2,512 research outputs found
QCD corrections to polarization of J/\psi and \Upsilon at Fermilab Tevatron and CERN LHC
In this work, we present more detail of the calculation on the NLO QCD
corrections to polarization of direct J/psi production via color singlet at
Tevatron and LHC, as well as the results for Upsilon for the first time. Our
results show that the J/psi polarization status drastically changes from
transverse polarization dominant at LO into longitudinal polarization dominant
in the whole range of the transverse momentum of J/psi when the NLO
corrections are counted. For Upsilon production, the p_t distribution of the
polarization status behaves almost the same as that for J/psi except that the
NLO result is transverse polarization at small p_t range. Although the
theoretical evaluation predicts a larger longitudinal polarization than the
measured value at Tevatron, it may provide a solution towards the previous
large discrepancy for J/psi and Upsilon polarization between theoretical
predication and experimental measurement, and suggests that the next important
step is to calculate the NLO corrections to hadronproduction of color octet
state J/psi^(8) and Upsilon^(8). Our calculations are performed in two ways,
namely we do and do not analytically sum over the polarizations, and then check
them with each other.Comment: 12 pages, 12 figures, two columns, use revtex4; to appear in PR
An effective method of calculating the non-Markovianity for single channel open systems
We propose an effective method which can simplify the optimization of the
increase of the trace distance over all pairs of initial states in calculating
the non-Markovianity for single channel open systems. For the
amplitude damping channel, we can unify the results of Breuer . [Phys.
Rev. Lett. \bf 103\rm, 210401 (2009)] in the large-detuning case and the
results of Xu . [Phys. Rev. A \bf 81\rm, 044105 (2010)] in the
resonant case; furthermore, for the general off-resonant cases we can obtain a
very tight lower bound of .
As another application of our method, we also discuss for the
non-Markovian depolarizing channel.Comment: 7 pages, 3 figures,to be published in Phys. Rev.
Diameter estimates in K\"ahler geometry
Diameter estimates for K\"ahler metrics are established which require only an
entropy bound and no lower bound on the Ricci curvature. The proof builds on
recent PDE techniques for estimates for the Monge-Amp\`ere equation,
with a key improvement allowing degeneracies of the volume form of codimension
strictly greater than one. As a consequence, diameter bounds are obtained for
long-time solutions of the K\"ahler-Ricci flow and finite-time solutions when
the limiting class is big, as well as for special fibrations of Calabi-Yau
manifolds
Discovering New Gauge Bosons of Electroweak Symmetry Breaking at LHC-8
We study the physics potential of the 8TeV LHC (LHC-8) to discover, during
its 2012 run, a large class of extended gauge models or extra dimensional
models whose low energy behavior is well represented by an SU(2)^2 x U(1) gauge
structure. We analyze this class of models and find that with a combined
integrated luminosity of 40-60/fb at the LHC-8, the first new Kaluza-Klein mode
of the W gauge boson can be discovered up to a mass of about 370-400 GeV, when
produced in association with a Z boson.Comment: PRD final version (only minor refinements showing the consistency
with new LHC data), 11 pages, 5 Figs, 2 Table
General theory of decoy-state quantum cryptography with source errors
The existing theory of decoy-state quantum cryptography assumes the exact
control of each states from Alice's source. Such exact control is impossible in
practice. We develop the theory of decoy-state method so that it is
unconditionally secure even there are state errors of sources, if the range of
a few parameters in the states are known. This theory simplifies the practical
implementation of the decoy-state quantum key distribution because the
unconditional security can be achieved with a slightly shortened final key,
even though the small errors of pulses are not corrected.Comment: Our results can be used securely for any source of diagonal states,
including the Plug-&-Play protocol with whatever error pattern, if we know
the ranges of errors of a few parameter
Experimental Free-Space Distribution of Entangled Photon Pairs over a Noisy Ground Atmosphere of 13km
We report free-space distribution of entangled photon pairs over a noisy
ground atmosphere of 13km. It is shown that the desired entanglement can still
survive after the two entangled photons have passed through the noisy ground
atmosphere. This is confirmed by observing a space-like separated violation of
Bell inequality of . On this basis, we exploit the distributed
entangled photon source to demonstrate the BB84 quantum cryptography scheme.
The distribution distance of entangled photon pairs achieved in the experiment
is for the first time well beyond the effective thickness of the aerosphere,
hence presenting a significant step towards satellite-based global quantum
communication.Comment: 4 pages, 3 figure
Development of Ultra-High Sensivity Silicon Carbide Detectors
A variety of silicon carbide (SiC) detectors have been developed to study the sensitivity of SiC ultraviolet (UV) detectors, including Schottky photodiodes, p-i-n photodiodes, avalanche photodiodes (APDs), and single photon-counting APDs. Due to the very wide bandgap and thus extremely low leakage current, Sic photo-detectors showed excellent sensitivity. The specific detectivity, D*, of SiC photodiodes are orders of magnitude higher than that of their competitors, such as Si photodiodes, and comparable to the D* of photomultiplier tubes (PMTs). To pursue the ultimate detection sensitivity, SiC APDs and single photon-counting avalanche diodes (SPADs) have also been fabricated. By operating the SiC APDs at a linear mode gain over 10(exp 6), SPADs in UV have been demonstrated. SiC UV detectors have great potential for use in solar blind UV detection and biosensing. Moreover, SiC detectors have excellent radiation hardness and high temperature tolerance which makes them ideal for extreme environment applications such as in space or on the surface of the Moon or Mars
Evolutionary Consequences of Dusty Tori in Active Galactic Nuclei
Deep surveys of {\em Chandra} and {\em HST} (Hubble Space Telescope) show
that active galactic nucleus (AGN) populations are changing with hard X-ray
luminosities. This arises an interesting question whether the dusty torus is
evolving with the central engines. We assemble a sample of 50 radio-quiet PG
quasars to tackle this problem. The covering factors of the dusty tori can be
estimated from the multiwavelength continuum. We find they are strongly
correlated with the hard X-ray luminosity. Interestingly this correlation
agrees with the fraction of type II AGNs discovered by {\em Chandra} and {\em
HST}, implying strong evidence for that the AGN population changing results
from the evolution of the tori. We also find that the frequencies of the dips
around 1m in the continuum correlate with the covering factors in the
present sample, indicating the dip frequencies are adjusted by the covering
factors. In the scenario of fueling black hole from the torus, the covering
factor is a good and the dip frequency is a potential indicator of the torus
evolution.Comment: 4 pages in emulateapj5.sty. Accepted by ApJ Letter
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