940 research outputs found
Next-to-leading order QCD predictions for associated production of top squarks and charginos at the CERN LHC
We present the calculations of the complete next-to-leading order (NLO)
inclusive total cross sections for the associated production processes in the Minimal Supersymmetric Standard Model at
the CERN Large Hadron Collider. Our calculations show that the total cross
sections for the production for the lighter top
squark masses in the region 100 GeV 160 GeV can reach 1 pb
in the favorable parameter space allowed by the current precise experiments,
and in other cases the total cross sections generally vary from 10 fb to
several hundred fb except both 500 GeV and the
production channel. Moreover, we find that the
NLO QCD corrections in general enhance the leading order total cross sections
significantly, and vastly reduce the dependence of the total cross sections on
the renormalization/factorization scale, which leads to increased confidence in
predictions based on these results.Comment: 42 pages, 13 figures, RevTex4. Journal-ref adde
Spin Correlations in top quark pair production near threshold at the Linear Collider
We investigate the spin correlations in top quark pair production near
threshold at the linear collider. Comparing with the results above
the threshold region, we find that near the threshold region the off-diagonal
basis, the optimized decomposition of the top quark spins above the threshold
region, does not exist, and the beamline basis is the optimal basis, in which
there are the dominant spin components: the up-down (UD) component for scattering and the down-up (DU) component for scattering can
make up more than 50% of the total cross section, respectively.Comment: 12 pages, 3 figures, minor modification
via SUSY FCNC couplings in the unconstrained MSSM
We recalculate the branching ratios for () induced by
SUSY FCNC couplings within the general unconstrained MSSM framework using mass
eigenstate approach. Our results show that the branching ratios for these
decays are larger than ones reported in previous literatures in the MSSM with
R-parity conservation, and they can reach , , and
, respectively, for favorable parameter values allowed by current
precise experiments. Thus, the branching ratios for and may be measurable at the LHC.Comment: 15 pages, 3 figures, minor changs in the Table
Next-to-leading order QCD predictions for pair production of neutral Higgs bosons at the CERN Large Hadron Collider
We present the calculations of the complete NLO inclusive total cross
sections for pair production of neutral Higgs bosons through
annihilation in the minimal supersymmetric standard model at the CERN Large
Hadron Collider. In our calculations, we used both the DREG scheme and the DRED
scheme and found that the NLO total cross sections in the above two schemes are
the same. Our results show that the -annihilation contributions can
exceed ones of fusion and annihilation for ,
and productions when is large. In the case of , the
NLO corrections enhance the LO total cross sections significantly, which can
reach a few tens percent, while for , the corrections are relatively
small, and are negative in most parameter space. Moreover, the NLO QCD
corrections can reduce the dependence of the total cross sections on the
renormalization/factorization scale, especially for . We also use the
CTEQ6.1 PDF sets to estimate the uncertainty of LO and NLO total cross
sections, and find that the uncertainty arising from the choice of PDFs
increases with the increasing .Comment: 43 pages, 16 figures, minor changes, some references added, a version
to appear in PR
Next-to-Leading Order QCD Corrections to the Direct Top Quark Production via Model-independent FCNC Couplings at Hadron Colliders
We calculated the next-to-leading order (NLO) QCD corrections to the cross
sections for direct top quark productions induced by model--independent flavour
changing neutral current couplings at hadron colliders. The NLO results
increase the experimental sensitivity to the anomalous couplings. Our results
show that the NLO QCD corrections enhance the leading order (LO) total cross
sections at the Tevatron Run 2 about 60% for both of and
couplings, and enhance the LO total cross sections at the LHC
about 40% for couplings and 50% for couplings,
respectively. Moreover, the NLO QCD corrections vastly reduce the dependence of
the total cross sections on the renormalization or factorization scale, which
leads to increased confidence in predictions based on these results.Comment: 15 pages, 4 figures; published versio
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Eocene–early Oligocene climate and vegetation change in southern China: Evidence from the Maoming Basin
Although the Eocene-Oligocene climate transition marks a critical point in the development of the ‘icehouse’ global climate of the present little is known about this important change in the terrestrial realm at low latitudes. Our palynological study of the Shangcun Formation shows it to be early Oligocene in age: palyno-assemblages in the lower part of the formation indicate a cool interval dominated by conifer pollen in the earliest Oligocene followed by a warmer regime in the second half of the early Oligocene. To quantify middle Eocene to late early Oligocene climate conditions at low (~ 20°N) palaeolatitudes in southern Asia several thousand leaf fossil specimens from the Maoming Basin, southern China, were subjected to a multivariate (CLAMP) analysis of leaf form. For terrestrial palaeoclimate comparisons to be valid the palaeoaltitude at which the proxy data are obtained must be known. We find that leaves preserved in the Youganwo (middle Eocene), Huangniuling (late Eocene) and Shangcun (early Oligocene) formations were likely to have been deposited well above sea level at different palaeoelevations. In the Youganwo Formation fine-grained sediments were deposited at an altitude of ~ 1.5 km, after which the basin dropped to ~ 0.5 km by the time the upper Huangniuling sediments were deposited. The basin floor then rose again by 0.5 km reaching an altitude of approximately 1 km in which the Shangcun Formation fine-grained sediments were accumulated. Within the context of these elevation changes the prevailing climates experienced by the Youganwo, Lower Huangniuling, Upper Huangniuling and Shangcun fossil floras were humid subtropical with hot summers and warm winters, but witnessed a progressive increase in rainfall seasonality. By the early Oligocene rainfall seasonality was similar to that of the modern monsoonal climate of Guangdong Province, southern China. All floras show leaf physiognomic spectra most similar to those growing under the influence of the modern Indonesia-Australia Monsoon, but with no evidence of any adaptation to today's South or East Asia Monsoon regimes. The Upper Huangniuling Flora, rich in dipterocarp plant megafossils, grew in the warmest conditions with the highest cold month mean temperature and at the lowest altitude
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