310 research outputs found
Discrete Ambiguities in the Measurement of the Weak Phase Gamma
Several time-independent methods have been devised for measuring the phase
gamma of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is shown that
such measurements generally suffer from discrete ambiguity which is at least
8-fold, not 4-fold as commonly stated. This has serious experimental
implications, which are explored in methods involving B->DK decays. The
measurement sensitivity and new physics discovery potential are estimated using
a full Monte Carlo detector simulation with realistic background estimates.Comment: 15 pages, 2 figures, fixed typ
Heavy Baryonic Decays of \Lambda_b \to \Lambda \eta^{(\prime)} and Nonspectator Contribution
We calculate the branching ratios of the hadronic \Lambda_b decays to \eta
and \eta^\prime in the factorization approximation where the form factors are
estimated via QCD sum rules and the pole model. Our results indicate that,
contrary to B\to K\eta^{(\prime)} decays, the branching ratios for
\Lambda_b\to\Lambda\eta and \Lambda_b\to\Lambda\eta^\prime are more or less the
same in the hadronic \Lambda_b transitions. We estimate the branching ratio of
\Lambda_b\to\Lambda\eta^{(\prime)} to be 10.80 (10.32)\times 10^{-6} in QCD sum
rules, and 2.78 (2.96)\times 10^{-6} in the pole model. We also estimate the
nonfactorizable gluon fusion contribution to \Lambda_b\to\Lambda\eta^\prime
decay by dividing this process into strong and weak vertices. Our results point
to an enhancement of more than an order of magnitude due to this mechanism.Comment: 16 pages, ReVTeX, 5 eps figure
Accretion disk in the eclipsing binary AU Mon
We analyze the CoRoT and V-passband ground-based light curves of the
interacting close binary AU Mon, assuming that there is a geometrically and
optically thick accretion disk around the hotter and more massive star, as
inferred from photometric and spectroscopic characteristics of the binary. Our
model fits the observations very well and provides estimates for the orbital
elements and physical parameters of the components and of the accretion disk.Comment: Accepted for publication in MNRA
Astronomical Spectroscopy
Spectroscopy is one of the most important tools that an astronomer has for
studying the universe. This chapter begins by discussing the basics, including
the different types of optical spectrographs, with extension to the ultraviolet
and the near-infrared. Emphasis is given to the fundamentals of how
spectrographs are used, and the trade-offs involved in designing an
observational experiment. It then covers observing and reduction techniques,
noting that some of the standard practices of flat-fielding often actually
degrade the quality of the data rather than improve it. Although the focus is
on point sources, spatially resolved spectroscopy of extended sources is also
briefly discussed. Discussion of differential extinction, the impact of
crowding, multi-object techniques, optimal extractions, flat-fielding
considerations, and determining radial velocities and velocity dispersions
provide the spectroscopist with the fundamentals needed to obtain the best
data. Finally the chapter combines the previous material by providing some
examples of real-life observing experiences with several typical instruments.Comment: An abridged version of a chapter to appear in Planets, Stars and
Stellar Systems, to be published in 2011 by Springer. Slightly revise
A novel topographic parameterization scheme indicates that martian gullies display the signature of liquid water
Martian gullies resemble gullies carved by water on Earth, yet are thought to have formed in an extremely cold (2-driven processes. That this argument persists demonstrates the limitations of morphological interpretations made from 2D images, especially when similar-looking landforms can form by very different processes. To overcome this we have devised a parameterization scheme, based on statistical discriminant analysis and hydrological terrain analysis of meter-scale digital topography data, which can distinguish between dry and wet surface processes acting on a landscape. Applying this approach to new meter-scale topographic datasets of Earth, the Moon and Mars, we demonstrate that martian gullied slopes are dissimilar to dry, gullied slopes on Earth and the Moon, but are similar to both terrestrial debris flows and fluvial gullies. We conclude that liquid water was integral to the process by which martian gullies formed. Finally, our work shows that quantitative 3D analyses of landscape have great potential as a tool in planetary science, enabling remote assessment of processes acting on planetary surfaces
The Possibility of Large Direct CP Violation in B to K pi-Like Modes Due to Long Distance Rescattering Effects and Implications for the Angle gamma
We consider the strong rescattering effects that can occur in the decays such
as B -> K pi, K* pi, K rho... and their impact on direct CP violation in these
modes. First we discuss, in general, how the CPT theorem constrains the
resulting pattern of partial rate asymmetries leading to different brands of
direct CP. Traditional discussions have centered around the absorptive part of
the penguin graph which has Delta I=0 in b -> s transitions and as a result
causes ``simple'' CP violation; long-distance final state rescattering effects,
in general, will lead to a different pattern of CP: ``compound'' CP violation.
Predictions of simple CP are quite distinct from that of compound CP. Final
states rescattering phases in B decays are unlikely to be small possibly
causing large compound CP violating partial rate asymmetries in these modes.
CPT theorem requires a cancellation of PRA due to compound CP amongst the
states themselves; thus there can be no net cancellation with other
states such as K*\pi, K\rho etc. Therefore, each class of such modes, namely K
pi, K rho, K^*pi, K a_1 etc. can have large direct CP emanating from
rescattering effects. Various repercussions for the angle are also
discussed.Comment: 45 pages; 5 figures. In replacement we have : 1) corrected many
typos, 2) added references, 3) decided to subdivide Simple CP into 2
categories and 4) Modified figure 3 to explain tha
Theory of CP Violation
CP violation in K and B decays is reviewed in the Standard Model (SM) and
beyond the SM. In K decays, one is seeking first evidence for CP violation in
direct decays. This would not give a precise quantitative test
for the present explanation of CP violation in terms of a phase in the
Cabibbo-Kobayashi-Maskawa (CKM) matrix. Such tests are provided by a variety of
CP asymmetries in neutral and charged B decays. Certain features,
characterizing CP violation beyond the standard model, are outlined in the B
meson system.Comment: 13 pages, To appear in Proceedings of the Fifth Topical Seminar on
The Irresistible Rise of the Standard Model, San Miniato al Todesco, Italy,
April 21-25, 199
Water induced sediment levitation enhances downslope transport on Mars
On Mars, locally warm surface temperatures (~293 K) occur, leading to the possibility of (transient) liquid water on the surface. However, water exposed to the martian atmosphere will boil, and the sediment transport capacity of such unstable water is not well understood. Here, we present laboratory studies of a newly recognized transport mechanism: “levitation” of saturated sediment bodies on a cushion of vapor released by boiling. Sediment transport where this mechanism is active is about nine times greater than without this effect, reducing the amount of water required to transport comparable sediment volumes by nearly an order of magnitude. Our calculations show that the effect of levitation could persist up to ~48 times longer under reduced martian gravity. Sediment levitation must therefore be considered when evaluating the formation of recent and present-day martian mass wasting features, as much less water may be required to form such features than previously thought
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