6,248 research outputs found
Semileptonic B Decays at BABAR
We present results on semileptonic B decays obtained with the BABAR detector.
The large data set accumulated at the PEP-II asymmetric-energy B-Factory allows
a new measurement technique, where the hadronic decay of one B meson is fully
reconstructed and the semileptonic decay of the recoiling B meson is studied.
Traditional analysis techniques of inclusive and exclusive B decays complement
this approach with very high statistics data samples. These measurements play
an important role in the tests of the description of CP violation in the
Standard Model: The determinations of the Cabibbo-Kobayashi-Maskawa matrix
elements |Vcb| and |Vub| provide constraints on the unitarity of the CKM
triangle. Furthermore, the experimental measurement of parameters of Heavy
Quark Effective Theory test the consistency of the theoretical description of
semileptonic B decays.Comment: Invited Brief Review, to appear in Modern Physics Letters
Luminosity Dependent Evolution of Lyman Break Galaxies from redshift 5 to 3
In this contribution we briefly describe our recent results on the properties
of Lyman break galaxies at z~5 obtained from deep and wide blank field surveys
using Subaru telescope, and through the comparison with samples at lower
redshift ranges we discuss the evolution of star-forming galaxies in the early
universe.Comment: 2 pages, 1 figure, for the proceedings of the IAU Symposium 235,
Galaxies Across the Hubble Time, J. Palous & F. Combes, ed
Non-ergodic transitions in many-body Langevin systems: a method of dynamical system reduction
We study a non-ergodic transition in a many-body Langevin system. We first
derive an equation for the two-point time correlation function of density
fluctuations, ignoring the contributions of the third- and fourth-order
cumulants. For this equation, with the average density fixed, we find that
there is a critical temperature at which the qualitative nature of the
trajectories around the trivial solution changes. Using a method of dynamical
system reduction around the critical temperature, we simplify the equation for
the time correlation function into a two-dimensional ordinary differential
equation. Analyzing this differential equation, we demonstrate that a
non-ergodic transition occurs at some temperature slightly higher than the
critical temperature.Comment: 8 pages, 1 figure; ver.3: Calculation errors have been fixe
Photoabsorption spectra in the continuum of molecules and atomic clusters
We present linear response theories in the continuum capable of describing
photoionization spectra and dynamic polarizabilities of finite systems with no
spatial symmetry. Our formulations are based on the time-dependent local
density approximation with uniform grid representation in the three-dimensional
Cartesian coordinate. Effects of the continuum are taken into account either
with a Green's function method or with a complex absorbing potential in a
real-time method. The two methods are applied to a negatively charged cluster
in the spherical jellium model and to some small molecules (silane, acetylene
and ethylene).Comment: 13 pages, 9 figure
CO(J=6-5) Observations of the Quasar SDSS1044-0125 at z = 5.8
We present a result of the quasar CO(J=6-5) observations of SDSSp
J104433.04-012502.2 at z = 5.8. Ten-days observations with the Nobeyama
Millimeter Array yielded an rms noise level of ~ 2.1 mJy/beam in a frequency
range from 101.28 GHz to 101.99 GHz at a velocity resolution of 120 km/s. No
significant clear emission line was detected in the observed field and
frequency range. Three sigma upper limit on the CO(J=6-5) luminosity of the
object is 2.8 x 10^10 K km/s pc^2, corresponding to a molecular gas mass of 1.2
x 10^11 Solar Mass, if a conversion factor of 4.5 Solar Mass /(K km/s pc^2) is
adopted. The obtained upper limit on CO luminosity is slightly smaller than
those observed in quasars at z=4-5 toward which CO emissions are detected.Comment: 4 pages, 3 figures, LaTeX2e, to appear in Publication of Astronomical
Society of Japan (PASJ), Postscript file available at
ftp://ftp.kusastro.kyoto-u.ac.jp/pub/iwata/preprint/sdss1044/sdss.ps.g
Star Formation at the Twilight of the Dark Ages: Which Stars Reionized the Universe?
We calculate the global star formation rate density (SFRD) from z ~ 30-3
using a semi-analytic model incorporating the hierarchical assembly of dark
matter halos, gas cooling via atomic hydrogen, star formation, supernova
feedback, and suppression of gas collapse in small halos due to the presence of
a photoionizing background. We compare the results with the predictions of
simpler models based on the rate of dark matter halo growth and a fixed ratio
of stellar-to-dark mass, and with observational constraints on the SFRD at 3 <
z < 6. We also estimate the star formation rate due to very massive, metal-free
Pop III stars using a simple model based on the halo formation rate, calibrated
against detailed hydrodynamic simulations of Pop III star formation. We find
that the total production rate of hydrogen-ionizing photons during the probable
epoch of reionization (15 < z < 20) is approximately equally divided between
Pop II and Pop III stars, and that if reionization is late (less than about 15,
close to the lower limit of the range allowed by the WMAP results), then Pop II
stars alone may be able to reionize the Universe.Comment: submitted to ApJ
Precise study of asymptotic physics with subradiant ultracold molecules
Weakly bound molecules have physical properties without atomic analogues,
even as the bond length approaches dissociation. In particular, the internal
symmetries of homonuclear diatomic molecules result in formation of two-body
superradiant and subradiant excited states. While superradiance has been
demonstrated in a variety of systems, subradiance is more elusive due to the
inherently weak interaction with the environment. Here we characterize the
properties of deeply subradiant molecular states with intrinsic quality factors
exceeding via precise optical spectroscopy with the longest
molecule-light coherent interaction times to date. We find that two competing
effects limit the lifetimes of the subradiant molecules, with different
asymptotic behaviors. The first is radiative decay via weak magnetic-dipole and
electric-quadrupole interactions. We prove that its rate increases
quadratically with the bond length, confirming quantum mechanical predictions.
The second is nonradiative decay through weak gyroscopic predissociation, with
a rate proportional to the vibrational mode spacing and sensitive to
short-range physics. This work bridges the gap between atomic and molecular
metrology based on lattice-clock techniques, yielding new understanding of
long-range interatomic interactions and placing ultracold molecules at the
forefront of precision measurements.Comment: 12 pages, 6 figure
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