90 research outputs found
Bound-state effects on gluino-pair production at hadron colliders
We study bound-state effects on the pair production of gluinos at hadron colliders, in a context of the minimal supersymmetric extension of the standard model. Due to the expected large mass and the octet color-charge of gluinos, the bound-state effects can be substantial at the LHC. We find significant deformation of the invariant-mass distributions of a gluino-pair near the mass threshold, as well as an additional correction to the total cross-section. Both the invariant-mass distribution and the correction to the total cross section depend crucially on the decay width of the gluino
T-odd Asymmetry in W+jet Events at the LHC
W bosons produced at high transverse momentum in hadron collisions can have
polarization along the direction perpendicular to the production plane, which
is odd under na\ddot{\i}ve-T-reversal where both the three-momenta and
angular momenta are reversed. Perturbative QCD predicts non-zero polarization
at the one-loop level, which can be measured as parity-odd components in the
angular distribution of charged leptons from the decay of W bosons. We perform
a detector-level simulation with the generator MadGraph5_aMC@NLO, and
demonstrate that the asymmetry can be observed at the 8 TeV LHC with 20
fb of data. If confirmed, it will be the first experimental measurement
of the sign of the imaginary part of one-loop QCD amplitudes.Comment: 5 pages, 2 figure
Non-Gaussian Distribution of Electron Beams due to Incoherent
A theory is presented on the equilibrium particle distribution in electron rings, when each electron is being affected by, in addition to the synchrotron radiation effects, incoherent stochastic processes, such as a collision with atoms in the residual gas
Parity-Odd Asymmetries in W-Jet Events at the Tevatron
Parity-odd asymmetries in the decay angular distribution of a W boson
produced with a hard jet in p\bar{p} collisions arise only from QCD
rescattering effects. If observed, these asymmetries will provide a first
demonstration that perturbative QCD calculation is valid for the absorptive
part of scattering amplitudes. We propose a simple observable to measure these
asymmetries and perform realistic Monte Carlo simulations at Tevatron energies.
It is shown that the Tevatron Run-II should provide sufficient statistics to
test the prediction.Comment: 4pages, 2figures, revtex, references and discussions added, version
to appear in PRL, typo correcte
The Decay of Tau Leptons Produced in Neutrino-Nucleon Scatterings
Energy and angular distributions of the tau decay products in the
CERN-to-Gran Sasso appearance experiments are studied for the decay
modes and (l=e or mu). We find that the
decay particle distributions in the laboratory frame are significantly affected
by the tau polarization. Rather strong azimuthal asymmetry of and
about the tau momentum axis is predicted, which may have observable
consequences even at small statistics experiments.Comment: 14 pages, 6 eps figures; comments on Fig. 1 added, Fig. 4 improved to
see clearl
Bound-state Effects on Top Quark Production at Hadron Colliders
We study bound-state effects on the t\bar{t} production cross section in the
threshold region at hadron colliders. The bound-state effects are important
particularly at the LHC where the gluon fusion is the dominant subprocess. Due
to the formation of t\bar{t} resonances in the J=0 color-singlet channel of gg
\to t\bar{t} and the large width of the top quark, the t\bar{t} invariant-mass
distribution peaks at a few GeV below the t\bar{t} threshold, and it is
significantly enhanced over the naive NLO prediction until several GeV above
the threshold. We present predictions of the t\bar{t} invariant-mass
distribution which incorporate both the bound-state effects and initial-state
radiations up to NLO. The bound-state effects would lead to a substantial
deformation of top-quark kinematical distributions in the threshold region.Comment: 14 page, 6 figures; hard-vertex factors modified; cross sections
changed accordingly; all qualitative features unchanged, nevertheless;
discussion and references added; version to appear in PL
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