6,798 research outputs found
A Comprehensive Spectroscopic Analysis of DB White Dwarfs
We present a detailed analysis of 108 helium-line (DB) white dwarfs based on
model atmosphere fits to high signal-to-noise optical spectroscopy. We derive a
mean mass of 0.67 Mo for our sample, with a dispersion of only 0.09 Mo. White
dwarfs also showing hydrogen lines, the DBA stars, comprise 44% of our sample,
and their mass distribution appears similar to that of DB stars. As in our
previous investigation, we find no evidence for the existence of low-mass (M <
0.5 Mo) DB white dwarfs. We derive a luminosity function based on a subset of
DB white dwarfs identified in the Palomar-Green survey. We show that 20% of all
white dwarfs in the temperature range of interest are DB stars, although the
fraction drops to half this value above Teff ~ 20,000 K. We also show that the
persistence of DB stars with no hydrogen features at low temperatures is
difficult to reconcile with a scenario involving accretion from the
interstellar medium, often invoked to account for the observed hydrogen
abundances in DBA stars. We present evidence for the existence of two different
evolutionary channels that produce DB white dwarfs: the standard model where DA
stars are transformed into DB stars through the convective dilution of a thin
hydrogen layer, and a second channel where DB stars retain a helium-atmosphere
throughout their evolution. We finally demonstrate that the instability strip
of pulsating V777 Her white dwarfs contains no nonvariables, if the hydrogen
content of these stars is properly accounted for.Comment: 74 pages including 30 figures, accepted for publication in the
Astrophysical Journa
Quantum sensitivity limit of a Sagnac hybrid interferometer based on slow-light propagation in ultra-cold gases
The light--matter-wave Sagnac interferometer based on ultra-slow light
proposed recently in (Phys. Rev. Lett. 92, 253201 (2004)) is analyzed in
detail. In particular the effect of confining potentials is examined and it is
shown that the ultra-slow light attains a rotational phase shift equivalent to
that of a matter wave, if and only if the coherence transfer from light to
atoms associated with slow light is associated with a momentum transfer and if
an ultra-cold gas in a ring trap is used. The quantum sensitivity limit of the
Sagnac interferometer is determined and the minimum detectable rotation rate
calculated. It is shown that the slow-light interferometer allows for a
significantly higher signal-to-noise ratio as possible in current matter-wave
gyroscopes.Comment: 12 pages, 6 figure
Erratum: Measurements of prompt charm production cross-sections in pp collisions at root s = 13 TeV (vol 03, 159, 2016)
C. Baesso, M. Cruz Torres, C. Göbel, J. Molina Rodriguez are associated to Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil Y. Xie, J. Yu are associated to Center for High Energy Physics, Tsinghua University, Beijing, China D. A. Milanes, I. A. Monroy, J. A. Rodriguez Lopez are associated to LPNHE, UniversitĂ© Pierre et Marie Curie, UniversitĂ© Paris Diderot, CNRS/IN2P3, Paris, France O. GrĂŒnberg, M. HeĂ, C. VoĂ, R. Waldi are associated to Physikalisches Institut, Ruprecht-Karls-UniversitĂ€t Heidelberg, Heidelberg, Germany T. Likhomanenko, A. Malinin, V. Shevchenko, A. Ustyuzhanin are associated to Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia D. Derkach, E. Khairullin, T. Likhomanenko, A. Ustyuzhanin are associated to Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia F. Martinez Vidal, A. Oyanguren, P. Ruiz Valls, C. Sanchez Mayordomo are associated to Universitat de Barcelona, Barcelona, Spain C. J. G. Onderwater is associated to Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands Deceased (T. M. Karbach
Erratum to: Measurements of the S-wave fraction in B0 â K+ÏâÎŒ+ÎŒâ decays and the B0 â Kâ(892)0ÎŒ+ÎŒâ differential branching fraction
Deceased (T.M. Karbach). C. Baesso, M. Cruz Torres, C. Göbel, J. Molina Rodriguez are associated to Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil J. He, X. Lyu, Y. Zhang, Y. Zheng are associated to Center for High Energy Physics, Tsinghua University, Beijing, China Y. Xie, H. Yin, J. Yu are associated to Center for High Energy Physics, Tsinghua University, Beijing, China D. A. Milanes, I. A. Monroy, J. A. Rodriguez Lopez are associated to LPNHE, UniversitĂ© Pierre et Marie Curie, UniversitĂ© Paris Diderot, CNRS/IN2P3, Paris, France O. GrĂŒnberg, M. HeĂ, C. VoĂ, R. Waldi are associated to Physikalisches Institut, Ruprecht-Karls-UniversitĂ€t Heidelberg, Heidelberg, Germany T. Likhomanenko, A. Malinin, A. Petrov, V. Shevchenko, A. Ustyuzhanin are associated to Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia M. Borisyak, D. Derkach, M. Hushchyn, E. Khairullin, T. Likhomanenko, A. Rogozhnikov, A. Ustyuzhanin are associated to Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia F. Martinez Vidal, A. Oyanguren, C. Remon Alepuz, P. Ruiz Valls, C. Sanchez Mayordomo are associated to Universitat de Barcelona, Barcelona, Spain C. J. G. Onderwater is associated to Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherland
Erratum: Measurement of forward J/psi production cross-sections in pp collisions at root s = 13 TeV (vol 10, pg 172, 2015)
An issue has been identified in the simulated samples used to calculate the track reconstruction efficiencies, which affects the published J/Ï production cross-section in pp collisions at âs = 13 TeV [1]. A brief description of the nature of the problem is provided and then the corrected results are given
Measurement of CP asymmetry in D-0 -> K- K+ decays
A measurement of the time-integrated CP asymmetry in the Cabibbo-suppressed decay D-0 -> K- K+ is performed using pp collision data, corresponding to an integrated luminosity of 3 fb(-1), collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in D*(+) -> D-0 pi(+) and D*(-) -> (D) over bar (0)pi(-) decays. The time-integrated CP asymmetry A(CP)(K- K+) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D-0 -> K- pi(+), D+ -> K- pi(+) pi(+) and D+ -> (K) over bar (0)pi(+) decays used as calibration channels. It is found to be A(CP)(K- K+) = (0.14 +/- 0.15 (stat) +/- 0.10 (syst))%. A combination of this result with previous LHCb measurements yields A(CP)(K- K+) = (0.04 +/- 0.12 (stat) +/- 0.10 (syst))%, A(CP)(pi(-) pi(+)) = (0.07 +/- 0.14 (stat) +/- 0.11 (syst))%. These are the most precise measurements from a single experiment. The result for ACP(K- K+) is the most precise determination of a time-integrated CP asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry
Study of 5 and 10 mm thick CZT strip detectors
We report progress in the study of 5 and 10 mm thick CZT strip detectors featuring orthogonal coplanar anode contacts. This novel anode geometry combines the advantages of pixel detectors with those of double-sided strip detectors. Like pixel detectors, these are electron-only devices that perform well as hard x-ray and y-ray spectrometers and imagers even in the thicker configurations required for reasonable detection efficiency at 1 MeV. Like double-sided strip detectors in an N x N configuration, these detectors require only 2N readout channels to form N2 âpixelsâ. Unlike doublesided strip detectors, all signal contacts for spectroscopy and 3- d imaging are formed on one detector surface. Polymer flip chip bonding to a ceramic substrate is employed resulting in a rugged and compact detector assembly. Prototype detector modules 5 mm thick have been fabricated and tested. Prototype modules, 10 mm thick, are currently in procurement. Measurements confirm these devices are efficient detectors throughout their volume. Sub-millimeter position resolution and energy resolution (FWHM) better than 3% at 662 keV and 15% at 60 keV throughout the detector volume are demonstrated. Options for processing the signals from the non-collecting anode strip contacts are discussed. Results from tests of one prototype circuit are presented. We also report on detector simulation studies aimed at defining an optimum geometry for the anode contacts and at determining optimum operating conditions and the requirements of the signal processing electronics
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