1,179 research outputs found
Top Pair Production Beyond Double-Pole Approximation: pp, pp~ --> 6 Fermions and 0, 1 or 2 Additional Partons
Hadron collider cross sections for tt~ production and di-lepton,
single-lepton and all-jet decays with up to 2 additional jets are calculated
using complete LO matrix elements with 6-, 7- and 8-particle final states. The
fixed-width, complex-mass and overall-factor schemes (FWS, CMS & OFS) are
employed and the quality of narrow-width and double-pole approximations (NWA &
DPA) is investigated for inclusive production and suppressed backgrounds to new
particle searches. NWA and DPA cross sections differ by 1% or less. The
inclusion of sub- and non-resonant amplitudes effects a cross section increase
of 5-8% at pp supercolliders, but only minor changes at the Tevatron. On-shell
tt~/Wtb backgrounds for the H --> WW decay in weak boson fusion, the hadronic
\tau decay of a heavy H^\pm and the \phi --> hh --> \tau\tau bb~ radion decay
at the LHC are updated, with corrections ranging from 3% to 30%. FWS and CMS
cross sections are uniformly consistent, but OFS cross sections are up to 6%
smaller for some backgrounds.Comment: 20 pages, 6 tables, 1 figur
Three Numerical Puzzles and the Top Quark's Chiral Weak-Moment
Versus the standard model's t --> W b decay helicity amplitudes, three
numerical puzzles occur at the 0.1 % level when one considers the amplitudes in
the case of an additional (f_M + f_E) coupling of relative strength 53 GeV. The
puzzles are theoretical ones which involve the t --> W b decay helicity
amplitudes in the two cases, the relative strength of this additional coupling,
and the observed masses of these three particles. A deeper analytic realization
is obtained for two of them. Equivalent realizations are given for the
remaining one. An empirical consequence of these analytic realizations is that
it is important to search for effects of a large chiral weak-moment of the
top-quark, the effective mass-scale is about 53 GeV. A full theoretical
resolution would include relating the origin of such a chiral weak-moment and
the mass generation of the top-quark, the W-boson, and probably the b-quark.Comment: 18 pages, 1 postscript table (revised to better explain notation,
model #1, add a little material...
Determining the Structure of Higgs Couplings at the LHC
Higgs boson production via weak boson fusion at the CERN Large Hadron
Collider has the capability to determine the dominant CP nature of a Higgs
boson, via the tensor structure of its coupling to weak bosons. This
information is contained in the azimuthal angle distribution of the two
outgoing forward tagging jets. The technique is independent of both the Higgs
boson mass and the observed decay channel.Comment: 5 pages, 4 figures, version accepted for publication in PR
Finite-Width Effects in Top Quark Production at Hadron Colliders
Production cross sections for t\bar{t} and t\bar{t}j events at hadron
colliders are calculated, including finite width effects and off resonance
contributions for the entire decay chain, t --> bW --> b\ell\nu, for both top
quarks. Resulting background rates to Higgs search at the CERN LHC are updated
for inclusive H --> WW studies and for H --> \tau\tau and H --> WW decays in
weak boson fusion events. Finite width effects are large, increasing
t\bar{t}(j) rates by 20% or more, after typical cuts which are employed for
top-background rejection.Comment: 32 pages, 11 figures, 7 tables; minor changes, reference added, to be
published in Phys. Rev.
Next-to-leading order jet distributions for Higgs boson production via weak-boson fusion
The weak-boson fusion process is expected to provide crucial information on
Higgs boson couplings at the Large Hadron Collider at CERN. The achievable
statistical accuracy demands comparison with next-to-leading order QCD
calculations, which are presented here in the form of a fully flexible parton
Monte Carlo program. QCD corrections are determined for jet distributions and
are shown to be modest, of order 5 to 10% in most cases, but reaching 30%
occasionally. Remaining scale uncertainties range from order 5% or less for
distributions to below +-2% for the Higgs boson cross section in typical
weak-boson fusion search regions.Comment: 19 pages, 8 figure
Gluon-induced W-boson pair production at the LHC
Pair production of W bosons constitutes an important background to Higgs
boson and new physics searches at the Large Hadron Collider LHC. We have
calculated the loop-induced gluon-fusion process gg -> W*W* -> leptons,
including intermediate light and heavy quarks and allowing for arbitrary
invariant masses of the W bosons. While formally of next-to-next-to-leading
order, the gg -> W*W* -> leptons process is enhanced by the large gluon flux at
the LHC and by experimental Higgs search cuts, and increases the
next-to-leading order WW background estimate for Higgs searches by about 30%.
We have extended our previous calculation to include the contribution from the
intermediate top-bottom massive quark loop and the Higgs signal process. We
provide updated results for cross sections and differential distributions and
study the interference between the different gluon scattering contributions. We
describe important analytical and numerical aspects of our calculation and
present the public GG2WW event generator.Comment: 20 pages, 4 figure
NLO Higgs boson production via vector-boson fusion matched with shower in POWHEG
We present a next-to-leading order calculation of Higgs boson production in
vector-boson fusion processes interfaced to shower Monte Carlo programs,
implemented according to the POWHEG method.Comment: 16 pages, 9 figures. A few references and a new figure adde
QCD corrections to electroweak l nu_l jj and l^+ l^- jj production
The production of W or Z bosons in association with two jets is an important
background to the Higgs boson search in vector-boson fusion at the LHC. The
purely electroweak component of this background is dominated by vector-boson
fusion, which exhibits kinematic distributions very similar to the Higgs boson
signal. We consider the next-to-leading order QCD corrections to the
electroweak production of l nu_l jj and l^+ l^- jj events at the LHC, within
typical vector-boson fusion cuts. We show that the QCD corrections are modest,
increasing the total cross sections by about 10%. Remaining scale uncertainties
are below 2%. A fully-flexible next-to-leading order partonic Monte Carlo
program allows to demonstrate these features for cross sections within typical
vector-boson-fusion acceptance cuts. Modest corrections are also found for
distributions.Comment: 26 pages, 10 figures. PRD final version. One reference corrected,
introduction expande
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