45 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
How strange is pion electroproduction?
We consider pion production in parity-violating electron scattering (PVES) in
the presence of nucleon strangeness in the framework of partial wave analysis
with unitarity. Using the experimental bounds on the strange form factors
obtained in elastic PVES, we study the sensitivity of the parity-violating
asymmetry to strange nucleon form factors. For forward kinematics and electron
energies above 1 GeV, we observe that this sensitivity may reach about 20\% in
the threshold region. With parity-violating asymmetries being as large as tens
p.p.m., this study suggests that threshold pion production in PVES can be used
as a promising way to better constrain strangeness contributions. Using this
model for the neutral current pion production, we update the estimate for the
dispersive -box correction to the weak charge of the proton. In the
kinematics of the Qweak experiment, our new prediction reads Re, an improvement over the
previous uncertainty estimate of . Our new prediction in
the kinematics of the upcoming MESA/P2 experiment reads Re.Comment: 18 pages, 10 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
Mixed EW-QCD two-loop amplitudes for and scheme independence of multi-loop corrections
We perform a dedicated study of the -initiated two-loop
electroweak-QCD Drell-Yan scattering amplitude in dimensional regularization
schemes for vanishing light quark and lepton masses. For the relative order
and one-loop Standard Model corrections, details of our
comparison to the original literature are given. The infrared pole terms of the
mixed two-loop amplitude are governed by a known generalization of the dipole
formula and we show explicitly that exactly the same two-loop polarized hard
scattering functions are obtained in both the standard 't
Hooft-Veltman-Breitenlohner-Maison scheme and Kreimer's
anticommuting scheme.Comment: 65 pages, 6 figures; ancillary files with result