4,975 research outputs found
U-Spin Tests of the Standard Model and New Physics
Within the standard model, a relation involving branching ratios and direct
CP asymmetries holds for the B-decay pairs that are related by U-spin. The
violation of this relation indicates new physics (NP). In this paper, we assume
that the NP affects only the Delta S = 1 decays, and show that the NP operators
are generally the same as those appearing in B -> pi K decays. The fit to the
latest B -> pi K data shows that only one NP operator is sizeable. As a
consequence, the relation is expected to be violated for only one decay pair:
Bd -> K0 pi0 and Bs -> Kbar0 pi0.Comment: 12 pages, latex, no figures. References changed to follow MPL
guidelines; info added about U-spin breaking and small NP strong phases;
discussion added about final-state pi-K rescattering; analysis and
conclusions unaltere
A Study of Overall Tribological Problems in Developing R407c Rotary Compressor with Polyolester Oils
Practical long-distance quantum key distribution system using decoy levels
Quantum key distribution (QKD) has the potential for widespread real-world
applications. To date no secure long-distance experiment has demonstrated the
truly practical operation needed to move QKD from the laboratory to the real
world due largely to limitations in synchronization and poor detector
performance. Here we report results obtained using a fully automated, robust
QKD system based on the Bennett Brassard 1984 protocol (BB84) with low-noise
superconducting nanowire single-photon detectors (SNSPDs) and decoy levels.
Secret key is produced with unconditional security over a record 144.3 km of
optical fibre, an increase of more than a factor of five compared to the
previous record for unconditionally secure key generation in a practical QKD
system.Comment: 9 page
Microstructure-dependent DC set switching behaviors of Ge-Sb-Te-based phase-change random access memory devices accessed by in situ TEM
Phase-change random access memory (PCRAM) is one of the most promising nonvolatile memory devices. However, inability to secure consistent and reliable switching operations in nanometer-scale programing volumes limits its practical use for highdensity applications. Here, we report in situ transmission electron microscopy investigation of the DC set switching of Ge-Sb-Te (GST)-based vertical PCRAM cells. We demonstrate that the microstructure of GST, particularly the passive component surrounding the dome-shaped active switching volume, plays a critical role in determining the local temperature distribution and is therefore responsible for inconsistent cell-to-cell switching behaviors. As demonstrated by a PCRAM cell with a highly crystallized GST matrix, the excessive Joule heat can cause melting and evaporation of the switching volume, resulting in device failure. The failure occurred via two-step void formation due to accelerated phase separation in the molten GST by the polaritydependent atomic migration of constituent elements. The presented real-time observations contribute to the understanding of inconsistent switching and premature failure of GST-based PCRAM cells and can guide future design of reliable PCRAM.1176Ysciescopu
Experimental and theoretical investigation of phosphorus in-situ doping of germanium epitaxial layers
Cataloged from PDF version of article.We investigate phosphorus in-situ doping characteristics in germanium (Ge) during epitaxial growth by spreading resistance profiling analysis. In addition, we present an accurate model for the kinetics of the diffusion in the in-situ process, modeling combined growth and diffusion events. The activation energy and pre-exponential factor for phosphorus (P) diffusion are determined to be 1.91 eV and 3.75 x 10(-5) cm(2)/s. These results show that P in-situ doping diffusivity is low enough to form shallow junctions for high performance Ge devices. (C) 2013 Elsevier B.V. All rights reserve
CP Violation in the Top-Quark Pair Production at a Next Linear Collider
We provide a detailed, model-independent, study for CP violation effects due
to the T-odd top-quark electric dipole moment (EDM) and weak dipole moment
(WDM) in the top-quark pair production via and two-photon annihilation
at a next linear collider (NLC). There are two methods in detecting CP
violation effects in these processes. One method makes use of measurements of
various spin correlations in the final decay products of the produced top-quark
pair, while the other is to measure various CP-odd polarization asymmetry
effects of the initial states. In the case only the first method can
be used, and in the case both methods can be employed. We
provide a complete classification of angular correlations of the and
decay products under CP and CP\tilde{T} which greatly faciliate CP
tests in the mode. Concentrating on the second method with the Compton
back-scattered high-energetic laser light off the electron or positron beam in
the two-photon mode, we construct two CP-odd and CP\tilde{T}-even initial
polarization configurations and apply them to investigating CP-violating
effects due to the top-quark EDM. With a typical set of experimental parameters
at the NLC, we compare the 1-\sigma sensitivities to the top-quark EDM and WDM
in the mode and the two-photon mode. Some model expectation values of
the T-odd parameters are compared with the results.Comment: 45 pages(LaTeX), 10 eps figures, uses epsfig.st
Polarity control of carrier injection at ferroelectric/metal interfaces for electrically switchable diode and photovoltaic effects
We investigated a switchable ferroelectric diode effect and its physical
mechanism in Pt/BiFeO3/SrRuO3 thin-film capacitors. Our results of electrical
measurements support that, near the Pt/BiFeO3 interface of as-grown samples, a
defective layer (possibly, an oxygen-vacancy-rich layer) becomes formed and
disturbs carrier injection. We therefore used an electrical training process to
obtain ferroelectric control of the diode polarity where, by changing the
polarization direction using an external bias, we could switch the transport
characteristics between forward and reverse diodes. Our system is characterized
with a rectangular polarization hysteresis loop, with which we confirmed that
the diode polarity switching occurred at the ferroelectric coercive voltage.
Moreover, we observed a simultaneous switching of the diode polarity and the
associated photovoltaic response dependent on the ferroelectric domain
configurations. Our detailed study suggests that the polarization charge can
affect the Schottky barrier at the ferroelectric/metal interfaces, resulting in
a modulation of the interfacial carrier injection. The amount of
polarization-modulated carrier injection can affect the transition voltage
value at which a space-charge-limited bulk current-voltage (J-V) behavior is
changed from Ohmic (i.e., J ~ V) to nonlinear (i.e., J ~ V^n with n \geq 2).
This combination of bulk conduction and polarization-modulated carrier
injection explains the detailed physical mechanism underlying the switchable
diode effect in ferroelectric capacitors.Comment: Accepted for publication in Phys. Rev.
Bounds on New Physics from B -> V1 V2 Decays
We consider the possibility that physics beyond the standard model
contributes to the decays B -> V1 V2, where V1 and V2 are vector mesons. We
show that a time-dependent angular analysis of B -> V1 V2 decays provides many
tests for this new physics (NP). Furthermore, although one cannot solve for the
NP parameters, we show that this angular analysis allows one to put bounds on
these parameters. This can be useful in estimating the scale of NP, and can
tell us whether any NP found directly at future high-energy colliders can be
responsible for effects seen in B -> V1 V2 decays.Comment: 23 pages, plain LaTeX, 5 figures (included
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