956 research outputs found
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
Novel CP-violating Effects in B decays from Charged-Higgs in a Two-Higgs Doublet Model for the Top Quark
We explore charged-Higgs cp-violating effects in a specific type III
two-Higgs doublet model which is theoretically attractive as it accommodates
the large mass of the top quark in a natural fashion. Two new CP-violating
phases arise from the right-handed up quark sector. We consider CP violation in
both neutral and charged B decays. Some of the important findings are as
follows. 1) Large direct-CP asymmetry is found to be possible for B+- to psi/J
K+-. 2) Sizable D-anti-D mixing effect at the percent level is found to be
admissible despite the stringent constraints from the data on K-anti-K mixing,
b to s gamma and B to tau nu decays. 3) A simple but distinctive CP asymmetry
pattern emerges in decays of B_d and B_s mesons, including B_d to psi/J K_S, D+
D-, and B_s to D_s+ D_s-, psi eta/eta^prime, psi/J K_S. 4) The effect of
D-anti-D mixing on the CP asymmetry in B+- to D/anti-D K+- and on the
extraction of the angle gamma of the unitarity triangle from such decays can be
significant.Comment: 32 pages, 5 figures, section V.A revised, version to appear in PR
New lanostanes and naphthoquinones isolated from Antrodia salmonea and their antioxidative burst activity in human leukocytes
Four new compounds were isolated from the basidiomata of the fungus Antrodia salmonea, a newly identified species of Antrodia (Aphyllophorales) in Taiwan. These new compounds are named as lanosta-8,24-diene-3 beta,15 alpha,21-triol (1), 24-methylenelanost-8-ene-3 beta,15 alpha,21-triol (2), 2,3-dimethoxy-5-(2',5'-dimethoxy-3',4'-methylenedioxyphenyl)-7-methyl-[1,4]-naphthoquinone (3), and 2,3-dimethoxy-6-(2,5'-dimethoxy-3',4'-methylenedioxyphenyl)-7-methyl-[1,4]-naphthoquinone (4), respectively. Their structures were elucidated by spectroscopic methods. An in vitro cellular functional assay was performed to evaluate their anti-oxidative burst activity in human leukocytes. They showed inhibitory effects against phorbol 12-myristate-13-acetate (PMA), a direct protein kinase C activator, induced oxidative burst in neutrophils (PMN) and mononuclear cells (MNC) with 50% inhibitory concentration (IC50) ranging from 3.5 to 25.8 mu M. The potency order of these compounds in PMA-activated leukocytes was as 1 > 3 > 4 > 2. They were relatively less effective in formyl-Met-Leu-Phe (fMLP), a G-protein coupled receptor agonist, induced oxidative burst, except for compounds 3 and 4 in fMLP-activated PMN. These results indicated that three (1, 3, and 4) of these four newly identified compounds displayed antioxidative effect in human leukocytes with different potency and might confer anti-inflammatory activity to these drugs
Anomalous c-axis charge dynamics in copper oxide materials
Within the t-J model, the c-axis charge dynamics of the copper oxide
materials in the underdoped and optimally doped regimes is studied by
considering the incoherent interlayer hopping. It is shown that the c-axis
charge dynamics is mainly governed by the scattering from the in-plane
fluctuation. In the optimally doped regime, the c-axis resistivity is a linear
in temperatures, and shows the metallic-like behavior for all temperatures,
while the c-axis resistivity in the underdoped regime is characterized by a
crossover from the high temperature metallic-like behavior to the low
temperature semiconducting-like behavior, which are consistent with experiments
and numerical simulations.Comment: 6 pages, Latex, Three figures are adde
A first-principles approach to electrical transport in atomic-scale nanostructures
We present a first-principles numerical implementation of Landauer formalism
for electrical transport in nanostructures characterized down to the atomic
level. The novelty and interest of our method lies essentially on two facts.
First of all, it makes use of the versatile Gaussian98 code, which is widely
used within the quantum chemistry community. Secondly, it incorporates the
semi-infinite electrodes in a very generic and efficient way by means of Bethe
lattices. We name this method the Gaussian Embedded Cluster Method (GECM). In
order to make contact with other proposed implementations, we illustrate our
technique by calculating the conductance in some well-studied systems such as
metallic (Al and Au) nanocontacts and C-atom chains connected to metallic (Al
and Au) electrodes. In the case of Al nanocontacts the conductance turns out to
be quite dependent on the detailed atomic arrangement. On the contrary, the
conductance in Au nanocontacts presents quite universal features. In the case
of C chains, where the self-consistency guarantees the local charge transfer
and the correct alignment of the molecular and electrode levels, we find that
the conductance oscillates with the number of atoms in the chain regardless of
the type of electrode. However, for short chains and Al electrodes the even-odd
periodicity is reversed at equilibrium bond distances.Comment: 14 pages, two-column format, submitted to PR
Evidence of the Purely Leptonic Decay B- --> tau- nu_tau-bar
We present the first evidence of the decay B- --> tau- nu_tau-bar using 414
fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at
the KEKB asymmetric-energy e+e- collider. Events are tagged by fully
reconstructing one of the B mesons in hadronic modes. We detect the signal with
a significance of 3.5 standard deviations including systematics, and measure
the branching fraction to be Br(B- --> tau- nu_tau-bar) = (1.79
+0.56-0.49(stat) +0.46-0.51(syst))*10^-4. This implies that f_B = 0.229
+0.036-0.031(stat) +0.034-0.037(syst) GeV and is the first direct measurement
of this quantity.Comment: 6 pages, 3 figures, to appear in Physical Review Letter
Search for \bar{B}^0\to\Lambda_c^+\bar{\Lambda}_c^- decay at Belle
We search for the doubly charmed baryonic decay
, in a data sample of
events accumulated at the resonance with the Belle
detector at the KEKB asymmetric e^+e^- collider. We find no significant signal
and set an upper limit of at 90%
confidence level. The result is significantly below a naive extrapolation from
assuming a simple Cabibbo-suppression
factor of . The small branching fraction could be attributed
to a suppression due to the large momentum of the baryonic decay products,
which has been observed in other charmed baryonic two-body B decays. trend
observed in other charmed baryonic two-body B decays.Comment: 12 page, 5 figures. Contribution paper for conferences EPS2007 and
Lepton Photon 2007, Belle-Conference-070
Observation of B+ -> K+ eta gamma
We report measurements of radiative B decays with K eta gamma final states,
using a data sample of 253 /fb recorded at the Upsilon(4S) resonance with the
Belle detector at the KEKB e+e- storage ring. We observe B+ -> K+ eta gamma for
the first time with a branching fraction of (8.4 +- 1.5(stat) +1.2 -0.9(syst))
X 10^{-6} for M(Keta) K0 eta gamma.
We also search for B -> K3*(1780) gamma.Comment: 12 pages, 5 figures, accepted by Phys. Lett.
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
Search for B -> h(*) nu nubar Decays at Belle
We present a search for the rare decays B -> h(*) nu nubar, where h(*) stands
for a light meson. A data sample of 535 million BBbar pairs collected with the
Belle detector at the KEKB e+e- collider is used. Signal candidates are
required to have an accompanying B meson fully reconstructed in a hadronic mode
and signal-side particles consistent with a single h(*) meson. No significant
signal is observed and we set upper limits on the branching fractions at 90%
confidence level. The limits on B0 -> K*0 nu nubar and B+ -> K+ nu nubar decays
are more stringent than the previous constraints, while the first searches for
B0 -> K0 nu nubar, pi0 nu nubar, rho0 nu nubar, phi nu nubar and B+ -> K*+ nu
nubar, rho+ nu nubar are reported.Comment: 6 pages, 2 figures, submit to PR
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