Digital Commons Network^™

Measurement Of Deeply Virtual Compton Scattering At Hera, S. Chekanov, M. Derrick, D. Krakauer, J. H. Loizides, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan

Faculty Publications

The cross-section for deeply virtual Compton scattering in the reaction ep → eγp has been measured with the ZEUS detector at HERA using integrated luminosities of 95.0 pb-1 of e+p and 16.7 pb-1 of e-p collisions. Differential cross-sections are presented as a function of the exchanged-photon virtuality, Q2, and the centre-of-mass energy, W, of the γ*p system in the region 5 < Q2 < 100 GeV2 and 40 < W < 140 GeV. The measured cross-sections rise steeply with increasing W. The measurements are compared to QCD-based calculations. © 2003 Elsevier B.V. All rights reserved.

Dynamics Underlying Fully Differential Cross Sections For Fast C⁶⁺ + He Collisions, Ronald E. Olson, J. Fiol

Physics Faculty Research & Creative Works

Single ionization of helium by impact of 100 MeV u^-1 C⁶⁺ ions is investigated using the three-body classical trajectory Monte Carlo method. Fully differential cross section calculations are compared to recently published data for ionized electrons emitted both in the scattering plane, and in the plane perpendicular to it that contains the initial velocity. the present calculations show good agreement with the experimental data, and improve upon continuum-distorted-wave results. the collision mechanisms that lead to the different structures observed in the fully differential cross sections are investigated and include those of the binary and recoil peaks for in-plane …

Measurement Of The Mass Difference M(DS+)–M (D+) At Cdf Ii, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present a measurement of the mass difference m(D_s⁺)– m (D⁺), where both the D_s⁺ and D⁺ are reconstructed in the Φπ⁺ decay channel. This measurement uses 11.6 pb^-1 of data collected by CDF II using the new displaced-track trigger. The mass difference is found to be m(D_s⁺)–m (D⁺)=99.41±0.38(stat)±0.21(syst) MeV/c².

Liberating The Inflaton From Primordial Spectrum Constraints, Christian Armendariz-Picon

Physics - All Scholarship

I discuss a mechanism that renders the spectral index of the primordial spectrum and the inflationary stage independent of each other. If a scalar field acquires an appropriate time-dependent mass, it is possible to generate an adiabatic, Gaussian scale invariant spectrum of density perturbations during any stage of inflation. As an illustration, I present a simple model where the time-dependent mass arises from the coupling of the inflaton to a second scalar. The mechanism I propose might help to implement a successful inflationary scenario in particle physics theories that do not yield slow-roll potentials.

Solar Neutrinos, Sno And Neutrino-Deuteron Reactions, Vladimir Gudkov, Kuniharu Kubodera

Faculty Publications

The standard nuclear physics approach and effective field theory approach for calculations of neutrino–deuteron cross sections for the solar neutrino energies are considered. Their main features, the level of accuracy and problems to be addressed for further developments are discussed.

Ξ‾ And Ω Distributions In Hadron–Nucleus Interactions, R. Vogt, Thomas D. Gutierrez

Physics

Strange baryons have long been known to exhibit a leading particle effect. A recent comparison of Ξ‾ production in π‾, n, and Σ‾ interactions with nuclei show this effect clearly. These data are supplemented by earlier measurements of Ξ‾ and Ω production by a Ξ‾ beam. We calculate the Ξ‾ and Ω x_F distributions and nuclear dependence in hA interactions using the intrinsic model.

Nonpolar Second-Order Nonlinear And Electrooptic Materials: Axially Ordered Chiral Polymers And Liquid Crystals, Kenneth D. Singer, Rolfe G. Petschek, Victor Ostroverkhov

Faculty Scholarship

This article reviews our work on the development and optimization of chiral, nonpolar media with large second-order nonlinear optical responses. We show how molecular engineering, theory, and measurements can be used to optimize this promising class of nonlinear optical materials. We describe how supramolecular alignment into easily processable materials takes advantage of the relevant molecular hyperpolarizabilities. A wide variety of techniques can be used to fabricate bulk materials belonging to the chiral nonpolar symmetry groups, D∞ and D2. The microscopic chromophore alignment schemes that optimize the nonlinear optical response in such materials are deduced from general symmetry considerations for both …

Identification Of Dynamic Properties Of Materials For The Nuclear Waste Package, Brendan O'Toole, Mohamed Trabia, Amy J. Smiecinski

Publications (YM)

Stainless steel 316L, titanium alloy grade 7, and alloy C22 are currently under consideration as candidate materials for use in various components associated with the spent nuclear fuel package, which must be designed to withstand structural deformation caused by static, thermal, and handling loads. In addition, it has to maintain its integrity in case of accidents, where it may be subjected to high loads over a very short period of time. Mechanical characteristics of these three materials under dynamic loading are not well documented. This paper describes the procedures and results obtained from experiments performed over a range of slow …

On The Nitrogen Vacancy In Gan, David C. Look, Gary C. Farlow, P. J. Drevinsky, D. F. Bliss, J. R. Sizelove

Physics Faculty Publications

The dominant electrically active defect produced by 0.42 MeV electron irradiation in GaN is a 70 meV donor. Since only N-sublattice displacements can be produced at this energy, and since theory predicts that the N interstitial is a deep acceptor in n-type GaN, we argue that the 70 meV donor is most likely the isolated N vacancy. The background shallow donors, in the 24–26 meV range, actually decrease in concentration, probably due to interactions with mobile N interstitials that are produced by the irradiation. Thus, the recent assignment of a photoluminescence (PL) line as an exciton bound to a …

Toy Models For The Falling Chimney, Gabriele U. Varieschi, Kaoru Kamiya

Physics Faculty Works

In this paper we review the theory of the ‘‘falling chimney,’’ which deals with the breaking in mid-air of tall structures when they fall to the ground. We show that these ruptures can be caused by either shear forces typically developing near the base, or by the bending of the structure which is caused primarily by the internal bending moment. In the latter case the breaking is more likely to occur between one-third and one-half of the height of the chimney. Small scale toy models are used to reproduce the dynamics of the falling chimney. By examining photos taken during …

Perturbation Approach To The Self-Energy Of Non-S Hydrogenic States, Eric Olivier Le Bigot, Ulrich D. Jentschura, Peter J. Mohr, Paul Indelicato, Gerhard Soff

Physics Faculty Research & Creative Works

We present results on the self-energy correction to the energy levels of hydrogen and hydrogenlike ions. The self energy represents the largest QED correction to the relativistic (Dirac-Coulomb) energy of a bound electron. We focus on the perturbation expansion of the self energy of non-S states, and provide estimates of the so-called A₆₀ perturbative coefficient, which can be considered as a relativistic Bethe logarithm. Precise values of A₆₀ are given for many P, D, F and G states, while estimates are given for other electronic states. These results can be used in high-precision spectroscopy experiments in hydrogen and …

Resonant Photoemission In F-Electron Systems: Pu And Gd, James G. Tobin, Brandon W. Chung, Roland K. Schulze, Jeff Russell Terry, John Douglas Farr, David K. Shuh, K. Heinzelman, Eli Rotenberg, George Daniel Waddill, Gerrit V. Van Der Laan

Physics Faculty Research & Creative Works

Resonant photoemission in the Pu 5f and Pu 6p states is compared to that in the Gd 4f and Gd 5p states. Spectral simulations, based upon an atomic model with angular momentum coupling, are compared to the Gd and Pu results. Additional spectroscopic measurements of Pu, including core level photoemission and x-ray absorption, are also presented.

Curvature-Induced Defect Unbinding In Toroidal Geometries, Mark Bowick, David R. Nelson, Alex Travesset

Physics - All Scholarship

Toroidal templates such as vesicles with hexatic bond orientational order are discussed. The total energy including disclination charges is explicitly computed for hexatic order embedded in a toroidal geometry. Related results apply for tilt or nematic order on the torus in the one Frank constant approximation. Although there is no topological necessity for defects in the ground state, we find that excess disclination defects are nevertheless energetically favored for fat torii or moderate vesicle sizes. Some experimental consequences are discussed.

Search For ΝΜ→ΝE Oscillations In The Nomad Experiment, Nomad Collaboration, P. Astier, D. Autiero, A. Baldisseri, M. Baldo-Ceolin, M. Banner, G. Bassompierre, K. Benslama, N. Besson, I. Bird, B. Blumenfeld, F. Bobisut, J. Bouchez, S. Boyd, A. Bueno, S. Buyatov, L. Camilleri, A. Cardini, P. W. Cattaneo, V. Cavasinni, Roberto Petti, Et. Al.

Faculty Publications

We present the results of a search for ν_µ → ν_e oscillations in the NOMAD experiment at CERN. The experiment looked for the appearance of ν_e in a predominantly ν_µ wide-band neutrino beam at the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are ∆m² < 0.4 eV² for maximal mixing and sin²(2θ)−3 for large ∆m². This result excludes the LSND allowed region of oscillation parameters with ∆m² ≳∆10 eV².

Large Nc And Chiral Dynamics, Joseph Schechter, Masayasu Harada, Francesco Sannino

Physics - All Scholarship

We study the dependence on the number of colors of the leading pi pi scattering amplitude in chiral dynamics. We demonstrate the existence of a critical number of colors for and above which the low energy pi pi scattering amplitude computed from the simple sum of the current algebra and vector meson terms is crossing symmetric and unitary at leading order in a truncated and regularized 1/Nc expansion. The critical number of colors turns out to be Nc=6 and is insensitive to the explicit breaking of chiral symmetry. Below this critical value, an additional state is needed to enforce the …

Percolation Of Satisfiability In Finite Dimensions, Alan Middleton, J. M. Schwarz

Physics - All Scholarship

The satisfiability and optimization of finite-dimensional Boolean formulas are studied using percolation theory, rare region arguments, and boundary effects. In contrast with mean-field results, there is no satisfiability transition, though there is a logical connectivity transition. In part of the disconnected phase, rare regions lead to a divergent running time for optimization algorithms. The thermodynamic ground state for the NP-hard two-dimensional maximum-satisfiability problem is typically unique. These results have implications for the computational study of disordered materials.

Exact Lattice Supersymmetry From Topological Field Theory, Simon Catterall

Physics - All Scholarship

We discuss the connection between supersymmetric field theories and topological field theories and show how this connection may be used to construct local lattice field theories which maintain an exact supersymmetry. It is shown how metric independence of the continuum topological field theory allows us to derive the lattice theory by blocking out of the continuum in a deformed geometry. This, in turn, allows us to prove the cut-off independence of certain supersymmetric Ward identities.

Stabilization Of Extra Dimensions At Tree Level, Scott Watson, Robert H. Brandenberger

Physics - All Scholarship

By considering the effects of string winding and momentum modes on a time dependent background, we find a method by which six compact dimensions become stabilized naturally at the self-dual radius while three dimensions grow large.

Analysis Of Resonance Structure In The Above-Threshold Ionization Photoelectron Spectra Of Magnesium, Glen D. Gillen, L D. Van Woerkom

Physics

Using high-resolution photoelectron spectroscopy and 120-fs, 800-nm Ti:sapphire laser pulses, we observe and analyze intensity-dependent resonant population of specific intermediate excited states of neutral magnesium atoms and their subsequent photoionization in the laser field. Various participating states are identified using angular-momentum selection rules, partial yields, and angular distributions. Several unexpected results are observed and discussed, including peaks that do not correspond to expected resonant processes, and order-to-order variations in the photoelectron spectra.

Driven Depinning Of Strongly Disordered Media And Anisotropic Mean-Field Limits, M. Christina Marchetti, A. Alan Middleton, Karl Saunders, J. M. Schwarz

Physics

Extended systems driven through strong disorder are modeled generically using coarse-grained degrees of freedom that interact elastically in the directions parallel to the drive and slip along at least one of the directions transverse to the motion. In the limit of infinite-range elastic and viscous coupling this model has a tricritical point separating a region where the depinning is continuous, in the universality class of elastic depinning, from a region where depinning is hysteretic. Many of the collective transport models discussed in the literature are special cases of the generic model.

Scale Invariance Without Inflation?, Christian Armendariz-Picon, Eugene A. Lim

Physics - All Scholarship

We propose a new alternative mechanism to seed a scale invariant spectrum of primordial density perturbations that does not rely on inflation. In our scenario, a perfect fluid dominates the early stages of an expanding, non-inflating universe. Because the speed of sound of the fluid decays, perturbations are left frozen behind the sound horizon, with a spectral index that depends on the fluid equation of state. We explore here a toy model that realizes this idea. Although the model can explain an adiabatic, Gaussian, scale invariant spectrum of primordial perturbations, it turns out that in its simplest form it cannot …

High Resolution, High Sensitivity Imaging Of The Galactic Center At 330 Mhz, Michael E. Nord, Crystal L. Brogan, Scott D. Hyman, T. Joseph W. Lazio, Namir E. Kassim, Ted N. Larosa, K. Anantharamaiah, Nebojsa Duric

Faculty Articles

We present results derived from a wide field, sub-arcminute resolution VLA image of the Galactic Center region at 330 MHz (λ = 90 cm). With a resolution of ∼7″ × 12″ and an rms noise of 1.6 mJy beam⁻¹, this image represents a significant increase in resolution and sensitivity over the previously published VLA image at this frequency (eg. LaRosa et al. 2000). The improvement in sensitivity has significantly increased the census of small diameter sources in the region, resulted in the detection of two new Non-Thermal Filaments (NTFs) and 18 new NTF candidates, and resulted in …

Afci Quarterly Input – Unlv July Through September, 2003, Harry Reid Center For Environmental Studies. Nuclear Science And Technology Division

Transmutation Research Program Reports (TRP)

Quarterly report highlighting research projects and objectives of the Transmutation Research Program at the Nuclear Science & Technology Division, Harry Reid Research Center.

The University of Nevada, Las Vegas supports the AFCI through research and development of technologies for economic and environmentally sound refinement of spent nuclear fuel. The UNLV program has four components: infrastructure, international collaboration, student-based research, and management and program support.

Low-Energy Operators In Effective Theories, C Felline, Nirav P. Mehta, J Piekarewicz, James R. Shepard

Physics and Astronomy Faculty Research

Modern effective-theory techniques are applied to the nuclear many-body problem. A novel approach is proposed for the renormalization of operators in a manner consistent with the construction of the effective potential. To test this approach, a one-dimensional, yet realistic, nucleon-nucleon potential is introduced. An effective potential is then constructed by tuning its parameters to reproduce the exact effective-range expansion and a variety of bare operators are renormalized in a fashion compatible with this construction. Predictions for the expectation values of these effective operators in the ground state reproduce the results of the exact theory with remarkable accuracy (at the 0.5% …

Two-Loop Bethe-Logarithm Correction In Hydrogenlike Atoms, Krzysztof Pachucki, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

We calculate the two-loop Bethe logarithm correction to atomic energy levels in hydrogenlike systems. The two-loop Bethe logarithm is a low-energy quantum electrodynamic (QED) effect involving multiple summations over virtual excited atomic states. Although much smaller in absolute magnitude than the well-known one-loop Bethe logarithm, the two-loop analog is quite significant when compared to the current experimental accuracy of the 1 S – 2 S transition: It contributes - 8.19 and - 0.84 k H z for the 1 S and the 2 S state, respectively. The two-loop Bethe logarithm has been the largest unknown correction to the hydrogen Lamb …

Observation Of A Narrow Resonance Of Mass 2.46 Gev/C2 Decaying To DS*+ Π0 And Confirmation Of The D*SJ (2317) State, Dave Z. Besson, Kenneth A. Bloom, Cornell Electronic Storage Ring

Kenneth Bloom Publications

Using 13.5 fb^-1 of e⁺e^- annihilation data collected with the CLEO II detector, we have observed a narrow resonance decaying to D_s^*+π⁰ with a mass near 2.46 GeV/c². The search for such a state was motivated by the recent discovery by the BaBar Collaboration of a narrow state at 2.32 GeV/c², the D_sJ^*(2317) ⁺, that decays to D_s⁺ π⁰. Reconstructing the D_s⁺ π⁰ and D_s^*+ π⁰ final states in CLEO data, we …

Anisotropic Inflation And The Origin Of Four Large Dimensions, Christian Armendariz-Picon, Vikram Duvvuri

Physics - All Scholarship

In the context of (4+d)-dimensional general relativity, we propose an inflationary scenario wherein 3 spatial dimensions grow large, while d extra dimensions remain small. Our model requires that a self-interacting d-form acquire a vacuum expectation value along the extra dimensions. This causes 3 spatial dimensions to inflate, whilst keeping the size of the extra dimensions nearly constant. We do not require an additional stabilization mechanism for the radion, as stable solutions exist for flat, and for negatively curved compact extra dimensions. From a four-dimensional perspective, the radion does not couple to the inflaton; and, the small amplitude of the CMB …

High-Field Measurements Of Electron Decoherence Time In Metallic Nanowires: Switching Off Magnetic Impurity Spins, P. Mohanty, Richard A. Webb

Faculty Publications

We report low-temperature measurements of electron decoherence time in a series of pure gold wires, 18 nm thick and 30 nm wide. At fields up to 15 T, large enough to polarize any concentration of magnetic impurity spins, conductance fluctuation measurements show almost no temperature dependence of the decoherence time below 300 mK, both in the correlation field for interference and the root-mean-square value of the fluctuations. Combined with previous low-field weak localization measurements on samples from similar material, our experiment suggests that the ubiquitous saturation of decoherence time in these samples is not due to any mechanism based on …

Reply To Comment On “Mev Magnetosheath Ions Energized At The Bow Shock” By J. Chen, Ta Fritz, And Rb Sheldon, S. Chang, J. D. Scudder, K. Kudela, Harlan E. Spence, J. F. Fennell, R. P. Lepping, R. P. Lin, C. T. Russell

Physics & Astronomy

No abstract provided.

Dramatic Nondipole Effects In Low-Energy Photoionization: Experimental And Theoretical Study Of Xe 5s, Oliver Hemmers, Renaud Guillemin, E. P. Kanter, B. Krassig, Dennis W. Lindle, S. H. Southworth, R. Wehlitz, J. Baker, A. C. Hudson, M. Lotrakul, D. Rolles, Wayne C. Stolte, I. Tran, A. Wolska, S. Yu, M. Ya Amusia, K. T. Cheng, L. V. Chernysheva, W. R. Johnson, S. T. Manson

Environmental Studies Faculty Publications

The Xe 5s nondipole photoelectron parameter γ is obtained experimentally and theoretically from threshold to ∼200  eV photon energy. Significant nondipole effects are seen even in the threshold region of this valence shell photoionization. In addition, contrary to previous understanding, clear evidence of interchannel coupling among quadrupole photoionization channels is found.