520 research outputs found
Effects of Higgs sector CP violation in top-quark pair production at the LHC
A striking manifestation of CP violation in the electroweak symmetry breaking
sector would be the existence of neutral Higgs boson(s) with undefined CP
parity. We analyse signatures of such a boson, with a mass of about 300 GeV or
larger, produced in high energy proton-proton collisions at LHC energies in its
top-quark antitop-quark decay channel. The large irreducible
background is taken into account. We propose, both for the dilepton and the
lepton + jets decay channels of , several correlations and asymmetries
with which (Higgs sector) CP violation can be traced. We show that for
judiciously chosen cuts on the invariant mass these CP observables
yield, for an LHC integrated luminosity of 100 , statistically
significant signals for a range of Higgs boson masses and Yukawa couplings.Comment: 36 pages, 25 Postscript figure
Chiral-invariant CP-violating Effective Interactions in Z Decays to three Jets
Tests of CP violation by appropriate momentum correlations in jets
and in particular in probe CP-violating effective couplings --
that manifest themselves as form factors -- which conserve the quark chirality
and quark flavour. By giving two examples we show that such couplings can be
induced at one-loop order in extensions of the Standard Model with CP violation
beyond the Kobayashi-Maskawa phase. In one of the models we compute the
chirality-conserving part of the CP-violating -gluon amplitude for
massless quarks, determine the resulting effective dimension
couplings in the local limit, and discuss the possible size of the effects.
Finally we show that in models with excited quarks the chiral-invariant
CP-violating effective interactions could be quite large if appropriate
couplings are of a size characteristic of a strong interactionComment: 14 pages, LaTeX with 4 postscript figures, epsf macro include
Spin properties of top quark pairs produced at hadron colliders
We discuss the spin properties of top quark pairs produced at hadron
colliders at next-to-leading order in the coupling constant alpha_s of the
strong interaction. Specifically we present, for some decay channels, results
for differential angular distributions that are sensitive to t tbar spin
correlations.Comment: Invited talk given by A. Brandenburg at the Cracow epiphany
conference on heavy flavours, 3 - 6 January 2003, Cracow, Polan
QCD corrections to top quark spin correlations at hadron colliders
Future hadron collider experiments will allow for a detailed investigation of
spin correlation effects. In this talk, recent progress in the
theoretical description of these effects is reported. In particular,
next-to-leading order results for the spin correlations in
are presented, using various spin quantization axes.Comment: 5 pages, 5 figures. Talk presented at the conference `QCD 00',
Montpellier, 6-13th July 2000, to appear in the proceeding
Investigation of Top quark spin correlations at hadron collider
We report on our results about hadronic production at NLO QCD
including spin effects, especially on spin correlations.Comment: talk given at the 32nd International Conference on High Energy
Physics (ICHEP'04), Beijing, China, 16-22 Aug. 200
CP Violation Beyond the Standard Model and Tau Pair Production in Collisions
We show that the CP-violating dipole form factors of the tau lepton can be of
the order of in units of the length scale set by the inverse
boson mass. We propose a few observables which are sensitive to these form
factors at LEP2 and higher e^+e^- collision energies.Comment: 11 pages LaTeX + 2 figure
Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions and
We have computed the cross section for production by gluon-gluon
fusion at next-to-leading order (NLO) in the QCD coupling, keeping the full
dependence on the spins. Furthermore we have determined to the same
order the spin dependent cross sections for the processes . Together with our previous results for these results allow for predictions, at NLO QCD, of the
hadronic production of pairs in a general spin configuration. As an
application we have determined the degree of correlation of the and spins at NLO, using various spin quantisation axes.Comment: 10 pages, 8 figure
Top Production in Hadron-Hadron Collisions and Anomalous Top-Gluon Couplings
We discuss the influence of anomalous tbar-t-G couplings on total and
differential tbar-t production cross sections in hadron-hadron collisions. We
study in detail the effects of a chromoelectric and a chromomagnetic dipole
moment, d' and \mu', of the top quark. In the d'-\mu' plane, we find a whole
region where the anomalous couplings give a zero net contribution to the total
top production rate. In differential cross sections, the anomalous moments have
to be quite sizable to give measurable effects. We estimate the values of d'
and \mu' which are allowed by the present Tevatron experimental results on top
production. A chromoelectric dipole moment of the top violates CP invariance.
We discuss a simple CP-odd observable which allows for a direct search for CP
violation in top production.Comment: footnote pg. 4 changed, acknowledgments extende
CP Violation in radiative Z Decays
We propose to test the CP symmetry in the reactions Z -> mu+ mu- gamma and Z
-> tau+ tau- gamma. The experimental analysis of angular correlations allows to
determine a set of effective couplings: the electric and weak dipole moments of
the muon and the tau lepton, and in particular chirality conserving 4-particle
couplings, all of which can be induced by CP--violation in renormalizable
theories of electroweak interactions beyond the Standard Model. We update an
indirect bound on the weak dipole moment of the muon.Comment: 19 pages, Latex, 4 Figures in PostScript forma
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