is to find the optimal parameters of a hypothetical “perfect luminescent material” that obeys the Kennard Stepanov (K-S) thermodynamic relationship between emission and absorption. The optimization balances the efficiency losses in the wavelength shift and PV conversion with the efficiency losses due to re-scattering of light out of the collector. The theoretical limits of efficiency are provided for one, two and three layer configurations; the results show that a single layer configuration is far from optimal and adding a second layer in the LSC with wavelength shifted material in the near infrared region significantly increases the power output, while the gain in power by adding a third layer is relatively small. The results of this study provide a theoretical upper limit to the performance of an LSC and give guidance for the properties required for luminescent materials, such as quantum nanocrystals, to operate efficiently in planar LSC configurations.

Laser trapping of 225Ra and 226Ra with repumping by room-temperature blackbody radiation.

We have demonstrated Zeeman slowing and capture of neutral 225Ra and 226Ra atoms in a magneto-optical trap. The intercombination transition 1S0-->3P1 is the only quasicycling transition in radium and was used for laser-cooling and trapping. Repumping along the 3D1-->1P1 transition extended the lifetime of the trap from milliseconds to seconds. Room-temperature blackbody radiation was demonstrated to provide repumping from the metastable 3P0 level. We measured the isotope shift and hyperfine splittings on the 3D1-->1P1 transition with the laser-cooled atoms, and set a limit on the lifetime of the 3D1 level based on the measured blackbody repumping rate. Laser-cooled and trapped radium is an attractive system for studying fundamental symmetries.

High-precision measurement of the proton elastic form factor ratio mu_pG_E/G_M at low Q^2.

Abstract We report a new, high-precision measurement of the proton elastic form factor ratio μ p G E / G M for the four-momentum transfer squared Q 2 = 0.3 – 0.7 ( GeV / c ) 2 . The measurement was performed at Jefferson Lab (JLab) in Hall A using recoil polarimetry. With a total uncertainty of approximately 1%, the new data clearly show that the deviation of the ratio μ p G E / G M from unity observed in previous polarization measurements at high Q 2 continues down to the lowest Q 2 value of this measurement. The updated global fit that includes the new results yields an electric (magnetic) form factor roughly 2% smaller (1% larger) than the previous global fit in this Q 2 range. We obtain new extractions of the proton electric and magnetic radii, which are 〈 r E 2 〉 1 / 2 = 0.875 ± 0.010 fm and 〈 r M 2 〉 1 / 2 = 0.867 ± 0.020 fm . The charge radius is consistent with other recent extractions based on the electron–proton interaction, including the atomic hydrogen Lamb shift measurements, which suggests a missing correction in the comparison of measurements of the proton charge radius using electron probes and the recent extraction from the muonic hydrogen Lamb shift.

Pion parton distribution function in the valence region

The parton distribution function of the pion in the valence region is extracted in a next-to-leading order analysis from Fermilab E-615 pionic Drell-Yan data. The effects of the parametrization of the pions valence distributions are examined. Modern nucleon parton distributions and nuclear corrections were used and possible effects from higher twist contributions were considered in the analysis. In the next-to-leading order analysis, the high-x dependence of the pion structure function differs from that of the leading order analysis, but not enough to agree with the expectations of pQCD and Dyson-Schwinger calculations.