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Observation of B^+\to\eta\rho^+ and Search for B^0 Decays to\eta^\prime\eta, \eta\pi^0, \eta^\prime\pi^0, and \omega\pi^0

Description: The authors present measurements of branching fractions for five B-meson decays to two-body charmless final states. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 459 million B{bar B} pairs. The results for branching fractions are, in units of 10{sup -6} (upper limits at 90% C.L.): {Beta}(B{sup +} {yields} {eta}{rho}{sup +}) = 9.9 {+-} 1.2 {+-} 0.8, {Beta}(B{sup 0} {yields} {eta}{prime}{eta}) = 0.5 {+-} 0.4 {+-} 0.1 (< 1.2), {Beta}(B{sup 0} {yields} {eta}{pi}{sup 0}) = 0.9 {+-} 0.4 {+-} 0.1 (< 1.5), {Beta}(B{sup 0} {yields} {eta}{prime}{pi}{sup 0}) = 0.9 {+-} 0.4 {+-} 0.1 (< 1.5), and {Beta}(B{sup 0}{sup 0} {yields} {omega}{pi}{sup 0}) = {eta}{rho}{sup +} mode, they measure the charge asymmetry {Alpha}{sub ch} (B{sup +} {yields} {eta}{rho}{sup +}) = 0.13 {+-} 0.11 {+-} 0.02.
Date: April 22, 2008
Creator: Aubert, Bernard; Bona, Marcella; Karyotakis, Y.; Lees, J.P.; Poireau, V.; Prencipe, E. et al.
Partner: UNT Libraries Government Documents Department

Observation of Decays $B^0\to D_s^{(*)+}\pi^-$ and$B^0\to D_s^{(*)-}K^+$

Description: The authors report the observation of decays B{sup 0} {yields} D{sub s}{sup (*)+} {pi}{sup -} and B{sup 0} {yields} D{sub s}{sup (*)-} K{sup +} in a sample of 230 x 10{sup 6} {Upsilon}(4S) {yields} B{bar B} events recorded with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} storage ring. They measure the branching fractions {Beta}(B{sup 0} {yields} D{sub s}{sup +}{pi}{sup -}) = (1.3 {+-} 0.3(stat) {+-} 0.2(syst)) x 10{sup -5}, {Beta}(B{sup 0} {yields} D{sub s}{sup -}K{sup +}) = (2.5 {+-} 0.4(stat) {+-} 0.4(syst)) x 10{sup -5}, {Beta}(B{sup 0} {yields} D*{sub s}{sup +} {pi}{sup -}) = (2.8 {+-} 0.6(stat) {+-} 0.5 (syst)) x 10{sup -5}, and {Beta}(B{sup 0} {yields} D*{sub s}{sup -} K{sup +}) = (2.0 {+-} 0.5(stat) {+-} 0.4(syst)) x 10{sup -5}. The significance of the measurements to differ from zero are 5, 9, 6, and 5 standard deviations, respectively.
Date: April 19, 2006
Creator: Aubert, B.
Partner: UNT Libraries Government Documents Department

Persistent Patterns in Accretion Disks

Description: We present a set of new characteristic frequencies associated with accretion disks around compact objects. These frequencies arise from persistent rotating patterns in the disk that are finite in radial extent and driven purely by the gravity of the central body. Their existence depends on general relativistic corrections to orbital motion and, if observed, could be used to probe the strong gravity region around a black hole. We also discuss a possible connection to the puzzle of quasi-periodic oscillations.
Date: April 3, 2006
Creator: Amin, Mustafa A.; Frolov, Andrei V. & /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Performance of the FONT3 Fast Analogue Intra-Train Beam-Based Feedback System at ATF

Description: We report results of beam tests of the FONT3 intra-train position feedback system prototype at the Accelerator Test Facility (ATF) at KEK. The feedback system incorporates a novel beam position monitor (BPM) processor with latency below 5 nanoseconds, and a kicker driver amplifier with similar low latency. The 56 nanosecond-long bunchtrain in the ATF extraction line was used to test the prototype feedback system. The achieved latency of 23ns provides a demonstration of intra-train feedback on very short timescales relevant even for the CLIC Linear Collider design.
Date: April 16, 2007
Creator: Burrows, P.; /Queen Mary, U. of London; Christian, G.B.; Hartin, A.F.; Dabiri Khah, H.; White, G.R. et al.
Partner: UNT Libraries Government Documents Department

Information Resources in High-Energy Physics: Surveying the Present Landscape and Charting the Future Course

Description: Access to previous results is of paramount importance in the scientific process. Recent progress in information management focuses on building e-infrastructures for the optimization of the research workflow, through both policy-driven and user-pulled dynamics. For decades, High-Energy Physics (HEP) has pioneered innovative solutions in the field of information management and dissemination. In light of a transforming information environment, it is important to assess the current usage of information resources by researchers and HEP provides a unique test-bed for this assessment. A survey of about 10% of practitioners in the field reveals usage trends and information needs. Community-based services, such as the pioneering arXiv and SPIRES systems, largely answer the need of the scientists, with a limited but increasing fraction of younger users relying on Google. Commercial services offered by publishers or database vendors are essentially unused in the field. The survey offers an insight into the most important features that users require to optimize their research workflow. These results inform the future evolution of information management in HEP and, as these researchers are traditionally 'early adopters' of innovation in scholarly communication, can inspire developments of disciplinary repositories serving other communities.
Date: April 22, 2008
Creator: Gentil-Beccot, Anne; Mele, Salvatore; Holtkamp, Annette; O'Connell, Heath B. & Brooks, Travis C.
Partner: UNT Libraries Government Documents Department

The GLAST Mission, LAT and GRBs

Description: The GLAST Large Area Telescope (LAT) is the next generation satellite experiment for high-energy gamma-ray astronomy. It is a pair conversion telescope built with a plastic anticoincidence shield, a segmented CsI electromagnetic calorimeter, and the largest silicon strip tracker ever built. It will cover the energy range from 30 MeV to 300 GeV, shedding light on many issues left open by its predecessor EGRET. One of the most exciting science topics is the detection and observation of gamma-ray bursts (GRBs). In this paper we present the work done so far by the GRB LAT science group in studying the performance of the LAT detector to observe GRBs.We report on the simulation framework developed by the group as well as on the science tools dedicated to GRBs data analysis. We present the LAT sensitivity to GRBs obtained with such simulations, and, finally, the general scheme of GRBs detection that will be adopted on orbit.
Date: April 5, 2006
Creator: Omodei, Nicola & /INFN, Pisa
Partner: UNT Libraries Government Documents Department

Hose Instability and Wake Generation By An Intense Electron Beam in a Self-Ionized Gas

Description: The propagation of an intense relativistic electron beam through a gas that is self-ionized by the beam's space charge and wakefields is examined analytically and with 3D particle-in-cell simulations. Instability arises from the coupling between a beam and the offset plasma channel it creates when it is perturbed. The traditional electron hose instability in a preformed plasma is replaced with this slower growth instability depending on the radius of the ionization channel compared to the electron blowout radius. A new regime for hose stable plasma wakefield acceleration is suggested.
Date: April 12, 2006
Creator: Deng, S.; Barnes, C.D.; Clayton, C.E.; O'Connell, C.; Decker, F.J.; Fonseca, R.A. et al.
Partner: UNT Libraries Government Documents Department

GRBs from the First Stars

Description: We present an estimate of the Gamma Ray Bursts which should be expected from metal-free, elusive first generation of stars known as PopulationIII (PopIII). We derive the GRB rate from these stars from the Stellar Formation Rate obtained in several Reionization scenarios available in the literature. In all of the analyzed models we find that GRBs from PopIII are subdominant with respect to the ''standard'' (PopII) ones up to z {approx} 10.
Date: April 16, 2007
Creator: Iocco, Fabio & /Naples U. /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

High Energy Neutrino Flash From Far-UV/X-Ray Flares of Gamma-Ray Bursts

Description: The recent observations of bright optical and X-ray flares by the Swift satellite suggest these are produced by the late activities of the central engine. We study the neutrino emission from far-UV/X-ray flares under the late internal shock model. Since the efficiency of pion production in the highest energy is higher than that of the prompt bursts, such neutrino flashes from flares can give comparable or larger contributions to a diffuse very high energy neutrino background if the total energy input into flares is comparable to the radiated energy of the prompt bursts. These signals are very important because they have possibility to probe the nature of flares (baryonic or magnetic, the photon field, the magnetic field, and so on).
Date: April 25, 2006
Creator: Murase, Kohta; /Kyoto U., Yukawa Inst., Kyoto; Nagataki, Shigehiro & /Kyoto U., Yukawa Inst., Kyoto /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Bootstrapping One-Loop QCD Amplitudeswith General Helicities

Description: The recently developed on-shell bootstrap for computing one-loop amplitudes in non-supersymmetric theories such as QCD combines the unitarity method with loop-level on-shell recursion. For generic helicity configurations, the recursion relations may involve undetermined contributions from non-standard complex singularities or from large values of the shift parameter. Here we develop a strategy for sidestepping difficulties through use of pairs of recursion relations. To illustrate the strategy, we present sets of recursion relations needed for obtaining n-gluon amplitudes in QCD. We give a recursive solution for the one-loop n-gluon QCD amplitudes with three or four color-adjacent gluons of negative helicity and the remaining ones of positive helicity. We provide an explicit analytic formula for the QCD amplitude A{sub 6;1}(1{sup -}, 2{sup -}, 3{sup -}, 4{sup +}, 5{sup +}, 6{sup +}), as well as numerical results for A{sub 7;1}(1{sup -}, 2{sup -}, 3{sup -}, 4{sup +}, 5{sup +}, 6{sup +}, 7{sup +}), A{sub 8;1}(1{sup -}, 2{sup -}, 3{sup -}, 4{sup +}, 5{sup +}, 6{sup +}, 7{sup +}, 8{sup +}), and A{sub 8;1}(1{sup -}, 2{sup -}, 3{sup -}, 4{sup -}, 5{sup +}, 6{sup +}, 7{sup +}, 8{sup +}). We expect the on-shell bootstrap approach to have widespread applications to phenomenological studies at colliders.
Date: April 25, 2006
Creator: Berger, Carola F.; Bern, Zvi; Dixon, Lance J.; Forde, Darren & Kosower, David A.
Partner: UNT Libraries Government Documents Department

Analysis of Laser-Driven Particle Acceleration fromPlanar Transparent Boundaries

Description: This article explores the interaction between a monochromatic plane wave laser beam and a relativistic electron in the presence of a thin dielectric transparent boundary. It is found that the sign of the interaction between the laser and the electron in the downstream space is determined by the optical phase delay of the laser caused by the boundary, and that it can add to or cancel the interaction in the upstream space. Both the inverse-transition radiation picture and the electric field path integral method show this result.
Date: April 7, 2006
Creator: Plettner, T. & /SLAC /Stanford U., Ginzton Lab.
Partner: UNT Libraries Government Documents Department

Babar: Sin(2beta) With Charm

Description: We present measurements of time-dependent CP asymmetries of neutral B decays to several charm and charmonium final states. Data have been collected with the BABAR detector at the PEP-II storage ring at the Stanford Linear Accelerator Center. In the absence of penguin contribution, the Standard Model predicts the time-dependent CP asymmetry parameters S and C are to be {eta}{sub CP} sin(2{beta}) and 0, respectively.
Date: April 12, 2006
Creator: Grenier, P. & U., /Ecole Polytechnique /Clermont-Ferrand
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

Babar Silicon Vertex Tracker: Status and Prospects

Description: The BABAR Silicon Vertex Tracker (SVT) has been efficiently operated for six years since the start of data taking in 1999. Due to higher than expected background levels some unforeseen effects have appeared. We discuss: a shift in the pedestal for the channels of the AToM readout chips that are most exposed to radiation; an anomalous increase in the bias leakage current for the modules in the outer layers. Estimates of future radiation doses and occupancies are shown together with the extrapolated detector performance and lifetime, in light of the new observations.
Date: April 27, 2006
Creator: Re, V.; Bondioli, M.; Bruinsma, M.; Curry, S.; Kirkby, D.; Berryhill, J. et al.
Partner: UNT Libraries Government Documents Department

Unification and Dark Matter in a Minimal Scalar Extension of the Standard Model

Description: The six Higgs doublet model is a minimal extension of the Standard Model (SM) that addresses dark matter and gauge coupling unification. Another Higgs doublet in the 5 representation of a discrete symmetry group, such as S{sub 6}, is added to the SM. The lightest components of the 5-Higgs are neutral, stable and serve as dark matter so long as the discrete symmetry is not broken. Direct and indirect detection signals, as well as collider signatures are discussed. The five-fold multiplicity of the dark matter decreases its mass and typically helps make the dark matter more visible in upcoming experiments.
Date: April 25, 2007
Creator: Lisanti, Mariangela & Wacker, Jay G.
Partner: UNT Libraries Government Documents Department

Very High Energy Gamma Rays from Supernova Remnants and Constraints on the Galactic Interstellar Radiation Field

Description: The large-scale Galactic interstellar radiation field (ISRF) is the result of stellar emission and dust re-processing of starlight. Where the energy density of the ISRF is high (e.g., the Galactic Centre), the dominant {gamma}-ray emission in individual supernova remnants (SNRs), such as G0.9+0.1, may come from inverse Compton (IC) scattering of the ISRF. Several models of the ISRF exist. The most recent one, which has been calculated by us, predicts a significantly higher ISRF than the well used model of Mathis, Mezger, and Panagia [1]. However, comparison with data is limited to local observations. Based on our current estimate of the ISRF we predict the gamma-ray emission in the SNRs G0.9+0.1 and RXJ1713, and pair-production absorption features above 20 TeV in the spectra of G0.9+0.1, J1713-381, and J1634-472. We discuss how GLAST, along with current and future very high energy instruments, may be able to provide upper bounds on the large-scale ISRF.
Date: April 30, 2007
Creator: Porter, T.A.; Moskalenko, I.V. & Strong, A.W.
Partner: UNT Libraries Government Documents Department

A Universe without Weak Interactions

Description: A universe without weak interactions is constructed that undergoes big-bang nucleosynthesis, matter domination, structure formation, and star formation. The stars in this universe are able to burn for billions of years, synthesize elements up to iron, and undergo supernova explosions, dispersing heavy elements into the interstellar medium. These definitive claims are supported by a detailed analysis where this hypothetical ''Weakless Universe'' is matched to our Universe by simultaneously adjusting Standard Model and cosmological parameters. For instance, chemistry and nuclear physics are essentially unchanged. The apparent habitability of the Weakless Universe suggests that the anthropic principle does not determine the scale of electroweak breaking, or even require that it be smaller than the Planck scale, so long as technically natural parameters may be suitably adjusted. Whether the multi-parameter adjustment is realized or probable is dependent on the ultraviolet completion, such as the string landscape. Considering a similar analysis for the cosmological constant, however, we argue that no adjustments of other parameters are able to allow the cosmological constant to raise up even remotely close to the Planck scale while obtaining macroscopic structure. The fine-tuning problems associated with the electroweak breaking scale and the cosmological constant therefore appear to be qualitatively different from the perspective of obtaining a habitable universe.
Date: April 7, 2006
Creator: Harnik, Roni; Kribs, Graham D. & Perez, Gilad
Partner: UNT Libraries Government Documents Department

Two-dimensional Vortex Behavior in Highly Underdoped YBa_2Cu_3O_{6+x} Observed byScanning Hall Probe Microscopy

Description: We report scanning Hall probe microscopy of highly underdoped superconducting YBa{sub 2}Cu{sub 3}O{sub 6+z} with T{sub c} ranging from 5 to 15 K which showed distinct flux bundles with less than one superconducting flux quantum ({Phi}{sub 0}) through the sample surface. The sub-{Phi}{sub 0} features occurred more frequently for lower T{sub c}, were more mobile than conventional vortices, and occurred more readily when the sample was cooled with an in-plane field component. We show that these features are consistent with kinked stacks of pancake vortices.
Date: April 22, 2008
Creator: Guikema, J.W.; Bluhm, Hendrik; /Stanford U., Appl. Phys. Dept.; Bonn, D.A.; Liang, Ruixing; Hardy, W.N. et al.
Partner: UNT Libraries Government Documents Department

Attenuation of VHE Gamma Rays by the Milky Way Interstellar Radiation Field

Description: The attenuation of very high energy gamma rays by pair production on the Galactic interstellar radiation field has long been thought of as negligible. However, a new calculation of the interstellar radiation field consistent with multi-wavelength observations by DIRBE and FIRAS indicates that the energy density of the Galactic interstellar radiation field is higher, particularly in the Galactic center, than previously thought. We have made a calculation of the attenuation of very high energy gamma rays in the Galaxy using this new interstellar radiation field which takes into account its nonuniform spatial and angular distributions. We find that the maximum attenuation occurs around 100 TeV at the level of about 25% for sources located at the Galactic center, and is important for both Galactic and extragalactic sources.
Date: April 19, 2006
Creator: Moskalenko, Igor V.; /Stanford U., HEPL; Porter, Troy A.; U., /Louisiana State; Strong, Andrew W. & /Garching, Max Planck Inst., MPE
Partner: UNT Libraries Government Documents Department

On the Putative Detection of Z>0 X-Ray Absorption Features in the Spectrum of Mrk 421

Description: In a series of papers, Nicastro et al. have claimed the detection of z > 0 O VII absorption features in the spectrum of Mrk 421 obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We evaluate those claims in the context of a high quality spectrum of the same source obtained with the Reflection Grating Spectrometer (RGS) on XMM-Newton. The data comprise over 955 ksec of usable exposure time and more than 2.6 x 10{sup 4} counts per 50 m{angstrom} at 21.6 {angstrom}. We concentrate on the spectrally clean region (21.3 < {lambda} < 22.5 {angstrom}) where sharp features due to the astrophysically abundant O VII may reveal an intervening, warm-hot intergalactic medium (WHIM). In spite of the fact that the sensitivity of the RGS data is higher than that of the original LETGS data presented by Nicastro et al., we do not confirm detection of any of the intervening systems claimed to date. Rather, we detect only three unsurprising, astrophysically expected features down to the log (N{sub i}) {approx} 14.6 (3{sigma}) sensitivity level. Each of the two purported WHIM features is rejected with a statistical confidence that exceeds that reported for its initial detection. While we can not rule out the existence of fainter, WHIM related features in these spectra, we suggest that previous discovery claims were premature. A more recent paper by Williams et al. claims to have demonstrated that the RGS data we analyze here do not have the resolution or statistical quality required to confirm or deny the LETGS detections. We show that the Williams et al. reduction of the RGS data was highly flawed, leading to an artificial and spurious degradation of the instrument response. We carefully highlight the differences between our analysis presented here and those published by Williams et al.
Date: April 28, 2006
Creator: Rasmussen, Andrew P.; /SLAC /KIPAC, Menlo Park; Kahn, Steven M.; /SLAC /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Paerels, Frits; /Columbia U., Astron. Astrophys. et al.
Partner: UNT Libraries Government Documents Department