278 research outputs found
Top Quark Charge Asymmetry: Searching for Light Axigluons in top pair + jet Production at the LHC
We investigate the discovery potential of light color-octet bosons in the
mass range of 100 - 400 GeV in exclusive top-pair plus jet production at the
LHC. We study the impact of such bosons on the incline, the energy and the
rapidity asymmetries. We show that light axigluons with large couplings to
quarks can be discovered at the LHC with a luminosity of a few inverse fb.
Almost all of the considered axigluon parameter space can be probed using the
already available 2011/2012 LHC data. In a small-coupling scenario, axigluons
could be discovered using the charge asymmetry with 65 inverse fb at the LHC
and a center of mass energy of 14 TeV. We furthermore show that top pair+jet
production could reveal the existence of scenarios where axigluons couple with
a different strength to up- and down-type quarks.Comment: 25 pages, 11 figures, 1 tabl
Top-Quark Charge Asymmetry with a Jet Handle
Pairs of top and antitop quarks are produced at the LHC to a large extent in
association with a hard jet. We investigate the charge asymmetry in top pair +
jet production in quantum chromodynamics (QCD) and with additional massive
color-octet vector bosons. The total charge asymmetry at the LHC is suppressed
by the large charge-symmetric background from gluon-gluon fusion. We show to
what extent the asymmetry can be enhanced by suitable phase space cuts and, in
particular, elaborate on the kinematics of the hard jet in the top pair + jet
final state. We demonstrate that in QCD, the asymmetry amounts to -1.5% for
central jets without an excessive reduction of the cross section. By applying
additional kinematical cuts, the asymmetry can be enhanced to -4%, but at the
cost of a strong reduction of the cross section. Massive color-octet states can
generate sizeable effects in top pair + jet production, both on the charge
asymmetry and on the cross section. The charge asymmetry probes both vector and
axial-vector couplings to quarks. We show that massive color octets can
generate asymmetries up to +-10% for moderate and up to +-30% for strong
kinematical cuts to be used in experimental analyses at the LHC. Jet kinematics
can be used to obtain further information about the nature of the couplings and
thereby to discriminate between different models.Comment: 29 pages, 12 figure
Lepton-mass effects in the decays and
We consider lepton-mass effects in the cascade decays and . Since the scale of the problem
is set by the off-shellness of the respective gauge bosons in the
limits and not by
, lepton-mass effects are non-negligible for the modes in
particular close to the threshold of the off-shell decays. Lepton-mass effects
show up e.g.\ in the three-fold joint angular decay distribution for the
decays. Nonzero lepton masses lead to leptonic helicity-flip contributions
which in turn can generate novel angular dependencies in the respective
three-fold angular decay distributions. Lepton-mass effects are more pronounced
in the mode which, in part, is due
to the fact that the ratio of lepton helicity flip/nonflip contributions in the
decay is four times larger than in the decay
. We also briefly consider the corresponding
off-shell -- off-shell decays and .Comment: 45 pages, 9 figures and 6 tables, published versio
MSSM corrections to the top-antitop quark forward-backward asymmetry at the Tevatron
We study the effects of the complete supersymmetric QCD and electroweak
one-loop corrections to the ttbar forward-backward asymmetry at the Fermilab
Tevatron collider. We work in the complex Minimal Supersymmetric Standard Model
(MSSM), only restricted by the condition of minimal flavor violation (MFV). We
perform a comprehensive scan over the relevant parameter space of the complex
MFV-MSSM and determine the maximal possible contributions of these MSSM loop
corrections to the forward-backward asymmetry in the ttbar center-of-mass
frame.Comment: 25 pages, 9 figure
Higgs CP properties using the tau decay modes at the ILC
We investigate the prospects of determining the CP nature of the 126 GeV
neutral spin-0 (Higgs) boson h, discovered at the LHC, at a future linear
collider. We consider the production of h by the Higgsstrahlung process and its
subsequent decays to tau leptons. We investigate how precisely a possible
pseudoscalar component of h can be detected by the measurement of a suitably
defined angular distribution, if all major decay modes of the tau lepton are
used. From our numerical simulations, we estimate the expected precision to the
scalar-pseudoscalar mixing angle, including estimates of the background and of
measurement uncertainties, to be 2.8 degree for Higgs-boson production at a
center-of-mass energy of 250 GeV and for a collider with integrated luminosity
of 1 inverse attobarn.Comment: Journal versio
q_T Uncertainties for W and Z Production
Analysis of semi-inclusive DIS hadroproduction suggests broadening of
transverse momentum distributions at small x below 1E-3 ~ 1E-2 which can be
modeled in the Collins-Soper-Sterman formalism by a modification of impact
parameter dependent parton densities. We investigate these consequences for the
production of electroweak bosons at the Tevatron and the LHC. If substantial
small-x broadening is observed in forward Z boson production in the Tevatron
Run-2, it will strongly affect the predicted q_T distributions for W and Z
boson production at the LHC.Comment: 4 pages, 2 figures; contribution to the XIII International Workshop
on Deep Inelastic Scattering (DIS 2005
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