13,398 research outputs found
versus suppression in proton-nucleus collisions from factorization violating soft color exchanges
We argue that the large suppression of the inclusive cross-section
relative to the inclusive cross-section in proton-nucleus (p+A)
collisions can be attributed to factorization breaking effects in the formation
of quarkonium. These factorization breaking effects arise from soft color
exchanges between charm-anticharm pairs undergoing hadronization and comoving
partons that are long-lived on time scales of quarkonium formation. We compute
the short distance pair production of heavy quarks in the Color Glass
Condensate (CGC) effective field theory and employ an improved Color
Evaporation model (ICEM) to describe their hadronization into quarkonium at
large distances. The combined CGC+ICEM model provides a quantitative
description of and data in proton-proton (p+p) collisions
from both RHIC and the LHC. Factorization breaking effects in hadronization,
due to additional parton comovers in the nucleus, are introduced heuristically
by imposing a cutoff , representing the momentum kick from soft color
exchanges, in the ICEM model. Such soft exchanges have no perceptible effect on
suppression in p+A collisions. In contrast, the interplay of the
physics of these soft exchanges at large distances, with the physics of
semi-hard rescattering at short distances, causes a significant additional
suppression of yields relative to that of the . A good fit
of all RHIC and LHC and data, for transverse momenta
GeV in p+p and p+A collisions, is obtained for
MeV.Comment: 16 pages, 12 figures. v2: version accepted for publication in PR
Enhanced critical current density of MgB2 superconductor synthesized in high magnetic fields
The effect of high magnetic fields on the current carrying properties of both
MgB2 bulks and Fe-sheathed tapes was investigated following different thermal
sequences. It is found that application of a large magnetic field during
processing results in the quite uniform microstructure and the better
connectivity between the MgB2 grains. As a result, the Jc of these samples has
shown much higher value than that of the MgB2 samples in the absence of
magnetic field. The possible mechanism of the Jc enhancement under an external
magnetic field is also discussed.Comment: Presented at ISS2005, Tsukuba, 24-26 Oct., 2005; Revised versio
Significantly enhanced critical current densities in MgB2 tapes made by a scaleable, nano-carbon addition route
Nanocarbon-doped Fe-sheathed MgB2 tapes with different doping levels were
prepared by the in situ powder-in-tube method. Compared to the undoped tapes,
Jc for all the C-doped samples was enhanced by more than an order of magnitude
in magnetic fields above 9 T. At 4.2 K, the transport Jc for the 5 at% doped
tapes reached 1.85x104 A/cm2 at 10 T and 2.8x103 A/cm2 at 14 T, respectively.
Moreover, the critical temperature for the doped tapes decreased slightly.
Transmission electron microscopy showed a number of intra-granular dislocations
and the dispersed nanoparticles embedded within MgB2 grains induced by the C
doping. The mechanism for the enhancement of flux pinning is also discussed.
These results indicate that powder-in-tube-processed MgB2 tape is very
promising for high-field applications.Comment: 13 pages, 5 figures. to be published soo
Rational-operator-based depth-from-defocus approach to scene reconstruction
This paper presents a rational-operator-based approach to depth from defocus (DfD) for the reconstruction of three-dimensional scenes from two-dimensional images, which enables fast DfD computation that is independent of scene textures. Two variants of the approach, one using the Gaussian rational operators (ROs) that are based on the Gaussian point spread function (PSF) and the second based on the generalized Gaussian PSF, are considered. A novel DfD correction method is also presented to further improve the performance of the approach. Experimental results are considered for real scenes and show that both approaches outperform existing RO-based methods
Improved critical current densities in MgB2 tapes with ZrB2 doping
MgB2/Fe tapes with 2.5-15 at.% ZrB2 additions were prepared through the in
situ powder-in-tube method. Compared to the pure tape, a significant
improvement in the in-field critical current density Jc was observed, most
notably for 10 at.% doping, while the critical temperature decreased slightly.
At 4.2 K, the transport Jc for the 10 at.% doped sample increased by more than
an order of magnitude than the undoped one in magnetic fields above 9 T.
Nanoscale segregates or defects caused by the ZrB2 additions which act as
effective flux pinning centers are proposed to be the main reason for the
improved Jc field performance.Comment: 14 pages, 6 figure
Power-dependent internal loss in Josephson bifurcation amplifiers
We have studied nonlinear superconducting resonators: lambda/2
coplanar-waveguide (CPW) resonators with Josephson junctions (JJs) placed in
the middle and lambda/4 CPW resonators terminated by JJs, which can be used for
the qubit readout as "bifurcation amplifiers." The nonlinearity of the
resonators arises from the Josephson junctions, and because of the
nonlinearity, the resonators with appropriate parameters are expected to show a
hysteretic response to the frequency sweep, or "bifurcation," when they are
driven with a sufficiently large power. We designed and fabricated resonators
whose resonant frequencies were around 10 GHz. We characterized the resonators
at low temperatures, T<0.05 K, and confirmed that they indeed exhibited
hysteresis. The sizes of the hysteresis, however, are sometimes considerably
smaller than the predictions based on the loaded quality factor in the weak
drive regime. When the discrepancy appears, it is mostly explained by taking
into account the internal loss, which often increases in our resonators with
increasing drive power in the relevant power range. As a possible origin of the
power-dependent loss, the quasiparticle channel of conductance of the JJs is
discussed.Comment: 8 pages, 9 figure
Breaking Tri-bimaximal Mixing and Large
The long baseline neutrino experiment, T2K, and the reactor experiment,
Double Chooz will soon present new data. If we expect to be
0.1-0.2, which is close to the present experimental upper bound, we should not
persist in the paradigm of the tri-bimaximal mixing. We discuss breaking the
tri-bimaximal mixing by adding a simple mass matrix, which could be derived
from some non-Abelian discrete symmetries. It is found that
is expected in our model independent analysis of the
generalized mass matrix for the normal or inverted hierarchical neutrino mass
spectrum. On the other hand, and are
expected to be not far from 1/2 and 1/3, respectively. As a typical example, we
also discuss the flavor model with the 1 and 1' flavons, which break the
tri-bimaximal mixing considerably. In this modified version of the Altarelli
and Feruglio model, is predicted to be around 0.15 in the
case of the normal hierarchical neutrino masses , and 0.2 in
the case of the inverted hierarchy . The form of the neutrino
mass matrix looks rather interesting --- it is suggestive of other discrete
symmetries as well.Comment: 10 pages, 12 figures, final versio
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