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D. Smith

Publications and source records attributed to D. Smith.

At least 109 records · Page 6Linked to original sources
arXiv2001

Evidence for Neutrino Oscillations from the Observation of Electron Anti-neutrinos in a Muon Anti-Neutrino Beam

A search for muon anti-neutrino to electron anti-neutrino oscillations was conducted by the Liquid Scintillator Neutrino Detector at the Los Alamos Neutron Science Center using muon anti-neutrinos from positive muon decay at rest. A total excess of 87.9 +/- 22.4 +/- 6.0 events consistent with electron anti-neutrino plus proton scattering to positron plus neutron was observed above the expected background. This excess corresponds to an oscillation probability of (0.264 +/- 0.067 +/- 0.045), which is consistent with an earlier analysis. In conjunction with other known limits on neutrino oscillations, the LSND data suggest that neutrino oscillations occur in the 0.2-10 eV^2/c^4 Delta-m^2 range, indicating a neutrino mass greater than 0.4 eV/c^2.

hep-ex↗
arXiv2001

Observations of the Optical Counterpart to XTE J1118+480 During Outburst by the ROTSE-I Telescope

The X-ray nova XTE J1118+480 exhibited two outbursts in the early part of 2000. As detected by the Rossi X-ray Timing Explorer (RXTE), the first outburst began in early January and the second began in early March. Routine imaging of the northern sky by the Robotic Optical Transient Search Experiment (ROTSE) shows the optical counterpart to XTE J1118+480 during both outbursts. These data include over 60 epochs from January to June 2000. A search of the ROTSE data archives reveal no previous optical outbursts of this source in selected data between April 1998 and January 2000. While the X-ray to optical flux ratio of XTE J1118+480 was low during both outbursts, we suggest that they were full X-ray novae and not mini-outbursts based on comparison with similar sources. The ROTSE measurements taken during the March 2000 outburst also indicate a rapid rise in the optical flux that preceded the X-ray emission measured by the RXTE by approximately 10 days. Using these results, we estimate a pre-outburst accretion disk inner truncation radius of 1.2 x 10^4 Schwarzschild radii.

astro-ph↗
arXiv2001

Vortex dynamics in layered superconductors with correlated defects: influence of interlayer coupling

We report a detailed study of the vortex dynamics and vortex phase diagrams of two amorphous Ta_0.3Ge_0.7/Ge multilayered films with intrinsic coplanar defects, but different interlayer coupling. A pinned Bose-glass phase in the more weakly coupled sample exists only below a cross-over field H* in striking contrast to the strongly coupled film. Above H* the flux lines are thought to break up into pancake vortices and the cross-over field is significantly increased when the field is aligned along the extended defects. The two films show different vortex creep excitations in the Bose-glass phase.

cond-mat.supr-con↗
arXiv2001

Measurement of electron-neutrino electron elastic scattering

The cross section for the elastic scattering reaction nu_e+e- -> nu_e+e- was measured by the Liquid Scintillator Neutrino Detector using a mu+ decay-at-rest nu_e beam at the Los Alamos Neutron Science Center. The standard model of electroweak physics predicts a large destructive interference between the charge current and neutral current channels for this reaction. The measured cross section, sigma_{nu_e e-}=[10.1 +- 1.1(stat.) +- 1.0(syst.)]x E_{nu_e} (MeV) x 10^{-45} cm^2, agrees well with standard model expectations. The measured value of the interference parameter, I=-1.01 +- 0.13(stat.) +- 0.12(syst.), is in good agreement with the standard model expectation of I^{SM}=-1.09. Limits are placed on neutrino flavor-changing neutral currents. An upper limit on the muon-neutrino magnetic moment of 6.8 x 10^{-10} mu_{Bohr} is obtained using the nu_mu and \bar{nu}_mu fluxes from pi+ and mu+ decay.

hep-ex↗
arXiv2000

BeppoSAX Observations of Markarian 501 in June 1999

We present the preliminary results of a long BeppoSAX observation of the BL Lac object Mkn501 carried out in June 1999. The source was fainter than found during the BeppoSAX pointings of 1997 and 1998, but is still detected with a good signal-to-noise ratio up to ~40 keV. The X-ray spectrum in the energy range 0.1-40 keV, produced through synchrotron radiation, is steeper than in the previous years, it is clearly curved, and peaks (in nu*F_nu) at ~0.5 keV. This energy is much lower than those at which the synchrotron component was found to peak in 1997 and 1998. Some intraday variability suggests that activity of the source on small time scales accompanies the large long time scale changes of brightness and spectrum.

astro-ph↗
arXiv1999

Discovery of the Optical Transient of the Gamma Ray Burst 990308

The optical transient of the faint Gamma Ray Burst 990308 was detected by the QUEST camera on the Venezuelan 1-m Schmidt telescope starting 3.28 hours after the burst. Our photometry gives $V = 18.32 \pm 0.07$, $R = 18.14 \pm 0.06$, $B = 18.65 \pm 0.23$, and $R = 18.22 \pm 0.05$ for times ranging from 3.28 to 3.47 hours after the burst. The colors correspond to a spectral slope of close to $f_ν \propto ν^{1/3}$. Within the standard synchrotron fireball model, this requires that the external medium be less dense than $10^{4} cm^{-3}$, the electrons contain $> 20%$ of the shock energy, and the magnetic field energy must be less than 24% of the energy in the electrons for normal interstellar or circumstellar densities. We also report upper limits of $V > 12.0$ at 132 s (with LOTIS), $V > 13.4$ from 132-1029s (with LOTIS), $V > 15.3$ at 28.2 min (with Super-LOTIS), and a 8.5 GHz flux of $< 114 μJy$ at 110 days (with the Very Large Array). WIYN 3.5-m and Keck 10-m telescopes reveal this location to be empty of any host galaxy to $R > 25.7$ and $K > 23.3$. The lack of a host galaxy likely implies that it is either substantially subluminous or more distant than a red shift of $\sim 1.2$.

astro-ph↗
arXiv1999

The May 1989 outburst of the Soft X-ray Transient GS 2023+338 (V404 Cyg)

We re-analyze archival Ginga data of the soft X-ray transient source GS 2023+338 covering the beginning of its May 1989 outburst. The source showed a number of rather unusual features: very high and apparently saturated luminosity, dramatic flux and spectral variability (often on ~1 sec time scale), generally very hard spectrum, with no obvious soft thermal component characteristic for soft/high state. We describe the spectrum obtained at the maximum of flux and we demonstrate that it is very different from spectra of other soft X-ray transients at similar luminosity. We confirm previous suggestions that the dramatic variability was due to heavy and strongly variable photo-electric absorption. We also demonstrate that for a short time the source's spectrum did look like a typical soft/high state spectrum but that this coincided with very heavy absorption.

astro-ph↗
arXiv1998

Oscillations of solar and atmospheric neutrinos

Motivated by recent results from SuperKamiokande, we study both solar and atmospheric neutrino fluxes in the context of oscillations of the three known neutrinos. We aim at a global view which identifies the various possibilities, rather than attempting the most accurate determination of the parameters of each scenario. For solar neutrinos we emphasise the importance of performing a general analysis, independent of any particular solar model and we consider the possibility that any one of the techniques --- chlorine, gallium or water Cerenkov --- has a large unknown systematic error, so that its results should be discarded. The atmospheric neutrino anomaly is studied by paying special attention to the ratios of upward and downward going nu_e and nu_mu fluxes. Both anomalies can be described in a minimal scheme where the respective oscillation frequencies are widely separated or in non-minimal schemes with two comparable oscillation frequencies. We discuss explicit forms of neutrino mass matrices in which both atmospheric and solar neutrino fluxes are explained. In the minimal scheme we identify only two `zeroth order' textures that can result from unbroken symmetries. Finally we discuss experimental strategies for the determination of the various oscillation parameters.

hep-ph↗
arXiv1998

X-ray spectral evolution of GS 2023+338 (V404 Cyg) during decline after outburst

We have re-analyzed archival GINGA data of the soft X-ray transient source GS2023+308 (V404 Cyg) covering the decline phase of its May 1989 outburst. Our spectral modelling includes the relativistically smeared Compton reflected continuum and iron Kαfluorescent line near 6.5 keV produced by X-ray illumination of the accretion disc. This gives a powerful diagnostic of the accretion geometry, with the amplitude of the reprocessed components showing the solid angle subtended by the disc, while the detailed shape of the relativistic smearing shows how close this material is to the black hole event horizon. We find that reflection is always significantly present in the spectra, but that its fractional contribution decreases as the decline progresses. The amount of relativistic smearing is also consistent with decreasing during the decline, although this is poorly constrained except for the brightest spectra. One plausible scenario explaining this evolution is of an optically thick disc with inner radius increasing as a function of time, with the X-ray source in the form of a central corona. This is similar to the evolution inferred for other X-ray transient sources, such as Nova Muscae, except that the underlying power law spectrum of GS 2023+338 stayed constant as the disc geometry changed. This challenges the underlying assumption of almost all models for the spectra of accreting black holes, namely that the hard X-rays are formed by Comptonization of seed photons from the accretion disc.

astro-ph↗
arXiv1998

Second Product Line Practice Workshop Report

The second Software Engineering Institute Product Line Practice Workshop was a hands-on meeting held in November 1997 to share industry practices in software product lines and to explore the technical and non-technical issues involved. This report synthesizes the workshop presentations and discussions, which identified factors involved in product line practices and analyzed issues in the areas of software engineering, technical management, and enterprise management.

cs.SE↗
arXiv1998

A new analysis method for very high definition Imaging Atmospheric Cherenkov Telescopes as applied to the CAT telescope

A new method of shower-image analysis is presented which appears very powerful as applied to those Cherenkov Imaging Telescopes with very high definition imaging capability. It provides hadron rejection on the basis of a single cut on the image shape, and simultaneously determines the energy of the electromagnetic shower and the position of the shower axis with respect to the detector. The source location is also reconstructed for each individual gamma-ray shower, even with one single telescope, so for a point source the hadron rejection can be further improved. As an example, this new method is applied to data from the CAT (Cherenkov Array at Themis) imaging telescope, which has been operational since Autumn, 1996.

astro-ph↗
arXiv1998

The CAT Imaging Telescope for Very-High-Energy Gamma-Ray Astronomy

The CAT (Cherenkov Array at Themis) imaging telescope, equipped with a very-high-definition camera (546 fast phototubes with 0.12 degrees spacing surrounded by 54 larger tubes in two guard rings) started operation in Autumn 1996 on the site of the former solar plant Themis (France). Using the atmospheric Cherenkov technique, it detects and identifies very high energy gamma-rays in the range 250 GeV to a few tens of TeV. The instrument, which has detected three sources (Crab nebula, Mrk 421 and Mrk 501), is described in detail.

astro-ph↗
arXiv1997

Performances of the CAT imaging telescope and some preliminary results on Mkn 180 and the Crab

The CAT imaging telesope, which uses the Atmospheric Cherenkov Technique to observe TeV gamma-ray sources, has been operating since September 1996. Located in southern France, it features a fine grained camera consisting of 546 PMT with a pixel size of 0.12 degrees. Strong gamma-ray signals from Mkn 501 above 200 GeV were detected during observations made in April 1997. The high signal/noise ratio for these data enables direct characterization of the gamma-ray images as recorded in the camera. These results are used to validate the Monte-Carlo simulations of the response of the telescope to gamma-ray showers and to improve its performances. Observational results on Mkn 180 and the Crab nebula spectrum are presented.

astro-ph↗
arXiv1997

Evidence for nu_mu -> nu_e Neutrino Oscillations from LSND

A search for nu_mu -> nu_e oscillations has been conducted with the LSND apparatus at the Los Alamos Meson Physics Facility. Using nu_mu from pi^+ decay in flight, the nu_e appearance is detected via the charged-current reaction C(nu_e,e^-)X. Two independent analyses observe a total of 40 beam-on high-energy electron events (60 < E_e < 200 MeV) consistent with the above signature. This number is significantly above the 21.9 +- 2.1 events expected from the nu_e contamination in the beam and the beam-off background. If interpreted as an oscillation signal, the observed oscillation probability of (2.6 +- 1.0 +- 0.5) x 10^{-3} is consistent with the previously reported nu_mu_bar -> nu_e_bar oscillation evidence from LSND.

nucl-ex↗
arXiv1997

A letter of intent for an experiment to measure nu_mu to nu_e oscillations and nu_mu disappearance at the Fermilab Booster (BooNE)

This Letter of Intent to the Fermilab Program Advisory Committee describes a search for neutrino oscillations at the Fermilab booster. It is motivated by the LSND observation of nu_mu -> nu_e appearance. The booster neutrino experiment (BooNE) will be capable of observing both nu_mu -> nu_e appearance and nu_mu disappearance. In addition, the experiment will be able to measure Delta m^2 and sin^2(2theta) and search for CP violation in the lepton sector.

nucl-ex↗
arXiv1997

Evidence for nu_mu -> nu_e Oscillations from Pion Decay in Flight Neutrinos

A search for nu_mu -> nu_e oscillations has been conducted at the Los Alamos Meson Physics Facility using nu_mu from pi^+ decay in flight. An excess in the number of beam-related events from the C(nu_e,e^-)X inclusive reaction is observed. The excess is too large to be explained by normal nu_e contamination in the beam at a confidence level greater than 99%. If interpreted as an oscillation signal, the observed oscillation probability of (2.6 +- 1.0 +- 0.5) x 10^{-3} is consistent with the previously reported nu_mu_bar -> nu_e_bar oscillation evidence from LSND.

nucl-ex↗