614 research outputs found
Apparatus for Cold, Pressurized Biogeochemical Experiments
A laboratory apparatus has been devised as a means of studying plausible biogeochemical reactions under high-pressure, low-temperature aqueous, anaerobic conditions like those conjectured to prevail in a liquid water ocean on Europa (the fourth largest moon of the planet Jupiter). The experiments to be performed by use of this apparatus are intended to enhance understanding of how life (if any) could originate and evolve in the Europa ocean environment. Inasmuch as terrestrial barophilic, psychrophilic organisms that thrive under anaerobic conditions are used in the experiments, the experiments may also contribute to terrestrial biogeochemistry. The apparatus (see figure) includes a bolt-closure reaction vessel secured inside a refrigerator that maintains a temperature of 4 C. Pressurized water is supplied to the interior of the vessel by a hydrostatic pump, which is attached to the vessel via high-pressure fittings. The terrestrial organisms used in the experiments thus far have been several facultative barophilic, psychrophilic stains of Shewanella bacteria. In the experiments, these organisms have been tested for reduction of ferric ion by growing them in the presence of a ferric food source under optimized terrestrial conditions. The short-term goal of these experiments has been to select Shewanella strains that exhibit iron-reduction capability and test their ability to facilitate biogeochemical reduction of iron under temperature and pressure conditions imitating those in Europa s ocean. It is anticipated, that, once growth under Europa-like conditions has been achieved, the selected Shewanella strains will be used to facilitate biogeochemical reactions of sulfate and carbonate with hydrogen gas. Any disequilibrium of the products with the environment would be interpreted as signifying biogenic activity and the possibility of life in Europa s ocean
Calibration and performance of the Galileo solid-state imaging system in Jupiter orbit
The solid-state imaging subsystem (SSI) on the National Aeronautics and Space Administrationâs (NASAâs) Galileo Jupiter orbiter spacecraft has successfully completed its 2-yr primary mission exploring the Jovian system. The SSI has remained in remarkably stable calibration during the 8-yr flight, and the quality of the returned images is exceptional. Absolute spectral radiometric calibration has been determined to 4 to 6% across its eight spectral filters. Software and calibration files are available to enable radiometric, geometric, modulation transfer function (MTF), and scattered light image calibration. The charge-coupled device (CCD) detector endured the harsh radiation environment at Jupiter without significant damage and exhibited transient image noise effects at about the expected levels. A lossy integer cosine transform (ICT) data compressor proved essential to achieving the SSI science objectives given the low data transmission rate available from Jupiter due to a communication antenna failure. The ICT compressor does introduce certain artifacts in the images that must be controlled to acceptable levels by judicious choice of compression control parameter settings. The SSI teamâs expertise in using the compressor improved throughout the orbital operations phase and, coupled with a strategy using multiple playback passes of the spacecraft tape recorder, resulted in the successful return of 1645 unique images of Jupiter and its satellites
Calibration and performance of the Galileo solid-state imaging system in Jupiter orbit
The solid-state imaging subsystem (SSI) on the National Aeronautics and Space Administrationâs (NASAâs) Galileo Jupiter orbiter spacecraft has successfully completed its 2-yr primary mission exploring the Jovian system. The SSI has remained in remarkably stable calibration during the 8-yr flight, and the quality of the returned images is exceptional. Absolute spectral radiometric calibration has been determined to 4 to 6% across its eight spectral filters. Software and calibration files are available to enable radiometric, geometric, modulation transfer function (MTF), and scattered light image calibration. The charge-coupled device (CCD) detector endured the harsh radiation environment at Jupiter without significant damage and exhibited transient image noise effects at about the expected levels. A lossy integer cosine transform (ICT) data compressor proved essential to achieving the SSI science objectives given the low data transmission rate available from Jupiter due to a communication antenna failure. The ICT compressor does introduce certain artifacts in the images that must be controlled to acceptable levels by judicious choice of compression control parameter settings. The SSI teamâs expertise in using the compressor improved throughout the orbital operations phase and, coupled with a strategy using multiple playback passes of the spacecraft tape recorder, resulted in the successful return of 1645 unique images of Jupiter and its satellites
Observation of an Excited Bc+ State
Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+Ï+Ï- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bcâ(2S31)+ state reconstructed without the low-energy photon from the Bcâ(1S31)+âBc+Îł decay following Bcâ(2S31)+âBcâ(1S31)+Ï+Ï-. A second state is seen with a global (local) statistical significance of 2.2Ï (3.2Ï) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date
Updated Determination of Dâ°âDÂŻâ°Mixing and CP Violation Parameters with Dâ°âKâșÏâ» Decays
We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of Dâ°âKâșÏâ» to Dâ°âKâ»Ïâș rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of 5.0ââfbâ»Âč recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be xâČÂČ=(3.9±2.7)Ă10â»â”, yâČ=(5.28±0.52)Ă10â»Âł, and R[subscript D]=(3.454±0.031)Ă10â»Âł. Without this assumption, the measurement is performed separately for Dâ° and D[over ÂŻ]â° mesons, yielding a direct CP-violating asymmetry A[subscript D]=(-0.1±9.1)Ă10â»Âł, and magnitude of the ratio of mixing parameters 1.00<|q/p|<1.35 at the 68.3% confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed
Observation of Dâ° Meson Decays to Î âșÏâ»ÎŒâșΌ⻠and KâșKâ»ÎŒâșΌ⻠Final States
The first observation of the Dâ°âÏâșÏâ»ÎŒâșΌ⻠and Dâ°âKâșKâ»ÎŒâșΌ⻠decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to 2ââfbâ»Âč of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay Dâ°âKâ»Ïâș[ÎŒâșÎŒâ»][subscript Ïâ°/Ï], where the two muons are consistent with coming from the decay of a Ïâ° or Ï meson. The results are B(Dâ°âÏâșÏâ»ÎŒâșÎŒâ»)=(9.64±0.48±0.51±0.97)Ă10â»â· and B(Dâ°âKâșKâ»ÎŒâșÎŒâ»)=(1.54±0.27±0.09±0.16)Ă10â»â·, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated
Measurement of CP observables in B± â D(â)K± and B± â D(â)ϱ decays
Measurements of CP observables in B ± âD (â) K ± and B ± âD (â) Ï Â± decays are presented, where D (â) indicates a neutral D or D â meson that is an admixture of D (â)0 and DÂŻ (â)0 states. Decays of the D â meson to the DÏ 0 and DÎł final states are partially reconstructed without inclusion of the neutral pion or photon, resulting in distinctive shapes in the B candidate invariant mass distribution. Decays of the D meson are fully reconstructed in the K ± Ï â , K + K â and Ï + Ï â final states. The analysis uses a sample of charged B mesons produced in pp collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 2.0, 1.0 and 2.0 fb â1 taken at centre-of-mass energies of s=7, 8 and 13 TeV, respectively. The study of B ± âD â K ± and B ± âD â Ï Â± decays using a partial reconstruction method is the first of its kind, while the measurement of B ± âDK ± and B ± âDÏ Â± decays is an update of previous LHCb measurements. The B ± âDK ± results are the most precise to date
Measurement of the mass and production rate of Îâb baryons
The first measurement of the production rate of Xi(-)(b) baryons in pp collisions relative to that of Lambda(0 )(b)baryons is reported, using data samples collected by the LHCb experiment, and corresponding to integrated luminosities of 1, 2 and 1.6 fb(-1) at root s = 7, 8 and 13 TeV, respectively. In the kinematic region 2 < eta < 6 and p(T) < 20 GeV/c, we measure f(Xi b-)/f(Lambda b0) B(Xi(-)(b)-> J/psi Xi(-))/B(Lambda(0)(b)-> J/psi Lambda)= (10.8 +/- 0.9 +/- 0.8) x 10(-2) [root s = 7,8 TeV], f(Xi b-)/f(Lambda b0) B(Xi(-)(b)-> J/psi Xi(-))/B(Lambda(0)(b)-> J/psi Lambda) =(13.1 +/- 1.1 +/- 1.0) x 10(-2) [root s = 13 TeV], where and f(Xi b-) and f(Lambda)(b0) the fragmentation fractions of b quarks into Xi(-)(b) and Lambda(0)(b) baryons, respectively; B represents branching fractions; and the uncertainties are due to statistical and experimental systematic sources. The values of f(Xi b-)/f(Lambda b0) are obtained by invoking SU(3) symmetry in the Xi(-)(b)-> J/psi Xi(-) and Lambda(0)(b)-> J/psi Lambda decays. Production asymmetries between Xi(-)(b) and (Xi) over bar (+)(b) baryons are also reported. The mass of the Xi(-)(b) baryon is also measured relative to that of the Lambda(0)(b) baryon, from which it is found that m(Xi(-)(b)) = 5796.70 +/- 0.39 +/- 0.15 +/- 0.17 MeV/c(2), where the last uncertainty is due to the precision on the known Lambda(0)(b) mass. This result represents the most precise determination of the Xi(-)(b) mass
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