1,683 research outputs found
Diphoton excess at 750 GeV: gluon-gluon fusion or quark-antiquark annihilation?
Recently, ATLAS and CMS collaboration reported an excess in the diphoton
events, which can be explained by a new resonance with mass around 750 GeV. In
this work, we explored the possibility of identifying if the hypothetical new
resonance is produced through gluon-gluon fusion or quark-antiquark
annihilation, or tagging the beam. Three different observables for beam
tagging, namely the rapidity and transverse momentum distribution of the
diphoton, and one tagged bottom-jet cross section, are proposed. Combining the
information gained from these observables, a clear distinction of the
production mechanism for the diphoton resonance is promising.Comment: 20 pages, 7 figure
Top-Quark Decay at Next-to-Next-to-Leading Order in QCD
We present the complete calculation of the top-quark decay width at
next-to-next-to-leading order in QCD, including next-to-leading electroweak
corrections as well as finite bottom quark mass and boson width effects. In
particular, we also show the first results of the fully differential decay
rates for top-quark semileptonic decay at
next-to-next-to-leading order in QCD. Our method is based on the understanding
of the invariant mass distribution of the final-state jet in the singular limit
from effective field theory. Our result can be used to study arbitrary
infrared-safe observables of top-quark decay with the highest perturbative
accuracy.Comment: 5 pages, 6 figures; version accepted for publication in Physical
Review Letter
Next-to-leading order QCD corrections to associated production via the flavor-changing neutral-current couplings at hadron colliders
We present the complete next-to-leading order (NLO) QCD corrections to
associated production induced by the model-independent and
flavor-changing neutral-current couplings at hadron colliders, respectively.
Our results show that, for the coupling the NLO QCD corrections can
enhance the total cross sections by about 60% and 42%, and for the
coupling by about 51% and 43% at the Tevatron and LHC, respectively. The NLO
corrections, for the couplings, can enhance the total cross sections by
about 27%, and by about 42% for the coupling at the LHC. We also consider
the mixing effects between the and couplings for this process,
which can either be large or small depending on the values of the anomalous
couplings. Besides, the NLO corrections reduce the dependence of the total
cross sections on the renormalization or factorization scale significantly,
which lead to increased confidence on the theoretical predictions. And we also
evaluate the NLO corrections to several important kinematic distributions.Comment: Published version in Phys. Rev.
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
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Precision QCD Event Shapes at Hadron Colliders: The Transverse Energy-Energy Correlator in the Back-to-Back Limit.
We present an operator-based factorization formula for the transverse energy-energy correlator (TEEC) hadron collider event shape in the back-to-back (dijet) limit. This factorization formula exhibits a remarkably symmetric form, being a projection onto a scattering plane of a more standard transverse momentum dependent factorization. Soft radiation is incorporated through a dijet soft function, which can be elegantly obtained to next-to-next-to-leading order (NNLO) due to the symmetries of the problem. We present numerical results for the TEEC resummed to next-to-next-to-leading logarithm (NNLL) matched to fixed order at the LHC. Our results constitute the first NNLL resummation for a dijet event shape observable at a hadron collider, and the first analytic result for a hadron collider dijet soft function at NNLO. We anticipate that the theoretical simplicity of the TEEC observable will make it indispensable for precision studies of QCD at the LHC, and as a playground for theoretical studies of factorization and its violation
Next-to-leading order QCD corrections to the single top quark production via model-independent t-q-g flavor-changing neutral-current couplings at hadron colliders
We present the calculations of the complete next-to-leading order (NLO) QCD
effects on the single top productions induced by model-independent
flavor-changing neutral-current couplings at hadron colliders. Our results show
that, for the coupling the NLO QCD corrections can enhance the total
cross sections by about 60% and 30%, and for the coupling by about 50%
and 20% at the Tevatron and LHC, respectively, which means that the NLO
corrections can increase the experimental sensitivity to the FCNC couplings by
about 10%30%. Moreover, the NLO corrections reduce the dependence of the
total cross sections on the renormalization or factorization scale
significantly, which lead to increased confidence on the theoretical
predictions. Besides, we also evaluate the NLO corrections to several important
kinematic distributions, and find that for most of them the NLO corrections are
almost the same and do not change the shape of the distributions.Comment: minor changes, version published in PR
NNLO QCD Corrections to t-channel Single Top-Quark Production and Decay
We present a fully differential next-to-next-to-leading order calculation of
t-channel single top-quark production and decay at the LHC under narrow-width
approximation and neglecting cross-talk between incoming protons. We focus on
the fiducial cross sections at 13 TeV, finding that the next-to-next-to-leading
order QCD corrections can reach the level of -6%. The scale variations are
reduced to the level of a percent. Our results can be used to improve
experimental acceptance estimates and the measurements of the single top-quark
production cross section and the top-quark electroweak couplings.Comment: 6 pages, 4 figures, version appear on PRD rapid communicatio
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