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Performance of 2nd Generation BaBar Resistive Plate Chambers (open access)

Performance of 2nd Generation BaBar Resistive Plate Chambers

The BaBar detector has operated nearly 200 Resistive Plate Chambers (RPCs), constructed as part of an upgrade of the forward endcap muon detector, for the past two years. The RPCs experience widely different background and luminosity-driven singles rates (0.01-10 Hz/cm{sup 2}) depending on position within the endcap. Some regions have integrated over 0.3 C/cm{sup 2}. RPC efficiency measured with cosmic rays is high and stable. The average efficiency measured with beam is also high. However, a few of the highest rate RPCs have suffered efficiency losses of 5-15%. Although constructed with improved techniques and minimal use of linseed oil, many of the RPCs, which are operated in streamer mode, have shown increased dark currents and noise rates that are correlated with the direction of the gas flow and the integrated current. Studies of the above aging effects are presented and correlated with detector operating conditions.
Date: July 12, 2005
Creator: Anulli, F.; Baldini, R.; Calcaterra, A.; de Sangro, R.; Finocchiaro, G.; Patteri, P. et al.
System: The UNT Digital Library
Performance Verification of the Astro-E2 X-ray spectrometer in the flight configuration (open access)

Performance Verification of the Astro-E2 X-ray spectrometer in the flight configuration

The X-ray Spectrometer (XRS) is a high resolution, non-dispersive cryogenic detector on board the X-ray satellite, Astro-E2 (Suzaku), which was successfully launched on July 10, 2005. The XRS achieves an energy resolution of 6 eV at 6 keV (FWHM) and covers a broad energy range of {approx} 0.07-10 keV. The XRS will enable powerful plasma diagnostics of a variety of astrophysical objects such as the dynamics of gas in clusters of galaxies. The XRS was integrated to the spacecraft in September 2004, and took a series of spacecraft tests until April 2005. We describe results of the XRS performance verification in the spacecraft configuration. First, the noise level was extremely low on the spacecraft, and most of the pixels achieved an energy resolution of 5-6 eV at 5.9 keV. Microphonics from the mechanical cooler was one of the concerns, but they did not interfere with the detector, when the dewar was integrated to the spacecraft and filled with solid neon. To attain the best energy resolution, however, correction of gain drift is mandatory. The XRS has a dedicated calibration pixel for that purpose, and drift correction using the calibration pixel is very effective when the gain variation is due to …
Date: September 12, 2005
Creator: Ota, N.; Boyce, K. R.; Brown, G. V.; Cottam, J.; Fujimoto, R.; Furusho, T. et al.
System: The UNT Digital Library
POTENTIAL FOR HIGGS PHYSICS AT THE LHC AND SUPER-LHC. (open access)

POTENTIAL FOR HIGGS PHYSICS AT THE LHC AND SUPER-LHC.

The expected sensitivity of the LHC experiments to the discovery of the Higgs boson and the measurement of its properties is presented in the context of both the standard model and the its minimal supersymmetric extension. Prospects for a luminosity-upgraded ''Super-LHC'' are also presented. If it exists, the LHC should discover standard model Higgs boson, measure its mass accurately, and make various measurements of its couplings, spin and CP properties. In the context of the CP-conserving MSSM, the LHC should be able to discover one or more Higgs bosons over the entire m{sub A}-tan {beta} plane, with two or more observable in many cases. The large number of channels available insure a robust discovery and offer many opportunities for additional measurements. Observation of H {yields} {mu}{mu}, measurement of the tri-linear Higgs self-coupling, and various search channels are statistics-limited, and only possible with a luminosity upgrade. A luminosity upgrade would substantially improve some of the coupling measurements and generally extend the sensitivity in the MSSM Higgs plane. Efforts are ongoing to understand the upgrade of the LHC to the Super-LHC.
Date: December 12, 2005
Creator: CRANMER, K.S.
System: The UNT Digital Library
Practical Twistor Spinoffs: On-Shell Tree and Loop Recursion Relations (open access)

Practical Twistor Spinoffs: On-Shell Tree and Loop Recursion Relations

I briefly review how on-shell recursion relations, whose development was stimulated by recent twistor-space approaches, have been applied to compute tree and one-loop amplitudes in QCD.
Date: July 12, 2005
Creator: Dixon, Lance J.
System: The UNT Digital Library
Production of [15O] Water at Low-Energy Proton Cyclotrons (open access)

Production of [15O] Water at Low-Energy Proton Cyclotrons

We report a simple system for producing [15O]H2O from nitrogen-15 in a nitrogen/hydrogen gas target with recycling of the target nitrogen, allowing production on low-energy proton-only accelerators with minimal consumption of isotopically enriched nitrogen-15. The radiolabeled water is separated from the target gas and radiolytically produced ammonia by temporary freezing in a small trap at -40 C.
Date: December 12, 2005
Creator: Powell, James & O'Neil, James P.
System: The UNT Digital Library
Pseudorapidity Asymmetry and Centrality Dependence of Charged Hadron Spectra in d+Au collisions at sqrt(sNN) = 200 GeV (open access)

Pseudorapidity Asymmetry and Centrality Dependence of Charged Hadron Spectra in d+Au collisions at sqrt(sNN) = 200 GeV

The pseudorapidity asymmetry and centrality dependence of charged hadron spectra in d+Au collisions at {radical}s{sub NN} = 200 GeV are presented. The charged particle density at mid-rapidity, its pseudorapidity asymmetry and centrality dependence are reasonably reproduced by a Multi-Phase Transport model, by HIJING, and by the latest calculations in a saturation model. Ratios of transverse momentum spectra between backward and forward pseudorapidity are above unity for p{sub T} below 5 GeV/c. The ratio of central to peripheral spectra in d+Au collisions shows enhancement at 2 < p{sub T} < 6 GeV/c, with a larger effect at backward rapidity than forward rapidity. Our measurements are in qualitative agreement with gluon saturation and in contrast to calculations based on incoherent multiple partonic scatterings.
Date: January 12, 2005
Creator: Adams, J.; Aggarwal, M. M.; Ahammed, Z.; Amonett, J.; Anderson, B. D.; Arkhipkin, D. et al.
System: The UNT Digital Library
Radiation-Matter Coupling for Low Density Plasmas (open access)

Radiation-Matter Coupling for Low Density Plasmas

Radiation can have a dramatic effect on the material properties of low density plasmas, altering bulk properties such as energy density and specific heat as well as spectral characteristics such as opacity and emissivity. The response of the material to radiation must be considered when constructing transport algorithms that are intended to provide self-consistent solutions for both the radiation field and plasma properties. It consistent can affect almost every aspect of the numerical solution, from the overall solution strategy down to details of the acceleration algorithms. We discuss these issues in the context of one approach towards improving the stability and convergence of the solution, with examples relevant to high-energy density physics. We also present a direct solution technique for the energy linearized multigroup radiation transport equations that sidesteps the need for a multigroup acceleration process and can be used to benchmark the performance of iterative algorithms.
Date: July 12, 2005
Creator: Scott, H A
System: The UNT Digital Library
RADIONUCLIDE DISPERSION RATES BY AEOLIAN, FLUVIAL, AND POROUS MEDIA TRANSPORT (open access)

RADIONUCLIDE DISPERSION RATES BY AEOLIAN, FLUVIAL, AND POROUS MEDIA TRANSPORT

None
Date: October 12, 2005
Creator: Walton, J.; P.Goodell; Beshears, C.; French, D. & Kelts, A.
System: The UNT Digital Library
Registration and Fusion of X-Ray and Ultrasound Images for As-Built Modeling (open access)

Registration and Fusion of X-Ray and Ultrasound Images for As-Built Modeling

None
Date: September 12, 2005
Creator: Clark, G A & Jackson, J A
System: The UNT Digital Library
Relativistic Bound States (open access)

Relativistic Bound States

The Hamiltonian for Dirac's second-order equation depends nonlinearly on the potential V and the energy E. For this reason the magnetic contribution to the Hamiltonian for s-waves, which has a short range, is attractive for a repulsive Coulomb potential (V > 0) and repulsive for an attractive Coulomb potential (V < 0). Previous studies are confined to the latter case, where strong net attraction near a high-Z nucleus accelerates electrons to velocities close to the speed of light. The Hamiltonian is linear in the product EV/mc{sup 2}. Usually solutions are found in the regime E = mc{sup 2} + {var_epsilon}, where except for high Z, |{var_epsilon}| << mc{sup 2}. Here they show that for V > 0 the attractive magnetic term and the repulsive linear term combine to support a bound state at E = 0.5 mc{sup 2} corresponding to a binding energy E{sub b} = -{var_epsilon} = 0.5 mc{sup 2}.
Date: December 12, 2005
Creator: Ritchie, A. B.
System: The UNT Digital Library
Relaxation of atomic polarization in para+n-coated alkali-metal vapor cells (open access)

Relaxation of atomic polarization in para+n-coated alkali-metal vapor cells

None
Date: January 12, 2005
Creator: Graf, Miriam T.; Kimball, Derek F.; Rochester, Simon M.; Kerner, Katherine; Wong, Clement; Budker, Dmitry et al.
System: The UNT Digital Library
Roadmap for High Efficiency Solid-State Neutron Detectors (open access)

Roadmap for High Efficiency Solid-State Neutron Detectors

Solid-state thermal neutron detectors are generally fabricated in a planar configuration by coating a layer of neutron-to-alpha converter material onto a semiconductor. The as-created alpha particles in the material are expected to impinge the semiconductor and create electron-hole pairs which provide the electrical signal. These devices are limited in efficiency to a range near (2-5%)/cm{sup 2} due to the conflicting thickness requirements of the converter layer. In this case, the layer is required to be thick enough to capture the incoming neutron flux while at the same time adequately thin to allow the alpha particles to reach the semiconductor. A three dimensional matrix structure has great potential to satisfy these two requirements in one device. Such structures can be realized by using PIN diode pillar elements to extend in the third dimension with the converter material filling the rest of the matrix. Our strategy to fabricate this structure is based on both ''top-down'' and ''bottom-up'' approaches. The ''top down'' approach employs high-density plasma etching techniques, while the ''bottom up'' approach draws on the growth of nanowires by chemical vapor deposition. From our simulations for structures with pillar diameters from 2 {micro}m down to 100 nm, the detector efficiency is expected …
Date: July 12, 2005
Creator: Nikolic, R.; Cheung, C.; Reinhardt, C. & Wang, T.
System: The UNT Digital Library
Second Phase Precipitation in As-Welded and Solution Annealed Alloy 22 Welds (open access)

Second Phase Precipitation in As-Welded and Solution Annealed Alloy 22 Welds

The precipitation characteristics of tetrahedrally close-packed (TCP) phases during the welding and the subsequent solution annealing process of Alloy 22 1 1/2 inch thick plate double-U prototypical welds are investigated. Electron backscatter diffraction (EBSD) was used to provide large scale microstructural observation of the weld cross section, and scanning electron microscopy (SEM) was used to map the location of the TCP phases. Analysis shows that TCP precipitation occurs congruent to the weld passes, with the solution annealing reducing the sizes of coarser precipitates.
Date: January 12, 2005
Creator: El-Dasher, B S & Torres, S G
System: The UNT Digital Library
Single Bunch Monopole Instability (open access)

Single Bunch Monopole Instability

We study single bunch stability with respect to monopole longitudinal oscillations in electron storage rings. Our analysis is different from the standard approach based on the linearized Vlasov equation. Rather, we reduce the full nonlinear Fokker-Planck equation to a Schroedinger-like equation which is subsequently analyzed by perturbation theory. We show that the Haissinski solution [3] may become unstable with respect to monopole oscillations and derive a stability criterion in terms of the ring impedance.
Date: September 12, 2005
Creator: Podobedov, B. & Heifets, S.
System: The UNT Digital Library
Solid-Solid Phase Transition Kinetics of FOX-7 (open access)

Solid-Solid Phase Transition Kinetics of FOX-7

Since it was developed in the late 1990s, 1,1-diamino-2,2-dinitroethene (FOX-7), with lower sensitivity and comparable performance to RDX, has received increasing interest. This paper will present our results for the phase changes of FOX-7 using DSC and HFC (Heat Flow Calorimetry). DSC thermal curves recorded at linear heating rates of 0.10, 0.35 and 1.0 C min{sup -1} show two endothermic peaks and two exothermic peaks. The two endothermic peaks represent solid-solid phase transitions, which have been observed in the literature at 114 C ({beta}-{gamma}) and 159 C ({gamma}-{delta}) by both DSC and XPD (X-ray powder diffraction) measurements. The first transition shifts from 114.5 to 115.8 C as the heating rate increases from 0.10 to 1.0 C min{sup -1}, while the second transition shifts from 158.5 to 160.4 C. Cyclical heating experiments show the endotherms and exotherms for a first heating through the {gamma} phase to the {delta} phase, a cooling and reversion to the {alpha} or {beta} phase, and a second heating to the {gamma} and {delta} phases. The data are interpreted using kinetic models with thermodynamic constraints.
Date: July 12, 2005
Creator: Burnham, A K; Weese, R K; Wang, R; Kwok, Q M & Jones, D G
System: The UNT Digital Library
Spectroscopic Observations and Analysis of the Unusual Type Ia SN1999ac (open access)

Spectroscopic Observations and Analysis of the Unusual Type Ia SN1999ac

The authors present optical spectra of the peculiar Type Ia supernova (SN Ia) 1999ac. The data extend from -15 to +42 days with respect to B-band maximum and reveal an event that is unusual in several respects. prior to B-band maximum, the spectra resemble those of SN 1999aa, a slowly declining event, but possess stronger Si II and Ca II signatures (more characteristic of a spectroscopically normal SN). Spectra after B-band maximum appear more normal. The expansion velocities inferred from the Iron lines appear to be lower than average; whereas, the expansion velocity inferred from Calcium H and K are higher than average. The expansion velocities inferred from the Iron lines appear to be lower than average; whereas, the expansion velocity inferred from Calcium H and K are higher than average. The expansion velocities inferred from Si II are among the slowest ever observed, though SN 1999ac is not particularly dim. The analysis of the parameters v{sub 10}(Si II), R(Si II), v, and {Delta}m{sub 15} further underlines the unique characteristics of SN 1999ac. They find convincing evidence of C II {lambda}6580 in the day -15 spectrum with ejection velocity v > 16,000 km s{sup -1}, but this signature disappears by …
Date: July 12, 2005
Creator: Garavini, G.; Aldering, G.; Amadon, A.; Amanullah, R.; Astier, P.; Balland, C. et al.
System: The UNT Digital Library
Spectroscopy and New Particles in BaBar (open access)

Spectroscopy and New Particles in BaBar

Results on charmonium states and searches for pentaquark states at the BABAR experiment are presented.
Date: September 12, 2005
Creator: Petersen, B.Aa.
System: The UNT Digital Library
SPH and Material Failure: Progress Report (open access)

SPH and Material Failure: Progress Report

Smoothed Particle Hydrodynamics (SPH) is a meshless Lagrangian technique for modeling hydrodynamics, and as such offers some unique advantages when applied to problems of material failure and breakup. The two most important of these advantages are: (1) SPH is Lagrangian and robust--i.e., it is never necessary to advect or remap. Damage models typically involve a number of complex history variables (such as the damage associated with the Lagrangian mass, crack orientations, etc.), and advecting these quantities as is required in a mesh based algorithm is a very challenging problem. (2) SPH allows the Lagrangian points to move about, reconnect, or separate as dictated by the material flow. This naturally allows for the points to move apart as distinct fragments of material form, resulting in gaps or cracks between the fragments. Typically mesh based algorithms represent the ''cracks'' between fragments as zones of failed material, which is quite different than allowing voids devoid of material to form.
Date: April 12, 2005
Creator: Owen, J M
System: The UNT Digital Library
The stars of Austin's social universe (open access)

The stars of Austin's social universe

Article about Austin's social elite with an attached list of the city's top 500 social stars.
Date: May 12, 2005
Creator: Spezia, Karen Odom & Barron, Katy
System: The UNT Digital Library
STATISTICAL CHALLENGES FOR SEARCHES FOR NEW PHYSICS AT THE LHC. (open access)

STATISTICAL CHALLENGES FOR SEARCHES FOR NEW PHYSICS AT THE LHC.

Because the emphasis of the LHC is on 5{sigma} discoveries and the LHC environment induces high systematic errors, many of the common statistical procedures used in High Energy Physics are not adequate. I review the basic ingredients of LHC searches, the sources of systematics, and the performance of several methods. Finally, I indicate the methods that seem most promising for the LHC and areas that are in need of further study.
Date: September 12, 2005
Creator: Cranmer, Kyle
System: The UNT Digital Library
A Study of Electrochemical Reduction of Ethylene and Propylene Carbonate Electrolytes on Graphite Using ATR-FTIR Spectroscopy (open access)

A Study of Electrochemical Reduction of Ethylene and Propylene Carbonate Electrolytes on Graphite Using ATR-FTIR Spectroscopy

We present results testing the hypothesis that there is a different reaction pathway for the electrochemical reduction of PC versus EC-based electrolytes at graphite electrodes with LiPF6 as the salt in common. We examined the reduction products formed using ex-situ Fourier Transform Infrared (FTIR) spectroscopy in attenuated total reflection (ATR) geometry. The results show the pathway for reduction of PC leads nearly entirely to lithium carbonate as the solid product (and presumably ethylene gas as the co-product) while EC follows a path producing a mixture of organic and inorganic compounds. Possible explanations for the difference in reaction pathway are discussed.
Date: May 12, 2005
Creator: Zhuang, Guorong V.; Yang, Hui; Blizanac, Berislav & Ross, Philip N., Jr.
System: The UNT Digital Library
Study of Inclusive And Exclusive B ---> X/U L Nu Decays And the Measurement of |V(Ub)| With the BaBar Detector (open access)

Study of Inclusive And Exclusive B ---> X/U L Nu Decays And the Measurement of |V(Ub)| With the BaBar Detector

We report studies of B {yields} X{sub u}{ell}{nu} decays, based on a sample of 88 million B{bar B} events recorded with the BABAR detector. From both tagged and untagged B{bar B} events we have isolated inclusive charmless decays in kinematic regions for which the dominant background from B {yields} X{sub c}{ell}{nu} is reduced by making requirements on different variables: the electron energy E{sub l}, the momentum transfer q{sup 2}, and the hadronic mass m{sub X}. Using theoretical calculations we extrapolate to the total decay rate to determine the CKM matrix element |V{sub ub}|. In addition, we have measured the branching fraction for exclusive semileptonic decays, such as B {yields} {pi}({rho}, {omega}, {eta}, a{sub 0}){ell}{nu}. A high signal purity is achieved by selecting events in which a decay of the second B meson is either fully or partially reconstructed.
Date: October 12, 2005
Creator: del Re, D. & /UC, San Diego
System: The UNT Digital Library
Study of the Polarization Dependence of Two Beam Interactions (open access)

Study of the Polarization Dependence of Two Beam Interactions

None
Date: June 12, 2005
Creator: Kirkwood, R. K.; Moody, J.; Niemann, C.; Langdon, A. B.; Williams, E. A.; Cohen, B. I. et al.
System: The UNT Digital Library
Survey and Alignment for the ALS Project at LBL Berkeley (open access)

Survey and Alignment for the ALS Project at LBL Berkeley

The Advanced Light Source (ALS), now under construction at Lawrence Berkeley Laboratory, is a synchrotron radiation source of the third generation designed to produce extremely bright photon beams in the UV and soft X-ray regions. Its main accelerator components are a 1-1.9 GeV electron storage ring with 196.8 m circumference and 12 super-periods, a 1.5 GeV booster synchrotron with 75.0 m circumference and 4 super-periods, and a 50 MeV linac, as shown in Fig. 1. The storage ring has particularly tight positioning tolerances for lattice magnets and other components to assure the required operational characteristics. The general survey and alignment concept for the ALS is based on a network of fixed monuments installed in the building floor, to which all component positions are referred. Measurements include electronic distance measurements and separate sightings for horizontal and vertical directions, partially with automated electronic data capture. Most of the data processing is accomplished by running a customized version of PC-GEONET. It provides raw data storage, data reduction, and the calculation of adjusted coordinates, as well as an option for error analysis. PC-GEONET has also been used to establish an observation plan for the monuments and calculate their expected position accuracies, based on approximate …
Date: August 12, 2005
Creator: Keller, R.; Lauritzen, T. & Friedsam, H.
System: The UNT Digital Library