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Solid-State Modulators for RF And Fast Kickers

Description: As the switching capabilities of solid-state devices increase, these devices are being incorporated into modulator designs for high voltage accelerator applications. Solid-state modulators based on inductive adder circuit topology have demonstrated great versatility with regard to pulse width and pulse repetition rate while maintaining fast pulse rise and fall times. Additionally, these modulators are capable of being scaled to higher output voltage and power levels. An explanation of the basic circuit operation will be presented as well as test data of several different hardware systems.
Date: March 14, 2006
Creator: Cook, E. G.; Akana, G. L.; Gower, E. J.; Hawkins, S. A.; Hickman, B. C.; Brooksby, C. A. et al.
Partner: UNT Libraries Government Documents Department

Observation of B+ to b_1+K0 and Search for B-meson Decays to b_10K0 and b_1pi0

Description: We present the results of searches for decays of B mesons to final states with a b{sub 1} meson and a neutral pion or kaon. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 465 million B{bar B} pairs produced in e{sup +}e{sup -} annihilation. The results for the branching fractions are, in units of 10{sup -6}, {Beta}(B{sup +} {yields} b{sub 1}{sup +}K{sup 0}) = 9.6 {+-} 1.7 {+-} 0.9, {Beta}(B{sup 0} {yields} b{sub 1}{sup 0}K{sup 0}) = 5.1 {+-} 1.8 {+-} 0.5 (< 7.8), {Beta}(B{sup +} {yields} b{sub 1}{sup +} {pi}{sup 0}) = 1.8 {+-} 0.9 {+-} 0.2 (<3.3), and {Beta}(B{sup 0} {yields} b{sub 1}{sup 0}{pi}{sup 0}) = 0.4 {+-} 0.8 {+-} 0.2 (<1.9), with the assumption that {Beta}(b{sub 1} {yields} {omega}{pi}) = 1. They also measure the charge asymmetry {Alpha}{sub ch} (B{sup +} {yields} b{sub 1}{sup +}K{sup 0}) = -0.03 {+-} 0.15 {+-} 0.02. The first error quoted is statistical, the second systematic, and the upper limits in parentheses indicate the 90% confidence level.
Date: May 14, 2008
Creator: Aubert, B.
Partner: UNT Libraries Government Documents Department

Observation of CP Violation in B0 to K+pi- and B0 to pi+pi-

Description: The authors report observations of CP violation in the decays B{sup 0} {yields} K{sup +}{pi}{sup -} and B{sup 0} {yields} {pi}{sup +}{pi}{sup -} in a sample of 383 million {Upsilon}(4S) {yields} B{bar B} events. They find 4372 {+-} 82 B{sup 0} {yields} K{sup +}{pi}{sup -} decays and measure the direct Cp-violating charge asymmetry {Alpha}{sub K{pi}} = -0.107 {+-} 0.018(stat){sub -0.004}{sup +0.007}(syst), which excludes the CP-conserving hypothesis with a significance of 5.5 standard deviations. In the same sample they find 1139 {+-} 49 B{sup 0} {yields} {pi}{sup +}{pi}{sup -} decays and measure the CP-violating asymmetries S{sub {pi}{pi}} = -0.60 {+-} 0.11(stat) {+-} 0.03(syst) and C{sub {pi}{pi}} = -0.21 {+-} 0.09(stat) {+-} 0.02(syst). CP conservation in B{sup 0} {yields} {pi}{sup +}{pi}{sup -} (S{sub {pi}{pi}} = C{sub {pi}{pi}} = 0) is excluded at a confidence level 1-C.L. = 8 x 10{sup -8}, corresponding to 5.4 standard deviations.
Date: March 14, 2007
Creator: Aubert, B.
Partner: UNT Libraries Government Documents Department

Observation of the Semileptonic Decays B to D*taunu and Evidence for B to D tau nu

Description: We present measurements of the semileptonic decays B{sup -} {yields} D{sup 0}{tau}{sup -}{bar {nu}}{sub {tau}}, B{sup -} {yields} D{sup *0}{tau}{sup -}{bar {nu}}{sub {tau}}, B{sup -} {yields} D{sup +}{tau}{sup -}{bar {nu}}{sub {tau}}, and B{sup -} {yields} D{sup *+}{tau}{sup -}{bar {nu}}{sub {tau}}, which are potentially sensitive to non-Standard Model amplitudes, The data sample comprises 232 x 10{sup 6} {Upsilon}(4s) {yields} B{bar B} decays collected with the BABAR detector. From a combined fit to B{sup -} and {bar B}{sup 0} channels, we obtain the branching fractions {beta}(B {yields} D{sub {tau}}{sup -}{bar {nu}}{sub {tau}}) = (0:86 {+-} 0:24 {+-} 0:11 {+-} 0:06)% and {beta}(B {yields} D*{tau}{sup -}{bar {nu}}{sub {tau}}) = (1:62 {+-} 0:31 {+-} 0:10 {+-} 0:05)% (normalized for the {bar B}{sup 0}), , where the uncertainties are statistical, systematic, and normalization-mode-related.
Date: September 14, 2007
Creator: B., Aubert
Partner: UNT Libraries Government Documents Department

Observation of Femtosecond Bunch Length Using a Transverse Deflecting Structure

Description: The design of the VUV-FEL at DESY demands bunch lengths in the order of 50 fs and below. For the diagnostic of such very short bunches a transverse deflecting RF structure (LOLA) has been installed which streaks the beam according to the longitudinal distribution. Tests in the VUV-FEL yielded a rich substructure of the bunches. The most pronounced peak in the has a rms length of approximately 50 fs during FEL operation and below 20 fs FWHM at maximum compression. Depending on the transverse focusing a resolution well below 50 fs was achieved.
Date: December 14, 2005
Creator: Huning, M.; Bolzmann, A.; Schlarb, H.; /DESY; Frisch, J.; McCormick, D. et al.
Partner: UNT Libraries Government Documents Department

Improved Electron Yield and Spin-Polarizaton from III-V Photocathodes Via Bias Enhanced Carrier Drift

Description: Spin-polarized electrons are commonly used in high energy physics. Future work will benefit from greater polarization. Polarizations approaching 90% have been achieved at the expense of yield. The primary paths to higher polarization are material design and electron transport. Our work addresses the latter. Photoexcited electrons may be preferentially emitted or suppressed by an electric field applied across the active region. We are tuning this forward bias for maximum polarization and yield, together with other parameters, e.g., doping profile. Preliminary measurements have been carried out on bulk and thin film GaAs. As expected, the yield change far from the bandgap is quite large for bulk material. The bias is applied to the bottom (non-activated) side of the cathode so that the accelerating potential as measured with respect to the ground potential chamber walls is unchanged for different front-to-back cathode bias values. The size of the bias to cause an appreciable effect is rather small reflecting the low drift kinetic energy in the zero bias case.
Date: September 14, 2005
Creator: Mulhollan, Gregory A.; Bierman, John; Sci., /Saxet Surface; Brachmann, Axel; Clendenin, James E.; Garwin, Edward et al.
Partner: UNT Libraries Government Documents Department

Experimental Tests of the GDH and Other Sum Rules at SLAC

Description: Recent measurements from SLAC of the polarized nucleon structure functions g{sub 1} and g{sub 2} have been used to experimentally test the Bjorken, Ellis-Jaffe, Burkhardt-Cottingham, and Efremov-Leader-Teryaev sum rules. In the future, the SLAC E159 experiment will extend structure function measurements using real photons to 40 GeV, enabling a definitive test of the high energy convergence of the GDH sum rule for both proton and deuteron targets.
Date: June 14, 2005
Creator: Bosted, P.E. & /Massachusetts U., Amherst
Partner: UNT Libraries Government Documents Department

The Black Hole in the Throat - Thermodynamics of Strongly Coupled Cascading Gauge Theories

Description: We numerically construct black hole solutions corresponding to the deconfined, chirally symmetric phase of strongly coupled cascading gauge theories at various temperatures. We compute the free energy as a function of the temperature, and we show that it becomes positive below some critical temperature, indicating the possibility of a first order phase transition at which the theory deconfines and restores the chiral symmetry.
Date: June 14, 2007
Creator: Aharony, Ofer; /Weizmann Inst. /Stanford U., ITP /SLAC; Buchel, Alex; Phys., /Western Ontario U. /Perimeter Inst. Theor.; Kerner, Patrick & U., /Western Ontario
Partner: UNT Libraries Government Documents Department

B0 to K0K0bar and Other Hadronic b to d Decays

Description: The b {yields} d penguin-dominated modes B {yields} K{bar K} have been observed at the B factories. in addition, the BABAR collaboration has reported the first time-dependent CP-violation measurement in B{sup 0} {yields} K{sup 0}{bar K}{sup 0}.
Date: March 14, 2007
Creator: Biesiada, J.
Partner: UNT Libraries Government Documents Department

BaBar: Rare Charmless B Decays

Description: Three two body and two resonance decays of the B mesons have been measured using data from the BABAR detector: B{sup 0} {yields} {pi}{sup {+-}}, K{sup {-+}}, K{sup +}K{sup -}, K{sub S}{sup 0}{pi}{sup +}{pi}{sup -} and B{sup 0} {yields} a{sub 1}{sup +}(1260){pi}{sup -}. The branching ratio and that of some intermediate resonances are presented along with the Cp asymmetry of the decay B{sup 0} {yields} K*{sup +}{pi}{sup -}.
Date: April 14, 2006
Creator: Hutchcroft, D. & U., /Liverpool
Partner: UNT Libraries Government Documents Department

Unique Identification of Lee-Wick Gauge Bosons at Linear Colliders

Description: Grinstein, O'Connell and Wise have recently presented an extension of the Standard Model (SM), based on the ideas of Lee and Wick (LW), which demonstrates an interesting way to remove the quadratically divergent contributions to the Higgs mass induced by radiative corrections. This model predicts the existence of negative-norm copies of the usual SM fields at the TeV scale with ghost-like propagators and negative decay widths, but with otherwise SM-like couplings. In earlier work, it was demonstrated that the LW states in the gauge boson sector of these models, though easy to observe, cannot be uniquely identified as such at the LHC. In this paper, we address the issue of whether or not this problem can be resolved at an e{sup +}e{sup -} collider with a suitable center of mass energy range. We find that measurements of the cross section and the left-right polarization asymmetry associated with Bhabha scattering can lead to a unique identification of the neutral electroweak gauge bosons of the Lee-Wick type.
Date: December 14, 2007
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

VHE Gamma-Rays From Westerlund 2 And Implications for the Inferred Energetics

Description: The H.E.S.S. collaboration recently reported the discovery of VHE {gamma}-ray emission coincident with the young stellar cluster Westerlund 2. This system is known to host a population of hot, massive stars, and, most particularly, the WR binary WR 20a. Particle acceleration to TeV energies in Westerlund 2 can be accomplished in several alternative scenarios, therefore we only discuss energetic constraints based on the total available kinetic energy in the system, the actual mass loss rates of respective cluster members, and implied gamma-ray production from processes such as inverse Compton scattering or neutral pion decay. From the inferred gamma-ray luminosity of the order of 10{sup 35} erg/s, implications for the efficiency of converting available kinetic energy into non-thermal radiation associated with stellar winds in the Westerlund 2 cluster are discussed under consideration of either the presence or absence of wind clumping.
Date: November 14, 2007
Creator: Reimer, O.; /Stanford U., HEPL /KIPAC, Menlo Park; Aharonian, F.; /Heidelberg, Max Planck Inst. /Dublin Inst.; Hinton, J.; U., /Leeds et al.
Partner: UNT Libraries Government Documents Department

AGN-Induced Cavities in NGC 1399 And NGC 4649

Description: We present an analysis of archival Chandra and VLA observations of the E0 galaxy NGC1399 and the E2 galaxy NGC4649 in which we investigate cavities in the surrounding X-ray emitting medium caused by the central AGN. We calculate the jet power required for the AGN to evacuate these cavities and find values of {approx} 8x10{sup 41} erg s-1 and {approx} 14x10{sup 41} erg s{sup -1} for the lobes of NGC1399 and {approx} 7x10{sup 41} erg s{sup -1} and {approx} 6x1041 erg s{sup -1} for those of NGC4649. We also calculate the k/f values for each cavity, where k is the ratio of the total particle energy to that of electrons radiating in the range of 10 MHz to 10 GHz, and f is the volume filling factor of the plasma in the cavity. We find that the values of k/f for the lobes of NGC1399 are {approx} 93 and {approx} 190, and those of the lobes of NGC4649 are {approx} 15000 and {approx} 12000. We conclude that the assumed spectrum describes the electron distribution in the lobes of NGC1399 reasonably well, and that there are few entrained particles. For NGC4649, either there are many entrained particles or the model spectrum does not accurately describe the population of electrons.
Date: November 14, 2007
Creator: Shurkin, K.; U., /New Mexico; Dunn, R.J.H.; U., /Southampton; Gentile, G.; Taylor, G.B. et al.
Partner: UNT Libraries Government Documents Department

The Radiation Dose Measurement System for the BaBar Electromagnetic Calorimeter

Description: An array of 116 p-channel radiation sensitive MOSFET transistors (RadFETs) has been operational for the past 6 years at the BaBar experiment at the PEP-II asymmetric B-Factory at the Stanford Linear Accelerator Center (SLAC). This system maps the integrated dose absorbed by different regions of the Electromagnetic Calorimeter (EMC) during the running of the experiment. We report on the design and implementation of the system and finally, the performance of the monitoring system during the last 6 years of BaBar data-taking.
Date: August 14, 2006
Creator: Khan, A.; U., /Brunel; Meyer, W.T.; U., /Iowa State; Stelzer, J.; /Stanford U., Phys. Dept. et al.
Partner: UNT Libraries Government Documents Department

Active Damping of the E-P Instability at the LANL PSR

Description: A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos National Laboratory Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). Evidence obtained from these tests suggests that further improvement in performance is limited by beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback. Here we describe the present system configuration, system optimization, results of several recent experimental tests, and results from studies of factors limiting its performance.
Date: November 14, 2007
Creator: McCrady, R.; Macek, R.J.; Zaugg, T.; Alamos, /Los; Assadi, S.; Deibele, C. et al.
Partner: UNT Libraries Government Documents Department

On the Possible Association of Ultra High Energy Cosmic Rays with Nearby Active Galaxies

Description: Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of cosmic rays (CRs) with energies >57 EeV that suggests a correlation with the positions of active galactic nuclei (AGN) located within {approx}75 Mpc. However, this analysis does not take into account AGN morphology. A detailed study of the sample of AGN whose positions correlate with the CR events shows that most of them are classified as Seyfert 2 and low-ionization nuclear emission-line region (LINER) galaxies which do not differ from other local AGN of the same types. Therefore, the claimed correlation between the CR events observed by the Pierre Auger Observatory and local active galaxies should be considered as resulting from a chance coincidence, if the production of the highest energy CRs is not episodic in nature, but operates in a single object on long ({ge} Myr) timescales. Additionally, most of the selected sources do not show significant jet activity, and hence--in the framework of the jet paradigm--there are no reasons for expecting them to accelerate CRs up to the highest energies, {approx}10{sup 20} eV, at all. If the extragalactic magnetic fields and the sources of these CRs are coupled with matter, it is possible that the deflection angle is larger than expected in the case of a uniform source distribution due to effectively larger fields. A future analysis has to take into account AGN morphology and may yield a correlation with a larger deflection angle and/or more distant sources. We further argue that Cen A alone could be associated with at least 4 events due to its large radio extent, and Cen B can be associated with more than 1 event due to its proximity to the Galactic plane and, correspondingly, the stronger Galactic magnetic field the ultra high energy CRs (UHECRs) encounter ...
Date: May 14, 2008
Creator: Moskalenko, Igor V.; Stawarz, Lukasz; Porter, Troy A. & Cheung, Chi C.
Partner: UNT Libraries Government Documents Department

A Parameterization Invariant Approach to the Statistical Estimation of the CKM Phase alpha

Description: In contrast to previous analyses, we demonstrate a Bayesian approach to the estimation of the CKM phase {alpha} that is invariant to parameterization. We also show that in addition to computing the marginal posterior in a Bayesian manner, the distribution must also be interpreted from a subjective Bayesian viewpoint. Doing so gives a very natural interpretation to the distribution. We also comment on the effect of removing information about {beta}{sup 00}.
Date: April 14, 2008
Creator: Morris, Robin D.; /RIACS, Mtn. View; Cohen-Tanugi, Johann & /SLAC
Partner: UNT Libraries Government Documents Department

Origin of Charge Density at LaAlO3 on SrTiO3 Heterointerfaces: Possibility of Intrinsic Doping

Description: As discovered by Ohtomo and Hwang, a large sheet charge density with high mobility exists at the interface between SrTiO{sub 3} and LaAlO{sub 3}. Based on transport, spectroscopic, and oxygen-annealing experiments, we conclude that extrinsic defects in the form of oxygen vacancies introduced by the pulsed laser deposition process used by all researchers to date to make these samples is the source of the large carrier densities. Annealing experiments show a limiting carrier density. We also present a model that explains the high mobility based on carrier redistribution due to an increased dielectric constant.
Date: June 14, 2007
Creator: Siemons, W.; /Stanford U., Geballe Lab. /Twente U., Enschede; Koster, Gertjan; /Stanford U., Geballe Lab.; Yamamoto, Hideki; /Stanford U., Geballe Lab. /NTT Basic Res. Lab. et al.
Partner: UNT Libraries Government Documents Department

HESS J1023-575: Non-Thermal Particle Acceleration Associated With the Young Stellar Cluster Westerlund 2

Description: The results from H.E.S.S. observations towards Westerlund 2 are presented. The detection of very-high-energy gamma-ray emission towards the young stellar cluster Westerlund 2 in the HII complex RCW49 by H.E.S.S. provides ample evidence that particle acceleration to extreme energies is associated with this region. A variety of possible emission scenarios is mentioned, ranging from high-energy gamma-ray production in the colliding wind zone of the massive Wolf-Rayet binary WR 20a, collective wind scenarios, diffusive shock acceleration at the boundaries of wind-blown bubbles in the stellar cluster, and outbreak phenomena from hot stellar winds into the interstellar medium. These scenarios are briefly compared to the characteristics of the associated new VHE gamma-ray source HESS J1023-575, and conclusions on the validity of the respective emission scenarios for high-energy gamma-ray production in the Westerlund 2 system are drawn.
Date: November 14, 2007
Creator: Reimer, O.; /Stanford U., HEPL /KIPAC, Menlo Park; Hinton, J.; U., /Leeds; Hofmann, W.; Hoppe, S. et al.
Partner: UNT Libraries Government Documents Department

Energy Doubling of 42 GeV Electrons in a Meter-scale Plasma Wakefield Accelerator

Description: The energy frontier of particle physics is several trillion electron volts, but colliders capable of reaching this regime (such as the Large Hadron Collider and the International Linear Collider) are costly and time-consuming to build; it is therefore important to explore new methods of accelerating particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields that are orders of magnitude larger than those used in conventional colliders. In these accelerators, a drive beam (either laser or particle) produces a plasma wave (wakefield) that accelerates charged particles. The ultimate utility of plasma accelerators will depend on sustaining ultrahigh accelerating fields over a substantial length to achieve a significant energy gain. Here we show that an energy gain of more than 42 GeV is achieved in a plasma wakefield accelerator of 85 cm length, driven by a 42 GeV electron beam at the Stanford Linear Accelerator Center (SLAC). The results are in excellent agreement with the predictions of three-dimensional particle-in-cell simulations. Most of the beam electrons lose energy to the plasma wave, but some electrons in the back of the same beam pulse are accelerated with a field of {approx} 52GV m{sup -1}. This effectively doubles their energy, producing the energy gain of the 3-km-long SLAC accelerator in less than a meter for a small fraction of the electrons in the injected bunch. This is an important step towards demonstrating the viability of plasma accelerators for high-energy physics applications.
Date: March 14, 2007
Creator: Blumenfeld, Ian; Clayton, Christopher E.; Decker, Franz-Josef; Hogan, Mark J.; Huang, Chengkun; Ischebeck, Rasmus et al.
Partner: UNT Libraries Government Documents Department

FERMI@Elettra: A Seeded Harmonic Cascade FEL for EUV and Soft X-Rays

Description: We describe the machine layout and major performance parameters for the FERMI FEL project funded for construction at Sincrotrone Trieste, Italy, within the next five years. The project will be the first user facility based on seeded harmonic cascade FEL's, providing controlled, high peak-power pulses. With a high-brightness rf photocathode gun, and using the existing 1.2 GeV S-band linac, the facility will provide tunable output over a range from {approx}100 nm to {approx}10 nm, with pulse duration from 40 fs to {approx} 1ps, peak power {approx}GW, and with fully variable output polarization. Initially, two FEL cascades are planned; a single-stage harmonic generation to operate > 40 nm, and a two-stage cascade operating from {approx}40 nm to {approx}10 nm or shorter wavelength. The output is spatially and temporally coherent, with peak power in the GW range. Lasers provide modulation to the electron beam, as well as driving the photocathode and other systems, and the facility will integrate laser systems with the accelerator infrastructure, including a state-of-the-art optical timing system providing synchronization of rf signals, lasers, and x-ray pulses. Major systems and overall facility layout are described, and key performance parameters summarized.
Date: December 14, 2005
Creator: Bocchetta, C.J.; Bulfone, D.; Craievich, P.; Danailov, M.B.; D'Auria, G.; De Ninno, G. et al.
Partner: UNT Libraries Government Documents Department

Gamma-ray Albedo of the Moon

Description: We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of gamma-rays from the Moon is very steep with an effective cutoff around 3 GeV (600 MeV for the inner part of the Moon disc). Since it is the only (almost) black spot in the gamma-ray sky, it provides a unique opportunity for calibration of gamma-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). The albedo flux depends on the incident CR spectrum which changes over the solar cycle. Therefore, it is possible to monitor the CR spectrum using the albedo gamma-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo -rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the GLAST LAT to monitor the CR spectrum near the Earth beyond the lifetime of PAMELA.
Date: June 14, 2007
Creator: Moskalenko, Igor V. & Porter, Troy A.
Partner: UNT Libraries Government Documents Department