537 research outputs found
Final State Rescattering and Color-suppressed \bar B^0-> D^{(*)0} h^0 Decays
The color-suppressed \bar B^0-> D^{(*)0}\pi^0, D^{(*)0}\eta, D^0\omega decay
modes have just been observed for the first time. The rates are all larger than
expected, hinting at the presence of final state interactions. Considering \bar
B^0-> D^{(*)0}\pi^0 mode alone, an elastic D^{(*)}\pi -> D^{(*)}\pi
rescattering phase difference \delta \equiv \delta_{1/2} - \delta_{3/2} \sim
30^\circ would suffice, but the \bar B^0-> D^{(*)0}\eta, D^0\omega modes compel
one to extend the elastic formalism to SU(3) symmetry. We find that a universal
a_2/a_1=0.25 and two strong phase differences 20^\circ \sim \theta < \delta <
\delta^\prime \sim 50^\circ can describe both DP and D^*P modes rather well;
the large phase of order 50^\circ is needed to account for the strength of {\it
both} the D^{(*)0}\pi^0 and D^{(*)0}\eta modes. For DV modes, the nonet
symmetry reduces the number of physical phases to just one, giving better
predictive power. Two solutions are found. We predict the rates of the \bar
B^0-> D^{+}_s K^-, D^{*+}_s K^-, D^0\rho^0, D^+_s K^{*-} and D^0\phi modes, as
well as \bar B^0-> D^{0}\bar K^0, D^{*0}\bar K^0, D^{0}\bar K^{*0} modes. The
formalism may have implications for rates and CP asymmetries of charmless
modes.Comment: REVTeX4, 18 pages, 5 figures, to appear in Phys. Rev.
Charmless Exclusive Baryonic B Decays
We present a systematical study of two-body and three-body charmless baryonic
B decays. Branching ratios for two-body modes are in general very small,
typically less than , except that \B(B^-\to p \bar\Delta^{--})\sim
1\times 10^{-6}. In general, due to
the large coupling constant for . For three-body modes we
focus on octet baryon final states. The leading three-dominated modes are with a branching ratio of
order for and
for . The penguin-dominated decays with strangeness
in the meson, e.g., and , have appreciable rates and the mass
spectrum peaks at low mass. The penguin-dominated modes containing a strange
baryon, e.g., , have
branching ratios of order . In contrast, the decay
rate of is smaller. We explain why some of
charmless three-body final states in which baryon-antibaryon pair production is
accompanied by a meson have a larger rate than their two-body counterparts:
either the pole diagrams for the former have an anti-triplet bottom baryon
intermediate state, which has a large coupling to the meson and the
nucleon, or they are dominated by the factorizable external -emission
process.Comment: 46 pages and 3 figures, to appear in Phys. Rev. D. Major changes are:
(i) Calculations of two-body baryonic B decays involving a Delta resonance
are modified, and (ii) Penguin-dominated modes B-> Sigma+N(bar)+p are
discusse
Charmless Two-body Baryonic B Decays
We study charmless two-body baryonic B decays in a diagramatic approach.
Relations on decay amplitudes are obtained. In general there are more than one
tree and more than one penguin amplitudes. The number of independent amplitudes
can be reduced in the large m_B limit. It leads to more predictive results.
Some prominent modes for experimental searches are pointed out.Comment: 15 pages, 2 figures. To appear in Phys. Rev.
B -> J/psi K^* Decays in QCD Factorization
The hadronic decay B -> J K^* is analyzed within the framework of QCD
factorization. The spin amplitudes A_0, A_\parallel and A_\perp in the
transversity basis and their relative phases are studied using various
different form-factor models for B-K^* transition. The effective parameters
a_2^h for helicity h=0,+,- states receive different nonfactorizable
contributions and hence they are helicity dependent, contrary to naive
factorization where a_2^h are universal and polarization independent. QCD
factorization breaks down even at the twist-2 level for transverse hard
spectator interactions. Although a nontrivial strong phase for the A_\parallel
amplitude can be achieved by adjusting the phase of an infrared divergent
contribution, the present QCD factorization calculation cannot say anything
definite about the phase phi_\parallel. Unlike B -> J/psi K decays, the
longitudinal parameter a_2^0 for B -> J/psi K^* does not receive twist-3
corrections and is not large enough to account for the observed branching ratio
and the fraction of longitudinal polarization. Possible enhancement mechanisms
for a_2^0 are discussed.Comment: 21 pages, 1 figure, a table and a reference added, some typos
correcte
Charmless Three-Body Baryonic B Decays
Motivated by recent data on B-> p pbar K decay, we study various charmless
three-body baryonic B decay modes, including Lambda pbar pi, Sigma0 pbar pi, p
pbar pi, p pbar Kbar0, in a factorization approach. These modes have rates of
order 10^{-6}. There are two mechanisms for the baryon pair production,
current-produced and transition. The behavior of decay spectra from these
baryon production mechanisms can be understood by using QCD counting rules.
Predictions on rates and decay spectra can be checked in the near future.Comment: 26 pages, 9 figures; version to appear in Phys. Rev.
Signatures of Electronic Nematic Phase at Isotropic-Nematic Phase Transition
The electronic nematic phase occurs when the point-group symmetry of the
lattice structure is broken, due to electron-electron interactions. We study a
model for the nematic phase on a square lattice with emphasis on the phase
transition between isotropic and nematic phases within mean field theory. We
find the transition to be first order, with dramatic changes in the Fermi
surface topology accompanying the transition. Furthermore, we study the
conductivity tensor and Hall constant as probes of the nematic phase and its
transition. The relevance of our findings to Hall resistivity experiments in
the high- cuprates is discussed.Comment: 5 pages, 3 figure
Phenomenological Analysis of B->PP Decays with QCD Factorization
In this paper, we study nonleptonic charmless B decays to two light
pseudoscalar mesons within the frame of QCD factorization, including the
contributions from the chirally enhanced power corrections and weak
annihilation. Predictions for the CP-averaged branching ratios and CP-violating
asymmetries are given. Within the reasonable range of the parameters, we find
that our predictions for the branching ratios of B -> PP are consistent with
the present experimental data. But because of the logarithmic divergences at
the endpoints in the hard spectator scatterings and weak annihilation, there
are still large uncertainties in these predictions.Comment: 34 pages, 5 figures. to appear in PR
Semi-inclusive B Decays and Direct CP Violation in QCD Factorization
We have systematically investigated the semi-inclusive B decays B->MX, which
are manifestations of the quark decay b->Mq, within the framework of
QCD-improved factorization. These decays are theoretically clean and have
distinctive experimental signatures. We focus on a class of these that do not
require any form factor information and therefore may be especially suitable
for extracting information on the angles and of the unitarity
triangle. The nonfactorizable effects, such as vertex-type and penguin-type
corrections to the two-body b decay and hard spectator corrections to the
3-body decay are calculable in the heavy quark limit. QCD factorization is
applicable when the emitted meson is a light meson or a charmonium. We discuss
the issue of the CPT constraint on partial rate asymmetries. The strong phase
coming from final-state rescattering due to hard gluon exchange between the
final states can induce large rate asymmetries for tree-dominated
color-suppressed modes . The nonfactorizable
hard spectator interactions in the 3-body decay, though phase-space suppressed,
are extremely important for the tree-dominated modes
, and the
penguin-dominated mode . In fact, they are dominated by the
hard spectator corrections. Our result for is in
agreement with experiment. The semi-inclusive decay modes: , ,
and are the most promising ones in searching for
direct CP violation. In fact, they have branching ratios of order
and CP rate asymmetries of order .Comment: 28 page
Studies of Prototype CsI(Tl) Crystal Scintillators for Low-Energy Neutrino Experiments
Crystal scintillators provide potential merits for the pursuit of low-energy
low-background experiments. A CsI(Tl) scintillating crystal detector is being
constructed to study low-energy neutrino physics at a nuclear reactor, while
projects are underway to adopt this technique for dark matter searches. The
choice of the geometrical parameters of the crystal modules, as well as the
optimization of the read-out scheme, are the results of an R&D program.
Crystals with 40 cm in length were developed. The detector requirements and the
achieved performance of the prototypes are presented. Future prospects for this
technique are discussed.Comment: 32 pages, 14 figure
A CsI(Tl) Scintillating Crystal Detector for the Studies of Low Energy Neutrino Interactions
Scintillating crystal detector may offer some potential advantages in the
low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed
near the core of Nuclear Power Station II in Taiwan is being constructed for
the studies of electron-neutrino scatterings and other keV-MeV range neutrino
interactions. The motivations of this detector approach, the physics to be
addressed, the basic experimental design, and the characteristic performance of
prototype modules are described. The expected background channels and their
experimental handles are discussed.Comment: 34 pages, 11 figures, submitted to Nucl. Instrum. Method
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