268 research outputs found

    Temperature and Emission-Measure Profiles Along Long-Lived Solar Coronal Loops Observed with TRACE

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    We report an initial study of temperature and emission measure distributions along four steady loops observed with the Transition Region and Coronal Explorer (TRACE) at the limb of the Sun. The temperature diagnostic is the filter ratio of the extreme-ultraviolet 171-angstrom and 195-angstrom passbands. The emission measure diagnostic is the count rate in the 171-angstrom passband. We find essentially no temperature variation along the loops. We compare the observed loop structure with theoretical isothermal and nonisothermal static loop structure.Comment: 10 pages, 3 postscript figures (LaTeX, uses aaspp4.sty). Accepted by ApJ Letter

    In Pursuit of New Physics with B_s Decays

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    The presence of a sizeable CP-violating phase in B_s^0-B_s^0-bar mixing would be an unambiguous signal of physics beyond the Standard Model. We analyse various possibilities to detect such a new phase considering both tagged and untagged decays. The effects of a sizeable width difference Delta Gamma between the B_s mass eigenstates, on which the untagged analyses rely, are included in all formulae. A novel method to find this phase from simple measurements of lifetimes and branching ratios in untagged decays is proposed. This method does not involve two-exponential fits, which require much larger statistics. For the tagged decays, an outstanding role is played by the observables of the time-dependent angular distribution of the B_s -> J/psi [-> l^+ l^-] \phi [-> K^+K^-] decay products. We list the formulae needed for the angular analysis in the presence of both a new CP-violating phase and a sizeable Delta Gamma, and propose methods to remove a remaining discrete ambiguity in the new phase. This phase can therefore be determined in an unambiguous way.Comment: minor changes, lattice prediction of Delta Gamma updated, appears in PR

    CP violation and CKM phases from angular distributions for BsB_s decays into admixtures of CP eigenstates

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    We investigate the time-evolutions of angular distributions for BsB_s decays into final states that are admixtures of CP-even and CP-odd configurations. A sizable lifetime difference between the BsB_s mass eigenstates allows a probe of CP violation in time-dependent untagged angular distributions. Interference effects between different final state configurations of BsDs+DsB_s\to D^{*+}_s D^{*-}_s, J/ψϕJ/\psi \phi determine the Wolfenstein parameter η\eta from untagged data samples, or -- if one uses Vub/Vcb|V_{ub}|/|V_{cb}| as an additional input -- the notoriously difficult to measure CKM angle γ\gamma. Another determination of γ\gamma is possible by using isospin symmetry of strong interactions to relate untagged data samples of BsK+KB_s\to K^{\ast+} K^{\ast-} and BsK0K0B_s\to K^{\ast0} \overline{K^{\ast0}}. We note that the untagged angular distribution for Bsρ0ϕB_s\to\rho^0 \phi provides interesting information about electroweak penguins.Comment: 19 pages, LaTeX, no figure

    A Salmonid EST Genomic Study: Genes, Duplications, Phylogeny and Microarrays

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    Background: Salmonids are of interest because of their relatively recent genome duplication, and their extensive usein wild fisheries and aquaculture. A comprehensive gene list and a comparison of genes in some of the different speciesprovide valuable genomic information for one of the most widely studied groups of fish.Results: 298,304 expressed sequence tags (ESTs) from Atlantic salmon (69% of the total), 11,664 chinook, 10,813sockeye, 10,051 brook trout, 10,975 grayling, 8,630 lake whitefish, and 3,624 northern pike ESTs were obtained in thisstudy and have been deposited into the public databases. Contigs were built and putative full-length Atlantic salmonclones have been identified. A database containing ESTs, assemblies, consensus sequences, open reading frames, genepredictions and putative annotation is available. The overall similarity between Atlantic salmon ESTs and those of rainbowtrout, chinook, sockeye, brook trout, grayling, lake whitefish, northern pike and rainbow smelt is 93.4, 94.2, 94.6, 94.4,92.5, 91.7, 89.6, and 86.2% respectively. An analysis of 78 transcript sets show Salmo as a sister group to Oncorhynchusand Salvelinus within Salmoninae, and Thymallinae as a sister group to Salmoninae and Coregoninae within Salmonidae.Extensive gene duplication is consistent with a genome duplication in the common ancestor of salmonids. Using all of theavailable EST data, a new expanded salmonid cDNA microarray of 32,000 features was created. Cross-specieshybridizations to this cDNA microarray indicate that this resource will be useful for studies of all 68 salmonid species.Conclusion: An extensive collection and analysis of salmonid RNA putative transcripts indicate that Pacific salmon,Atlantic salmon and charr are 94–96% similar while the more distant whitefish, grayling, pike and smelt are 93, 92, 89 and86% similar to salmon. The salmonid transcriptome reveals a complex history of gene duplication that is consistent withan ancestral salmonid genome duplication hypothesis. Genome resources, including a new 32 K microarray, providevaluable new tools to study salmonids

    Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering: Determined by the OLYMPUS Experiment

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    The OLYMPUS collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, R2γR_{2\gamma}, a direct measure of the contribution of hard two-photon exchange to the elastic cross section. In the OLYMPUS measurement, 2.01~GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of 20°\approx 20\degree to 80°80\degree. The relative luminosity between the two beam species was monitored using tracking telescopes of interleaved GEM and MWPC detectors at 12°12\degree, as well as symmetric M{\o}ller/Bhabha calorimeters at 1.29°1.29\degree. A total integrated luminosity of 4.5~fb1^{-1} was collected. In the extraction of R2γR_{2\gamma}, radiative effects were taken into account using a Monte Carlo generator to simulate the convolutions of internal bremsstrahlung with experiment-specific conditions such as detector acceptance and reconstruction efficiency. The resulting values of R2γR_{2\gamma}, presented here for a wide range of virtual photon polarization 0.456<ϵ<0.9780.456<\epsilon<0.978, are smaller than some hadronic two-photon exchange calculations predict, but are in reasonable agreement with a subtracted dispersion model and a phenomenological fit to the form factor data.Comment: 5 pages, 3 figures, 2 table

    Towards new frontiers in the exploration of charmless non-leptonic B decays

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    Non-leptonic BB decays into charmless final states offer an important laboratory to study CP violation and the dynamics of strong interactions. Particularly interesting are Bs0KK+B^0_s\to K^-K^+ and Bd0ππ+B^0_d\to\pi^-\pi^+ decays, which are related by the UU-spin symmetry of strong interactions, and allow for the extraction of CP-violating phases and tests of the Standard Model. The theoretical precision is limited by UU-spin-breaking corrections and innovative methods are needed in view of the impressive future experimental precision expected in the era of Belle II and the LHCb upgrade. We have recently proposed a novel method to determine the Bs0B_s^0-Bˉs0\bar{B}_s^0 mixing phase ϕs\phi_s from the Bs0KK+B_s^0\to K^-K^+, Bd0ππ+B_d^0\to \pi^-\pi^+ system, where semileptonic Bs0K+νB^0_s\to K^-\ell^+\nu_\ell, Bd0π+νB^0_d\to \pi^-\ell^+\nu_\ell decays are a new ingredient and the theoretical situation is very favourable. We discuss this strategy in detail, with a focus on penguin contributions as well as exchange and penguin-annihilation topologies which can be probed by a variety of non-leptonic BB decays into charmless final states. We show that a theoretical precision as high as O(0.5){\cal O}(0.5^\circ) for ϕs\phi_s can be attained in the future, thereby offering unprecedented prospects for the search for new sources of CP violation.Comment: 50 pages, 25 figure

    The first determination of Generalized Polarizabilities of the proton by a Virtual Compton Scattering experiment

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    Absolute differential cross sections for the reaction (e+p -> e+p+gamma) have been measured at a four-momentum transfer with virtuality Q^2=0.33 GeV^2 and polarization \epsilon = 0.62 in the range 33.6 to 111.5 MeV/c for the momentum of the outgoing photon in the photon-proton center of mass frame. The experiment has been performed with the high resolution spectrometers at the Mainz Microtron MAMI. From the photon angular distributions, two structure functions which are a linear combination of the generalized polarizabilities have been determined for the first time.Comment: 4 pages, 3 figure

    Angular distributions and the physics of charmed-meson production at the 4.028-GeV resonance

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    A detailed study of angular distributions arising from D{anti D}, D* anti D} , and D*{anti D}* production at {radical}s= 4.028 GeV is made, including the subsequent decays D*{yields}D{pi} and D* {yields} D{gamma}. The production amplitudes are unique except for the D*{anti D}* case, where there are two p-wave amplitudes (S = 0, 2) and one small f-wave amplitude (S = 2). It is shown that observations of the angular distributions and correlations of the {pi}{sup 0}'s and {gamma}&#x27;s from the D* {yields} D{pi}{sup 0} and D* {yields} D{gamma} decays provide an effective way of measuring the p-wave amplitudes. These amplitudes are a reflection of the underlying hadronic interactions among the charmed and uncharmed quarks
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