51ÁÔÆæÈë¿Ú

Abstract:

We measure the branching ratio of the purely leptonic decay of the D+ meson with unprecedented precision as B(D+→μ+ν)=(3.82±0. 32±0.09)×10-4, using 818pb-1 of data taken on the ψ(3770) resonance with the CLEO-c detector at the CESR collider. We use this determination to derive a value for the pseudoscalar decay constant fD+, combining with measurements of the D+ lifetime and assuming |Vcd|=|Vus|. We find fD+=(205.8±8.5±2.5)MeV. The decay rate asymmetry Γ(D+→μ+ν)-Γ(D-→μ-ν̄)Γ(D+→μ +ν)+Γ(D-→μ-ν̄)=0.08±0.08, consistent with no CP violation. We also set 90% confidence level upper limits on B(D+→τ+ν )<1.2×10-3 and B(D+→e+ν)<8.8×10-6. © 2008 The American Physical Society.

Abstract:

We present the first detection of CS in the Antennae galaxies towards the NGC 4038 nucleus, as well as the first detections of two high-J (5-4 and 7-6) CS lines in the center of M 82. The CS(7-6) line in M 82 shows a profile that is surprisingly different to those of other low-J CS transitions we observed. This implies the presence of a separate, denser and warmer molecular gas component. The derived physical properties and the likely location of the CS(7-6) emission suggests an association with the supershell in the centre of M 82.

Abstract:

We perform a Dalitz plot analysis of D+→K-π+π+ decay with the CLEO-c data set of 572pb-1 of e+e- collisions accumulated at the ψ(3770). This corresponds to 1.6×106 D+D- pairs from which we select 140793 candidate events with a small background of 1.1%. We compare our results with previous measurements using the isobar model. We modify the isobar model with an improved description of some of the contributing resonances and get better agreement with our data. We also consider a quasi-model-independent approach and measure the magnitude and phase of the contributing Kπ S wave in the range of invariant masses from the threshold to the maximum in this decay. This gives an improved description of our data over the isobar model. Finally we allow for an isospin-two π+π+ S wave contribution and find that adding this to both the isobar model and the quasi-model-independent approach gives the best description of our data. © 2008 The American Physical Society.

Abstract:

In order to understand the formation and subsequent evolution of galaxies one must first distinguish between the two main morphological classes of massive systems: spirals and early-type systems. This paper introduces a project, Galaxy Zoo, which provides visual morphological classifications for nearly one million galaxies, extracted from the Sloan Digital Sky Survey (SDSS). This achievement was made possible by inviting the general public to visually inspect and classify these galaxies via the internet. The project has obtained more than 40,000,000 individual classifications made by ~100,000 participants. We discuss the motivation and strategy for this project, and detail how the classifications were performed and processed. We find that Galaxy Zoo results are consistent with those for subsets of SDSS galaxies classified by professional astronomers, thus demonstrating that our data provides a robust morphological catalogue. Obtaining morphologies by direct visual inspection avoids introducing biases associated with proxies for morphology such as colour, concentration or structual parameters. In addition, this catalogue can be used to directly compare SDSS morphologies with older data sets. The colour--magnitude diagrams for each morphological class are shown, and we illustrate how these distributions differ from those inferred using colour alone as a proxy for morphology.