302 research outputs found
Precise QCD predictions on top quark pair production mediated by massive color octet vector boson at hadron colliders
We present a theoretical framework for systematically calculating
next-to-leading order (NLO) QCD effects to various experimental observables in
models with massive COVB in a model independent way at hadron colliders.
Specifically, we show the numerical results for the NLO QCD corrections to
total cross sections, invariant mass distribution and AFB of top quark pairs
production mediated by a massive COVB in both the fixed scale (top quark mass)
scheme and the dynamical scale (top pair invariant mass) scheme. Our results
show that the NLO QCD calculations in the dynamical scale scheme is more
reasonable than the fixed scheme and the naive estimate of the NLO effects by
simple rescaling of the LO results with the SM NLO K-factor is not appropriate.Comment: 6 pages, 5 figures, 2 tables; version published in EPJ
Next-to-leading order QCD corrections to a heavy resonance production and decay into top quark pair at the LHC
We present a complete next-to-leading order (NLO) QCD calculation to a heavy
resonance production and decay into a top quark pair at the LHC, where the
resonance could be either a Randall-Sundrum (RS) Kaluza-Klein (KK) graviton
or an extra gauge boson . The complete NLO QCD corrections can enhance the
total cross sections by about and for the and
the , respectively, depending on the resonance mass. We also explore in
detail the NLO corrections to the polar angle distributions of the top quark,
and our results show that the shapes of the NLO distributions can be different
from the leading order (LO) ones for the KK graviton. Moreover, we study the
NLO corrections to the spin correlations of the top quark pair production via
the above process, and find that the corrections are small.Comment: Published version in PR
Nonperturbative Effect in Threshold Resummation
We show that the conventional threshold resummation calculation cannot
describe well the low energy Drell-Yan (DY) data without including the
non-perturbative correction terms which are deduced from analyzing the
asymptotic behavior of the resummation formalism. It is demonstrated that the
non-perturbative correction is generally small for the large invariant mass DY
pairs produced at the Tevatron and the LHC.Comment: JHEP06(2009)03
One-loop Helicity Amplitudes for Top Quark Pair Production in Randall-Sundrum Model
In this paper, we show how to calculate analytically the one-loop helicity
amplitudes for the process induced by KK gluon,
using the spinor-helicity formalism. A minimal set of Feynman rules which are
uniquely fixed by gauge invariance and the color representation of the KK gluon
are derived and used in the calculation. Our results can be applied to a
variety of models containing a massive color octet vector boson.Comment: 37 pages, 10 figures, journal versio
Next-to-leading order QCD corrections to the top quark decay via the Flavor-Changing Neutral-Current operators with mixing effects
In this paper detailed calculations of the complete
corrections to top quark decay widths are presented
(). Besides describing in detail the calculations in our previous
paper (arXiv:0810.3889), we also include the mixing effects of the
Flavor-Changing Neutral-Current (FCNC) operators for and , which were not considered in our previous paper. The results for are the same as in our previous paper. But the mixing effects can either
be large or small, and increase or decrease the branching ratios for and , depending on the values of the anomalous couplings
(,
and ).Comment: 21 pages, 12 figure
Research status quo and prospection of mechanical characteristics of rock under high temperature and high pressure
AbstractThe mechanical features of rock have significant relevance to temperature. The problems related to temperature are becoming a hot geotechnical research field. The paper summarized the rheological characteristics, failure, instability modes at high temperature and high pressure, rules of elastic modulus and thermal expand coefficient changing with temperature, as well as the thermal-induced failure characteristics of rock affected by temperature and pressure, and finally prospects the research directions of high temperature rock mechanics
Signatures of the light gluino in the top quark production
If a light gluino, with a mass of the order of GeV, exists in the minimal
supersymmetric extension of the Standard Model, then it can contribute to the
production rate of the top quark pairs at hadron colliders via the process
gluino + gluino --> t + tbar. Because the top quark is heavy, the masses of the
superpartners of the left-handed and right-handed top quarks can be very
different such that a parity-violating observable can be induced at the tree
level. We discuss the phenomenology of this parity violating asymmetry at the
CERN Large Hadron Collider.Comment: 23 pages, 5 Postscript figure
Improved resummation prediction on Higgs boson production at hadron colliders
We improve the resummation calculations in the ResBos program for the Higgs
boson production via gluon-gluon fusion by including the NNLO Wilson
coefficient functions and G-functions. The improvement leads to increasing the
total cross section predictions of the new ResBos program, dubbed as ResBos2,
for Higgs boson production by about 8% and 6% at the Tevatron and the LHC,
respectively, as compared to the old ResBos program. Furthermore, the improved
predictions are compared with those from the programs HNNLO and HqT2. We find
that they agree well for the total cross sections but differ slightly for the
transverse momentum distributions. With ResBos2, we present the
distributions of the two variables and , which can have better
experimental resolutions than , for the process of Higgs boson decaying
into a photon pair. Theoretical uncertainties of the ResBos2 predictions are
also discussed.Comment: 15 pages, 8 figures, 2 table
Next-to-leading QCD effect to the quark compositeness search at the LHC
Recently, the CMS and ATLAS Collaborations at the CERN Large Hadron Collider
(LHC) have set exclusion limits on the quark compositeness scale by comparing
their data to the leading order and the scaled next-to-leading order (NLO) QCD
calculations, respectively. In this Letter, we present the exact NLO QCD
corrections to the dijet production induced by the quark contact interactions.
We show that as compared to the exact calculation, the scaled NLO QCD
prediction adopted by the ATLAS Collaboration has overestimated the new physics
effect on some direct observables by more than 30% and renders a higher limit
on the quark compositeness scale. The destructive contribution from the exact
NLO correction will also lower the compositeness scale limit set by the CMS
Collaboration.Comment: Published version in Phys.Rev.Let
Next-to-leading order QCD corrections to the top quark decay via model-independent FCNC couplings
D0 and CDF collaborations at the Fermilab Tevatron have searched for
non-standard-model single top-quark production and set upper limits on the
anomalous top quark flavor-changing neutral current (FCNC) couplings
and using the measurement of
total cross section calculated at the next-to-leading order (NLO) in QCD. In
this Letter, we report on the effect of anomalous FCNC couplings to various
decay branching ratios of the top quark, calculated at the NLO. This result is
not only mandatory for a consistent treatment of both the top quark production
and decay via FCNC couplings by D0 and CDF at the Tevatron but is also
important for the study of ATLAS and CMS sensitivity to these anomalous
couplings at the CERN LHC. We find that the NLO corrections to the partial
decay widths of the three decay channels , and
are at the order of 10% in magnitude and modify their branching
ratios by about 20%, 0.4% and 2%, respectively, as compared to their leading
order predictions.Comment: 4 pages, 3 figures, minor changes, typos correcte
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