18,310 research outputs found
Cs adsorption on Si(001) surface: ab initio study
First-principles calculations using density functional theory based on
norm-conserving pseudopotentials have been performed to investigate the Cs
adsorption on the Si(001) surface for 0.5 and 1 ML coverages. We found that the
saturation coverage corresponds to 1 ML adsorption with two Cs atoms occupying
the double layer model sites. While the 0.5 ML covered surface is of metallic
nature, we found that 1 ML of Cs adsorption corresponds to saturation coverage
and leads to a semiconducting surface. The results for the electronic behavior
and surface work function suggest that adsorption of Cs takes place via
polarized covalent bonding.Comment: 8 pages, 7 figure
Phylogeny-structured carbohydrate metabolism across microbiomes collected from different units in wastewater treatment process
With respect to global priority for bioenergy production from plant biomass, understanding the fundamental genetic associations underlying carbohydrate metabolisms is crucial for the development of effective biorefinery process. Compared with gut microbiome of ruminal animals and wood-feed insects, knowledge on carbohydrate metabolisms of engineered biosystems is limited.published_or_final_versio
Radiative decays of charmonium into light mesons
We apply perturbative QCD to the radiative decays of charmonia and into light mesons. We perform a complete numerical calculation for the quark-gluon loop diagrams involved in these processes. The calculated decay branching ratios to P-wave mesons and fit the data well, while that of (if treated as an meson) is predicted to be , which implies that can not be the or meson. Decays of P-wave charmonia (J=0,1,2) are also studied, and the branching ratio of is predicted to be , which may be tested by CLEO-c and BESIII with future experiments
Next-to-Leading Order QCD Correction to at GeV}
One of the most challenging open problems in heavy quarkonium physics is the
double charm production in annihilation at B factories. The measured
cross section of is much larger than leading
order (LO) theoretical predictions. With the nonrelativistic QCD factorization
formalism, we calculate the next-to-leading order (NLO) QCD correction to this
process. Taking all one-loop self-energy, triangle, box, and pentagon diagrams
into account, and factoring the Coulomb-singular term into the bound
state wave function, we get an ultraviolet and infrared finite correction to
the cross section of at GeV. We
find that the NLO QCD correction can substantially enhance the cross section
with a K factor (the ratio of NLO to LO) of about 1.8-2.1; hence it greatly
reduces the large discrepancy between theory and experiment. With and , the NLO cross section is estimated to be 18.9 fb, which
reaches to the lower bound of experiment.Comment: Version appeared in PRL, Figure 3 added showing the renormalization
scale dependence of the cross section, new BaBar data adde
Higher Charmonia and X,Y,Z states with Screened Potential
We incorporate the color-screening effect due to light quark pair creation
into the heavy quark-antiquark potential, and investigate the effects of
screened potential on the spectrum of higher charmonium. We calculate the
masses, electromagnetic decays, and E1 transitions of charmonium states in the
screened potential model, and propose possible assignments for the newly
discovered charmonium or charmonium-like states. We find the masses
of higher charmonia with screened potential are considerably lower than those
with unscreened potential. The mass agrees well with that of
the Z(3930), and the mass of is compatible with rather
than . In particular, the discovered four states in the ISR
process, i.e., may be assigned as the
states respectively. The X(3940) and
X(4160) found in the double charmonium production in annihilation may
be assigned as the and states. Based on the
calculated E1 transition widths for and
and other results, we argue that the X(3872)
may be a dominated charmonium state with some admixture of the
component. Possible problems encountered in these assignments
and comparisons with other interpretations for these states are
discussed in detail. We emphasize that more theoretical and experimental
investigations are urgently needed to clarify these assignments and other
interpretations.Comment: Total width of X(3872) reestimated, references added; 12 pages, 1
figure; published version in PR
Pseuduscalar Heavy Quarkonium Decays With Both Relativistic and QCD Radiative Corrections
We estimate the decay rates of ,
, and ,
, by taking into account both relativistic and
QCD radiative corrections. The decay amplitudes are derived in the
Bethe-Salpeter formalism. The Bethe-Salpeter equation with a QCD-inspired
interquark potential are used to calculate the wave functions and decay widths
for these states. We find that the relativistic correction to the
ratio is negative and tends to compensate the positive contribution from
the QCD radiative correction. Our estimate gives and ,
which are smaller than their nonrelativistic values. The hadronic widths
and are then indicated accordingly to the first order
QCD radiative correction, if . The decay widths for
states are also estimated. We show that when making the assmption
that the quarks are on their mass shells our expressions for the decay widths
will become identical with that in the NRQCD theory to the next to leading
order of and .Comment: 14 pages LaTex (2 figures included
On the theoretical and experimental uncertainties in the extraction of the J/psi absorption cross section in cold nuclear matter
We investigate the cold nuclear matter effects on production, whose
understanding is fundamental to study the quark-gluon plasma. Two of these
effects are of particular relevance: the shadowing of the parton distributions
and the nuclear absorption of the pair. If 's are not
produced {\it via} a process as suggested by recent theoretical
works, one has to modify accordingly the way to compute the nuclear shadowing.
This naturally induces differences in the absorption cross-section fit to the
data. A careful analysis of these differences however requires taking into
account the experimental uncertainties and their correlations, as done in this
work for Au collisions at \sqrtsNN=200\mathrm{GeV}, using several
shadowing parametrisations.Comment: 6 pages, 1 table, 3 figures, Submitted to J. Phys. G, talk given at
the International Conference on Strangeness in Quark Matter (SQM2009),
Buzios, Brasil, Sep. 27 - Oct. 2, 200
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